Real-time alignment of the LHCb vertex detector and observation of charmless baryonic decays $B^0_{(s)} \rightarrow p \overline{p} h^+ h^{\prime-}$

This thesis presents measurements of the branching fractions of the charmless baryonic decays $B^0_{(s)}\to p\overline{p} h^+h^{\prime-}$ , where $h^{(\prime)}$ denotes a kaon or a pion. Three new modes ($B^0\to p\overline{p} \pi^+\pi^-$, $B^0_{s}\to p\overline{p} K^+K^-$ and $B^0_{s}\to p\overline{p} K^{\pm}\pi^{\mp}$) are observed for the first time and evidence is found for a fourth ($B^0\to p\overline{p} K^+K^-$). The inclusive branching fraction of $B^0\to p\overline{p} K^{\pm}\pi^{\mp}$ is measured for the first time and the upper limit is set on the branching fraction of the $B^0_{s}\to p\overline{p} \pi^+\pi^-$ decay. This represents the first observation of four-body charmless baryonic decays of a $B_s$ meson and one of the first observations of baryonic $B^0_{s}$ decays. The implementation of the real-time alignment of LHCb's vertex detector is also described. The novel real-time alignment and calibration strategy adopted by LHCb is essential to allow more stable data taking conditions and an optimal "offline-quality" reconstruction to be performed at the trigger level, ensuring more efficient trigger selections and the possibility to perform physics analyses directly on the trigger output.