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LHCb - Large Hadron Collider beauty experiment

When cross-validated, this parameter is usually set to values such as [0. With you are various dissidents like people who feared being Made a Slave.


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The left image above shows the increase of integrated luminosity as a fuction of time depending in which LHC ring protons and lead Pb ions are located; the first one p or Pb indicates which beam is pointed towards the one-sided LHCb detector. In total 31 nb -1 were recorded. The right image above shows a typical high multiplicity proton-lead-ion collision event, the left one below shows a zoom around the collision vertex and the right one below shows the event as seen from above.

Particles identified as pions orange , kaons red , protons magenta , electrons blue or muons green are shown in different colours. In addition to collected p-lead collisions, LHCb collected data from proton-helium interactions at the same time.

This was achieving by injecting helium gas as a target directly in the region of the LHCb Vertex Locator VELO , and recording those occasions when the circulating protons hit these near-stationary helium nuclei. A traditional end of the year shutdown period starts now. It is used for maintenance and improvements of the LHC and its detectors. This time it will be longer due to major installation work carried-out in one the LHC detectors.

LHCb plans for this period include some relatively minor maintenance work on the detector, together with more major interventions on the access lift and the crane in the underground cavern. It is planned that protons will start to circulate again in the LHC at the beginning of May and that the first proton-proton collisions for physics will take place in mid of June.

The result is surprising because the measured decay rate is high compared to theoretical predictions, and it was not yet thought that there were sufficient data collected to see a signal. It will be a nice challenge for theoretical physicists to understand the origin of this unexpected result. The image shows the D s K invariant mass distribution for different charge combinations of D s and K mesons. The B s meson contribution is shown as the dashed red line while the other shaded areas represent different background components.

The CP-violating asymmetries were measured as a function of the beauty meson decay time, as shown in the image. As apparent in the figure, the characteristic fast B s meson oscillation pattern is observed. The analysis has demonstrated that high purity is possible in this decay mode at LHCb owing to the absence of any significant physics backgrounds, as shown in the image.

While in items 1 , 2 and 3 the analyses used the full 3fb -1 LHC run 1 data sample, this analysis profited from an additional 1fb -1 collected during run 2 data taking period. Click on the images for higher resolution. In particular, precise measurements on the difference between the lifetime of D 0 mesons, composed of a c u quark pair, and their partner D 0 mesons, with opposite quark content c u when decaying either to a pair of pions or a pair of kaons were reported, in order to search for CP-violating effects in the Charm sector.

The phenomenon of CP violation, that is related to the difference between properties of matter and antimatter, is still unobserved in the charm-quark sector. As charm mesons are composed of up-type quarks only, this uniqueness makes the study of their properties particularly relevant.

Such properties might be sensitive to effects beyond those predicted by the Standard Model. According to the Standard Model, CP-violating asymmetries in the charm sector are expected to be very small, below the 10 -3 level for this measurement. Remarkably, the LHCb experiment is now approaching a level of precision where such small effects could be observed.

Charm mesons are produced either directly in the proton-proton collisions or in the decays of heavier beauty particles. Only the first category was used in this analysis. Two distinct measurements were done, which make use of the same data sample but with different experimental approaches.

These are the most precise measurements of CP violation ever made in the Charm sector, and are consistent with no CP violation with a precision of a few parts in 10 4. Many checks have been done in order to verify the good accuracy of the measurements to such an impressive level of precision. As an example, results obtained with two different orientations of the LHCb magnetic field, "up" and "down", are compared in the left image above for the data taken in LHCb has collected already 1 fb -1 integrated luminosity of data this year, three times more than in Given that 7 more weeks of proton-proton collisions remain in this year's schedule, it can be hoped that the final data set will be significantly larger.

Taking into account that the beauty-particle production rate at the higher collision energy of run 2 is more than twice that of run 1 see item 1 of ICHEP news , the total number of beauty-particle decays collected during run 2 is likely to be already higher than the total of run 1 by the end of this year. To reach this achievement LHCb has profited from the improvements to the data acquisition. In addition, the data accumulated in benefits from the revolutionary design of the new LHCb trigger.

The proton-proton collision period will end at November 1 st and then will be followed by a LHC machine maintenance period technical stop and three weeks of proton collisions with lead ions. The image shows the integrated luminosity progress during the different years of data taking.

The probability of b- and b -quark production cross-section in proton-proton collisions can be calculated in the framework of the theory of strong interactions, quantum chromodynamics QCD. This image is different from that presented at the conference, as described in the erratum to the corresponding paper.

This measurement is interesting since charmed D-meson decays are suitable for probing CP violation in the up-type quark sector. CP violation is related to the difference between the properties of matter and antimatter. Recent studies of CP violation in weak decays of D mesons show a good consistency with the hypothesis of CP symmetry so far, in agreement with the expectation of the Standard Model, which predicts very small violation in the charmed system.

