12 June 2018: HeRSCheL looks even further forward.
Conscience de classe et parti: Cette situation est complexe: Malaise diplomatique face à la solidarité internationale. Ovation pour le KPP. Mais la parole ne nous est jamais donnée pour expliquer sereinement notre position. Les plus emblématiques furent menées par le président néoconservateur George W. Une telle entreprise pouvait paraître psychologiquement hasardeuse: Nous avons pourtant mené à bien ces discussions.
Nous ne contestons pas que des enseignants aient pu rencontrer des difficultés avec leurs élèves. Peut-on imaginer le traumatisme subi par des enfants régulièrement confrontés à des propos racistes du même acabit  tenus à leur sujet? Une telle situation devient décidément de plus en plus préoccupante pour nos enfants.
Simplement en ouvrant les yeux sur ceux qui le soutiennent. Bonjour le progrès social! Vous avez sans doute remarqué que notre petit banquier gère les ralliements sur le mode psychorigide: Les élections, organisées par la bourgeoisie, avaient pour but de nous demander de choisir un Président, mais sans nous permettre de choisir sa politique: Cette élection est une nouveauté, parce que le candidat explique clairement sa politique: Les gouvernements actuels suivent à la lettre la leçon de Bush.
Face au chômage, il faut inventer des solutions et affronter la logique du profit. Il a depuis été régulièrement prolongé, officiellement dans le but de couvrir la période des élections nationales, prévues en avril-mai Selon les chiffres publiés le 6 décembre par le gouvernement, depuis novembre , 4.
Par ailleurs, en décembre , 95 personnes étaient encore assignées à résidence. Tout ceci pousse à un racisme de plus en plus décomplexé, assumé et revendiqué. Bien entendu, les causes des migrations et les causes de leur visibilité actuelle, dont les pays européens sont directement et évidemment responsables, ne sont jamais énoncées dans les discours sur les migrations actuelles. La France était pourtant en guerre bien avant les attentats, lesquels ont largement servi de prétexte à intensifier ces engagements militaires.
Marchant dans les pas de son prédécesseur, François Hollande endosse pleinement le costume de chef des armées. Sangaris, en République centrafricaine, vient conforter cette politique.
Présentées officiellement comme des victoires, ces interventions posent en réalité éminemment question. Ces conflits doivent être désignés par leur nom: Le discours belliciste entend anesthésier et tétaniser la population.
Les Rafale tuent des civils aussi innocents que ceux du Bataclan ou de Nice. Le 9 Septembre Par Emmanuelle Chevrière le 11 Septembre Par Fabienne Sintes le 11 Septembre Des guerres anciennes aux conflits sporadiques, de la culture mondiale à la culture la plus locale… Pour mieux comprendre un monde de plus en plus riche et incertain.
Du lundi au vendredi, en dernière partie d'En pistes! Par Claude Askolovitch le 12 Septembre Par Thierry Garcin le 12 Septembre Un éclairage quotidien sur les événements de l'actualité internationale, les tendances durables de la géopolitique, de la diplomatie, de l'économie ou de la démographie.
Jérôme Colombain s'intéresse aux innovations, aux produits high-tech, aux nouvelles technologies. Eclairage sur le monde virtuel et technologique. Par Bertrand Queneutte le 11 Septembre Par FIP le 11 Septembre Par Mouv' le 11 Septembre Olivier Besancenot se connecte sur insta et poste un rap!. L'ancien porte-parole du Nouveau Parti anticapitaliste s'oppose à la politique d'Emmanuel Macron et le fait savoir.
Ce n'est pas la première fois qu'il rappe Chaque jour, les journalistes de franceinfo, l'offre globale d'information en continu du service public reçoivent une personnalité politique de premier plan, et la questionnent sur l'actualité politique.
Dans le même esprit que les premières saisons de Musicopolis, Anne-Charlotte Rémond explore à présent chaque jour une oeuvre différente sa genèse, sa création dans son contexte géographique et historique. Par François-Régis Gaudry le 9 Septembre Par Mathieu Vidard le 11 Septembre Éclectisme, vulgarisation et pédagogie, sciences dures du vivant ou humaines: Par Dominique Seux le 12 Septembre Par Philippe Garbit le 12 Septembre The study of the CP violation in decays of B 0 and of B s 0 mesons into two charged particles h that do not contain charm quarks represents a powerful tool to test the CKM picture of the SM, and also to investigate the presence of physics beyond the SM.
