Home | Sitemap | Contact us
 
this site all CERN

Welcome to the LHCb experiment

The LHCb collaboration seen inside the LHCb cavern

LHCb is an experiment set up to explore what happened after the Big Bang that allowed matter to survive and build the Universe we inhabit today

Fourteen billion years ago, the Universe began with a bang. Crammed within an infinitely small space, energy coalesced to form equal quantities of matter and antimatter. But as the Universe cooled and expanded, its composition changed. Just one second after the Big Bang, antimatter had all but disappeared, leaving matter to form everything that we see around us — from the stars and galaxies, to the Earth and all life that it supports.


LHCb delivered and recorded luminosity in 2012, +1.1/fb indicates recorded luminosity in 2010-2011. The number of proton-proton (pp) collisions visible at LHCb, as well as the numbers of cc and bb quark pair produced within LHCb acceptance in 2010-2012 are also shown.

click the image to see the operational plot

Virtual Tours

Google Street View, QuickTime / Flash.

LHC and LHCb Status Displays,
LHCb Event Display,
LHCb event display decoded.

Quantum Diaries blogs about LHCb

see film "LHCb - the beauty experiment" at YouTube shortlisted by the NHK Japan Prize Festival 2011 and by the European Science TV and New Media Festival 2012,

for selected physics results click on: φs, B0s →μμ, B0d→K*μμ, ΔACP, assl, K0S →μμ, B→hhh,
γ angle, B and D oscillations, B0s oscillations, X(3872), BsCP, pA, Λb, Bc, Z(4430)


9 April 2014: Unambiguous observation of an exotic particle which cannot be classified within the traditional quark model

The LHCb Collaboration has published yesterday results of precise measurements of properties of the Z(4430)- particle which allow to determine unambiguously its exotic nature. In the traditional quark model, the strongly interacting particles (hadrons) are formed either from quark-antiquark pairs (mesons) or three quarks (baryons). Particle physicists were searching since 50 years for the particles, called exotic hadrons, which could not be classified within this scheme. Many candidates have been proposed but up to now there has not been unambiguous proof of their existence.

The first evidence for the Z(4430) particle has been presented in 2008 by the Belle Collaboration as narrow peak in the ψπ- mass distribution in the B → ψ- decays. In the latest Belle publication the observation of the Z(4430) particle is confirmed with a significance of 5.2σ and a 3.4σ evidence is presented that the quantum numbers JP = 1+ are favored over the other spin assignments. There are many so called charmonium cc neutral states in this mass region. The fact that the Z(4430) is a charged particle does not allow to classify it as a charmonium state making this particle an excellent exotic candidate. The BaBar collaboration could explain the Z(4430) enhancement in their data by a possible feature of experimental analysis (so called reflections, for experts), not contradicting in the same time the Belle evidence.

The LHCb Collaboration has reported today an analysis of about 25 200 B0 → ψ-, ψ → μ+μ- decays observed in 3 fb−1 of pp-collision data collected at √s = 7 and 8 TeV. The LHCb data sample exceeds by an order of magnitude that of Belle and BaBar together. The significance of the Z(4430)- signal is overwhelming, at least 13.9σ, confirming the existence of this state. The Z(4430)- quantum numbers are determined to be JP = 1+ by ruling out 0-, 1-, 2+ and 2- assignments at more than 9.7σ, confirming the evidence from Belle. The LHCb analysis establishes the, so called, resonant nature of the observed structure in the data, and in this way proving unambiguously that the Z(4430) is really a particle.

The minimal quark content of the Z(4430) state is ccdu. It is therefore a four quark state or a two-quark plus two-antiquark state.

click the images for higher resolution

The black points at the left image above show the ψπ- invariant mass squared distribution of the data. The blue histogram shows the Z(4430) contribution. The right image shows the so called Argand diagram proving to the experts that the Z(4430) structure seen in the data (black points) represents really the resonant particle production and decay, since it follows approximately a circular path (red circle).

Read more in the LHCb publication here, in the CERN Quantum Diaries in English and French and also in the "Quarks bonding differently at LHCb" blog. See special video at CERN CDS or YouTube.

24 March 2014: New LHCb results at the Rencontres de Moriond

The LHCb Collaboration has reported new important results at the Rencontres de Moriond EW Interactions and Unified Theories, March 15th - 22nd and QCD and High Energy Interaction, March 22nd – 29th.

The run 1 data taking period ended one year ago. The LHCb experiment collected 1fb-1 of data from the pp collisions at 7 TeV in 2011 and additional 2fb-1 at 8 TeV collisions in 2012. The results of analysis of beauty and charm particles decays were already presented at many conferences and reported in the news below. At this year Moriond conference more precise results of different analysis were presented using larger data sample and/or including other decay channels.

The decay of the beauty meson B into an excited K meson K* and a μ+ and μ- pair is considered as an important channel for new physics search, see 9 August 2013, 13 March 2012 and 22 July 2011 news for introduction. Different distributions and branching fractions have been studied for these B meson decays and compared with the Standard Model predictions. The differences in the results of measurements of neutral B meson decays into K*0μ+μ- and charged B+ meson decays into K*+μ+μ- is called an "isospin asymmetry". The Standard Model calculations predict this isospin asymmetry to be small what, in fact, was confirmed by the LHCb analysis of 2011 (1fb-1) data. On the other hand, when the physicists made similar analysis by replacing the excited kaon K* by its ground state K an evidence was obtained for a possible isospin asymmetry (see 25 May 2012 news). The analysis of full 3fb-1 data sample presented at the Rencontres de Moriond gave results consistent with the small asymmetry predicted by the Standard Model in both (K* and K) cases. However, even if the difference between results of measurements of neutral and charged B meson decays is small there is a tendency for differential branching fractions to have lower values than the theoretical predictions as seen in the images below.

click the images for higher resolution

Exotic states, particles which are not composed of quark and anti-quark pairs (mesons) or three quarks (baryons), have been searched for since nearly 50 years. One of the most famous candidates for such an exotic state is called the X(3872). The LHCb Collaboration has unambiguously determined its quantum numbers JPC to be 1++ (see 26 February 2013 news for introduction). Possible exotic explanations of the X(3872) nature include a DD* molecules or multi quark anti-quark system such as a diquark-diantiquark tetraquark or charmonium-molecule mixture. Classical interpretation of X(3872) as a pure cc charmonium state is not excluded but this assignment is very unlikely (see again 26 February 2013 news).

The LHCb Collaboration has presented at the Rencontres de Moriond a result of measurement of ratio of branching fractions of X(3872) decay into ψ(2S)γ and J/ψγ, Rψγ. This ratio is predicted to be different for different natures of X(3872) as seen in the image. The LHCb result 2.46 ± 0.64 ± 0.29 is more precise, but compatible with other experiments. It does not support a pure DD* molecule interpretation.

Read more in the LHCb presentations, LHCb papers and conference contribution here.

28 February 2014: First observation of photon polarisation in b→sγ transition.

The LHCb Collaboration has submitted today for publication a paper reporting the first observation of photon polarisation in b→sγ transition. The full 3 fb-1 Run 1 data sample was used to obtain this result. The Collaboration has presented already the first evidence for the photon polarization in this process at the summer 2013 conferences using about 2/3 of the whole data sample, see the news of 19 July 2013 for an introduction.

Photon polarization is the quantum mechanical description of the classical polarized sinusoidal plane electromagnetic wave. Individual photon can have either right or left circular polarization or a superposition of both, read more here.

The beauty particles decay mainly into charm particles, less frequently into strange particles. About once in every 3000 decays into strange particles a photon is emitted. At the underlying quark level a beauty b quark turns into a strange quark s by emitting a photon γ. This famous b→sγ transition is considered as a very interesting process in which signs of new physics could show up. The first evidence for this process was obtained by the CLEO Collaboration in 1993 and since then it was intensively studied in many experiments. This decays occurs only rarely since it requires a quantum fluctuation where a pair of heavy particles (a top quark and a W boson) appear and then rapidly vanish. The interaction between these particles is such that the emitted photon is expected to be almost 100% (left-handed) polarized. However, since the “virtual” top and W particles are not seen in the detector, they could equally well be replaced by other even heavier particles that are predicted in various theories that go beyond the Standard Model. Such theories have been proposed to address important unresolved questions in particle physics, such as the origin of the imbalance between matter and antimatter seen in the Universe. These models generally predict different values for the photon polarisation, and therefore it is seen as one of the most important measurements that can be made with the latest generation of experiments.

Researchers from the LHCb experiment have now succeeded to observe a non-vanishing value of the polarisation for the first time with a significance of 5.2σ. The analysis is based on nearly 14000 B+→K+π- π+ γ decays, for which the distribution of the γ angle with respect to the normal to the plane defined by the kaon and two pion system is studied in four intervals of the K+π- π+ mass which are shown in the image. The two curves are fits to the data points, allowing photon polarisation (solid blue curve) or setting it to zero (dashed red curve).

This investigation is conceptually similar to the historical Wu experiment that discovered parity violation by measuring the asymmetry of the direction of a particle emitted in a weak decay.

Read more in the LHCb publication here and in the CERN Courier article.

click the image for higher resolution

28 January 2014: How long can beauty and charm live together?

[ τ( Bc+) = 509 ± 8 ± 12 fs ]

In the Standard Model of Particle Physics the strongly interacting particles (hadrons) are composed of three quarks (baryons) or quark-antiquark pairs (mesons). There are six types of quarks, three light: up (u), down (d) and strange (s) and three heavy: charm (c), beauty (b) and top (t). The top quark decays so fast that it cannot form bound particle states with other quarks. The heaviest quark which can form baryons or mesons with other quarks is the beauty quark, about five times heavier than proton. The particle physics theory predicts that the lifetime of particles made of the beauty quark and light quarks should be almost identical. The earlier experimental results were not supporting this prediction. Recently the LHCb Collaboration has shown, by measuring precisely the Λb lifetime, that indeed the theoretical predictions are correct, see 15 July 2013 news for details.

But what about the lifetime of particles composed of two heavy quarks? The LHCb Collaboration submitted today for publication a result of lifetime measurement of the Bc+ meson, formed of a b and a c quark. The lifetime of the Bc+ meson is measured using semileptonic decays having a J/ψ meson and a muon in the final state. The J/ψ mesons decay in turn into a pair of muons. The measured lifetime is 509 ± 8 ± 12 fs with an uncertainty less than half of that of the combination of results of previous measurements. This lifetime is much shorter than the lifetime of particles composed of a beauty quark and lighter quarks and closer to the lifetime of charmed particles formed by a charm quark and lighter quarks. This precise result is also very interesting for theorists studying decays of this kind of particles. The calculations are challenging since the effects of both strong and weak interactions need to be taken into account.

The image on the left shows the lifetime distribution of the Bc+ candidates, with the fitted components indicated. The analysis is performed on a data sample of pp collisions at a centre-of-mass energy of 8 TeV, collected during 2012 and corresponding to an integrated luminosity of 2 fb-1. Further improvements are expected from the LHCb experiment using Bc+ → J/ψπ+ decays, where systematic uncertainties are expected to be largely uncorrelated with those affecting the present determination.

Read more in the LHCb publication and in the CERN Courier article.


click the image for higher resolution


24 January 2014: “Underground” news.

The last run 1 collisions took place at LHCb on February 2013. The proton beams should traverse again LHCb in early 2015. The period in between is called Long Shutdown 1 (LS1). What is happening at LHCb, 100m underground, during this period?

”LHCb operated with great success throughout LHC run 1 and has not been subject to any major intervention since its assembly in 2008. The current long shutdown offers a first opportunity for prolonged access, and hence an extensive programme of consolidation and maintenance work has been scheduled. This programme involves all general and detector related services, equipment and safety systems” writes Rolf Lindner, the LHCb Technical Coordinator. Read more details here.

The left image shows the installation of the 30 tons shielding for the LHCb muon detector where 2100 blocks were piled up in a confined space. The right one shows the LHCb dipole consolidation.

click the images for higher resolution

The LHCb underground cavern is also a very popular scientific “tourist” place. The total number of visitors in 2013 was 4524 for 392 visits guided by members of LHCb Collaboration. In addition about 2100 persons visited the LHCb detector and nearby LHC tunnel during CERN Open Days in September 2013. The CERN Visit Service showed the LHCb surface exhibition to 220 groups with 7935 visitors last year.

If you have not visited LHCb detector you can visit it “virtually” using the links from the LHCb public page (right column). The links include a Google Street View tour.

16 December 2013: LHCb VErtex LOcator VELO.

At LHCb the protons collide inside the VErtex LOcator detector (VELO). The VELO is composed of two halves, each consisting of 21 pairs of back-to-back silicon sensors, whose job is to precisely measure the position at which the charged particles pass (see left image below). You can watch the sophisticated construction process at the video here and can read more details about this detector here. Its sensitive detector elements are held out of harm's way while the beams are being injected and stabilized, but once safer, the silicon elements are moved mechanically in towards the beam to hunt for beauty and charm particles.

The LHCb VELO detector plays an essential role in locating precisely the pp collision point as well as the location of beauty and charm particle decays, see, for example, 12 March 2013 news. This detector is so important that the LHCb Collaboration decided to build a second identical Vertex Locator in order to replace the one located around beam should this ever be needed. Since the primary VELO detector is still working perfectly the replacement version is now displayed at the LHCb surface exhibition as seen in the right image below.

The LHCb Collaboration is working towards a major upgrade of the LHCb experiment for the restart of data-taking in 2019. Most of the subdetectors and electronics will be replaced so that the experiment can read out collision events at the full rate of 40 MHz. The upgrade will also allow LHCb to run at higher luminosity and eventually accumulate an order of magnitude more data than was foreseen with the current set-up.

The VELO performance will also be strongly improved. Pixel technology will be used to buid this third version of the detector. The new detector will contain 40 million pixels, each measuring 55 μm square. The pixels will form 26 planes arranged perpendicularly to the LHC beams over a length of 1 m (see image). The sensors will come so close to the interaction region that the LHC beams will have to thread their way through an aperture of only 3.5 mm radius.

Read more in CERN Courier article and in the LHCb VELO Upgrade Technical Design Report.

click the images for higher resolution

29 October 2013: New charm results.

[ x'2 = (5.5 ± 4.9)x10-5 ; y' = (4.8 ± 1.0)x10-3 ]
[ AΓ(KK) = (-0.35 ± 0.62 ± 0.12)x10-3 AΓ(ππ) = (0.33 ± 1.06 ± 0.14)x10-3 ]

The LHCb Collaboration has reported recently new important results on charm physics.