This is to be contrasted with K and B meson decays, where CP violation is well established, again in broad agreement with the predictions of the Standard Model. The image summarises the current situation. The LHCb results presented at Chicago are shown as a dashed green ellipse. As apparent from the image there is no evidence for CP violation yet. This decay was searched for in the past for a long time by other experiments.

It occurs at a rate of less than 1 time in 10 million B 0 decays. This result will help to refine the QCD calculations of the dynamics governing the decays of heavy-flavoured hadrons. The understanding of this dynamics is a fundamental ingredient in the search for new particles and interactions beyond those included in the Standard Model.

New physics models often predict a different value of photon polarisation than that predicted by the Standard Model. The lifetimes of the mesons in this sample have been analysed and from this study information has been extracted on the photon polarisation.

The result is consistent with the Standard Model prediction within 2 standard deviations. LHCb reported the measurement of the, so called, C and S observables. The results are consistent with the Standard Model expectation, which in the absence of these additional contributions, are S of around The images below show the comparison of the LHCb results with previous measurements by the BaBar and Belle collaborations.

The data could not be described by a model that contains only ordinary particles, i. Each of the four particles is observed with a significance exceeding five standard deviations. The sophisticated analysis of the angular distribution of B meson decay products observed with the LHCb detector a so-called multidimensional full amplitude analysis allowed LHCb to determine properties quantum numbers of the particles with high precision.

The high statistics of the LHCb data set and the sophisticated techniques exploited in the analysis will help to shed further light into the production mechanisms of these particles. More information can be found in the first paper , with further details given in the second. The interest in these four states is also that they are the only known exotic candidates which do not contain u and d quarks, which are the lightest quarks and those which human beings and the matter around us are made of.

As such, they may be more tightly bound than other exotic particles. The observation of the X , X and X particles was announced for the first time today.

Searches for this particle by the Belle and BaBar collaborations gave negative results. Rather, a multidimensional full amplitude analysis, as described in the two papers submitted today, is crucial for data interpretation, and has allowed LHCb to characterise fully the particles, and to determine their quantum numbers.

The LHCb collaboration has made several other important contributions to the investigation of exotic particles. In February the quantum numbers of X were determined. In July the first observation of two pentaquark particles, i. Contrary to statements of other competitors, based on the team's name, the LHCb team was not using bicycles to win the race. Its winning formula of precision measurements and proximity to the beam line allows it to locate the point vertex precisely where the beauty particles decay, as seen in many images on this page.

An introduction to beauty and charm oscillations can be found in the 7 November news item. Any difference in this probability would be a manifestation of CP-violation, which is the difference between the properties of matter and anti-matter. The label "s" indicates decays of B 0 s mesons composed of anti-beauty b and s quarks, while "sl" semileptonic indicates that leptons, in this case muons, are present among decay products.

The full run 1 data sample of 3 fb -1 was used to obtain this update of the 1 fb -1 measurement. The LHCb result is the most precise measurement of a s sl to date and is consistent with the value predicted in the framework of the Standard Model. For this particular quantity the amount of CP-violation is expected to be tiny and hence the predicted value of a s sl in the Standard Model is very small.

Therefore the possible contribution of as yet undiscovered effects, which help to drive the B 0 s - B 0 s oscillations, could lead to significant changes in a s sl. The precise LHCb result allows constraints to be placed on the properties of these possible new effects, and points the way for future theoretical and experimental studies. The image shows the overview of the most precise measurements of a s sl and a d sl. The a d sl results were obtained from analogous measurements of B 0 - B 0 oscillations.

The horizontal and vertical bands indicate the naive averages of pure a s sl and a d sl measurements obtained by different experiments. These averages are consistent with the small values predicted by the Standard Model and show no evidence for new physics effects. The yellow ellipse shows a result from a measurement of the D0 experiment at the Tevatron which is related but not uniquely determined by a linear combination of a s sl and a d sl.

This result could indicate the presence of a new physics contribution, see the 7 July news for details. However, this measurement is not in good agreement with the results for the individual measurements of a s sl and a d sl. The left image shows the LHC main information screen.

The right image shows a typical event fully reconstructed during data taking. Particles identified as pions, kaon, etc. The right image is a photograph of a meeting yesterday morning between LHCb physicists in preparation for today's data taking. LHCb can nevertheless use the collected data for physics commissioning with low-intensity stable beams. It is planned that the intensity will be increased during the following runs this weekend. During the coming week the LHC commissioning will continue and the data taking will resume at the beginning of May with increased proton-proton collision intensity.

During the first period of operation LHCb will profit from its revolutionary improvement of data acquisition and analysis developed a year ago. The calibration precise determination of the relationship between the detector response and physical quantity being measured and alignment process determination of the relative geometrical locations of the different sub-detectors with respect to each other now takes place automatically in the computer farm during data taking and the recorded data are immediately available for the physics analysis.