The results are the most precise from a single experiment and constitute the strongest evidence for time-dependent CP violation in the B s 0 meson decays to date. They also contribute to the determination of the CKM unitarity triangle. The results obtained are consistent with the hypothesis of CP conservation. Therefore, the B s 0 meson decay is visible in the invariant mass spectrum of four K mesons, see the red dashed line contribution in the image.
The data taking period ended this Sunday. Towards the end of the run at the centre-of-mass energy of 13 TeV, the LHC provided collisions at a reduced energy of 5 TeV to produce reference data for proton-lead and lead-lead collisions taken earlier in Run 2.
Besides the scientific interest of proton-proton p-p physics at 5 TeV for the LHCb heavy-ion programme see  ,  , the experiment has been taking at the same time a parallel stream of data from fixed-target collisions with another world first in high energy physics.
There have been typically bunches of protons circulating in each LHC ring, out of which collided inside the LHCb detector. LHCb physicists decided to use additional non-colliding bunches to accumulate the largest sample of proton-neon data in a fixed-target configuration.
The LHCb experiment has the unique ability of injecting gas, neon in this case, into the interaction region and therefore study processes that would otherwise be inaccessible. This gas-injection system was originally designed to help LHCb measure the brightness of the accelerator's beams, but is now being used for dedicated physics measurements. It has been the first time ever that an experiment has collected data in the collider and fixed-target modes simultaneously. LHCb physicists showed that it is possible to reconstruct both sets of data in parallel, align the detector elements and track particle trajectories correctly.
A real challenge has been to develop an online event selection trigger system handling efficiently both data taking conditions. The pink-dashed rectangle highlights the regions were p-p collision events were selected. The two other red-dashed rectangles show the region where only p-Ne collisions take place. LHCb continues to revolutionise data acquisition and analysis techniques. The calibration and alignment process takes place now automatically online and stored data are immediately available offline for physics analysis.
This time the collider and fixed-target modes of operation have been unified into the same data acquisition framework. In particle physics, a grand-unified theory is one in which at very high energies the electromagnetic, weak and strong interactions unify as a single force.
Today LHCb physicists have succeeded to unify very different concepts of data taking and analysis. The data taking period has been very successful, because of the excellent performances of both the LHC and the LHCb experiment itself. The image shows the growth of integrated luminosity during different years of LHC operation. The integrated luminosity is higher than that collected in The overall Run 2 luminosity , 3.
It will be used for maintenance and improvements to the LHC and its detectors. LHCb plans to exploit this period to perform maintenance work on many sub-detectors. It is planned that protons will start to circulate again in the LHC rings at the beginning of April and that the first p-p collisions for physics will take place in early May, marking the beginning of the last year of Run 2.
Read more in the CERN update. The purpose of the meeting is to consider the latest results from LHCb, discuss possible interpretations and identify important channels and observables to test leading theoretical frameworks in the near and long-term future of the experiment.
The LHCb detector is used to perform precision measurement across a range of areas of particle physics, notably including searches for new physics manifestations in flavour, studies of heavy-flavour spectroscopy and production of gauge bosons, searches for new exotic particles, and unique measurements with heavy ion and fixed-target collisions in the forward region. Precise calculations from theory are essential for the interpretation of LHCb results, as is evident from numerous news articles on this page.
The comparison of LHCb results with precise Standard Model predictions provided by the theory community is the key to looking for discrepancies that would indicate the existence, and the nature, of physics beyond our present knowledge. This series of joint LHCb-theory workshops is aimed at facilitating informal discussions between LHCb experimentalists and theorists, leading to a mutual exchange of information that is valuable for achieving progress.
More than physicists crowded the Main Auditorium through three days featuring various dedicated sessions see the photo above. The left image shows the steadily increasing number of participants as a function of time since the first workshop was held, clearly demonstrating that this series of workshops is more and more becoming a reference event for both the LHCb physicists and the theorists. Furthermore, intriguing results published by LHCb in recent years have been triggering additional interest and discussions within the physics community.