(1) Ten months ago, the LHCb Collaboration presented the first observation of the D0-D0 oscillations in which the D0 matter mesons turn into their antimatter partners. Contrary to the B0-B0 and B0s-B0s oscillations in which the mesons turn into their antimatter partners many times during their lifetime, the D0-D0 oscillations are very slow, over one hundred times the average lifetime (see 7 November 2012 news for introduction). LHCb has now updated this result using the full 2011 and 2012 data set of 3 fb-1. The new result is 2.5 times more precise. The values parameterizing the oscillations, the so-called mixing parameters y' and x'2, are shown above.

By now, CP violation, differences in the behaviour of matter and antimatter, has been observed in all oscillating neutral-meson (K0, B0, B0s) systems apart from the charm system. First evidence for charm CP violation (see 14 November 2011 news) has not been unambiguously confirmed to date (see 12 March 2013 news). The D0 mesons are the only mesons containing up-type quarks which undergo matter anti-matter oscillations (called also mixing) and therefore provide unique access to effects from physics beyond the Standard Model.

As part of the new analysis, LHCb has investigated whether there is a CP violating contribution to the oscillations, in contrast to the Standard Model expectation. This is done by investigating whether the oscillation parameters for mesons produced as D0 and D0 differ. Studying the D0 and D0 decays separately shows no evidence for CP violation and provides the most stringent bounds on the parameters (AD and |q/p| for experts) describing this violation from a single experiment.

(2) LHCb physicists measured the asymmetry AΓ of the inverse of effective lifetimes in decays of D0 and D0 mesons to the K- K+ and π-π+ final states. The measured values of the parameter AΓ shown above represent the world’s best measurements of this quantity, and are the first searches for CP violation in charm oscillations with sensitivity better than 10-3. They do not indicate CP violation, and show no difference in AΓ between the two final states.

The results of other experiments combined by the Heavy Flavor Averaging Group indicated a hint for possible non-zero values of the CP violation parameters (|q/p| and φ for experts). Both LHCb results presented above do not support this indication as seen in the image. The size of the contour with the new LHCb results is about a factor of two smaller in each of |q/p| and φ. They provide very stringent limits on the underlying parameters, thus constraining the room for physics beyond the Standard Model.

click the image for higher resolution

Read more in the LHCb presentations at the 6th International Workshop on Charm Physics Manchester, England, and in the paper here and here and also in the CERN Courier article.

8 October: 2013 Nobel prize in Physics.

The Nobel Prize committee of the Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2013 to François Englert and Peter Higgs for "the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider".

.

Congratulations to François Englert and Peter Higgs.

The image shows LHCb spokesperson Pierluigi Campana showing the LHCb detector to Peter Higgs on December 18th, 2012.

.

click the image for higher resolution

28-29 September 2013: CERN Open Day at LHCb.

see CERN Open Day web page here for details.

2 September 2013: Excellent performance of LHCb Ring Imaging Cherenkov (RICH) detectors.

The physics results presented on this web page were obtained thanks to the excellent LHC collider performance, to the excellent LHCb data acquisition and analysis, and certainly also to the excellent quality of LHCb detector. As an example the exceptional precision of the particle identification achieved by one of the two RICH detectors is shown in the left image below. RICH detectors work by measuring the emission of Cherenkov radiation. This phenomenon occurs when a charged particle passes through a certain medium faster than light does. As it travels, a cone of light is emitted, which the RICH detectors reflect onto an array of sensors using mirrors. The shape of the cone of light depends on the particle’s velocity, enabling the detector to determine its speed. Scientists can then combine this information with a record of its trajectory (collected using the tracking system and a magnetic field) to calculate its mass, charge, and therefore its identity.

But why the speed of light is lower in the medium? - see an explanation here.

click the images for higher resolution

The LHCb Collaboration has recently published a paper in the European Physics Journal C describing the performance of the LHCb RICH detectors. The Journal has honoured the excellent quality of LHCb detector by placing the RICH performance image on its cover page as seen in the right image above.

Read more about the LHCb detector at this web site here.

26 August 2013: Matter-antimatter quantum music.

A fascinating feature of quantum mechanics, in which the B0s, B0 and D0 particles turn into their antimatter partners and back, has been discussed already few times at this page, see 3 March 2013 and 7 November 2012 news. This feature is called oscillations or mixing. The B0s mesons oscillate with by far the highest frequency of about 3 million million times per second (3*1012), on average about 9 times during their lifetime. The B0 mesons oscillate about 37 times slower with a frequency of about 80 thousand million times per second (8*1010). A musical tone is defined by its frequency. LHCb physicists tried to hear this beautiful (involving beauty quarks) matter-antimatter quantum music.

The left video image above shows the last stage of the event filtering process. Two accumulations of events are clearly visible allowing to select the B0 and B0s particles. As the blue box moves through the image we are able to hear the background noise, then the loud tone of B0-B0 oscillations, the background noise again and then the tone of the B0s-B0s oscillations. The higher frequency B0s-B0s oscillations are experimentally more difficult to observe and therefore their tone is weaker. The very high-pitched quantum oscillation frequencies were reduced by millions of times in order to fit into the range that can be heard by humans. Additional explanations can be found in the right hand side video above.

Read also the CERN public page news. Experts can read more about the LHCb analysis, event selection and oscillation parameter measurements in a recent publication here.

9 August 2013: LHCb results hint at new physics?

The LHCb Collaboration has just published the results of a new analysis of the B0→K*0μ+μ- decay, with K*0→K+π-. These results were presented three weeks ago at the European Physical Society Conference on High Energy Physics, EPSHEP, Stockholm, Sweden, and triggered very interesting discussions. The analysis of the B0→K*μμ decay is considered as a very promising channel to search for new physics effects, see the 14 June 2013 news for an introduction. A contribution from new physics particles could modify the angular distributions of the decay products. LHCb physicists have studied different variables related to these angular distributions as functions of the μ+μ- invariant mass squared. In previously published results, no significant deviation from the Standard Model prediction has been found, see the 13 March 2012 news. In order to increase sensitivity to new physics effects LHCb physicists started to analyse additional observables (the so called Pi' observables) which are considered theoretically clean. This means that they are less sensitive than other observables to some theoretical parameters that are not precisely known (form-factors for experts). Four such observables, labelled P4', P5', P6' and P8', have been studied.

The image shows the distribution of the P5' observable as a function of the μ+μ- invariant mass squared q2. The black data points are compared with the Standard Model prediction. A 3.7σ deviation of data above the prediction is observed for the third bin corresponding to q2 between 4.3 and 8.68 GeV2/c4. Taking into account that this deviation is observed in one out of 24 bins investigated in this work (the so-called look-elsewhere effect), the significance of the deviation becomes 2.8σ.

.

click the image for higher resolution

These new results are of great interest to theorists, who are combining results from several measurements to search for effects of physics beyond the Standard Model. According to Joaquim Matias from Universitat Autonoma de Barcelona and colleagues the deviation in P5' and small discrepancies in the other angular observables for this decay, follow a pattern. In a recent paper the authors claim that a global analysis of the LHCb data, together with previous measurements, show a deviation of 4.5σ with respect to Standard Model expectations, which can be explained with the same mechanism (reduced Wilson coefficient C9 for experts). This demands further investigation, in particular to re-evaluate all the sources of theoretical uncertainty, and to understand the effects of correlations between the experimental measurements. A deep interplay between experimental and theoretical analyses will be essential to confirm or refute the pattern of new physics suggested by the B0→K*μ+μ- anomaly.

The results presented so far are based on 1fb-1 of data recorded from pp collisions at 7 TeV in 2011. Particle physicists are impatiently waiting for result of analysis of additional 2fb-1 of data taken at 8 TeV in 2012.

Read more in the LHCb presentation in Stockholm and in the LHCb paper here and in the CERN Courier article.

24 July 2013: The B0s→μμ decay is observed.

The CMS and the LHCb Collaborations have announced today at the 2013 European Physical Society Conference on High Energy Physics, EPSHEP, Stockholm, Sweden, that the B0s→μμ decay is observed. The LHCb Collaboration presented already at this conference the measurement of the B0s→μμ branching fraction of (2.9+1.1-1.0)x10-9 with a significance of 4.0σ (see the 19 July 2013 news). The CMS Collaboration presented the same day a similar result giving a branching fraction of (3.0+1.0-0.9)x10-9 with a significance of 4.3σ (see CMS public page article). The results of both experiments are compatible and, therefore, a decision was taken to combine them.

The CMS and the LHCb Collaborations have obtained a combined preliminary value of the B0s→μμ branching fraction of (2.9±0.7)x10-9. Although a thorough evaluation of the combined significance has not been performed, it is clear that the B0s→μμ decay is observed (with a significance above 5σ). The result is in agreement with the Standard Model prediction of (3.56±0.30)x10-9. The image shows the CMS and LHCb results and their combination together with the results of the CDF Collaboration as well as the D0 and ATLAS Collaborations 95% CL limits which are not included in the combination.

click the image for higher resolution

The search for the B0s→μμ decay was considered as one of the most stringent tests of the Standard Model. Now it is found at a rate consistent to within 25% with that calculated within the Standard Model. This provides a fine-grained filter for the new physics models. All models of physics beyond the Standard Model will have to test their compatibility with this important result.

Read more in the plenary presentation in Stockholm and in the CMS and LHCb conference contribution here and also in the CERN Quantum Diaries in English and French.

19 July 2013: First evidence of photon polarisation in b→sγ transition.

The LHCb Collaboration has just presented at the 2013 European Physical Society Conference on High Energy Physics, EPSHEP, Stockholm, Sweden, a first significant non-zero measurement of an observable proportional to the photon polarisation in b→sγ transition. The transition of a b-quark to an s-quark by emission of a photon (γ) is considered a very important process to investigate possible manifestation of new physics. This decay process is forbidden in the first approximation in the Standard Model (SM) of particle physics and moreover in the second-order processes that govern the process in the SM the emitted photon is expected to be strongly polarised. Therefore it is very sensitive to new physics effects arising from the exchange of new heavy particles in electroweak penguin diagrams (see 14 June 2013 news). Indeed, several models of new physics predict that the emitted photon should be less polarised than in the SM. Up to now different experiments have measured the decay rate of this process, ruling out significant deviations of the rate from the SM prediction and strongly reducing the allowed parameter space of new physics models. The photon polarisation was, however, never previously observed.

Free quarks are not observed in nature. Therefore physicists measure the b→sγ transition in decays of particles containing a b quark, like B mesons, into strange particles containing a s quark, like K mesons. The LHCb physicists have used the process B+→Kresγ where excited K meson states, Kres, decay in turn into three particles, K+, π- and π+. The red distribution in the image shows the contribution of more than 8000 signal events reconstructed and selected in the 2012 data sample, corresponding to an integrated luminosity of about 2 fb-1 collected in pp collisions at 8 TeV. The other distributions show different background contributions. An angular analysis of the B+ decay products has allowed to obtain first evidence, with 4.6σ significance, for photon polarization in the b→sγ transition with respect to the no-polarization scenario. Further theoretical analysis is, however, needed to obtain a numerical value for this polarization.

Read more in the LHCb presentation in Stockholm and in the LHCb conference note here.

click the image for higher resolution

19 July 2013: Measurement of the B0s→μμ branching fraction and search for B0→μμ decays at the LHCb experiment.

The LHCb Collaboration has just presented at the 2013 European Physical Society Conference on High Energy Physics, EPSHEP, Stockholm, Sweden, improved measurements for the rare decays B0s→μμ and B0→μμ. Last year at the Hadron Collider Particle Symposium in Kyoto, the Collaboration presented the first evidence, with 3.5σ significance, for the B0s→μμ decay using the total 1.0 fb-1 of data taken in 2011 and 1.1 fb-1 of the data accumulated in 2012, see 12 November 2012 news. The full LHCb data sample of 3.0 fb-1 was used to obtain today's result. The analysis strategy is very similar to that reported in November 2012 with an improved event selection algorithm (BDT). The significance of the result has been improved to 4.0σ making the evidence even stronger. A branching fraction of (2.9+1.1-1.0)x10-9 is obtained. The result is in agreement with the Standard Model prediction of (3.56±0.29)x10-9. It puts very strong constraints on the parameters of different models of new physics and squeezes even more than previous results the parameters of supersymmetric extensions of the Standard Model (SUSY) - see 30 March 2012 news for introduction.

The μ+μ- invariant mass spectrum for the BDT selection algorithm bins with the smallest background contribution is shown in the left image. The solid blue line shows that the data distribution presented as black dots is well understood and can be separated into different components presented with the help of different colour lines. The dashed red narrow distribution shows the B0s →μμ contribution around the B0s mass of 5372 MeV/c2. The green dashed line shows a possible B0 contribution. The B0 decay yield is not significant yet and an improved limit on the B0→μμ branching fraction of 7.4x10-10 at 95% CL is obtained.

.

click the images for higher resolution

A typical B0s →μμ decay candidate event is shown below. The two muon tracks from B0s decay are seen as a pair of purple tracks traversing the whole detector in the left image below. The right image shows the zoom around the proton-proton collision point, origin of many particle tracks. The two muon purple tracks originate from the B0s decay point located 50 mm from the proton-proton collision.

Read more in the LHCb presentation in Stockholm and in the LHCb paper here and in the CERN Press Release here.

18 July 2013: Observation of unexpected resonant structure in B→Kμμ decays.

The LHCb Collaboration has just presented at the 2013 European Physical Society Conference on High Energy Physics, EPSHEP, Stockholm, Sweden, a first observation of unexpected resonant structure in B+→K+μ+μ- decays. Precise study of this decay could uncover a possible contribution from new physics. This contribution could, however, hide behind the dominant B+→K+μ+μ- decay modes which proceed through the decay of the B+ to a cc resonance (charmonium) and a K+ meson, followed by the decay of the resonance to a μ+μ- pair. To probe for physics beyond the Standard Model it is necessary to remove regions of μ+μ- mass dominated by the resonances. Up to now only the J/ψ and ψ(2S) resonances were taken into account because contributions from resonances with masses above 3900 MeV, where the kaon has a low recoil against the dimuon pair, were thought to be negligible.

