Tristan Fillinger ; Jérôme Baudot

2022
Université de Strasbourg Strasbourg

Abstract: The Standard Model of particle physics, which describes the fundamental particles and their interactions, is the most successful theory in the history of science. For decades it has been tested by numerous scientific collaborations with great success. However, the theory remains incomplete. In order to find evidence of physics beyond the Standard Model, the experiments are upgraded to gather more and more data with higher accuracy. This thesis presents the proposition of a new vertex detector for the Belle~II experiment, along with its software implementation. With Belle, this thesis presents a new time-dependent measurement of the $CP$ violation with $B^0 \to K^{0}_{S} \pi^+ \pi^- \gamma$, which can improve the constrains on some Standard Model parameters. With Belle II, the rediscovery of $B^0 \to K^{0}_{S} \pi^+ \pi^- \gamma$ and the branching fraction measurement of $B^0 \to K^{0}_{S} \pi^0 \gamma$ with around 190 fb$^{-1}$ is described. The result of ${\cal B}\left(B^0 \to K^{0}_{S} \pi^0 \gamma\right) = \left(7.28 \pm 1.75\mathrm{(stat) \pm 1.03\mathrm{(syst) \right) \times 10^{-6}$ is compatible with the predictions.

Note: Presented on 30 09 2022
Note: PhD