Learn more in the workshop presentations. Click the images for higher resolution. Yesterday evening the first xenon-xenon ion collisions took place at LHC and the run lasted for seven hours. The right image shows a collision event recorded and analysed online by the LHCb data acquisition system.
Heavy ion collisions are studied at LHCb in order to understand the behaviour of the so-called quark-gluon plasma , a state of matter in which quarks and gluons are moving as free particles, similarly to what happened in the first instants of time after the Big Bang.
At the LHC, the properties of the quark-gluon plasma are usually studied in collisions of lead nuclei. Although there are no plans to use xenon-xenon collision for this purpose in the near future, one day of the LHC time was devoted to these collisions in order to study the properties of nuclear matter at high-energy density and high temperature.
The comparison of experimental measurements in lead-lead and in xenon-xenon collisions will bring new insights into the properties of the quark-gluon plasma. First test of lepton universality using charmed-beauty meson decays. The result that was reported is approximately 2 standard deviations from the Standard Model SM expectation. However, mass differences between various leptons play a role which must be accounted for when performing calculations of interaction rates.
Note the different horizontal scale. LHCb has also found other intriguing anomalies when performing tests of lepton universality. All these measurements were performed at LHCb using the entire Run 1 data sample, corresponding to an integrated luminosity of 3fb -1 at centre-of-mass energies of 7 and 8 TeV. Data collected in Run 2 already provide a sample of B-meson decays more than twice as large, and it will be of great importance to see whether future updates of these analyses with increased statistics will confirm the hints of discrepancies.
They are bound systems of a charm quark, c, and an anti-charm quark, c , held together by the strong nuclear force. Just like ordinary atoms, e. The image on the left represents the complexity of this spectrum along with some of the allowed decay transitions as a function of mass in the vertical axis versus spin and other quantum numbers in the horizontal axis.
The decay paths corresponding to the decays under study are highlighted in red. This discovery triggered rapid changes in high-energy physics at the time and these are commonly referred to as the "November Revolution".
The charmonium family was then intensively studied by a large number of experiments at different facilities. As it is experimentally very challenging to measure the energy of a photon precisely in the harsh environment of a hadron collider, high-precision measurements have not previously been made at a collider like the LHC.
The new analysis from LHCb applies an old "trick" in a new situation. This technique was first proposed in by R. Dalitz realised that quantum mechanical fluctuations permitted one or both of the photons to be virtual, allowing them to transform into an electron-positron pair. The new measurements have a similar precision to and are in good agreement with those obtained at previous dedicated experiments, notably E and E, that used antiproton annihilations into a hydrogen target to produce and study the charmonium states see the image below for a comparison amongst the various results available in the literature.
It will facilitate a better understanding of quantum chromodynamics QCD , i. The LHCb collaboration has reached a symbolic milestone this morning, announcing that the experiment has recorded a luminosity of 6 fb -1 integrated over the whole period of data taking The shift crew captured this moment by taking a photo of the live screen in the LHCb Control Centre, see the number pb -1 in the lower-left corner of the table in the image.
The luminosity delivered by the LHC collider was pb -1 during this period. Most of the results highlighted through the years in this page were obtained using the LHC Run 1 data sample, where the full sample corresponds to an integrated luminosity of 3 fb -1 at centre-of-mass energies of 7 and 8 TeV.
Since the production cross-section of beauty and charm particles at 13 TeV is about twice as large as that in Run 1, the total sample of beauty particles available for physics analyses is now about three times larger than that recorded during the Run 1 data taking period.
The door that will lead to obtain many more interesting results is open wide, as you will be able to see with our future reports in this page. A few other selected items are listed below. Proton collisions with lead nuclei p-Pb at the LHC are very important to understand nuclear effects relevant to the study of quark-gluon plasma formation in lead-lead Pb-Pb collisions.
Two sets of data were taken: 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. For the first time, beauty-hadron production is measured precisely at low momentum at the LHC in p-Pb and Pb-p collisions. In p-Pb, a weak suppression is observed, whereas in Pb-p no significant deviation from unity is found.