The image shows the μ+μ- mass distribution in the low recoil region. What was expected is a smoothly falling distribution, dominated by the non-resonant decay. However, two peaks are clearly visible, one at the low edge corresponding to the decay ψ(3770)→μ+μ- and a wide peak at a higher mass. The mean and width of the wider peak are 4191+9-8 MeV/c2 and 65+22-16 MeV/c2, which are compatible with the so-called ψ(4160) resonance (the name ψ(4160) is misleading, first measurements of the mass of this state gave values lower than it is now known to be). First observations of both the decay B+→ψ(4160)K+ and the subsequent decay ψ(4160)→μ+μ- are reported with statistical significance exceeding six standard deviations.

click the image for higher resolution

This observation is made possible due to quantum mechanical interference between the resonance and non-resonant signal. The resonance and the interference make up 20% of the yield in the low recoil region. This contribution is much larger than expected and in the future, with the large data sets available at LHCb, will need to be taken into acount when searching for new physics in rare decays such as B+→K+μ+μ-.

Read more in the LHCb presentation in Stockholm and in the LHCb paper here.

15 July 2013: A mystery of the beauty baryon lifetime resolved.

[ τb)/ τ(B0) = 0.976±0.012±0.006 ]
[ τ((Λb) = 1.482±0.018±0.012 ps ]

The LHCb Collaboration has just published an important precise measurement of the Λb beauty baryon lifetime. The Λb is a particle composed of the up (u), down (d) and beauty (b) quarks, so it can be understood as being like a neutron (composed of udd quarks) in which one of the d quarks has been replaced by the beauty (b) quark. Therefore the Λb baryon is about 6 times heavier than the neutron. The lifetime of the Λb baryon was first measured by experiments which took data at the electron-positron collider LEP in the 1990s. The results of the measurements were puzzling. It was a real nightmare for theoretical physicists. In fact, the calculations they were using, the Heavy Quark Expansion HQE, predicted that the Λb lifetime should be very similar to that of the B0 meson, but the LEP experiments found the Λb lifetime to be about 20% shorter than the B0 lifetime.

The LHCb Collaboration has recently discovered a new decay mode
Λb → J/ψpK-, J/ψ→μμ. The image shows the signal yield of more than 15,000 Λb decays in 1.0 fb-1 of LHCb data. This decay allows the precise measurement of the Λb decay point from the intersection of four charged tracks. The B0 decay point was also measured precisely using four charged tracks of the B0 decay into J/ψK*0, K*0→K+π-. In this way the LHCb collaboration made the most precise measurement of the Λb to B0 lifetime ratio to be 0.976±0.012±0.006, close to 1 and in agreement with the original HQE prediction. The mystery of the Λb lifetime is now resolved. Using previous determinations of the B0 meson lifetime, the Λb lifetime was found to be 1.482±0.018±0.012 ps.

click the image for higher resolution

Read more in the LHCb publication, in the CERN Courier article and in the CERN Quantum Diaries in English and French.

14 June 2013: LHCb: a place to find penguins.

How "penguins" can help LHCb to chase for new physics? - read explanations in the June issue of CERN Courier and then follow links to the LHCb physics results announced in the 13 March 2012 and 25 May 2012 news at this page.

The name of penguin appeared in particle physics in 1977 following a bet lost by CERN theoretical physicist John Ellis, see also explanations in the CERN Courier article. The original penguin diagram for b quark to s quark decay, where a gluon produces an ss pair, is shown in the image at the right hand side.

LHCb is investigating decays where a μ+μ- pair is produced from a photon or from a Z boson as seen in the diagram on the left named as an "electroweak penguin"; the diagram on the right is a "box" diagram.

See also the hangout video,
click the images for higher resolution

6 June 2013: LHCb PhD student wins the Swiss FameLab competition.

Donal Hill, LHCb PhD student, was nominated as the best Swiss FameLabber 2013 during the Swiss FameLab final in Zurich. Nine candidates selected in a previous heat in Geneva were evaluated by a judging panel and by the audience. Donal will represent Switzerland at the Cheltenham Science Festival in the UK in June 2013.

FameLab is an exciting competition for young researchers. It encourages scientists to inspire and excite public imagination with a vision of the 21st century of science.

Congratulations to Donal!

See Donal's presentation here, as well as the CERN bulletin article in English and French.

17 May 2013: LHCb physicist rewarded by the European Physical Society.

The High Energy Physics Division of the European Physical Society announced today the winners of its 2013 prizes, which will be awarded at the Europhysics Conference on High-Energy Physics (EPS-HEP 2013), Stockholm (Sweden) 18-24 July 2013. The 2013 Young Experimental Physicist Prize, for outstanding work by one or more young physicists in the field of Particle Physics and/or Particle Astrophysics, was awarded to Diego Martinez Santos “for his outstanding contributions to the trigger and commissioning of the LHCb experiment, and the analyses leading to first evidence for the rare decay B0s →μμ”.

Congratulations to Diego!

The European Physical Society recognized in this way the quality and the excellence of the LHCb experiment, and of the whole collaboration who built and is operating it.

Read more on the analysis of B0s →μμ data in the 12 November 2012 news.

10 May 2013: First and important results from the proton with lead ion collision 2013 run.

The LHCb Collaboration has just presented at the Workshop on proton-nucleus collisions at the LHC, Trento, Italy, the first results from the analysis of proton with lead ion collision run data taken in January-February 2013. Already these first results made an important contribution to the understanding of heavy ion collisions.

In the Standard Model of Cosmology quarks and gluons were freely moving in a state called a quark-gluon plasma until < 10-5 seconds after the Big Bang. As the Universe cooled, they became confined inside protons and neutrons. The theory of quark-gluon interactions, the strong force interaction theory, QCD, predicts that the state of quark-gluon plasma can also exists in high temperature matter created by high energy collisions between large atomic nuclei, called by physicists heavy ion collisions. But how to prove that the quark-gluon plasma is really formed? A reduced rate of J/ψ particle production in heavy ion collisions was considered as a "smoking gun" argument in favour of quark-gluon plasma formation by physicists analysing results of measurements performed in the CERN Super Proton Synchrotron (SPS) after 1986 and more recently in the Brookhaven RHIC collider. Profound analysis has shown, however, that reality is more complicated. In some models, for example, the J/ψ particle could also be regenerated in nuclear matter, partons (quark, gluons) could be saturated and/or lose energy, etc. in normal (so called cold) nuclear matter.

Data recording collisions of protons with lead ions were collected in the LHC experiments in January-February this year. In such collisions, formation of a quark-gluon plasma is not expected, and therefore measurements based on these data allow the study of interactions in cold nuclear matter. The analysis of J/ψ production was of particular interest.

The LHCb results are shown in the image at the left hand side. A reduced value of the nuclear attenuation factor RpA, the ratio of the J/ψ production in the proton with lead ion (pA) collisions to that in proton-proton collisions as a function of the rapidity y is clearly seen. The rapidity variable is related to the J/ψ production angle with respect to the incoming proton direction. The experimentally measured points (triangles with error bars) in the image show that the largest suppression is in the forward direction.

The colored distributions show theoretical predictions of RpA calculated by François Arleo from LAPTH, Annecy and Stéphane Peigné from Subatech, Nantes, taking into account the J/ψ energy loss (E. loss) in cold nuclear matter with and without the parton saturation effects. The LHCb results are in agreement with these predictions.

Two sets of data were taken: pA and Ap, where in the second case the direction of the proton and lead ion beams were reversed. This allowed the LHCb detector, recording the particles only on one side of the interaction point, to make measurements in both forward and backward directions with respect to the proton beam (positive and negative rapidity).

click the image for higher resolution

Read more in the LHCb presentation in Trento and in the LHCb conference note.

24 April 2013: First observation of CP violation in the decays of B0s mesons.

[ ACP(B0s→K-π+) = +0.27 ± 0.04 ± 0.01 ]
[ ACP(B0→K+π-) = -0.080 ± 0.007 ± 0.003 ]

The LHCb Collaboration has just submitted for publication a paper which sets an important milestone in the history of particle physics. A difference between properties of matter and antimatter, named CP violation by particle physicists, was discovered in 1964 in the decays of neutral K mesons and was rewarded with the 1980 Nobel Prize in Physics for James Cronin and Val Fitch. M. Kobayashi and T. Maskawa proposed in 1973 a mechanism which could incorporate CP violation within the Standard Model with not less than 6 quarks. In 2001, CP violation was observed in the decay of so-called Beauty Particles, the B0 mesons composed an anti-quark b and a quark d. The Standard model mechanism of CP violation was confirmed and therefore Kobayashi and Maskawa were rewarded with the 2008 Nobel Prize in Physics. In March 2012 the LHCb Collaboration reported an observation of CP violation in charged B± meson decays into DK±. Today, the LHCb Collaboration has announced an observation of CP violation in the decays of Strange Beauty particles, the B0s mesons composed of a beauty antiquark b bound with a strange quark s.

The B0 and B0s meson decays into K and π mesons were studied. The decay into a negative K meson red track and a positive π green track is show in the event displays above.

click the images for higher resolution

The four plots on the left hand side above show the Kπ invariant mass distribution divided into different components as shown by the legend in the top-right figure. The different charge combination of K and π indicates if the decaying B0 or B0s particle is a matter or an antimatter particle. The two upper plots show that the decay rates of B0 mesons are different, as was already well established by previous measurements. The zoom in the lower two plots shows that the difference is also visible around the B0s meson mass, as indicated by the two green Gaussian distributions. Mathematically this difference is described by the asymmetry ACP(B0s→K-π+) = +0.27 ± 0.04 ± 0.01, which differs from zero with significance exceeding five Gaussian standard deviations σ. Therefore this result represents the first observation of CP violation in the decays of B0s mesons. The corresponding asymmetry for B0 meson decays presented in the two upper images, ACP(B0→K+π-) = -0.080 ± 0.007 ± 0.003, is the most precise measurement of this quantity to date.

The full 1.0 fb-1 data sample collected in 2011 was used to obtain these results, the precision will be further improved using the total dataset available which has more than tripled thanks to the excellent 2012 data taking period.

More details can be found in the LHCb paper here. Read also the CERN Press Release in English and French, the CERN Bulletin article in English and French as well as CERN Courier article.

20 March 2013: LHCb 100th publication.

The LHCb Collaboration has submitted its 100th publication! It is signed by 621 authors from 63 different universities and laboratories from 17 countries. The paper "Search for direct CP violation in D0→h-h+ modes using semileptonic B decays" has been presented at the Rencontres de Moriond QCD, La Thuile, Italy, and is described in the 12 March 2013 news as the second independent analysis. You can celebrate this important moment in the life of our Collaboration with the help of a poster available in the LHCb secretariat or printing it directly from a file. The poster shows an event, described in the 12 March 2013 news, and used in the analysis.

The LHCb papers have made very important contributions to particle physics as described in other items on this page. However, even more important contributions are expected in the near future. In fact, most results presented in LHCb papers to date used the full 1.0 fb-1 data sample collected in 2011. The total dataset available for future analysis has more than tripled thanks to the excellent 2012 data taking period. The only published paper using the 2012 data is the analysis presented in the "First evidence for the B0s →μμ decay" paper, see 12 November 2012 news, in which already half of 2012 data sample was used.

The highlights of recent LHCb results showing the presentations at different conferences, conference contributions and papers can be found here.

12 March 2013: Improved search for CP violation in charm decays.

[ ΔACP = (−0.34 ± 0.15 ± 0.10 )%, pion tagged ]
[ ΔACP = (+0.49 ± 0.30 ± 0.14)%, muon tagged ]

The LHCb Collaboration presented today at the Rencontres de Moriond QCD, La Thuile, Italy, results of an improved search for the difference between properties of matter and antimatter, CP violation, in charm decays, see 14 November 2011 news for introduction. The difference (Δ) of CP asymmetry (ACP) between the decay rates of D (matter) and D (antimatter) mesons into K+K pairs and into π+π- pairs was measured. The results presented today profited from three improvements to the previous analysis: the full 1.0 fb-1 data sample collected in 2011 was used instead of 0.6 fb-1, the analysis technique was improved and also in addition another independent method was used to select matter D and antimatter D particle decays.

In the Standard Model CP violation was expected to be very small in the charm sector, whereas new physics effects could generate enhancements. Therefore the 14 November 2011 announcement by the LHCb Collaboration of 3.5σ evidence of CP violation in charm sector, ΔACP = (-0.82 ± 0.21 ± 0.11)%, triggered intensive theoretical activity with conclusions that some special Standard Model effects could generate CP violation effects even as big as about 1%. This interesting LHCb result was later confirmed by the CDF and Belle collaborations. The new improved LHCb result presented today, ΔACP = (−0.34 ± 0.15 ± 0.10 )%, is more precise thanks to the larger data sample and several improvements resulting in better background suppression by a factor of 2.5. The central value is, however, closer to zero than in the previous measurement, which it supersedes.

In the measurement presented above the D (matter) and D (antimatter) mesons were selected using the D* meson decays, D*+(-) → π+(-)D(D), which means that the presence of π+ in the decay identified matter D meson production while π- accompanied antimatter D production. LHCb physicists presented today also results of a second independent analysis in which the D and D mesons were selected using so called semileptonic beauty B decays, for example B+(-) → μ+(-)νD(D). In the second analysis, the positive charge of μ+ identified the D meson, while the negative one, μ-, the D production. The image at the left hand side shows a selected event. A zoom around the pp interaction point shows a B+ meson decay point located at the distance of 17 mm from the pp collision point and the D meson decay place still 9 mm further away. The second analysis also measures a value that is consistent with zero: ΔACP = (+0.49 ± 0.30 ± 0.14)%. A combination of the two LHCb results gives ΔACP = (-0.15 ± 0.16)%.

click the images for higher resolution

The image at the left hand side shows a comparison of different measurements of ΔACP. The previous LHCb result is shown as the shaded grey point. A naive world average is shown as the yellow band. As shown in the image, the two new LHCb results are consistent with each other and with other results at the 2σ level, but do not confirm the previous evidence of CP violation in the charm sector.

Theoretical work has shown that several well-motivated models could induce large CP violation effects in the charm sector. These new results constrain the parameter space of such models. Further update of this and related measurements will be needed to discover if – and at what level – nature distinguishes between charm and anticharm.

