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Étude de modes de désintégration non charmée du méson B et recherche de la violation de la symétrie CP

Abstract : The goal of the BaBar experiment is to search and measure $CP$ violation in the sector of the $B$ mesons et constrain the parameters of the standard model. One of the original features of its experimental design is the DIRC, the Cherenkov detector used to separate charged pions and kaons. A look-up table is implemented to correct for its alignment, and allows the DIRC to reach its design performance, a pion versus kaon separation power of $4\sigma$ at a momentum of $3\gevc$. The search for $CP$ violation in the decay channel $B^0$ to $\rho\pi$ should result in constraints on the angle $\alpha$ of the unitarity triangle, one of the parameters of the standard model. The goal of this analysis is to measure $CP$ violating parameters along with the other parameters entering the description of the decay time probability distribution function. A maximum likelihood method combines the time information with $\e^+\e^-\to q \bar(q)$ continuum background discriminating variables, some of which are summarized in a neural network. The other background, constituted of the other decay modes of the $B$, is taken into account with corrective terms in the fit. This analysis yields the best measurements for this channel up to date, and results in an indication of direct $CP$ violation. In order to use these measurements to constrain the parameters of the standard model, the long distance contribution of the decay amplitudes has to be extracted from a model. For one such model, ``QCD factorisation'', a validation test confronts the model predictions with the experimental data on the charmless decays of the $B$ mesons. The present status seems to be a disagreement, which could be reduced in the future with better experimental and theoretical knowledge of $B$ decays.
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Contributor : Pierre-François Giraud <>
Submitted on : Wednesday, July 30, 2003 - 4:36:36 PM
Last modification on : Monday, February 10, 2020 - 6:12:47 PM
Long-term archiving on: : Monday, September 20, 2010 - 11:39:50 AM

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Pierre-François Giraud. Étude de modes de désintégration non charmée du méson B et recherche de la violation de la symétrie CP. Physique des Hautes Energies - Expérience [hep-ex]. Université Paris Sud - Paris XI, 2003. Français. ⟨tel-00003154v2⟩

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