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.
On Particle Physics
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.
Review of Particle Physics
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.
- Ancestral Journeys: The Peopling of Europe from the First Venturers to the Vikings.
- The Cold War: An International History (The Making of the Contemporary World);
- My Friend Maigret (Inspector Maigret, Book 31).
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.
bakuaz.info/boutique-plaquenil-200mg-les-effets-secondaires.php 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.