More details can be found in the LHCb presentation in La Thuile, in CERN seminar, in the LHCb paper and conference contribution here. Read also the CERN Bulletin article here and the CERN Courier article.

3 March 2013: Precise search for new physics.

[ Δms = 17.768 ± 0.023 ± 0.006 ps-1 ]
[ φs = 0.01 ± 0.07 ± 0.01 rad ]
ΔΓs = 0.106 ± 0.011 ± 0.007 ps-1 ]

The LHCb Collaboration presented today at the Rencontres de Moriond EW, La Thuile, Italy, three important results of their more and more precise search for new physics. The 1 fb-1 data sample collected in 2011 was used to obtain these results.

(1) A fascinating feature of quantum mechanics, in which the B0s, B0 and D0 particles turn into their antimatter partners, has been discussed already at this page, see 15 March 2011 and 7 November 2012 news. This feature is called oscillations (mixing). The B0s mesons oscillate with by far the highest frequency of about 3 million million times per second (3*1012), on average about 9 times during their lifetime.

The B0s meson decays into D-sπ+ were used in this analysis with D-s decays into five different channels. The image at the left hand side illustrates the B0s-B0s oscillations in a spectacular way, showing how the matter turns into antimatter and back over many oscillation periods. The frequency of oscillation is defined by the Δms parameter. The value of this parameter as measured by the LHCb collaboration is shown above.

.

click the image for higher resolution

(2 - presented also at the Rencontres de Physique de la Vallée d'Aoste) Knowledge of the value of the parameter φs is very important for physicists, since it set the scale of the difference between properties of matter and antimatter, called CP violation by experts, in the B0s sector. The B0s decays into a J/ψφ and a J/ψππ were already studied, see 5 March 2012 and 27 August 2011 news for introduction. LHCb physicists have improved and finalized these measurements. One important improvement is in "flavour tagging", which determines whether the initial state was produced as a B0s or B0s meson. Better tagging gives better sensitivity in the final result. The values of the φs parameter together with the difference between the width of a heavy and light mass B meson system (see 5 March 2012 news) are shown above. The left image below shows the small allowed region for these two parameters.

click the images for higher resolution

(3) Finally, LHCb physicists have opened a door for important future measurements by presenting the results of a first study of the time-dependent CP-violating asymmetry in hadronic B0s meson decays into an φφ pair. Both φ mesons decayed in turn into a K+K- pair. The invariant mass spectrum for the four kaons is presented in the right image above showing a clear accumulation of B0s → φφ decays at the B0s mass. Using about 880 events the CP-violating phase φs was measured to be in the interval of [-2.46,-0.76] rad at 68% confidence level.

The results presented in this news represent the most precise measurements to date. They are in agreement with the Standard Model prediction. The parameter region in which the signs of new physics can still hide is significantly reduced. More details can be found in the LHCb presentations in La Thuile and in the LHCb papers here. Read also the CERN Courier article.

26 February 2013: X(3872) looks more and more exotic.

[ X(3872) JPC = 1++ ]

The LHCb Collaboration presented today at the Rencontres de Physique de la Vallée d'Aoste, La Thuile, Italy, an important result which makes the exotic nature of the X(3872) particle very probable.

In the quark model of particle physics proposed in 1964 by Murray Gell-Mann and George Zweig mesons, like the π (pion), are formed from quark and anti-quark pairs and baryons (like the proton) from three quarks. This model is very successful. Particles which cannot be described in this model, known as exotic states, have been searched for since nearly 50 years ago. Their existence has not yet been firmly established (except of a special case of pionium). One of the most famous candidates for such an exotic state is called the X(3872). It was discovered in B+ meson decay into an X(3872) and a K+ meson by the BELLE collaboration almost 10 years ago. Its existence was confirmed later by the CDF, D0 and BaBar experiments. LHCb has previously reported studies of the X(3872) in the data sample taken in 2010, see 27 October 2010 news. Particles are classified according to their quantum numbers JPC. An analysis by the CDF experiment has limited the possible values of X(3872) JPC to either 1++ or 2-+.

LHCb physicists have observed the X(3872) particle in the decay of a B+ meson into an X(3872) and a K+ meson. The X(3872) was observed in the invariant mass of a J/ψ particle and a π+π- pair, while the J/ψ was identified from its decay into μ+μ- pair. The image at the left hand side shows the difference between the invariant mass of the π+π-J/ψ combination and the J/ψ showing clearly the X(3872) and ψ(2S) enhancements over the smooth background distribution (the ψ(2S) particle decays also into a π+, π-, and J/ψ).

.

click the image for higher resolution

LHCb physicists made a sophisticated analysis of the whole B+ decay chain in 5 dimensions and unambiguously determined the quantum numbers of X(3782) to be 1++. The other previously allowed assignment of 2-+ was rejected with statistical significance over . About 300 signal events were selected among about 60 million million (6*1013) pp collisions seen by the LHCb detector at LHC during the 2011 data taking period. Details of analysis can be found on the LHCb staff page.

The exotic nature of the X(3872) would be unambiguously determined if its quantum numbers could not be described by the quark-antiquark combination. However, this is not the case. In fact, the mass of 3872 MeV is located in a region in which many charm quark-antiquark states are present bound by a strong force in an atom-like system called charmonium. The X(3872) has the quantum numbers of an as yet unobserved charmonium state called χc1(23P1). However, the charmonium spectrum is very well understood and the mass of the X(3872) makes this assignment very unlikely. Possible exotic explanations of the X(3872) nature include a DD* or multi quark anti-quark system such as a diquark-diantiquark tetraquark or charmonium-molecule mixture.

More details can be found in the LHCb presentation in La Thuile and in the LHCb paper here. Read also the CERN Courier article and the CERN Bulletin article in English and French.

14 February 2013: End of 2013 data taking period.

Today at 7:25 LHCb physicists have observed the last collision at the LHC. After a very succesfull period of proton with lead ion collisions the last few days of data taking were reserved for proton-proton collisions at 2.76 TeV. The two year shut-down period, called LS1, will start two days later in order to set-up LHC for doubling the proton-proton collision energy to 13 TeV at March 2015. LHCb Collaboration congratulates and thanks LHC team for excellent performance.

Read the CERN Bulletin article in English and French.

20 January 2013: Start of 2013 data taking period.

Today at 15:11 LHCb physicists have observed the first 2013 collisions of protons with lead ions in the LHCb detector. The 2013 data taking period has started. The proton - lead ion collisions were alredy observed by the LHCb on 13 September 2012 during the short test run.

15 November 2012: LHCb thanks LHC.

LHC collider has delivered at 9:50 today 2 fb-1 of luminosity to LHCb this year corresponding to about 100 million million of proton-proton collisions visible at LHCb. This was possible thanks to an exceptional performance of the machine and an impressive commitment from everybody involved in the operation of LHC in this very long running year. The image shows how the LHCb Collaboration thanks the LHC operation team on the LHC status screens which are visible in the control rooms all over CERN and on the Web. The collider is currently running with very high efficiency. This can be seen in the image where very long proton-proton collisions periods are interleaved by short set-up intervals.

click the image for higher resolution

12 November 2012: First evidence for the B0s →μμ decay.

[ Branching ratio B0s →μμ = (3.2+1.5-1.2)x10-9 ]

The LHCb Collaboration has presented today at the Hadron Collider Particle Symposium in Kyoto the result of the branching ratio measurement of the B0s meson decay into μ+μ- pair to be (3.2+1.5-1.2)x10-9. Both experimental and theoretical physicists were impatiently waiting for this result, an important milestone of the LHCb program. The significance of the measurement is 3.5σ and therefore is classified as the first evidence for the B0s →μμ decay. The result is in agreement with the Standard Model prediction of (3.54±0.30)x10-9 (for experts: this number takes into account a correction to the value (3.23±0.27)x10-9 due to the finite width difference of the B0s system). LHCb physicists had previously presented 15 March this year the lowest published limit of 4.5x10-9 for this decay, which allowed to squeeze strongly the parameters of supersymmetric extensions of the Standard Model (SUSY) - see 30 March 2012 news. The measurement presented today squeezes the parameter space even more.

The total 1.0 fb-1 of data taken in 2011 and 1.1 fb-1 of the data accumulated this year were used to obtain this result. A special event selection (BDT for experts) was used to classify data into bins with different ratios of B0s →μμ decays and background contributions. The μ+μ- invariant mass spectrum for the bins with the smallest background contribution is shown in the left image. The solid blue line shows that the data distribution presented as black dots is well understood and can be separated into different components presented with the help of different colour lines. The dashed red narrow distribution shows the B0s →μμ contribution around the B0s mass of 5366 MeV/c2.

The green dashed distribution shows a possible contribution from the B0 →μμ contribution around the B0 mass of 5280 MeV/c2. Within the Standard Model the branching ratio for this decay is expected to be about 30 times smaller than that for the B0s decay. A small excess of data over the background and Standard Model rate is observed, but is consistent with the Standard Model expectation. LHCb physicists have set a limit of 9.4x10-10 for this branching ratio.

click the image for higher resolution

A typical B0s →μμ decay candidate event is shown above. The two muon tracks from B0s decay are seen as a pair of purple tracks traversing the whole detector in the left image above. The right image shows the zoom around the proton-proton collision point, origin of many particle tracks. The two muon purple tracks originate from the B0s decay point located 14 mm from the proton-proton collision.

The precision of these results will be improved using an additional 1 fb-1 of data or more that will be available by the end of this year thanks to the strong and continuous support from the LHC operations team for the LHCb physics program.

More details can be found in the LHCb presentation in Kyoto and in the LHCb paper here and also in the CERN seminar. Read also the CERN Bulletin article in English and French, the CERN Courier article and also the CERN Quantum Diaries blog in English and French.

7 November 2012: Oscillating charm and beauty.

[ Δmd = 0.5156 ± 0.0051 ± 0.0033 ps-1 ]
[ x'2 = (-0.9 ± 1.3)x10-4 ; y' = (7.2 ± 2.4)x10-3 ]

A fascinating feature of quantum mechanics has been reported 15 March 2011 on this page. The strange beauty particle (matter) B0s composed of a beauty antiquark (b) bound with a strange quark s turns into its antimatter partner composed of a b quark and an s antiquark (s) with a frequency of about 3 million million times per second (3*1012). This feature is called "oscillations" or "mixing". The LHCb Collaboration has just published the first observation of similar oscillations of charm mesons D0 composed of a charm quark and an anti-up quark (D0-D0 oscillations) and the most precise measurement of a parameter defining the frequency of the oscillations of beauty mesons B0 composed of a beauty antiquark (b) bound with a d quark (B0-B0 oscillations).

The B0 decays into D+π- and J/ψK*0 were used to study B0-B0 oscillations. The images below show the asymmetry which is proportional to the difference between the number of events in which the matter (or antimatter) B0 particle decayed with the same flavour identity with which it was produced, and the number of events in which it did not, as a function of its lifetime. The B0-B0 oscillations are clearly visible. LHCb physicists have parametrized them with a value Δmd = 0.5156 ± 0.0051 ± 0.0033 ps-1 corresponding to the frequency of about 80 thousand million times per second (8*1010), about 37 times slower than B0s-B0s oscillations. The B0-B0 oscillations have been previously measured at LEP, Tevatron and B factories. The LHCb result is currently the most precise measurement of the Δmd parameter.

click the image for higher resolution

D0-D0 oscillations are very slow, over one hundred times the average lifetime of a D0 meson, so the full oscillation period cannot be observed. Instead, it is necessary to look for small changes in the flavour mixture (matter or antimatter) of the D0 mesons as a function of the time at which they decay. One of the best channels to search for this mixing is the D0 decay to the Kπ final state. The initial matter-antimatter identity can be identified by the charge of the accompanying pion in the decay D*+→D0π+ or D*-D0π-. The mixing effect (oscillation) appears as a decay-time dependence of the ratio R between the number of reconstructed “wrong-sign” (WS; D0→K+π-) and “right-sign” (RS; D0→K-π+) processes. In the absence of mixing, R is predicted to be constant as a function of the D0 decay time t, while, in case of mixing, it is predicted to be an approximately parabolic function of t. The left image below shows the WS over RS ratio R, as a function of decay time, from a total of 36 thousand WS and 8.4 million RS decays selected from the 1.0 fb-1 of data recorded in 2011. The horizontal dashed line shows the no-mixing hypothesis, the solid line is the best fit to data when mixing is allowed. The clear time dependence observed excludes the no-mixing hypothesis by 9.1 σ.

click the image for higher resolution

Comparison of values parameterizing the D0-D0 oscillations, y' and x'2, obtained by different experiments, are presented in right image above. The LHCb results exclude the no-mixing hypothesis by more than 5 σ for the first time and therefore can be classified as the first observation of this effect.

Since the Standard Model predictions for the mixing parameters have large uncertainties, the next step will be to focus on cleaner observables to search for possible new physics contributions. In particular, LHCb is now well placed to investigate whether there is a CP violating contribution to the oscillations, in contrast to the Standard Model expectation. This will be achieved by studying charm mixing in this and other decay channels and exploiting the large increase in available statistics following the successful 2012 LHC run.

Read more in the LHCb publications: D0-D0 and B0-B0 oscillations, in the CERN Courier article, and also in the USLHC Quantum Diaries blog.

5 October 2012: Measurement of the γ angle.

[ γ = (71.1+16.6-15.7)° only B±→DK decays ]
[ γ = 85.1° uncertainty regions [61.8,67.8]° and [77.9,92.4]°, B±→DK and B±→Dπ decays ]

LHCb is an experiment set up to explore what happened after the Big Bang that allowed matter to survive and build the Universe we inhabit today. Therefore LHCb physicists are measuring differences between properties of matter and antimatter, called CP violation by experts. CP violation was discovered experimentally in K meson decays in 1964. M. Kobayashi and T. Maskawa proposed in 1973 a mechanism which could incorporate CP violation within the Standard Model with not less than 6 quarks; they were awarded the Nobel prize of Physics in 2008 for this idea. The size of this violation is set by the parameter η, which is shown as the y axis in the figures below. Constraints on η and the related parameter ρ (the x-axis) are measured in various ways in different experiments as shown in the compilation made by the CKMfitter group in the left image below. The constraints show that in fact the values of ρ and η within the small colored region in the center of the images are compatible with the experimental results and confirm in this way the Kobayashi and Maskawa Standard Model mechanism of CP violation. However, since this mechanism does not explain the large quantity of matter observed in the Universe physicists are searching for other sources of CP violation outside the Standard Model.