Several extensions of the Standard Model predict that new heavy particles that decay to two energetic b-quarks could be accessible at the energy of LHC collisions. Moreover, the study of the Higgs-boson decay to a pair of b and b quarks at the LHC is of great interest, since the precise determination of the Higgs boson coupling to b-quarks is an important test of the Standard Model.
The decay of a Z boson to a b b pair provides a standard candle for direct searches of physics beyond the Standard Model in final states with b b quarks. Measurements of this decay can be used to demonstrate that no biases are induced by the b-jet reconstruction procedure and that the reconstruction efficiencies are evaluated correctly. A clear signal is observed by LHCb for the first time, as shown in the right image above.
The theoretical prediction and the measurement are compatible within one standard deviation. Additional data being collected by LHCb will enable a more stringent comparison with the theoretical prediction to be performed. This is a further example that illustrates that LHCb has become a general purpose forward experiment with a broad physics programme.
The B 0 meson decay into a p p pair is observed for the first time with a statistical significance of 5. The branching fraction is measured to be 1. This decay is the rarest fully hadronic decay of a B meson ever observed.
Studies of B mesons decaying to baryonic final states have been carried out since the late s. It was quickly realized that baryonic B decays differ from mesonic decays since two-body charmless decays are suppressed with respect to decays to multi-body final states. This observation provides a valuable input towards the understanding of the dynamics of hadronic B decays and allows for a better scrutiny of QCD models.
Please click the images for higher resolution versions. The image above shows an example of a Feynman diagram contributing to this decay. The signal candidates are consistent with particles that traveled a significant distance before decaying: This state is therefore incompatible with a strongly decaying particle, but is consistent with a longer-lived decay involving weak interactions as would be expected for this particle. The existence of doubly charmed baryons was already known to be a possibility in the s, after the discovery of the charm quark.
The image shows an artist view of this new particle. This discovery opens a new field of particle physics research. The image illustrates how half-spin baryons can be formed by assembling together the three light quarks u, d, s and the charm quark Particle Data Group, Phys.
Furthermore, other hadrons containing different configurations of two heavy quarks, for example two beauty quarks or a beauty and charm quark, are waiting to be discovered. Measurements of the properties of all these particles will allow for precise tests of QCD , the theory of strong interactions, in a unique environment. LHCb is very well equipped to face this very exciting challenge. Click images for higher resolution.
A special musical performance was given in Thoiry , a nearby village to CERN, where she discussed the photograph shown here right image. The photo was taken in Thoiry in , in front of the Hôtel Léger, during what we now call a conference dinner and included both Marie Curie and Albert Einstein.
They were both members of the International Committee on Intellectual Cooperation , an advisory organization for the League of Nations which aimed to promote international exchange between scientists, researchers, teachers, artists and intellectuals. He takes over from Guy Wilkinson from the University of Oxford. Giovanni and Chris will face the huge challenges of completing the run 2 data taking and preparing for the major LHCb detector upgrade to be installed during Long Shutdown 2, LS2.
In the meantime they dream that the analysis of the Run 2 data could yield the discovery of new physics! This has been possible because of the unique capabilities of LHCb in precisely reconstructing decay vertices. This property is called "lepton universality". However, differences in mass between the leptons must be accounted for. This ratio is precisely calculable in the SM owing to the cancellation of uncertainties in the ratio, and turns out to be about 0.
The average of all world results is brought, by including this new measurement, a little bit closer to the SM prediction and at the same time, due to improved precision, the discrepancy between the experimental world average and the SM prediction increases slightly to about 3. Any measurement exhibiting a conclusive breakdown of lepton universality, after mass related effects are accounted for, would be a clear sign of new physics.
Recently the CERN Theory Division organized a three-day workshop to discuss the interpretation and implications of these anomalies and their potential to shed some light into models of physics beyond the SM. Data collected in Run 2 already provide a sample of B-meson decays more than twice as large, and it will be of great importance to see whether updates of the Run 1 analyses will confirm the discrepancy.
