Measurement of the branching fractions of B0s → KShh decays in LHCb, insights on the CKM angle gamma and monitoring of the Scintillating Fibre Tracker for the LHCb upgrade ; Mesure des rapports d’embranchement des désintégrations B0→ Kshh avec l’expérience LHCb, mesure de l’angle CKM gamma et surveillance du Scintillating Fibre Tracker pour l’upgrade de LHCb

This thesis is organized in three parts around the analysis of charmless three-body B-meson decays. The first part concerns the extraction of the CKM angle gamma using a method that showed promising results during a previous analysis. The present thesis intends to extend this work to new decay modes. The study uses the results of amplitude analyses from the BABAR experiment. By combining the information available in several Dalitz planes, it is possible to extract constraints on gamma from charmless three-body B-meson decays. The thesis determines the constraints from the new (antisymmetric) final state, demonstrates that they are not currently competitive, and explains why this is the case. Options to improve the constraints, such as using a more detailed amplitude model based on substantially more data, or combining constraints from several symmetry states, are discussed. The second part of this thesis concerns the upgrade of the LHCb detector. The LHCb tracker is replaced by the Scintillating Fiber (SciFi) Tracker. This thesis discusses the developments of the monitoring of this sub-detector: an expert-level panel for LHCb control room as well as the update of the sub-detector calibration procedure. Finally, the third part of the thesis deals with an LHCb analysis: measuring the branching fractions of the B0 (s) -> Kshh' modes, where h (') is a pion or a kaon. The study uses data collected by LHCb during run 1 and run 2, for a total integrated luminosity of around 9/fb. This analysis is a step towards future amplitude analyses of B0 (s) -> KShh' decay modes. ; Cette thèse s’organise suivant trois volets autour de l'analyse des désintégrations de mésons B en trois particules non charmées. Le premier concerne l’extraction de l’angle CKM gamma suivant une méthode ayant fait ses preuves durant une précédente analyse. La présente thèse entend étendre ce travail à de nouveaux modes de désintégrations. L’étude se base sur les résultats d’analyses en amplitudes de l’expérience BABAR. En combinant les ...