JCJC - Jeunes chercheuses & jeunes chercheurs

Etude du Bc dans LHCb – BcLHCb

Submission summary

The project is managed by physicists members of the LHCb collaboration. The LHCb experiment is a Particle Physics experiment which will take place at CERN using proton collisions produced by the next Large Hadron Collider (LHC) which is under construction and which will start during the year 2008. This experiment is dedicated to the study of bottom quark properties.The projet aims at studying the Bc meson which has been recently discovered (1997) but which is still poorly known because only few events containing it were observered. Collisions at the LHC will produce larger numbers of Bc than what was produced up to now and the LHCb detector will be the ideal experiment to perform this study because it was designed and optimized to study specifically particles containing the b quark.The Bc main feature is that it is the ground state of two heavy quarks, the bottom quark, b, and the charm quark, c. This is the reason why there exist theoretical computations which predict precisely its mass and lifetime. The project's goal is to precisely measure these quantities to be able to compare with the predictions. On the other hand, Bc mainly decay to Bs. The Bs is a particle whose study will be the main goal of the LHCb experiment. Bs can oscillate but this has never been observer. The value of the mixing frequency is a crucial test of the standard model. Analysis methods are being developed to be able to observe the Bs oscillations but the use of Bs coming from Bc decays would be an original complement to the 'classical' analyses. The number of events obtained this way would be lower but they would not need any Bs flavour tagging which is one of the main difficulty of the 'classical' analyses. In the case where the Bs comes from a Bc decay, the flavour tagging is not necessary anymore because the same information is obtained with no error from the knowledge of the Bc charge.The project will contain several steps: * The first step is to study specific Bc Monte Carlo generators which describe Bc production mechanisms. These generators allow to compute precise momentum spectrum and production cross-section for Bc compared to these obtained with usual generators. This step should be done in close contact with theorists developing these generators. This study will allow to generate simulated event samples as close as possible to the reality to be able to efficiently develop analysis tools for real data. * The second step is to prepare analysis tools to study Bc when the first LHCb data will be available. One of the project main goal is to measure precisely the Bc mass but this kind of measurement is not common in the LHCb experiment: it will be necessary to understand the difficulties associated to this analysis (how to use the magnetic field measurement, how to understand track measurement errors). Also absolute Bc branching fractions should be determined which is not usual for LHCb analysis: a strategy should be developed for this measurement. * The last step of the project is to analyze LHCb data to reconstruct events with Bc. This analysis is CPU time consuming and will be done on data computer grids, in particular using national and regional French computing centers where LHCb data will be available. Local computer resources could also be set up with all necessary LHCb analysis tool available to provide additional computing resources for the Bc analysis.Estimates show that 1000 times more Bc events than what already exist could be reconstructed in LHCb per year. Since the LHC will ramp up progressively, this number is expected to be reached during 2009 and first precise Bc mass and lifetime values could be obtained during 2010.

Project coordination

Patrick ROBBE (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 110,000 euros
Beginning and duration of the scientific project: - 36 Months

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