Read more in the CERN update for scientists. This traditional winter shut-down period was "extended" due to major installation work carried out in another one of the LHC detectors. The recommissioning of the accelerator has proceeded very smoothly and first collisions arrived earlier than initially expected. During the technical stop LHCb performed relatively minor maintenance work on the detector, and, on the other hand, major interventions on the access lift and the crane in the underground cavern.
The LHCb detector and its data acquisition system are ready for a bumper year of data taking that will allow the experiment to obtain even more precise and interesting physics results. This measurement provides an important test of lepton universality LU , which is one of the most important ingredients of the Standard Model of particle physics. LU means that leptons e. In the LHCb measurement, the distance of the result from the SM prediction is found to be significant at the level of 2.
The numerical values are given at the top of the article, where the first uncertainty, which dominates, is statistical, and the second is systematic. The lower boundary of the low- q 2 region roughly corresponds to the di-muon production threshold.
The image also shows several independent SM theoretical predictions. A difference from the SM of 2. These differences are not yet at the level where they can be claimed to exhibit evidence for BSM physics, but they are intriguing when considered in the context of an earlier LHCb analysis.
This result created much interest in the particle physics community. Examples are shown in the Feynman diagrams below. The upper ones show the SM contributions. The left-lower one shows a possible contribution from a heavy Z-boson -like particle, named Z' , which would interact differently with muons and electrons. The lower-right diagram shows a possible contribution from a hypothetical scalar leptoquark LQ , which would interact with both quarks and leptons.
Alternatively, different, not yet predicted, and therefore even more interesting, BSM physics could be at play! Data collected in Run 2 already provide a sample twice as large, and it will be of great importance to see whether updates of the present analysis will confirm the discrepancy. Future LHCb measurements will be able to elucidate whether these tantalising hints are a manifestation of statistical fluctuations or whether LHCb is observing a glimpse of new physics.
The measurement is of antiproton production in proton-helium p-He collisions. Although the LHC collides protons with protons, the LHCb experiment has the unique ability to inject gas, for example helium, into the interaction region and therefore study processes that would otherwise be inaccessible, such as here the production of antiprotons from p-He interactions.
The forward geometry and particle identification capabilities of the LHCb detector are well suited to provide good reconstruction for antiprotons down to the low transverse momentum region where most of the production is expected. This result is very important for interpreting searches for dark matter in the Universe.
Dark matter is a hypothetical entity of unknown nature whose existence would explain a number of otherwise puzzling astronomical and cosmological observations.
The name refers to the fact that it does not interact with electromagnetic radiation like light. Although dark matter has not been directly observed, its existence and properties are inferred from its gravitational effects such as the motion of visible matter around galactic centres and precise measurements of temperature fluctuations in the cosmic microwave background. An interesting possibility is that dark matter is composed of some kind of stable elementary particles whose existence is proposed in different extensions of the Standard Model of particle physics.
In such a case these dark matter particles could collide and produce ordinary particles, in particular antiprotons. However antiprotons can also be produced in standard processes through collisions of cosmic rays with the interstellar medium, of which helium is a significant component. Therefore a potential signature of dark matter is the observation in space of a higher ratio of antiprotons to protons than would be expected from standard processes.
Also shown in the image is the prediction 'Fiducial' and, as coloured bands, the uncertainties on this prediction, which come from the limited knowledge of several of the ingredients in the calculation. Although the data points lie above the prediction, the current uncertainties are large enough to almost accommodate the discrepancy, thereby preventing an unambiguous interpretation.
The largest uncertainty is associated with the knowledge of the cross-sections, in particular that of p-He collisions. This is where LHCb enters the game.
In the image, the result is compared with the most popular models used in cosmic rays physics. The spread among model predictions indicate the large uncertainty on the process prior to this measurement.
In the s many different particles were discovered. Initially thought to be elementary, the ever growing list of discoveries led physicists to doubt this assumption. Therefore efforts were made to find a classification scheme in analogy to the periodic table of chemical elements.
The most successful such scheme was proposed by Gell-Mann. The regular structure of the decuplet enabled many properties of this new particle to be predicted, including its mass. This picture validated the Eightfold Way, and led Gell-Mann to propose the quark model in , which explains the structure of the octets and decuplet. The discoveries announced today are excited states of this system, analogous to the excited states of atoms. More details can be found in the LHCb publication.
