The branching fraction and CP asymmetry of $B^{\pm} \rightarrow \psi \pi^{\pm}$ and $B^{\pm} \rightarrow \pi^{\pm} \mu^{+} \mu^{-}$ decays

Two analyses are performed using data collected by the LHCb experiment during 2011. Both consider decays of charged $B$ mesons reconstructed in the $\pi^{\pm} \mu^{+} \mu^{-}$ final state. Decays involving dimuons provide an experimentally clean signature, even in the high-background environment of the $\sqrt{s}$ = 7 TeV proton-proton collisions at the LHC. The first analysis measures the $CP$ asymmetry of $B^{\pm} \rightarrow \psi \pi^{\pm}$ decays using 0.37 fb$^{-1}$ of data, where the dimuon decays of two resonances are considered, $J/\psi \rightarrow \mu^{+}\mu^{-}$ and $\psi (2S) \rightarrow \mu^{+}\mu^{-}$. The branching fraction is measured relative to the Cabibbo favoured $B^{\pm} \rightarrow \psi K^{\pm}$ mode. The second analysis uses 1 fb$^{-1}$ of data to make the first observation of the non-resonant $B^{\pm} \rightarrow \pi^{\pm} \mu^{+} \mu^{-}$ decay. The branching fraction is measured relative to that of $B^{\pm} \rightarrow K^{\pm} \mu^{+} \mu^{-}$, and measurements of the $CP$ asymmetry and the ratio of CKM matrix elements $|V_{td}/V_{ts}|$ are obtained. The branching fractions of the decays of interest are found to be \begin{eqnarray*} \mathcal{B}(B^{\pm} \to J/\psi \pi^{\pm}) &=& (3.88 \pm 0.11 \pm 0.15) \times 10^{-5} \, ,\\ \mathcal{B}(B^{\pm} \to \psi(2S) \pi^{\pm}) &=& (2.52 \pm 0.26 \pm 0.15) \times 10^{-5}\ {\rm and}\\ \mathcal{B}(B^{\pm} \to \pi^{\pm} \mu^{+} \mu^{-}) &=& (2.48 \pm ^{0.57} _{0.52} \pm 0.17) \times10^{-8} \, , \end{eqnarray*} where the first uncertainty is related to the statistical size of the sample and the second quantifies systematic effects. The measured $CP$ asymmetries in these modes are \begin{eqnarray*} A_{CP}^{J/\psi \pi} = 0.005 \pm 0.027 \pm 0.011 \, ,\\ A_{CP}^{\psi (2S) \pi} = 0.048 \pm 0.090 \pm 0.011 \, \, {\rm and}\\ A_{CP}^{\mu\mu \pi} = -0.045 \pm 0.220 \pm 0.066 \, , \end{eqnarray*} with no evidence of direct $CP$ violation seen. The ratio of matrix elements is measured as \begin{eqnarray*} \frac{|V_{td}|}{|V_{ts}|} = 0.274 \pm ^{0.031} _{0.028} \pm 0.008 \, , \end{eqnarray*} which is in agreement with previous results.