Hence it will be possible to begin analysing the new data for physics measurements very rapidly. Many exciting results have been reported on this web page.

They are based on data collected during the three-year Run 1 and the first year of Run 2. In this, the second year of Run 2, it is expected that LHCb will collect substantially more data than in This larger sample will enable LHCb to obtain even more precise, interesting and, hopefully, surprising results, see video. The image below shows the Workshop participants at the University of Manchester museum.

In the mids the LHC will be upgraded for higher luminosity operation. These works will necessitate a long-shutdown of at least 2. The meeting discussed enhancements to the LHCb experiment, dubbed a Phase Ib upgrade, that could be installed at this time. Although relatively modest, these improvements could bring significant physics benefits to the experiment.

In the second half of the s, the LHCb upgraded experiment that is currently under construction will reach the end of its planned programme. At this time a Phase II upgrade of the experiment could be foreseen. The goal would be to collect an integrated luminosity of at least fb -1 , with an instantaneous luminosity a factor ten above the upgrade that will operate in the s. Promising high luminosity scenarios for LHCb from the LHC machine perspective were shown which would potentially allow this goal to be reached, and each of the elements of the LHCb experiment presented their first thoughts on how these goals might be achieved.

The experimental physics programme, the theory perspectives of heavy flavour physics, and the anticipated reach of Belle II and the other LHC experiments were also considered. The parameters that describe the difference in behaviour between matter and antimatter, known as CP violation, are constrained in the so called CKM , or unitarity, triangle. The image displays the different rates of positive and negative B mesons, clearly indicating different properties of matter and antimatter.

A fascinating feature of quantum mechanics, in which the B 0 s , B 0 and D 0 particles turn into their antimatter partners, has been discussed already few times at this page, see 15 March , 7 November and 3 March news. This feature is called oscillation or mixing.

The image shows the characteristic oscillation pattern of B 0 mesons. An introduction to four-quark systems, or tetraquarks, can be found in the 9 April news. The LHCb Collaboration reported today a result of a similar analysis using a sample of B s 0 mesons 20 times higher than that used by the D0 Collaboration. No structure is seen in the region around the mass of MeV indicated by the arrow.

Hence the LHCb analysis does not confirm the D0 result. This year, for the first time, a competition has been proposed by the LHCb experiment. The aim of the exercise was to establish the best way of looking for a phenomenon that is not yet? This decay is forbidden in the Standard Model of particle physics and therefore its observation would indicate a discovery of "new physics", which is now the key goal of the LHC.

The awards of this competition were announced today at the Applying machine Learning to Experimental Physics workshop organized in the framework of the Twenty-ninth Annual Conference on Neural Information Processing Systems. Some machine learning algorithms are inspired by biological neural networks.

They are used to estimate functions that can depend on a large number of input information supplied by physicists, which is different for the signal and background events.

An output function is then generated indicating if the experimentally measured events look more or less like the signal or background events. The solutions presented by the winning teams were presented at the workshop. The LHCb collaboration have offered also two physics prizes for the most useful solutions for their analysis. The prizes were sponsored by Yandex and Intel. The competition may allow LHCb physicists to learn some computing tricks from the machine learning community.

This community, on the other hand, may possibly have improved their skills by having tackled this very challenging particle physics challenge. The LHCb collaboration has submitted today a paper reporting the study of correlations in particle production in proton-lead ion collisions at the LHC.

This allowed the LHCb detector, recording the particles only on one side of the interaction point, to make measurements in the case of the proton beam pointing towards the LHCb detector as well as in the opposite case of the lead beam pointing to it. The idea of the analysis is simple. In this way the plot bin sizes closer to the beam direction are expanded. A very precise Vertex Locator detector VELO , surrounding the proton-lead interaction region, is used to measure the number of produced particles in the collision and to define the activity of the event.

The numbers of particles observed in the LHCb detector are not identical in these two cases. Here LHCb physicists have introduced an original idea to the analysis and also made an important discovery.

The ridge-like near side effects were studied in heavy ion collision experiments in order to investigate a possible manifestation of a quark-gluon plasma formation, see 10 May news for an introduction. The observation of the similar near-side ridge correlations in proton-proton collisions by the CMS collaboration and in proton-lead collisions by the LHC experiments came as surprise since the formation of quark-gluon plasma was a priori not expected in these collisions. LHCb, the world's first dedicated b-physics experiment at a hadron collider, has obtained not only excellent heavy flavour results, but in addition the quality of the LHCb detector and its unique forward geometry allows it to obtain also important results in other fields, like electroweak physics or heavy ions physics, as reported today.

The LHCb contribution to the heavy-ion physics will increase significantly in the near future since presently, for the first time, the collaboration is taking also lead-lead collision data.

