Beauty meson to double open charm decays with the LHCb detector

Measurements of beauty meson to double open charm decays are presented. These measurements use data collected in proton-proton collisions by the LHCb detector at the Large Hadron Collider (LHC) between 2011 and 2018. Firstly a search for sixteen rare decays of the $B_c^+$ meson to two charm mesons is performed. Studies of the $B_c^+$ meson can improve understanding of heavy quark dynamics, and its decay to two charm mesons could be useful in measuring the Cabibbo-Kobayashi-Maskawa quark-mixing phase $\gamma$ in future LHC data taking periods. The first evidence of the $B_c^+\rightarrow D_s^+\overline{D}^0$ decay is found with a significance of 3.4 standard deviations and its branching fraction is measured. Upper confidence limits on the branching fractions of the other fifteen decays are improved. Secondly, the charge-parity asymmetries ($\mathcal{A}^{C\!P}$) and branching fractions of decays of the $B^-$ meson to two charm mesons are measured. No evidence of charge-parity violation is seen, but the first measurements of $\mathcal{A}^{C\!P}(B^-\rightarrow D_s^{*-}D^0)$ and $\mathcal{A}^{C\!P}(B^-\rightarrow D_s^- D^{*0})$ are made and the precision is improved on the $\mathcal{A}^{C\!P}$ of a further five decay modes. Moreover, ratios between the branching fractions of doubly charmed decays of the $B^-$ meson are measured for the first time. These results will help to constrain physics beyond the Standard Model. Finally, a generic beauty hadron neural network and exclusive selections for doubly charmed beauty meson decays are developed, which are implemented in the trigger for future data taking. The improvement in selection efficiency using these selections in the upgraded trigger system is evaluated. Additionally, prospects for measurements of doubly charmed beauty meson decays with future LHCb datasets are discussed. Sensitivity to rare doubly charmed $B_c^+$ meson decays and high-precision measurements of charge-parity violation will be enabled by the upgraded LHCb detector and trigger system.