Processes where a B meson decays into a pair of oppositely charged leptons are powerful probes in the search for physics beyond the Standard Model. This presentation provoked much interesting discussion. These decays are of great interest in the search for further manifestations of CP violation in baryonic B decays, see the first evidence for the violation of the CP symmetry in baryon decays.
A phase-1 upgrade of the experiment is currently being prepared and will be installed in the long-shutdown 2, in The measured branching fraction 3.
It is the most precise measurement of this quantity to date. The full 3 fb -1 of data collected during Run 1, and 1. The size of this contribution is not found to be significant, and so an upper limit is set for the decay at a value of 3. The other contributions show the contribution of background processes. The probability, or branching fraction, of the B s 0 meson to decay into two oppositely charged muons is very small in the SM and is well predicted.
On the other hand, a large class of theories that extend the SM, such as, for example, supersymmetry, allows significant modifications to this branching fraction and therefore an observation of any significant deviation from the SM prediction would indicate a discovery of new effects. The decay of a B s 0 meson into a muon pair has therefore long been regarded as one of the most promising places to search for these new effects.
This decay has been searched for more than 30 years by different experiments at different accelerators as shown in the image. The LHCb collaboration obtained the first evidence , with a significance of 3.
Previous results already severely constrained the type of SM-extension models that are still allowed, as described, for example, in the 30 March news. The results announced today isolate even more precisely the parameter region in which these new models can exist, and therefore focuses future experimental searches and theoretical attention. All candidate models of physics beyond the Standard Model will have to demonstrate their compatibility with this important result.
LHCb also reported today the first measurement of this quantity, and found it to be 2. The two muon tracks from the B s 0 decay are seen as a pair of green tracks traversing the whole detector in the left image. The right image shows the zoom around the proton-proton collision point, the origin of many particle tracks. The two muon green tracks originate from the B 0 s decay point located 17 mm from the proton-proton collision. This web based event display will run on your computer or smartphone without need to load any specialized software.
Stay tuned for updates from Run 2 data. The preliminary numbers and plots presented at the seminar have been replaced with the final ones on March The LHCb collaboration has published today in Nature Physics the first evidence for the violation of the CP symmetry in baryon decays with statistical significance of 3.
CP violation has been observed in K and B meson decays, but not yet in any baryon decay. In the quark model of particle physics mesons are composed of a quark and antiquark pair while baryons anti-baryons are composed of three quarks anti-quarks.
About and decays were found for the two decay modes, respectively. It is important to measure the size and nature of CP violation in these decays in order to determine whether they are consistent with the predictions of the Standard Model of particle physics or, if not, what extensions of the Standard Model would be required to explain them.
Once the signals have been established, the analysis turned to the study of matter-antimatter asymmetries. The statistical significance of these asymmetries differing from zero is 3. In the past, analogous large effects were also seen in three-body charmless B decays. The full 3 fb -1 run 1 data sample was used to obtain this result. The number of beauty particle decays recorded by LHCb in run 2 is already larger than that used in this analysis.
The data taking period ended this morning. This was a very successful year, both because of the excellent performance of the accelerator and of the LHCb experiment itself. The left and central images below show the growth in integrated luminosity during different years of LHC operation. Integrated luminosity is a measure of the number of proton-proton collisions produced by the accelerator.
The increase of integrated luminosity with time in was similar to that in ; the period of data taking was, however, shorter. This excellent performance is mainly due to the higher efficiency of the accelerator this year. LHCb has recorded 1. The total integrated luminosity recorded during run 2 reached now the target of 2 fb -1 compared to 3 fb -1 collected in run 1.
The cross-section for b- and b -quark production at 13 TeV proton-proton collision is about twice that of run 1 see 5 August news, item 1. Since the integrated luminosity is merely the instantaneous luminosity added up over the time the accelerator is operating, the 2 fb -1 Run 2 data sample contains a larger number of beauty particle decays than the 3 fb -1 Run 1 data sample. This is excellent news for future LHCb physics analyses.
The right image above shows a typical proton-proton collision event. The proton collisions with lead ions took place during last three weeks of data taking period. 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.