In August a Letter of Intent was submitted for LHCb, the world's first dedicated b-physics experiment at a hadron collider.

Today, the LHCb Collaboration has marked the 20 th anniversary of this event with a special celebratory meeting. Click the cartoon Adrien Miqueu author for higher resolution. So called "fixed-target" experiments at hadron accelerators, at which beauty particles were produced in collisions of accelerated protons with stationary objects were limited in their scope, as the rate of beauty particle production was small compared to production rate of other particles.

At hadron colliders, on the other hand, the beauty particle production rate is much higher. The Fermilab collider experiments CDF and D0 at the Tevatron , although not designed specifically for studies of beauty particles, took advantage of this opportunity and started to obtain interesting results in the s.

It was clear that the high proton-proton collision energy at the LHC would give rise to a very high beauty particle production rate. But how to conduct high precision experiments in this very difficult environment? At the LHC workshop in Evian in three b-physics experiments were proposed:. In June the LHC Committee decided not to approve any of the three individual experiments, but requested that the interested parties form one new collaboration to propose a single new experiment based on the collider mode to exploit its large b b cross section with a convincing trigger strategy.

Adopting the collider mode was the correct choice since not enough b hadrons would have been produced at the LHC in a fixed target setup, compared with the B-factory and Tevatron experiments, which had performed beyond original expectations. The design of the experiment was re-optimized in , a process in which many important improvements were made.

The tracking stations in the magnet were removed, reducing strongly secondary interactions of particles from the beauty particle decays, instead all the first tracking stations were made in silicon technology. The particle interactions in the collider beam tube were reduced by replacing the standard technology with one made of beryllium. Finally, improvements in technology allowed the whole LHCb detector to be read out to the computer farm at a 1MHz rate, thereby improving the beauty particle selection process.

But what could be the name of the experiment and its logo? Alternative name versions were used 20 years ago: The final name was fixed in with the cute choice for the LHCb logo.

The ideas imagined 20 years ago have been very successful and allowed excellent physics results to be obtained, as reported on this web page. In addition the production of all beauty mesons and baryons is observed at LHCb contrary to B-factory experiments, which are limited to studing light beauty meson decays only. By clicking on the physics result images at the same web page you can learn more about significant LHCb results.

The procedure of data-taking and analysis at hadron colliders is performed in two steps. An important part of the offline analysis is the determination of parameters which depend on the data-taking period, for example alignment determination of the relative geometrical locations of the different sub-detectors with respect to each other and calibration precise determination of the relationship between the detector response and physical quantity being measured.

The whole process takes a long time and uses a large amount of human and computer resources. In order to speed-up and simplify this procedure, the LHCb collaboration has made a revolutionary improvement to the data-taking and analysis process. The calibration and alignment process takes place now automatically online and the stored data are immediately available offline for physics analysis. In the following the new procedure is described in more detail.

Current technology does not allow all LHC proton-proton collision data to be stored and analysed. An event selection procedure is therefore necessary following the scientific goals of each experiment.

At LHCb the fast electronics hardware trigger reduces the 30 million per second 30 MHz LHC proton-proton collision rate as visible by the LHCb detector to 1 MHz using the characteristic properties of beauty and charm particle production and decays. The data are then read-out from the whole detector and are transferred at the 1 MHz rate to around electronic cards as the one shown in the left image.

The fast calculations performed in these cards allow the data volume to be greatly reduced by removing the content not containing information about the current event. The data from all these cards are then transferred to a predefined computer in the LHCb farm, shown in the right image, situated near the detector m underground.

The data transfer speed of the network between the cards and the computer farm is so high that it would be capable to carry the entire mobile phone traffic of a country such as Switzerland. The farm contains about computer boxes with a total of about 27 physical processors, nearly doubling the available processing power with respect to the LHC run 1 period.

At the first stage, HLT1, the less interesting events are removed and the data flow rate is reduced to kHz. An automatic procedure is then run which aligns around detector components and calculated about calibration constants, all within a few minutes. The alignment and calibration parameters are then used in the second stage of the software trigger, HLT2, processing the data stored in the Buffer with the same quality as would be the case in the offline analysis.

The additional selection reduces the data flow rate to The output data are directed into two samples. This new approach of making offline-quality information available to the trigger, and performing physics analysis directly on the trigger output data, represents a paradigm shift in data processing for particle physics experiments, and will have significant consequences for the future physics programme of LHCb.

This parameter quantifies the relative strengths of electromagnetism and the weak force. It is, therefore, an important experimental challenge to measure it. The electrons and positrons were collided at the energy of about 91 GeV at which the Z boson resonance was formed. The forward-backward asymmetry is related to how often the produced matter particle travels in a similar "forward" direction as the incoming matter particle involved in the collision.