An interesting possibility is to measure precisely the angle γ of the triangle shown in the right image below in processes in which the new physics contribution is possible and in processes in which it is not. Differences between measurements in these two cases would be a sign of new physics. The measurement of the angle γ in different processes is one of most important goals of the LHCb experiment. The value of this angle is known up to now with precision of only about 10 or 12°, as seen in the right image below, using the combination of results from other experiments.

click the image for higher resolution

LHCb physicists have just presented at the 7th International Workshop on the CKM Unitarity Triangle, Cincinnati, Ohio, USA, the measurement of the angle γ in processes where the contribution of new physics is not expected. These measurements will set a base for comparison with the measurement where observation of new physics effects is possible. The B±→DK and B±→Dπ decays were used with D mesons decays into KK, ππ, K0Sππ, K0SKK or Kπππ. The value of the angle γ = (71.1+16.6-15.7)° was obtained using only B±→DK decay results in the analysis. The image at the left hand side shows the confidence level of the signal as a function of angle γ, for the combination of B±→DK modes. The peak of the distribution gives the measured central value, and the width gives the error. The best value of the angle γ = 85.1° was obtained with the two corresponding uncertainty regions [61.8,67.8]° and [77.9,92.4]° (at 68% CL) when the B±→Dπ decays were included in addition.

The 2011 data sample (1.0 fb-1) was used in this analysis. The precision of the γ angle measurement is already comparable with that achieved by other experiments and the value of this angle is now known to a precision of less than 10 degrees, when this result is averaged with the latest results of other experiments. LHCb physicists are working on analyses of other decay modes that can help improve the precision. It is interesting to note that the data collected by LHCb in 2012 already exceeds the sample from 2011 and by the end of the year the total dataset should have more than tripled.

More details can be found in the LHCb presentation in Cincinnati and in the LHCb Conference Contribution here. Read also the CERN Courier article and the CERN Bulletin article in English and French.

3 October 2012: Matter antimatter asymmetry in three-body charmless B decays becomes more and more interesting.

[ ACP(B±→π±π+π-) = +0.120 ± 0.020 ± 0.019 ± 0.007 ]
[ ACP(B±→π±K+K-) = -0.153 ± 0.046 ± 0.019 ± 0.007 ]

Earlier this year, LHCb physicists reported at the ICHEP2012 Conference (see 7 July 2012 (2) news) the first evidence of inclusive CP asymmetry (differences between properties of matter and antimatter) in the charmless three-body B meson decays B±→K±π+π- and B±→K±K+K- in which the b-quark decays into a u,d or s-quark instead of its dominant decay into a charm c-quark. It was interesting to note that much larger asymmetries were observed in some small special regions, like invariant mass squared of the π+π- pair in the K±π+π- decay lower than 1 GeV2, or of the K+K- pair in the K±K+K- final state between 1.2 and 2 GeV2 (7 July 2012 (2) news).

click the image for higher resolution

These measurements have now, at the 7th International Workshop on the CKM Unitarity Triangle, Cincinnati, Ohio, USA, been complemented with results from the rarer B±→π±π+π- and B±→π±K+K- decays, finding evidence of even larger CP violation. A remarkable feature of the new LHCb results is that the CP violation effects appear to arise in some special kinematical regions that are not dominated by contributions from narrow resonances. For example, in B±→π±K+K- decays a broad feature at low K+K- invariant mass that was previously observed by the BaBar collaboration [PRL 99 (2007) 221801] appears to be present only in B+ decays, as shown by the filled triangles distribution in the left figure above, and not in the B- distribution (open triangles). This points to some interesting hadronic dynamics that could generate the observed direct CP violation. LHCb is now starting detailed studies of these channels, that can also exploit the three times larger data sample available after 2012 running, to further understand these effects. The results of these analysis will also establish whether the observed CP violation is consistent with the Standard Model expectation or has a more exotic origin.

The middle and right images above show the π±K+K- invariant mass distribution for B- and B+ decays with m2K+K- < 1.5 GeV2/c4. The difference between properties of matter and antimatter, the CP violation, is clearly seen as a difference between the height of two peaks located at the B mass (at 9σ level for experts).

More details can be found in the CERN Courier article, in the LHCb presentations in Cincinnati and in the CERN seminar here.

25 September 2012: Searching for new physics in rare kaon decays.

[ Branching ratio K0S →μμ < 9x10-9 at 90% CL ]

Having previously set the world's most restrictive limits on the dimuon decays of D0, B0 and B0s mesons, LHCb physicists have turned their attention to the search for similar decays of another member of the particle zoo, the K0S meson. Using the 2011 data sample, LHCb has set a limit on the branching ratio B(K0S→μ+μ-) to be less than 9x10-9, a factor of 30 improvement over the previous most restrictive limit measured in 1973. [For experts: the limit is at 90% confidence level.] While several techniques used were common with the search for B0s→μ+μ- (see news items of 8 April and 22 July 2011 and 5 March 2012 for more details), the challenge of this measurement lies in the specificity of kaon decays, which are very different from B decays for which LHCb detector was optimized.

The image below shows the invariant mass distribution of selected μ+μ- pairs, candidates for K0S decay. The dashed lines indicate the signal region around the K0S mass, where no significant signal is seen.

click the image for higher resolution

K meson decays into pairs of muons played a very important role in the history of particle physics. There are two types of K mesons: the short-lived, K0S ("K-short") and the long-lived, K0L ("K-long"). The results of branching ratio measurements of the K-long decay into muon pairs in the early 1970s disagreed strongly with the predictions of particle physics theory based on existence of three quarks u, d and s. The calculated branching ratios were of the order of 10-4 while the experimental limits were about 4 orders of magnitude lower. In order to solve this problem Glashow, Iliopoulos and Maiani proposed the existence of an additional quark, called a charm quark – a 1970s version of a new physics model. In the mechanism they proposed (GIM mechanism) a destructive virtual contribution of this new quark reduced very strongly the K-long decay rate into muon pairs. The discovery of the J/ψ state in November 1974 gave the first evidence for the existence of charm quark and at the same time confirmation of the GIM mechanism.

40 years later LHCb physicists are searching for K-short decays into muon pairs, again on the look-out for new physics. The branching ratio is calculated to be 5x10-12 within the framework of the Standard Model of particle physics with 6 quarks. Although the new limit 9x10-9 is still three orders of magnitude above the prediction, it starts to approach the level where new physics effects might begin to appear. Moreover, the data collected by LHCb in 2012 already exceed the sample from 2011 and by the end of the year the total dataset should have more than tripled.

Read more in the CERN Courier article, the CERN Quantum Diaries and LHCb publication.

13 September 2012: First proton-lead ion collisions at LHCb.

During the night, at 1:30 am, LHCb recorded the first proton-lead ion collisions at the LHC. The proton-lead physics data taking is planned to take place in January and February 2013. Today the LHC operational team made tests of collisions in order to prepare the set-up of the LHC collider and the LHC experiments for next year. Note that collisions of protons with lead ions are more difficult than proton-proton or lead-lead collisions. In fact the speed of protons and lead ions is slightly different, even though it is close to the speed of light at LHC. The LHC operators succeeded in making the proton path length inside LHC ring slightly longer than the lead-ion path length in order to compensate for this difference.

click the image for higher resolution

A typical proton-lead collision event at LHCb is shown in the left image above. Note that the lead ions arrive at the LHCb collision point from the right hand side and the protons from the left hand side. The right image shows the invariant mass spectrum of the decay products of Λ and Λ particles indicating excellent prospects for physics analysis of p-lead collision data early next year.

Read also the CERN Courier article.

21 August 2012: LHCb has doubled its recorded luminosity.

The data sample used to obtain the LHCb results presented on this page was obtained using the integrated luminosity of 1.11 fb-1 recorded by LHCb during the 2010-2011 data taking period. The same inegrated luminosity has just been recorded this year, which corresponds to doubling the total available integrated luminosity. The data sample which can be used for physics analysis has more than doubled in the same time, since it is expected that the cross-sections for bb and cc quark-antiquark pair production have increased by 15% and 12%, respectively, at the increased pp collision energy of 8 TeV this year. LHCb physicists expect to more than triple their data set this year by the end of pp collision run at December, which should allow them to obtain even more interesting physics results.

You can follow live the progress of delivered and recorded luminosity at LHCb, the number of proton-proton collisions visible at LHCb, as well as the number of bb and cc quark pairs produced within the LHCb acceptance at the image above on this page.

3 August 2012: 1 fb-1 of luminosity has been delivered to LHCb this year.

"This is great achievement considering that it comes about two months earlier than last year. Once more, the excellent performances of the machine, the skill and the commitment of the whole LHC team, made possible this result. We have also the exciting perspective of getting another 1 fb-1, or more, this year. This increased sample will allow us to push further our knowledge of Standard Model, and find finally where new physics is hiding so well." - said Pierluigi Campana, LHCb spokesperson.

12 July 2012: LHCb film shortlisted by the European Science TV and New Media Festival 2012.

"LHCb - A Beauty Experiment", a short documentary on LHCb, has been shortlisted by the European Science TV and New Media Festival 2012. The festival takes place in association with the ESOF 2012 Science Congress in Dublin at Trinity College on 13-15th July 2012. The goal of the festival is to help writers to develop TV drama that involves science and technology. It is interesting to note that the LHCb film was already shortlisted by the NHK Japan Prize Festival in October 2011. Watch the film on YouTube in different resolutions and with subtitles in 15 different languages.

Screen shots from the film show the LHCb control room on 23 November, 2009 (left) and on 30 March, 2010 (right).

7 July 2012 (1): Measurement of the flavour-specific matter antimatter asymmetry.

[ assl = (-0.24 ± 0.54 ± 0.33)% ]

Physicists from the LHCb experiment have today released results that help to shed light on one of the most significant experimental discrepancies with the Standard Model of particle physics. In 2010, and with an update in 2011, the D0 experiment, analyzing data taken at the proton-antiproton collider Tevatron at Fermilab, reported an interesting observation: that the number of events containing two positively charged muons is lower than the number of events containing two negatively charged muons, see 2010 Fermilab Press Release. The observed difference was close to 1%, measured with almost the full D0 data sample of 9 fb-1. Like-signed dimuons can be produced from the decay of particles containing the b quark, which can mix between their particle and antiparticle states. A difference between the number of positive and negative dimuons would be an indication of CP violation. The D0 result differs by 3.9σ from the tiny value predicted in the framework of the Standard Model and could indicate the presence of a new physics contribution. This difference can be expressed as an asymmetry, Absl, where the label "b" indicates decay of particles containing b-quarks and "sl" (semileptonic) indicates that the decay involves leptons, in this case muons. The decaying matter (antimatter) B particles are composed of b-antiquarks(quarks) and d- or s-quarks(antiquarks). D0 physicists could not distinguish which type of decaying particles is at the origin of the measured asymmetry, therefore they present the measured asymmetry Absl in the image below as an inclined band across the plane of individual asymmetries in the decays of Bd and Bs mesons, labelled adsl and assl, respectively. The vertical band shows the measurement of the adsl asymmetry by the BaBar and Belle collaborations working at the Υ(4S) resonance, which is in agreement with the Standard Model calculations shown as the SM point in the image.

click the image for higher resolution

LHCb physicists have presented today at the ICHEP2012 Conference in Melbourne the most precise determination to date of the corresponding asymmetry for the Bs meson, assl. The LHCb result assl = (-0.24 ± 0.54 ± 0.33)% is shown as the horizontal blue band in the image above. The B0s semileptonic decays into D±sμ final states were studied to obtain this result. The charmed D±s mesons were reconstructed in the φπ± mode. More details can be found in the LHCb presentation in Melbourne and in the LHCb Conference Contribution here. The LHCb result is consistent with the Standard Model prediction and does not confirm the deviation from the Standard Model reported by the D0 experiment. The D0 experiment previously published a result using Dsμ events, shown as the horizontal yellow band.

The full 2011 LHCb data sample was used to obtain this result. LHCb physicists expect to more than triple their data sample this year.

Read also the CERN Bulletin article in English and French, in the CERN Courier article and the CERN Quantum Diaries.

7 July 2012 (2): Evidence for matter antimatter asymmetry in three-body charmless B decays.

[ ACP(B±→K±π+π-) = +0.034 ± 0.009 ± 0.004 ± 0.007 ]
[ ACP(B±→K±K+K-) = -0.046 ± 0.009 ± 0.005 ± 0.007 ]

LHCb physicists have presented today at the ICHEP2012 Conference in Melbourne measurements of differences between properties of matter and antimatter (CP violation asymmetry) in the charmless three-body B meson decays B±→K±π+π- and B±→K±K+K-. The dominant B meson decays involve a beauty b-quark decay into a charm c-quark. In the rarer charmless decays (without charmed mesons) discussed here the b-quark decays into a u,d or s-quark. LHCb physicists have measured the charge asymmetry ACP obtained from the difference between negative and positive B event rates. The numerical values of measured asymmetries are shown above. The significance is 2.8σ for the B±→K±π+π- decay and 3.7σ for the B±→K±K+K- channel. The latter is the first evidence of inclusive CP asymmetry in charmless three-body B± decays.

click the image for higher resolution

The results presented here are obtained by integrating (summing) the asymmetries over all kinematical variables of particles observed in the decays of B mesons. It is interesting to note that much larger asymmetries are observed in some small special regions, like invariant mass squared of the π+π- pair in the K±π+π- decay lower than 1 GeV2, or of the K+K- pair in the K±K+K- final state between 1.2 and 2 GeV2, as seen in the images above. Note that the value plotted in the figures is the raw asymmetry ARAWCP, and does not include all the small corrections that are included in the numerical results. LHCb physicists are planning further study of this intriguing feature.

The full 2011 data sample was used to obtain this result. LHCb physicists expect to more than triple their data sample this year.

More details can be found in the LHCb presentation in Melbourne and in the LHCb Conference Contribution here. Read also the CERN Bulletin article in English and French and the CERN Quantum Diaries.

