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The observable Universe is mainly made up of matter, while almost all the antimatter disappeared in the very early times. One explanation is that the Universe obeys the Sakharov conditions, which means the existence of a C and CP symmetry violation. In Standard Model (SM), the main contribution to CP violation comes from the Cabibbo–Kobayashi–Maskawa (CKM) mechanism, implying a mixing complex unitary matrix (the CKM matrix) defining the coupling between up-type quarks and down-type quarks through the weak interaction. This matrix can be parameterized by four independent parameters measurable in experiments. One of the key goals of LHCb is to constrain those parameters. Specifically, the γ angle of the CKM matrix sets a benchmark for CP violation, to be compared with the SM predictions. In particular, direct measurements with tree-diagram decays, theoretically clean, set a “standard candle” for the SM. One can then test discrepancy with loop-level measurements that could be sensible to new physics phenomena. The CKMfitter group has notably proved that, with a 1-degree precision on direct measurements, one may test the Standard Model up to at least 17 TeV. The angle γ can be directly measured by amplitude modulation in the interference between the processes b → cubars and b → ucbars. This is the case in this study, where a binned model-independent analysis of the mode B± → Dh± with D → KS0π+π-π0 is presented, using a generalized BPGGSZ method, where an additional π0 meson is introduced. Among the possible sub-decays, there is two-body CP-odd eigen-state D → KS0ω(π+π-π0), while the CP-odd GLW modes have usually been supposed to be unfeasible by LHCb. The BPGGSZ method with the three-body decay D → KS0π+π- currently is the most precisely studied mode in LHCb. That is why we study the corresponding D four-body decay with an additional π0, which has been studied in Belle but still not in LHCb, where we get more than twice Belle statistics with Run 1 and 2, corresponding to 9 fb-1 of integrated luminosity. This method consists of analyzing the decay amplitude as a function of the D decay phase-space. This leads to a good sensitivity on γ thanks to the rich resonance structure of the D → KS0π+π-π0 decay but requires knowledge of the strong phase difference between the D0 and D0bar processes, which varies with the final-state kinematics. This analysis then takes as input a binned map of strong phase directly measured by CLEO-c experiment. This leaves this analysis strongly independent of any D decay amplitude model.
In addition, a large upgrade of the LHCb detector has been performed in the last years before Run 3 data taking. The expected instantaneous luminosity of 2.0 x 1033 cm2s-1 is five times larger than during the previous runs, mostly thanks to a new data acquisition system at 40 MHz. Such a frequency plus the increasing radiation constraints and the will to increase spatial resolution, leads to the construction of a new LHCb detector version (Upgrade I), holding peculiarly a state-of-the-art downstream tracker named SciFi (Scintillating Fibers). LPCA lab being actively involved in the SciFi project, notably in Front-End electronics (FEBs), it was then natural to participate to this effort. I took part, from the beginning of my thesis, to the end of its construction, and to the commissioning and monitoring. I will present some of my contributions to the SciFi subdetector including FEBs temperature monitoring (online and offline), during commissioning and data taking, and the fine time alignment in PACIFIC boards.
Maik Becker & Serena Maccolini