The measurement requires no detailed final-state identification. It is a very interesting challenge for measurements at other particle colliders to resolve this puzzle. The parton quark and antiquark distributions inside proton need to be known precisely. At the LHC the Z bosons used in this analysis are produced mainly in the collisions of valence quarks with high momentum and sea antiquarks with low momentum. The Z bosons then decay into a pair of electrons or muons.

The LHCb geometrical acceptance is ideal for this measurement. LHCb has measured the forward-backward asymmetry A FB in the angular distribution of muons in dimuon final states as a function of the dimuon mass both at 7 and 8 TeV centre-of-mass energies. An example of the angular asymmetry, for data taken at 8 TeV, is shown in the left image as measurement points compared to a shaded Standard Model prediction.

The precision of the measurement is not yet sufficient to shed light on the interpretation of the 3. However, it is very promising and shows that with the additional data, expected in LHC run 2 and beyond, a very interesting determination of this fundamental parameter should be possible.

The LHCb collaboration published today in Nature Physics a paper based on run 1 data which reports the determination of the parameter V ub describing the transition of a b quark to a u quark. Other measurements of V ub by previous experiments had returned two sets of inconsistent results, depending on which method was used to determine the parameter. Theorists had suggested that this discrepancy could be explained by the presence a new particle contributing to the decay process, which affected the result differently, depending on the measurement method.

Today's result from LHCb removes the need for this new particle, while the puzzle of why the original sets of measurements do not agree persists. The measurement of decays involving a neutrino is very challenging at a proton collider and it was quite a surprise that this measurement could be done. The image shows two simultaneous proton-proton collisions inside the LHCb detector shown by the pink ellipses.

While the SM does not predict the values of the parameters of the CKM matrix, the measurements of these parameters in different processes should be consistent with each other. If they are not, it is a sign of physics beyond the SM. Their results from exclusive and inclusive measurements showed a large difference. This could be explained by a new particle, in addition to the W boson, contributing to the quark transition.

In the right figure above, the crossing of the purple and the red band at about That the crossing of the purple band with the green band is exactly at zero removes the need for a new particle. However, it still leaves the puzzle as to why the inclusive and exclusive measurements do not agree.

Further intensive research, both at the experimental and theoretical level, will continue to try to understand this disagreement. Using this measurement they also determined the rate at which beauty quarks are produced at this new, higher energy. The first task of physicists when operating an experiment at a higher energy is to measure the probabilities of well-known processes. These can be compared to theoretical predictions to establish a firm base upon which to build searches for new physics.

How to measure these probabilities is explained in the "How bright is the LHC? The importance of this discovery is highlighted by the fact that the subsequent, rapid changes in high-energy physics at the time have become collectively known as the "November Revolution". The spokespersons of the experiments who made this discovery, Richter and Ting, were rewarded for their shared discovery with the Nobel Prize in Physics.

The first stage can be calculated with the theory of strong interactions, QCD. On the other hand, the second stage, after forty years of theoretical and experimental efforts, is still not fully understood.

The expected rise of the beauty particle production rate of about a factor 2 with respect to run 1 at 8 TeV is confirmed by the data. This increase in rate will enable LHCb to obtain even more precise, interesting and, hopefully, surprising results in the LHC run 2 as explained by Barbara , Mika and Patrick.

In the traditional quark model, the strongly interacting particles hadrons are formed either from quark-antiquark pairs mesons or three quarks baryons. Particles which cannot be classified within this scheme are called exotic hadrons.

In his fundamental paper , in which he proposed the quark model, Gell-Mann mentioned the possibility of adding a quark-antiquark pair to a minimal meson or baryon quark configuration. It has taken 50 years, however, for measurements to be performed that unambiguously demonstrate the existence of these exotics. Today, the collaboration has announced the observation of a pentaquark, that is a hadron consisting of five quarks.

Claimed discoveries of pentaquark states by other experiments in the past have turned out to be spurious. LHCb physicists have therefore performed a thorough analysis to demonstrate that the signals observed in their data cannot be produced by conventional hadrons, and that they have the properties expected from an exotic resonance, that is a short-lived particle lying outside the traditional quark-model.

The first one has a mass of The statistical significance of each of these resonances is more than 9 standard deviations. This wider state is clearly seen in the insert for which a more restricted range of the Kp invariant mass spectrum above 2 GeV was required. The images above prove to experts that this is indeed the case. The right one shows the so called Dalitz plot in which a distinct horizontal band near The kaon K and the proton p particles traverse the LHCb detector and are absorbed in the hadronic calorimeter.

A new field of research now opens up. The two possibilities are illustrated in the figure. The color of the central part of each quark is related to the strong interaction color charge, while the external part shows its electric charge. The quarks could be tightly bound , or they could also be loosely bound in meson-baryon molecule, in which color -neutral meson and baryon feel a residual strong force similar to the one that binds nucleons together within nuclei.

