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Mesure de la phase de violation de CP φs dans les désintégrations des mésons Bs

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This work fits within the activities of the LAPP LHCb group such as the expertise around the calorimeter system and the measurements of key CP observables in the B0 and Bs meson systems. In particular, the group targets the measurement of the CP-violating phase φs in decays of Bs to J/ψ η(η’), where the eta mesons decay into two photons. This phase relates to CP violation in interference between mixing and decay in the Bs system and is a sensitive probe for physics beyond the standard model thanks to very precise theory predictions. The above mentioned decays are complementary to the golden mode Bs -> J/ψ φ for the measurement of φs. Due to the relatively small efficiency with which neutral modes are reconstructed, we foresee optimizing the selections for the different decays of the η(η’) mesons and including Bs decays to heavier charmonia (ψ(2S), χc1). Some of these decays have not been observed yet. The work of the training period is to develop the selections for each mode and measure their branching ratios using the full LHCb data set.

Encadrant : Maximilien Chefdeville (

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