25 May 2012: Puzzling asymmetries.

The decay of the beauty meson B into an excited K meson K* and a μ+ and μ- pair is considered as an important channel for new physics search, see 13 March 2012 and 22 July 2011 news. Different distributions and branching fractions have been studied for these B meson decays and compared with the Standard Model predictions. Recently LHCb physicists have studied in addition the differences in the results of measurements of neutral B meson decays into K*0μ+μ- and charged B+ meson decays into K*+μ+μ-. Theoretical uncertainties of the Standard Model calculations are strongly reduced in these differences. Physicists call these differences "asymmetries" and since this case involves differences between the decays of particles with different charges, it is called an "isospin asymmetry" AI. The Standard Model calculations predict this isospin asymmetry to be small, as shown with the help of the color line in the left image below, where the prediction is presented as a function of the square of the di-muon invariant mass (q2). The experimentally measured distribution, shown by points with error bars, is consistent with this prediction.

click the image for higher resolution

A surprise came when the physicists made similar analysis by replacing the excited kaon K* by its ground state K. The negative asymmetry is clearly visible in the right image above (4.4σ different from zero after integration (summation) over the whole q2 region). The Standard Model calculation is not yet available for this asymmetry, but is, as in the Bs→K*μμ mode, expected to be very close to zero.

The images shown above were obtained with the full 2011 data sample. These results have been made possible by the strong and continuous support from the LHC operations team for the LHCb physics program, and the data sample is expected to more than double by the end of this year. In the meantime theorists will analyze this puzzling result in order to establish whether this effect can be accommodated in the framework of the Standard Model, or whether a new physics explanation is required.

Read more in CERN Bulletin article in English and French, in the CERN Courier article and LHCb publication.

16 May 2012: First observation of two excited states of Λb.

The quark model, independently proposed by physicists Murray Gell-Mann and George Zweig in 1964 to classify the strongly interacting particles called hadrons, is very successful. In this model baryons are composed of three quarks and mesons are composed of quark-antiquark pairs. The simplest baryon, the proton, which is the nucleus of the hydrogen atom, is composed of three light quarks uud while its neutral partner the neutron is composes of udd quarks. By replacing one of the d quarks by a heavier strange quark s we obtain a Λ particle composed of uds quarks. Furthermore by replacing in the Λ the s quark by a charm quark c or a beauty quark b we obtain a Λc or a Λb particle.

The three quarks forming the Λ, Λc and Λb are in their lowest quantum mechanical state. Like electrons in atoms quarks can form excited states with different values of angular momentum and quark spin orientation. These excited states were previously observed for the Λ and Λc particles. They were, however, never observed for the Λb particle.

The LHCb collaboration has made first observations of two excited states of Λb.

click the image for higher resolution

The Λb excited states have been reconstructed in three steps. In the first step the Λc+ particles were reconstructed through their decay into a proton p, a negative K- meson and a positive π+ meson. In the second step the Λc particles were combined with negative π- mesons in order to form the Λb particles. The Λb signal is clearly seen as the enhancement in the left image above showing the Λc+π- invariant mass spectrum. Finally the Λb particles have been combined with a pair of opposite sign pions π+π-. In the right image above two enhancements are clearly seen corresponding to the two Λb excited states with masses of 5912 and 5920 MeV, about 6 times the proton mass.

LHCb physicists have observed about 16 Λb(5912)→Λbπ+π- decays (4.9σ significance) and about 50 Λb(5920)→Λbπ+π- decays (10.1σ) among about 60 million million (6*1013) pp collisions seen by the LHCb detector at LHC during the 2011 data taking period.

Read more in CERN Bulletin article in English and French, in the CERN Courier article and LHCb publication.

27 April 2012: The rarest B decay ever observed.

The LHCb collaboration has made the first observation of the decay B+ → π+μ+μ-. With a branching ratio of about 2 per 100 million decays, this is the rarest decay of a B hadron ever observed, see CERN Courier article.

click the image for higher resolution

The image shows the invariant-mass distribution of selected π+μ+μ- combinations, showing the clear peak corresponding to B+ decays (green long-dash). Also shown are the components in the fit from partially reconstructed decays (red dotted) and misidentified K+μ+μ- (black dashed) and the total (blue solid line). Candidates for which the μ+μ- pair is consistent with coming from a J/ψ or ψ(2S) decay have been excluded.

6 April 2012: LHCb looks forward to electroweak physics.

Measurements of the production of W and Z bosons, see 10 June and 22 July 2010 news, allowed LHCb physicists to explore electroweak physics, see CERN Courier article.

click the image for higher resolution

The two images above show the complementarity of measurements made by different LHC experiments. The left image shows the x-Q2 kinematic region explored by the LHCb experiment (pink), compared with ATLAS and CMS (light green), as well as previous experiments. The right image shows LHCb's measurement of W charge asymmetry, shown as a function of lepton pseudorapidity, compared with theoretical predictions, and with results from the ATLAS and CMS experiments. More details and explanations can be found in the CERN Courier article.

30 March 2012: LHCb strongly squeezes SUSY parameter space.

Results presented by the LHCb Collaboration at the Rencontres de Moriond EW and QCD conferences allowed theorists to squeeze strongly the parameters of supersymmetric extensions of the Standard Model (SUSY), the most popular new physics model. The simplest version of this model, called the Minimal Supersymmetric Standard Model (MSSM), predicted the frequencies with which Bs and Bd mesons decay into pairs of oppositely charged muons to have values significantly different from the Standard Model (SM) prediction. This is shown in the left image below, which was presented by David Straub (SNS and INFN, Pisa) at the Moriond EW conference. The predictions for both frequencies (branching ratios BR) depend on different parameters of the MSSM and cover nearly all of the left image surface. The LHCb results, see 5 March 2012 news, limit the predictions that are still allowed to a small region around the SM expected value. It is interesting to note that certain combinations of MSSM parameters allow lower BR values than those predicted by the SM. The LHCb measurements of the parameter φs, which sets the scale for the difference between properties of matter and antimatter for the strange beauty Bs mesons, see 5 March 2012 news, also strongly limits the SUSY parameter space that is still allowed, as shown by the vertical lines on the right image below.

SUSY contributions to observables that can be measured in experiments depend, in general, on more than 100 free parameters. Therefore in order to be able to analyse experimental data physicists are using a simplified model, the Constrained MSSM (CMSSM), with 5 parameters m0, m1/2, A0, tan β and μ/|μ|. Nazila Mahmoudi (Clermont-Ferrand and CERN) presented the left image below at the Moriond QCD conference. The parameter space below and to the left of the red line is excluded by the results of searches for direct production of SUSY particles at the CMS experiment, while the large yellow region shows the parameter space excluded by the analysis of Bs →μμ decays at LHCb. The image is made for a relatively high value of the parameter tan β=50. The LHCb exclusion region is smaller at lower values of tan β as can be seen in the right image below, made with tan β=35. The green regions on both images are still not excluded by LHCb's measurements.

click the image for higher resolution

The images above illustrate that direct and indirect SUSY searches at LHC are complementary and show that the allowed parameter space is characterized by low tan β and high m0 and m1/2 within the CMSSM. LHCb's results have ruled out large deviations in several observables, but now LHCb physicists can start to probe the most interesting parameter region of new physics.

13 March 2012 (1): B0d →K*μμ, a first measurement of the zero-crossing point.

[ Zero crossing point B0d →K*μμ = 4.9+1.1-1.3 GeV2 ]

LHCb physicists have continued their search for physics beyond the Standard Model using the B0d decay into a K* meson (an excited kaon), and a μ+ and μ-. New physics contributions can change various distributions that describe the decay process. For example, the number of decays as a function of the square of the di-muon invariant mass (q2) and the di-muon forward-backward asymmetry (AFB) can both be affected in many new physics scenarios. The variable AFB indicates whether more or fewer muons of one sign are observed in the same direction as the K* than opposite to it. The distribution of AFB in function of q2 is shown below. The results have been announced today at the Rencontres de Moriond QCD conference.

click the image for higher resolution

The point at which the AFB distribution is crossing zero is well predicted within the Standard Model, and any deviation could indicate a possible contribution from new physics. LHCb physicists have already presented at the 2011 summer conferences a first indication that the asymmetry is changing sign. Today, using three times higher statistics, they presented the first measurement of the zero-crossing point of 4.9+1.1-1.3 GeV2. This value, showed by the hatched vertical region in the Figure, is in agreement with the Standard Model prediction showed by the colored line.

The LHCb Collaboration aims to more than double its data set this year. With the new data, the zero-crossing point will be measured with higher precision, and a possible difference with the Standards Model prediction may be discovered.

Read more in the LHCb staff page.

13 March 2012 (2): A first measurement of the CP asymmetry in the decay B0s →K+K-.

In a fascinating world of quantum mechanics the strange beauty particle (matter) B0s turns into its antimatter partner about 3 million million times per second (3*1012), see 15 March 2011 news. Therefore CP violation effects, which are differences between the properties of matter and antimatter, can appear as variations with decay time. A name "time-dependent CP violation" is therefore used.

click the image for higher resolution

The left figure shows the CP asymmetry in the B0d decay into π+π- pair and the right figure shows the asymmetry in the B0s decay into K+K- pair. It can be clearly seen, by comparing time scales of both figures, that the B0d mesons oscillate much slower than the B0s mesons. A new analysis from LHCb has measured the CP asymmetry separated into two components: the difference in the decay rate of B meson and anti-B meson (physicists call it "direct CP violation") and the quantum-mechanical phase difference between the B meson and anti-B meson decay ("mixing-induced"). These two components appear as a cosine-like and as a sine-like oscillation in the asymmetry plots above.

The results, announced today at the Rencontres de Moriond QCD conference, for the B0d → π+π- decay are Adirπ+π- = 0.11 ± 0.21 ± 0.03 and Amixπ+π- = -0.56 ± 0.17 ± 0.03, meaning the oscillation appears to come mainly from the sine-like component. These are the first measurements of these quantities at a hadron collider, and are consistent with previously published results from other experiments. The results for the B0s → K+K- decay - which are measured for the first time ever - are AdirK+K- = 0.02 ± 0.18 ± 0.04 and AmixK+K- = 0.17 ± 0.18 ± 0.05.

About 2/3 of data taken in 2011 were used in this analysis. The LHCb Collaboration aims to analyse three times more data by the end of this year. This will allow to see if CP violation occurs in the B0s → K+K- decay, and see if the amounts of direct and mixing-induced CP violation are as expected by the Standard Model.

Read more in the LHCb staff page.

5 March 2012 (1): Search for New Physics, an important milestone

[ Branching ratio B0s →μμ < 4.5x10-9 at 95% CL ]

The LHCb collaboration has announced today at the Rencontres de Moriond EW conference one of the most hotly anticipated results from the LHC. LHCb has shown that the frequency with which a Bs meson decays into a pair of oppositely charged muons is not larger than 4.5 times out of one billion decays. Theorists have calculated that, in the Standard Model, this decay should occur about 3 times in every billion, but that if new particles predicted by theories such as supersymmetry exist, the decay could occur much more often (see news items of 8 April and 22 July 2011 for more details). The new results represent a milestone in the search for "new physics" beyond the Standard Model.

click the image for higher resolution

The left figure shows the mass calculated from the two muons for events that survive all selection requirements. The blue area shows the shape of random combinations of muons, while the red area shows the shape expected for real Bs decays (with the hatched area indicating the uncertainty on the sum of the two contributions). The data are seen to be consistent with a small excess over the background-only hypothesis. This excess is slightly less than, but consistent with, the Standard Model expectation, as shown in the right figure. The blue points show how likely the data distribution is for a given rate of Bs decay. The black dashed line shows the expected shape of the curve for the Standard Model rate, with the green band indicating the uncertainty. The horizontal lines allow to set limits with different degrees of certainty: for experts, the solid red line gives the 95% C.L.

Measuring the rate of this Bs decay has been a major goal of particle physics experiments in the past decade, with the limit on its decay rate being gradually improved by CDF, D0, LHCb and CMS experiments. The latest results by LHCb set the tightest limits to date. More data is needed to finally discover if the decay occurs at a rate above, below, or at that predicted by the Standard Model. LHCb aims to more than double the size of its data set in 2012, which could be enough to finally answer this question.

Read more in CERN Press Release CERN Bulletin article, in the CERN Quantum Diaries blog and also in the LHCb staff page.

5 March 2012 (2): Heavier strange-beauty lives longer and improved φs measurements.

[ φs = -0.002 ± 0.083 ± 0.027 rad]

LHCb physicists have reported today at the Rencontres de Moriond EW conference important progress in measurement of the difference between properties of matter and antimatter for the strange beauty Bs mesons. The new results improve on those presented at the summer 2011 conferences. The size of this difference is controlled by the parameter φs, which is predicted to be small in the Standard Model. However, effects of new particles not predicted by the Standard Model can make the measured value much larger. The progress is shown in the image below: the remaining allowed region is shown in yellow and compared to the previous results from LHCb in blue, and from CDF and D0 experiments in green and red, respectively.

click the image for higher resolution

In the mysterious world of quantum mechanics the strange-beauty meson Bs matter antimatter system is alternatively described as a heavy and light mass Bs meson system. The mass difference Δms determinates the matter antimatter oscillation frequency, see 15 march 2011 news. The difference of their lifetimes was measured together with the value of φs. Since it was not previously know if the heavier or lighter Bs mesons live longer, LHCb physicists have obtained two possible values for φs corresponding to two blue regions in the image above. (The axis label ΔΓs corresponds to the difference of inverse lifetimes between the heavy and light Bs meson, physicists call it width (Γ) difference.) Recently LHCb physicists have succeeded to measure that the heavier strange-beauty Bs mesons live longer and in this way eliminated one of two blue regions in the image. Sophisticated quantum mechanical interference effects were used in this measurement. Experts can read details of the analysis in the published article.

The full sample of data collected in 2011, three times larger than that used in summer 2011, was used to obtain the result
φs = -0.001 ± 0.101 ± 0.027 rad using Bs decays into into a J/ψ meson and a φ meson; combining it with the measurement of the Bs decay into J/ψ and f0(980) LHCb physicists have obtained the final result φs = -0.002 ± 0.083 ± 0.027 rad.

2012 data taking period will start soon. Search for new physics in the small yellow region will continue.

Read more in CERN Press Release CERN Bulletin article, in the CERN Courier article, in the CERN Quantum Diaries blog and also in the LHCb staff page.