It is hoped that future measurements by LHCb will help to answer this question. Added in August LHC Run 2 started today. LHCb physicists have been eagerly awaiting this moment since 14 February when the last Run 1 collisions took place.

In these conditions the experiments could switch on safely their sensitive sub-detectors. The left image shows LHCb physicists in the control room. LHCb has published many results based on data collected during the first three-year Run 1. But this was only the beginning. Collisions at 13 TeV will double the production rates of beauty hadrons enabling LHCb to obtain even more precise, interesting and, hopefully, surprising results. However, differences in mass between the leptons must be accounted for, and affect decays involving these particles.

In particular, the presence of additional charged Higgs bosons, which are often required in these models, can have a large effect. Already a previous measurement from the BaBar collaboration was found to be 2.

Therefore, the particle physics community has been eagerly awaiting new results. An older, less precise measurement by Belle marked "Inclusive tag" is compatible with the same picture.

Taken together these results constitute an intriguing anomaly, and one that is sure to provoke much discussion. Click the image for higher resolution. The collisions were part of the ongoing accelerator tests, and are not useful for physics studies.

The collected data are, however, useful for refining the synchronization of the readout time of different parts of the calorimeters and muon detectors.

The image displays an event taken today. These collisions were the latest in a sequence of careful steps to prepare the LHC for physics operation at 13 TeV.

Proton beams first circulated again after a two year long shutdown on the 5 th April , and collided at the relatively low energy of GeV on the 5 th May. HeRSCheL, a system of forward shower counters, was installed during the two-year shutdown for distinguishing between processes where the interacting proton in the beam remains undetected passing down the beampipe with no activity recorded in HerScheL and processes in which a signal is observed.

It consists of several stations, like the one shown in the video , located around the LHC beam pipe in the accelerator tunnel on both sides of the LHCb detector. It is interesting to note that some of these detectors are over m away from LHCb, but still see particles from the same collision. Read more in the CERN news. Both measurements are statistically compatible with Standard Model SM predictions and allow stringent constraints to be placed on theories beyond the SM. This is one of the most important results obtained by the LHC experiments from the run 1 and tests the SM to the ninth decimal place.

The excellent performance of the CMS and LHCb detectors and their data analyses was crucial in obtaining this result as well as the outstanding performance of the LHC itself. The two experiments found a total of about B s 0 and B 0 decays into two muons in a sample comprising 10 12 beauty hadrons collected during and The SM of particle physics describes the fundamental particles and their interactions via the strong, electromagnetic, and weak forces. It provides precise predictions for measurable quantities that can be tested experimentally.

Prior to the start of operation of the LHC, no evidence for either decay mode had been found, despite around 30 years of searching at previous experiments. Upper limits on the branching fractions were an order of magnitude above the SM predictions. The probabilities, or branching fractions, of the B s 0 and B 0 mesons to decay into two oppositely charged muons are very small in the SM and are well predicted. On the other hand a large class of theories that extend the SM, like supersymmetry, allows significant modifications to these branching fractions and therefore an observation of any significant deviation from the SM prediction would indicate a discovery of new effects.

The B s 0 and B 0 meson decays into a muon pair have long been regarded among the most promising class of measurements where these new effects could show up. Previous LHCb results already severely constrained the type of SM-extension models that are still allowed, as described in the 30 March news.

The results announced in today's publication isolate even more precisely the parameter region in which these new models can exist, and therefore focuses future experimental searches and theoretical attention.

The two collaborations first released their individual results for B s 0 meson decay as described in 24 July news. While the results were in excellent agreement, both fell just below the five sigma statistical precision historically needed to claim an observation. The combined analysis improves the precision of the results and in the same time easily exceeds the 5 sigma requirement, reaching 6. This is the first time that a combined analysis of sets of data from more than one LHC experiment has been performed.

The B s 0 and B s 0 mesons are produced in the pp collision point and decay into a muon pair after a distance of the order of 1cm.

The left image shows the B s 0 meson decay into two muons presented as green tracks traversing the whole detector. The LHCb and CMS experiments will resume data taking in June with proton-proton collisions at a centre-of-mass energy of 13 TeV, which will approximately double the production rates for B s 0 and B 0 mesons and lead to further improvements in the precision of these crucial measurements.

Today, for the first time in over two years, protons have collided inside the LHCb detector. Although these collisions are not at the nominal energy of 13 TeV, and therefore not aimed for physics studies, the collected data are useful for precise synchronization of the readout time of different parts of the calorimeters and muon detectors with the time at which different particles originating from the proton-proton collision point traverse them.

The right image displays an event taken today. Click the picture and play with the 3D view of a few recorded events. In a follow up step, most probably tomorrow, LHCb physicists will inject neon gas into the LHC vacuum tube in order to measure the shape of the proton beam, by seeing where the proton-gas interactions occur.

