Search for a wrong-flavour contribution to $B_s \rightarrow D_s\pi$ decays and study of $C\!P$ violation in $B_s \rightarrow D_sK$ decays

This thesis presents a world-first measurement of the $C\!P$ parameters of $B_s \rightarrow D_s\pi$ with the aim of testing the flavour-specific nature of the decay. The measurement is made using $\int\mathcal{L}=1.0 \,\mbox{fb}^{-1}$ of $pp$ collisions recorded at a centre-of-mass energy of $\sqrt{s}=7 \mathrm{\,Te\kern -0.1em V}$ collected during 2011. The measured values of the $C\!P$ parameters are \begin{alignat}{3} \overline{S} &= &&0.197 \pm 0.150 \pm 0.025, \nonumber \\ \overline{D} &= -&&0.888 \pm 0.098 \pm 0.541, \nonumber \\ \Delta S &= &&0.066 \pm 0.083 \pm 0.004, \nonumber \\ \Delta D &= -&&0.062 \pm 0.050 \pm 0.169, \nonumber \end{alignat} where the first uncertainties are statistical and the second are systematic. These results are consistent with the Standard Model prediction. A measurement of the $C\!P$ parameters of $B_s \rightarrow D_sK$ is also presented, producing \begin{alignat}{2} C &= &&1.01 \pm 0.50 \pm 0.23, \nonumber \\ S_f &= -&&1.25 \pm 0.56 \pm 0.24, \nonumber \\ S_{\bar{f}} &= &&0.08 \pm 0.68 \pm 0.28, \nonumber \\ D_f &= -&&1.33 \pm 0.60 \pm 0.26, \nonumber \\ D_{\bar{f}} &= -&&0.81 \pm 0.56 \pm 0.26, \nonumber \end{alignat} where the first uncertainties are statistical and the second are systematic.