5 March 2012 (3): First evidence for CP violation in the decays of Bs mesons.

Measurement of CP violation, which describes differences between the properties of matter and antimatter, is a very important goal of LHCb. CP violation is well established in the K0 and B0 meson systems. Recent results from the LHCb collaboration have also provided evidence for CP violation in the decays of D0 mesons. Consequently, there now remains only one neutral heavy meson system, the B0s, where CP violation has not been seen.

click the image for higher resolution

The LHCb collaboration has recently submitted for publication the first evidence for CP violation in the decays of B0s mesons. The paper (available here for experts), submitted to Physical Review Letters, confirms the preliminary results shown at the EPS-HEP meeting in Grenoble, see 22 July 2011 news. The B meson decays into K and π mesons were studied. The decay into a positive K meson red track and a negative π green track is show in the event display above. The four plots on the right hand side show the Kπ invariant mass distribution divided into different components as shown by the legend in the top-right figure. The different charge combination of K and π indicates if the decaying B particle is a matter or an antimatter particle. The two upper plots show that the decay rates of B0d mesons are different, as known from previous experiments. The lower two plots show that the difference is also visible for the B0s mesons. The measured CP asymmetry for the B0d mesons ACP = -0.088 ± 0.011 ± 0.008 constitutes the most precise measurement available to date and the first observation (6σ) at a hadron collider. The measured CP asymmetry for the B0s mesons ACP = 0.27 ± 0.08 ± 0.02 is the first evidence (3.3σ) for CP violation in the decays of these mesons.

LHCb physicists have used 1/3 of data collected in 2011 in this analysis and expect to have ten times more data by the end of this year.

Read more in CERN Press Release CERN Bulletin article, in the CERN Quantum Diaries blog and also in the LHCb staff page.

1 December 2011: LHCb looks to the future.

After a very succesful 2011 data taking period the LHCb Collaboration is preparing next year's operation. The first 2012 collisions should be observed in April. At the same time LHCb physicists are also actively working on the longer term future in which data will be taken at a much higher rate, see CERN Courier article.

14 November 2011: CP violation in charm decays.

[ ΔACP = (-0.82 ± 0.21 ± 0.11)% ]

The LHCb Collaboration has presented today at the Hadron Collider Particle Symposium in Paris possible first evidence for CP violation, the difference between behaviour of matter (particles) and antimatter (antiparticles), in charm decays. The study of CP violation in both charm and beauty particle decays is central to the LHCb physics programme. In the Standard Model CP violation is expected to be very small in the charm sector, whereas new physics effects could generate enhancements.

In this new analysis the LHCb physicists have used data collected in the first half of the 2011 run to study the differences in decay rates of neutral D meson particles composed of a charm quark c bound with an up antiquark (u) and D meson antiparticles (D) composed of a charm antiquark (c) bound with an up quark (u). The decays of D*+ mesons into D mesons and π+, and D*- mesons into D mesons and π- were used to select the D and D mesons. In the next step of the analysis the difference (asymmetry ACP) between the decay rates of D and D mesons into K+K pairs as well as into π+π- pairs was measured. By determining the difference, ΔACP, in CP asymmetries for the K+K- and π+π- decays, the analysis strongly suppresses possible measurement biases which could arise through effects related to particle production, selection etc. The following preliminary result is obtained:

ΔACP = (-0.82 ± 0.21 (stat.) ± 0.11 (sys.) )% [ 3.5 sigma significance for experts ]

A very interesting period now begins. LHCb physicists are analysing the remainder of the data collected in 2011. If the result is confirmed theoretical work will be required to establish whether this effect can be accommodated in the framework of the Standard Model, or whether a new physics explanation is required.

click the image for higher resolution

The figures show the invariant mass distribution of the K-K+ (around 1.4 million) and π-π+ (around 0.4 million) pairs. The distributions are centered at the D meson mass of 1865 MeV.

Read more in CERN Bulletin article in English and French, in the CERN Courier, in the CERN Quantum Diaries blog in English and French and also in the LHCb staff page.

30 October 2011: End of 2011 proton-proton collision data taking period.

The 2011 proton-proton collision data taking period has ended today. LHC collider and LHCb experiment have been working extremaly well. LHCb has recorded all in all an impressive 1.1 fb-1 out of a 1.22 fb-1 delivered at 3.5 TeV.

“We’ve got from the LHC the amount of data we dreamt of at the beginning of the year and our results are putting the Standard Model of particle physics through a very tough test ” said LHCb Spokesperson Pierluigi Campana. “So far, it has come through with flying colours, but thanks to the great performance of the LHC, we are reaching levels of sensitivity where we can see beyond the Standard Model. The researchers, especially the young ones, are experiencing great excitement, looking forward to new physics.”

Read more in CERN Press release in English and French.

3 October 2011: 1 fb-1 of luminosity has been delivered to LHCb.

This is a very important milestone for LHCb which will allow LHCb physicists to reach an unprecedented accuracy in most of the core physics processes that are under study.

Read more in CERN Bulletin article in English and French.

click the image for higher resolution

The left hand image shows Mike Lamont (Operations Group Leader), Pierluigi Campana (LHCb Spokesperson), Steve Myers (Director for Accelerators and Technology), and Paul Collier (Head of the Beams Department) celebrate the LHCb milestone. The right hand image shows the zoom on the computer screen located above them and showing the LHC screen congratulating LHCb for its new record.

3 October 2011: LHCb film shortlisted by Japan Prize Festival

"LHCb - A Beauty Experiment", a short documentary on LHCb, has been shortlisted by the NHK Japan Prize Festival. Every year, the festival awards the very best in global educational media. Watch the film at YouTube in different resolutions and with subtitles.

27 August 2011: φs: different properties of matter and antimatter for Bs mesons

[ φs = 0.03 ± 0.16 ± 0.07 ]

LHCb physicists have presented today the most precise measurement of φs (the Bs mixing phase, for experts) at the Lepton Photon conference in Mumbai (India). The value of φs is precisely predicted in the Standard Model and sets the scale for the difference between properties of matter and antimatter for Bs mesons, known to physicists as CP violation. The predicted value is small and therefore the effects of new physics could change its value significantly - see the analogy in the 8 April news.

The decay of the strange-beauty particle B0s, composed of a beauty antiquark (b) bound with a strange quark (s), into a J/ψ meson and a φ meson was used for this measurement. The J/ψ meson decays in turn into a μ+μ- pair, and the φ decays to K+K pair. In order to make this difficult measurement LHCb physicists had to analyse the Bs decay particles in 3 dimensions as well as to measure precisely the fast oscillations of strange beauty - see 15 March news.

The "artist's view" below shows the result of the φs measurement in a plane together with the correlated measurement of another value, ΔΓs. The results of the measurement favour two regions, one of which is located around φs = -0.036 ± 0.002 rad, the Standard Model prediction. The LHCb measurement is in agreement with the Standard Model prediction but the shaded region representing the LHCb result indicates that there is still room for a new physics contribution. The hints for a larger contribution of new physics suggested by the CDF and D0 experiments at Fermilab, also shown in the figure, are not confirmed.

click the image for higher resolution

In February the LHCb Collaboration made first observation of the Bs decay into J/ψ f0(980) - see 27 February news. This decay contributed to the φs measurement.

Using both Bs decays LHCb physicists have obtained the value φs = 0.03 ± 0.16 ± 0.07.

Read also CERN Press Release in English and French.

Read also CERN Bulletin article in English and French.

Read also CERN Courier article.

22 July 2011 (1): Hunting for New Physics continues

[ Branching ratio B0s →μμ < 1.2x10-8 at 90% CL and 1.5x10-8 at 95% CL ]

LHCb physicists continue their search for new physics, see 8 April 2011 news for introduction. They have presented updated results during the International Europhysics Conference on High Energy Physics (EPS-HEP) at Grenoble this week. The LHCb physicists have succeeded in setting the limit for an enhanced decay rate of the strange beauty particle B0s, composed of a beauty antiquark (b) bound with a strange quark s, into a μ+ and μ- pair, as low as about 4 times the rate calculated within the Standard Model (limits 1.2x10-8 at 90% CL and 1.5x10-8 at 95% CL for experts). This result was obtained from the analysis of about 8 times more data than in the previous analysis.

click the image for higher resolution

The computer reconstructed images above show the most significant event compatible with the strange beauty B0s decay into muon pair seen as a pair of purple tracks traversing the whole detector. The right hand image shows a close-up around the proton-proton interaction point from which many tracks originate. The B0s decays about 1 cm from the proton-proton collision point into two muons (purple tracks). The invariant mass of muon pair corresponds to the B0s mass. The number of observed B0s candidates is slightly above the background predictions and compatible with the expected signal predicted by the Standard Model (SM) theory. This analysis is much more sensitive than previous experiments, and although large deviations (by more than a factor 4) from the SM are excluded, there is still plenty of room for new physics contributions. LHCb physicists are expecting to be able to analyse about three times as many events by the end of 2011, and about ten times more by the end of 2012, to give a final answer for the possibility of a new physics contribution to this interesting rare decay.

22 July 2011 (2): Hunting more for New Physics

LHCb Physicists have also presented results of their search for new physics using the B0d (composed of a beauty antiquark (b) bound with a down quark d) decay into an excited K meson, K*, and a μ+ and μ-. The partial rate as a function of the square of the di-muon invariant mass (q2) and the di-muon forward-backward asymmetry (AFB) can both be affected in many new physics scenarios. The variable AFB indicates whether more or fewer muons of one sign are observed in the forward direction than in the backward direction. The distribution of AFB in function of q2 is shown below.

click the image for higher resolution

The LHCb precision measurements shown in black are in agreement with the Standard Model (SM) theory and indicate for the first time that the asymmetry is changing sign as predicted by the SM. The results of measurements by other experiments are presented in the figure on the right hand side.

22 July 2011 (3): Different properties of matter and antimatter

An important part of the LHCb physics programme is reserved for studying differences between the properties of matter and antimatter (CP violation for experts). At the EPS-HEP meeting in Grenoble this week the LHCb physicists have presented distributions in which these differences can be clearly seen.

click the image for higher resolution

The blue line follows the measured points. After background subtraction (slightly sloping black line from left to right) the Kπ invariant mass distribution is divided into different components shown in different colours. The different charge combination of K and π indicates if the decaying B particle is a matter or an antimatter particle. The red curve in the upper plots shows the decay rate of B0d (matter, left plot) and anti-B0d (antimatter, right plot). The horizontal red dotted line helps to show that the decay rates of matter and antimatter B particles to Kπ mesons are different. The green distributions in lower plots show that the difference between matter and antimatter decay rate is also observed in B0s decays to Kπ.

1 June 2011: Pierluigi Campana - new spokesperson for the LHCb collaboration

Pierluigi Campana from the Istituto Nazionale di Fisica Nucleare in Frascati, begins his 3-year tenure as LHCb spokesperson this June. He replaces Andrei Golutvin, from Imperial College London and Russia’s Institute for Theoretical and Experimental Physics. As the new voice for the collaboration, Campana will lead the experiment through what should prove to be a very exciting phase.

Read more details at the LHCb Collaboration Web page and in the CERN Bulletin article in English and in French.

8 April 2011: Hunting for New Physics

Quantum mechanics allows energy non-conservation during a very short time, typical in particle collisions. This opens up the possibility to study signal for the existence of particles for which there is insufficient energy to produce them directly. This feature is used by LHCb physicists to search for heavy particles expected in new physics models - models that describe physics outside the Standard Model (SM) of particle physics. Since the effects of new physics are expected to be very small, LHCb physicists are looking for modifications of the properties of very rare SM processes which can be calculated with high precision. The rare decay of the strange beauty particle B0s, composed of a beauty antiquark (b) bound with a strange quark s, into a μ+ and μ- pair is an excellent candidate. Only one out of 3*109 B0s mesons should decay into a μ+μ- pair according to precise SM calcutions. This rate could be higher if new physics particles, such as those in models with an extended Higgs sector, for example, were to influence this decay.

LHCb physicists have not seen these decays in the data taken during the 2010 run and were able to set a limit which is about 19 times higher than the SM prediction, that is, the limit close to the one set by the Fermilab experiments CDF and D0 after many years of data taking. The figure below was used to set this limit at different levels of statistical probability.

click in the image to get it in higher resolution

LHCb physicists expect to observe the B0s mesons decay into μ+μ- pairs with the rate calculated within the SM using data taken this year and in 2012. An earlier observation of a higher rate will give interestng evidence for new physics.

Read more details in the CERN Courier article.

25 March 2011: LHCb movie

LHCb live and LHCb physics are presented in a short movie (about 15 min) "LHCb - the beauty experiment", available at YouTube and CDS. The YouTube version allows you to choose subtitle language (cc just below the movie window), as well as the image resolution including High Definition version 1080p.

15 March 2011: Oscillating Strange Beauty
or how matter turns into antimatter and back

Using data collected in proton–proton collisions at the LHC at a centre-of-mass energy of 7 TeV LHCb has observed a fascinating feature of quantum mechanics. The strange beauty particle (matter) B0s composed of a beauty antiquark (b) bound with a strange quark s turns into its antimatter partner composed of a b quark and an s antiquark (s) about 3 million million times per second (3*1012). The B0s particles have been identified through their decay into strange charm Ds particles (composed of a charm quark c bound with a strange s antiquark) and one or three πs. Of course, LHCb observes B0s particles and antiparticles only during their short lifetime in which they travel about 1 cm in the LHCb detector.

The plot shows the observation of these oscillations when all data have been folded into one oscillation period. The variable Amix is proportional to the difference between the number of events in which the produced matter(antimatter) B0s particle had the same identity during its decay, and the number of events in which it had not, as a function of its lifetime.

click in the image to get it in higher resolution

The B0s oscillations were observed for the first time by the Fermilab experiments CDF and D0 in 2006, see Press Release article. The oscillation parameters measured by the LHCb Collaboration show agreement with those measured at Fermilab.

27 February 2011: LHCb makes first observations of interesting B0s decays

Using data collected in proton–proton collisions at the LHC at a centre-of-mass energy of 7 TeV, the LHCb experiment has observed two new rare decay modes of B0s mesons for the first time. The decay B0s → J/ψ f0(980) will be important for studying differences between properties of matter and anti-matter (CP violation for experts) in the B0s system, while the decay B0s → D*–s2+ν will be valuable for testing predictions of strong interaction (QCD) theory.