This beam-gas imaging method, used only at LHCb, allows the "luminosity" of the colliding beams to be determined, and is described in the news item of 7 October The luminosity is a vital component in determining how often different physical processes occur in proton-proton collisions.

Measurements of these processes at the record proton-proton collision energy of 13 TeV are the among the first physics goals of LHCb at the restart of data taking in June. Today, for the first time in two years, both proton beams are circulating again in the LHC.

The picture shows the LHC operators steering the two beams. The proton beam already traversed the LHCb detector one month ago and then continued through one quarter of the LHC circumference, see 7 March news. The two month period of re-commissioning with beam starts now. Therefore the prospects for reaching the proton-proton collision energy of 13 TeV at run 2 are very good.

The LHCb detector and its data acquisition system are ready to take data at this highest proton-proton collision energy. LHCb physicists still continue to analyse the run 1 data obtaining exciting results, many of which have been reported on this website. They are looking forward to the first 13 TeV collisions that are expected in June and are convinced that a bright and exciting future lies ahead.

A previously published analysis of the experiments data sample found a deviation with respect to a calculation based on the Standard Model, see 9 August news. The particle physics community has been eagerly awaiting the results from the full data sample ever since. Physicists from the LHCb experiment have studied different angular observables as functions of the mass of the muon pair.

It was one of these observables, "P 5 ' ", that showed a local deviation with respect to the Standard Model calculation at a level of 3. These observables are therefore ideal for searching for the effects of new particles in this decay. The black points show the LHCb results presented for the first time today.

The Standard Model predictions are presented as orange boxes. These were taken from calculations described in a recent theoretical paper. The behaviour seen in the data sample, shown as the blue points for comparison, is confirmed using the full data set. In the next couple of years, the LHCb collaboration will improve the precision of their analysis with the help of data collected in run 2 of the LHC. It is also anticipated that the theoretical predictions the orange regions in the image will improve in precision.

Theorists will be busy trying to make sense of this measurement, and seeking for possible associations with other unexpected effects found in similar decays, for example the R K anomaly see 3 June news. Stay tuned for future developments on this page. A very large number of particles produced during this absorption process traversed the LHCb detector. Click the picture and play with the 3D view of these events. Both proton beams are expected to make the full turn of the LHC collider by the end of March and the first proton-proton collisions at the nominal Run 2 energy of 13 TeV are expected by the end of May.

The LHCb collaboration is ready to take high energy proton-proton collision data. The two year Long Shutdown LS1 period offered an opportunity for prolonged access, and hence an extensive programme of consolidation and maintenance work. In summer a detailed field measurement of the LHCb dipole magnet was performed followed by the re-installation of the beam pipe, see the left image, through which proton beams will circulate in both directions.

One section of the beryllium beam pipe was replaced. The new beam pipe support structure is now much lighter and therefore unwanted interactions with it of particles measured inside the LHCb detector are strongly reduced. This triangle is a geometrical representation of CP violating and associated parameters in the Standard Model. One side is defined to have unit length, the other two sides and three angles can be measured independently in different decays of beauty hadrons.

It is the task of experimental physicists to measure these properties and see if they provide a consistent description of the triangle. Any discrepancy would point to signs of New Physics beyond the Standard Model. The unitarity triangle is shown in the above left figure, with each experimental input represented by a coloured region. This possibility of two paths in the decay process is a B physics analogue of the classical quantum mechanics two-slit experiment, which is described in this pedagogical video.

The interference between the amplitudes for the two decay paths results in a time-dependent asymmetry between the decay time distributions of B 0 and B 0 mesons, as seen in the right image above. Their results were vital in confirming the broad validity of the Standard Model description of CP violation and led to the award of the Nobel Prize of Physics to the Japanese theorists M.

Maskawa, who had been central in developing this description. The solid blue diagonal band shows the new world combination of the B factory measurements with the new LHCb result.

It has been long-known that this measurement is a priori more difficult to perform in a hadron collider, such as the LHC, but the new result presented at La Thuile is an emphatic statement that LHCb can significantly contribute to our knowledge of this fundamental parameter. A still more precise result will be achievable with the data to be collected in run 2, which will allow for more stringent tests of the Standard Model.

The proton beam knocked at the LHC's very solid door this weekend and found it still closed, but nonetheless managed to provide the LHCb collaboration with very interesting data. One of these lines ends with a so-called beam stopper known as the "TED", located at the end of the line about m from the LHCb detector. However many muons were produced during the absorption process, and these muons passed through the TED and traversed the LHCb detector.

The collected data are also useful for detector studies and alignment purposes i. The image shows the shift leader, run coordinator, spokesperson and sub-detector experts in front of the LHCb data acquisition computer screens. LHCb took its last collision data on 14 th February Collisions are expected to resume again in Spring Click the images for higher resolution and read about the LHC side of the story here.

