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Abstract

This thesis describes two different scientific topics: the time synchronisation of the Scintillating Fibre (SciFi) Tracker and a Lepton Flavour Universality (LFU) study with the rare baryonic decay $\Lambda_b^0\rightarrow\Lambda^0\ell^+\ell^-$ ($\ell=e,\mu$) at the LHCb experiment.

The SciFi Tracker is a part of the LHCb Upgrade I. In the context of its commissioning and early operation, the time synchronisation procedure, hereinafter referred to as the time alignment, was developed to align the detector signal integration window to the incoming physics signal and thus to optimise the hit detection efficiency. The strategy of the time alignment is introduced and the system timing characteristics study based on the early data (2023-2024) is discussed.

LFU is a feature of the Standard Model (SM) of particle physics, which refers to the equal couplings of the electroweak interaction to the 3 generations of leptons. Assuming LFU, the relative branching fraction between the baryon decays $\Lambda_b^0\rightarrow\Lambda^0e^+e^-$ and $\Lambda_b^0\rightarrow\Lambda^0\mu^+\mu^-$ is expected to be close to 1.0. A deviation from this expectation can be caused by possible new physics. Using the data collected by the LHCb experiment from 2011 to 2012 (Run1) and from 2015 to 2018 (Run2), which corresponds to an integrated luminosity of 9 $\mathrm{fb}^{-1}$, this relative ratio can be probed. The procedure of this LFU study is described and, depending on the different kinematic regions, the preliminary expected sensitivity, either for the ratio observable or for the observation of $\Lambda_b^0\rightarrow\Lambda^0e^+e^-$, is reported.