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Etude de la violation de CP dans le canal B0->J/psi(ee) Ks, identification et reconstruction des électrons dans l'expérience LHCb

Abstract : LHCb experiment is dedicated to the study of CP violation in B meson system and rare B meson decay. In 2000, the collaboration decided to modify the spectrometer in order to minimize the amount of matter seen by particles and to optimise the trigger. It is the context of this thesis that is divided in three parts. First is relative to the electron identification and to the recovery of Bremsstrahlung photons emitted by electrons when they pass through matter. Electron identification is mainly based on information provided by calorimeter system but also uses RICH and muon system. A method based on reference histograms had been developed which combine information provided by these detectors. Electron identification efficiency, for electrons in ECAL acceptance is 95% and the pion misidentification rate 0.7% with a 65% purity of electron sample. Bremsstrahlung recovery allows the selection of J/psi decaying in e+e- pair and of B0d→ J/ps(ee) Ks channel which are described in the second part. The selection of this channel was developed in order to get an acceptable selection efficiency with a good rejection of background. A set of cinematic and topological cuts were designed and total selection efficiency is 0.176%, corresponding to 28000 untagged events reconstructed by year, with a ratio B/S included in [0.017;0.069] (at 90% of confidence level) for inclusive bb background. In the third part, B meson flavour tagging is presented. The addition of information provided by the vertex locator allows to reject electron coming from conversion and to improve slightly the performances. The sin(2beta) LHCb sensibility from B0d→ J/psi Ks decay is also determined. Statistical error, expected after one year of data taking, corresponding to an integrated luminosity of 2 fb-1 and bb pair cross section of 0.5 mb, vary from 0.015 to 0.020 according to the values of sin(2b), |lamda f| and B/S.
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Contributor : Herve Terrier <>
Submitted on : Friday, July 1, 2005 - 4:54:35 PM
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Hervé Terrier. Etude de la violation de CP dans le canal B0->J/psi(ee) Ks, identification et reconstruction des électrons dans l'expérience LHCb. Physique des Hautes Energies - Expérience [hep-ex]. Université de Savoie, 2005. Français. ⟨tel-00009645⟩

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