The LHCb collaboration has contributed with its International Masterclasses exercise, in which the lifetime of the charm particle called the D 0 meson may be measured using real proton-proton collision data recorded by the LHCb experiment during the data taking period.

The LHCb collaboration submitted today a paper reporting the discovery of two new particles. Like the protons that the LHC accelerates, the new particles are baryons made from three quarks bound together by the strong force. The types of quarks are different, however: Thanks to the heavyweight b quarks, they are more than six times as massive as the proton.

But the particles are more than just the sum of their parts: Each of the quarks has an attribute called " spin ". Both particles have extremely short lifetimes and do not fly any measurable distance before they decay. This is consistent with the pattern of masses: The masses, widths, production rates of these particles and more details on the analysis can be found in the LHCb publication.

The result shows the extraordinary precision that LHCb is capable of: By observing these particles and measuring their properties with such accuracy, LHCb physicists make a stringent test of models of nonperturbative Quantum Chromodynamics QCD. Theorists will be able to use these measurements as an anchor-point for future predictions. The predicted value is small and therefore the effects of New Physics could change its value significantly.

Here the Standard Model predicts very small effects, thereby allowing New Physics to manifest itself. This is to be contrasted with other manifestations of CP violation in the B s system, unaffected by oscillations, where the Standard Model expects large signatures.

Such a signature was already observed by LHCb, see 24 April news. The very clean enhancement at the B 0 s mass is clearly seen. No significant difference is observed between the different polarisation states. The parameter region in which New Physics could still hide is now even smaller than before. The green ellipse in the center represents the LHCb result and the grey ellipse shows the world average. The LHCb Collaboration has celebrated this week its th publication!

The LHCb Collaboration has just published the results of the luminosity calibration with a precision of 1. This is the most precise luminosity measurement achieved so far at a bunched-beam hadron collider see below. At the beginning of operation of a new particle collider, physicists start with measurements of probabilities of different physical processes and compare results with theoretical predictions.

Differences may indicate signs for new physics or needs for an improved understanding at higher energies of already known processes. The luminosity L depends on the number of particles in each collider beam per unit of time and on the size of overlap of both beams at the collision point. Cross-section predictions with similar or better precision are not available for proton-proton collisions. Therefore, purely experimental methods of luminosity measurements are used at the LHC.

The number of particles in each colliding beam per unit of time so called beam currents are measured using LHC equipment. Two methods are used to measure the size of overlap of both beams at the collision point. The idea was to measure the beams' overlap by scanning them across each other and monitoring the interaction rate. This method has been used by all four LHC experiments. The BGI method is based on reconstructing vertices of interactions between beam particles and residual gas nuclei in the beam vacuum in order to measure the angles, positions and shapes of the individual beams without displacing them.

This allows one to actually see the trace of the beams. The image shows the reconstructed positions of proton-beam-gas collision points. It is clearly seen that the proton beams are crossing at an angle. This is intentional since the protons in LHC are not continuously distributed around the ring but are concentrated in small regions called bunches so the LHC is a bunched-beam collider.

Colliding with an angle and not head-on assures that there are no unwanted collisions between bunches outside the region defined by the experiment. The luminosity was calibrated during special measurement periods and then relative changes were tracked by changes of counting rate of different sub-detectors. The vacuum pressure in the LHC was so low, that in order to increase the proton-beam-gas collision rate, LHCb physicists injected neon gas into the LHC vacuum tube during luminosity calibration periods.

Using the beam-gas data, LHCb physicists were able to reveal that a small fraction of the beam charge is spread outside the expected i. Since only collisions of protons located in the nominal bunches are included in physics measurements, it was very important to measure which fraction of the total beam current value measured with the LHC equipment participated in the collisions i.

Only LHCb could measure this fraction with sufficient precision and, therefore, the results of LHCb measurements of the charge fraction outside nominal bunch locations, called the "ghost" charge, were also used by the three other LHC experiments. We can compute it here using integration by parts. A quantity may decay via two or more different processes simultaneously. In general, these processes often called "decay modes", "decay channels", "decay routes" etc.

Partial mean life associated with individual processes is by definition the multiplicative inverse of corresponding partial decay constant: Terms "partial half-life" and "partial mean life" denote quantities derived from a decay constant as if the given decay mode were the only decay mode for the quantity. The term "partial half-life" is misleading, because it cannot be measured as a time interval for which a certain quantity is halved.

For a decay by three simultaneous exponential processes the total half-life can be computed as above:. Exponential decay occurs in a wide variety of situations.

Most of these fall into the domain of the natural sciences. Many decay processes that are often treated as exponential, are really only exponential so long as the sample is large and the law of large numbers holds. For small samples, a more general analysis is necessary, accounting for a Poisson process.

From Wikipedia, the free encyclopedia. European Journal of Physics. Retrieved from " https:

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