Search for charge-parity violation in the tau Yukawa coupling with CMS Run 3 data and preparation of the tracker irradiation tests for the high luminosity phase of the LHC

This thesis presents a search for charge-parity (CP) violation in Higgs boson decays to hadronic $\tau$ lepton decays ($\tau_h$) using early Run 3 CMS data at $\sqrt{s} = 13.6~\mathrm{TeV}$. A CP-sensitive observable is built from the decay planes of the $\tau_h \tau_h$ system, exploiting spin correlations. The misidentification rate of quark and gluon-jets as $\tau_h$ candidates is measured with a data-driven method. Machine learning techniques, notably a Lorentz Boost Network, are explored to improve the $\tau_h$ four-momentum reconstruction. A simultaneous fit method is developed to extract the $\tau_h$ identification and energy scale factors for Run 3. In parallel, the high luminosity LHC (HL-LHC) tracker upgrade is supported by the commissioning of an irradiation beamline at IPHC's cyclotron CYRCé. The first irradiation of a CROC-V1 pixel prototype module has validated the experimental setup and procedure, confirming the module's irradiation uniformity and IPHC’s readiness to conduct a module irradiation program.