The first new decay mode observed is of the decay B0s → J/ψ f0(980). The B0s consists of a b antiquark (b) bound with an s quark, and can decay to a J/ψ (cc) together with an ss state, which can be a φ or, more rarely, an f0. While the φ decays to K+K, the f0 decays to π+π. The figure shows the enhancement in the π+π invariant mass distribution in the region of 980 MeV indicating an observation of f0(980).

click in the image to get it in higher resolution

The observation of these two new decay modes demonstrates that the LHCb experiment is already competitive in the field of heavy flavour physics. Great progress is expected with the larger data sample due from the coming run, with the potential to constrain, or even observe, new physics.

Read more details in the CERN Courier article, which also includes description of the second decay.

Read more details in the National Science Foundation article.

27 October 2010: Exotic mesons

In 1964 Murray Gell-Mann and George Zweig proposed the quark model (QM) in which mesons, like π mesons, are formed from quark and anti-quark pairs and baryons (like protons) from three quarks. The model is very succesful, but recently particles which could not be classified in this model have been discovered. LHCb has observed one of these exotic state candidates called X(3872) using its decay into a J/ψ meson (see 6 September news) and a π+ π- pair. The J/ψ decays in turn into a μ+ and μ- pair. The invariant mass of J/ψ π+ π- is shown in the figure below. The left enhancement at the mass of 3686 GeV is consistent with the QM bound state ψ' of charm and anti-charm quarks, the right one at the mass of 3872 GeV has properties that are very difficult to reconcile with the Gell-Mann Zweig QM. Possible explanations include a meson-meson molecule (DD* for experts) or multi quark anti-quark system (diquark-diantiquark tetraquark meson for experts).

this plot was made using all data taken in 2010, click in the image to get it in higher resolution, click here to see original plot.

The particle with the mass of 3872 Gev was first observed by the BELLE collaboration in 2003 and is called X(3872). The observation of this particle at this early stage of data taking by LHCb confirms the excellent performance of the LHCb detector and data analysis.

-----------------------------------------------------------------------------------------------------------

13 October 2010: LHCb control room in action

LHCb physicists discussing data taking.

click in the image to see other photos.

-----------------------------------------------------------------------------------------------------------

24 September 2010: Young scientists at LHCb

The young scientists took part in the LHCb shifts during the European researchers’ night on Friday 24 September.

click in the image to see other photos.

Read CERN Bulletin article in English and French, as well as the one in the Symmetry Breaking.

-----------------------------------------------------------------------------------------------------------

6 September 2010: Beautiful atoms

The LHCb has observed beautiful atoms. The atoms are bound states of the beauty quark and anti-beauty quark. The atoms are bound by the strong force, the force which also binds quarks inside proton. The beautiful atom is 10 times heavier than the proton (yes, we can create mass from energy using famous Einstein formulae E=mc2), has a size sligtly smaller than the size of the proton but about 100 000 times smaller than the size of the hydrogen atom which is composed of a proton and an electron and is bound by the electromagnetic force. Just like ordinary atoms beauty and anti-beauty quarks form different quantum states with different angular momenta and different spin orientations (see figure below right). Only the states marked 1S, 2S and 3S are observed at LHCb by detecting their decay into a μ+ and μ- pair (left).

The figures above show the invariant mass of μ+ and μ- particles (left) and the schematic view of the beautifull atom quantum states (right), click in images to get them in higher resolution. The invariant mass plot was made using all data taken in 2010, click here to see original plot.

The beauty-anti-beauty atom, called "Upsilon" was discovered in 1977 at the proton-antiproton collider at Fermilab near Chicago.

The states 1S, 2S and 3S do not decay into Beauty Particles since their mass is lower than the sum of masses of Beauty and anti-Beauty particles (BB threshold in the figure). On the other hand the state 4S does decay. This feature is used by the experiments BABAR and BELLE producing the 4S state at e+e- colliders as a source of Beauty and anti-Beauty particles.

The charm and anti_charm quarks form two bound atom states 1S and 2S called J/ψ and ψ' observed at LHCb through their decay into a μ+ and μ- pair (left) and a e+ and e- pair (right).

click in images to get them in higher resolution.

-----------------------------------------------------------------------------------------------------------

22 July 2010: From a B to Z, LHCb explores the particle alphabet

LHCb has unveiled pictures of a Z boson inside the experiment. This boson is one of the best understood of all particle species. It shows us how the forces of electricity, magnetism and radiation are connected inside the Standard Model, our theory of particle physics. Measurements of how often we see Z bosons inside LHCb will provide a sensitive test of how well our theory describes this particle at the record breaking energies of the LHC.

click in images to get them in higher resolution

In this picture the Z boson has decayed immediately to two muons μ, shown by the thick white lines which point to the green muon chamber hits in the outer circle of the Eolas display (described in 10 June 2010 News). Not much else happens inside LHCb when a Z is at work – only a few other particles are visible – and this makes it an easy particle to find. We’re looking forward to collecting more of them now, and really testing how well the Standard Model performs for us.

-----------------------------------------------------------------------------------------------------------

12 July 2010: LHCb is younger!

The average age of the LHCb Collaboration members has strongly decreased after arrival of the LHCb summer students seen below in front of the Globe of Science and Innovation. The Summer Students follow the lectures given at the first floor of the Globe in the morning. During the breaks they can visit the new CERN exhibition "Universe of Particles" located on the ground floor and the rest of the time they make an important contribution to the LHCb data taking and data analysis.

click in image to get it in higher resolution

-----------------------------------------------------------------------------------------------------------

10 June 2010: The W boson in action

LHCb has taken its first snapshots of the W boson in action. This particle conveys the weak force, which makes certain forms of radioactivity possible. It is shown here having decayed to a muon μ (shown as a straight white line, pointing to the filled green muon detector hit circles in the 2D picture, and as a red line pointing to blue muon hits in the 3D picture), which we see, and a neutrino ν, which we don't, with very little else around it.

click in images to get them in higher resolution

Eolas (gaelic for 'knowledge') is a 2D view of a collision inside LHCb. It is a transmogrified view, chosen to illustrate where particles deposit energy as they fly outwards from the collision point. The radius represents flight through the detector along the beam direction - through the tracking detectors, then the first muon chamber, then the electromagnetic and hadronic calorimeters, and finally the last four muon chambers. The φ angle represents the angle in the x,y direction perpendicular to the beam. Information is colour coded. Particle tracks are shown by the dashed lines. The transverse momentum of the particle is shown by the solid white long along this path - the higher this is, the longer the solid white bar is. Yellow bars show energy deposited in the electromagnetic calorimeter, cyan energy deposited in the hadronic calorimeter. Deposits in muon chambers are illustrated by green circles. If these are filled, they are associated with a particle track passing through them.

We will use samples of W bosons to test our theory of particle physics, the Standard Model, to high precision. This is exciting because we don't know yet if our theory holds at LHC energies - if it doesn't, if there are new particles to find in nature, we'll see W bosons behaving in a way we don't expect. With these first snapshots taken, we're on our way to finding out.

The W boson was discovered in 1983 at CERN by the UA1 and UA2 experiments giving the Nobel Prize to Carlo Rubbia and Simon van der Meer.

-----------------------------------------------------------------------------------------------------------

7 May 2010: Strange Beauty and Charm

LHCb has reconstructed an event having all characteristics of a Strange Beauty Particle decay! A computer view of this event is shown below. The Strange Beauty Particle (called Bs) is composed of an anti-quark b (b is for beauty) and a quark s (s is for strange). It is produced by the collision of two 3.5 TeV protons from the LHC at a location marked as "PV" (Primary Vertex), together with many other particles (not shown). The Bs decays after travelling about 1.5 mm into three particles called μ-, Ds+ and neutrino ν at a place marked "SV" (Secondary Vertex). The ν is not detected since it can even traverse the whole Earth without any interaction. The Charm Particle Ds+ is composed of a c quark (c is for charm) and anti-quark s. The Ds+ particle decays in turn after travelling 6.5 mm into three long lived particles K+, K- and π+ in a place called "TV" (Tertiary Vertex). The K+, K- and π+ are traversing the LHCb detector where the tracking system is used to reconstruct their trajectories with such a very high precision that it is clear that the particles come from three different places called vertices.

click in image to get it in higher resolution

-----------------------------------------------------------------------------------------------------------

21 April 2010: First reconstructed Beauty Particle

LHCb has reconstructed its first Beauty Particle! You can see below a computer view of this event in two projections (images on the left hand side). The Beauty Particle (called B+) is composed of an anti-quark b (that has a very short lifetime of 1.5 thousandth of a nanosecond!) and a quark u. It is produced by the collision of two very high energy protons from the LHC at a location marked as "Primary vertex", together with many other particles (shown in black). The B+ decays after travelling about 2mm into two particles (called J/ψ and K+) at a place marked "B decay vertex". The J/ψ particle decays in turn immediately into two long lived particles called μ+ and μ-. The μ+ , μ- and K+ are traversing the LHCb detector where the tracking system is used to reconstruct their trajectories with such a very high precision, that it is clear they do not come from the primary vertex. The fact that the reconstructed tracks do not cross exactly in two points reflects experimental precision of computer reconstruction. The real particle tracks originate at the two vertices. The images on the right hand side show the same event when the tracks from the "Primary vertex" are forced to come from the "Primary vertex".

click in images to get them in higher resolution

The LHCb physicists have collected about 10 million proton-proton collisions in order to find this first Beauty Particle. The reconstruction of each event is not easy, there are about 100 particle tracks reconstructed in this event, see full event display below.

More details: LHCb physicists have calculated invariant mass of μ+ and μ- particles from the "B decay vertex" and found that it correspond to the J/ψ mass, see below invariant mass distribution of all μ+ and μ- pairs with the peak corresponding to the J/ψ decays. The reconstructed invariant mass of J/ψ and K+ is 5.32 GeV, in agreement with to the known B+ mass, 5.5 times higher than the colliding proton mass but 650 times smaller than the colliding proton energy (yes, we can create mass from energy using famous Einstein formulae E=mc2).

see comments in articles: NewScientist internet, magazine and ZDNet.

First

30.3.2010

Both proton beams made a full turn of LHC on Feb. 28th. A new period of great measurements with LHCb has started again and will continue for 18-24 months. On March 18th both beams have been accelerated to 3.5 TeV,

3.5x3.5 TeV

30.3.2010

see TV footage with preparation for collisions and photo above taken just after the first collisions at 12:59 on March 30 (click on picture to get it in higher resolution).

more pictures can be found here, here, and here.

proton-proton collisions

30.3.2010

Our first 3.5x3.5 TeV collision; other events can be found here.

Read CERN Bulletin article in English and French and also CERN Courier article.

see LHCb video on YouTube, and CDS as well as interview with Tara Shears.

International

8.3.2010

On March 8th, during during International Women's Day, many many women have been present in the LHCb control roon, ...

Women's

8.3.2010

see the photos taken at the LHCb control room (click in pictures to it in higher resolution, click here to get other photos), the video interview with Monica Pepe-Altarelli here, ...

Day

8.3.2010

the LHCb women poster (click in image to get higher resolution), and the CERN and the Fermilab Web pages.

2009 News

Below you may find interesting computer reconstructed events observed with the LHCb detector during the LHC restart period in November and December 2009. Click on picture to see it in higher resolution version.

Protons have ended to circulate at LHC on December 16th.

1.2 TeV collisions at LHCb

14.12.09

On December 14th 1.2 TeV proton beams have collided at LHCb during LHC machine studies. Many LHCb subdetectors, except for sensitive silicon detectors, recorded the world's highest energy pp collisions. Other events can be found here.

proton interactions with gas

12.12.09

Position of proton interactions inside the vertex detector with residual gas are shown in blue or red, proton-proton interactions in green (more details).

K0 reconstruction

12.12.09

So called "strange particles" are produced in the proton-proton collisions and decay inside LHCb detector into two other particles reconstructed as red tracks (more details).

High multiplicity events

12.12.09

A high multiplicity event with three muon tracks (green) recorded on December 12th. Other events can be found here.

More proton-proton collisions

8.12.09

On December 8th many long tracks were reconstructed using the detectors along the whole length of the LHCb. Collision vertex is clearly observed (bottom left). The tracks are curved in the magnetic field allowing measurement of the track momentum (top left). Other events can be found here.

More proton-proton collisions

6.12.09

On December 6th protons have again collided at LHCb. Few modules of sensitive LHCb Vertex Locator VELO recorded tracks clearly indicating proton-proton collision vertex location (see picture left bottom). Other reconstructed events can be found here.

RICH rings

6.12.09

LHCb RICH detectors are used to identify particles. The circles show possible position of measured points for different kinds of particles traversing the detector. The measured points clearly choose one possibility for every circle and in this way allow to identify particles.

First proton-proton collisions

23.11.09

A proton-proton collision candidate event. On November 23 protons from two beams circulated at LHC and have collided at LHCb.

LHC news video youTube

First proton-proton collisions

23.11.09

LHCb control room at this historical moment.

LHCb November 23 pp collision video youTube, CDS

First proton-proton collisions

23.11.09

Tracks originate from the expected region inside LHCb Vertex Locator detector VELO.

First proton-proton collisions

23.11.09

Another proton-proton collision candidate event.

Annimation

23.11.09

Animation (click on picture): pp collisions and proton beam gas collisions recorded on Nov. 23, 2009. Other reconstructed events can be found here.

First reconstructed pi0's

23.11.09

pi0 is the short lived particle decaying into two photons which were measured in the electromagnetic calorimeter ECAL. The plot above shows the nearly perfectly reconstructed pi0 mass.

First proton interactions

22.11.09

... reconstructed Vertex Locator VELO track. Other reconstructed events can be found here.

First proton interactions

22.11.09

... event reconstructed later (offline reconstruction). Particularly interesting is the blue track recorded in the Vertex Locator VELO and in the tracking chambers after the magnet.

First proton interactions

21.11.09

... not yet proton-proton interaction but interactions of the protons with residual gas inside LHC ring. Tracks reconstructed during data taking.

A splash from the LHC beam

21.11.09

LHC has restarted on November 21st. Two LHC beams have made a full turn of the LHC. Afterwards, after synchronization with the LHC accelerating system (RF capture in technical language), the beams made few hundred turns. During LHC operation LHCb has recoded splash events. The movie (click on picture) shows what LHCb detector has recorded every 25ns (1/(40 000 000) s) for a particular splash event; see individual events here.

News Archive »