Observation of the decay $B_{s}^{0} to eta_{c} phi$ and evidence for $B_{s}^{0} to eta_{c} pi^{+} pi^{-} $

A study of $B^{0}_{s} to eta_{c} phi$ and $B^{0}_{s} to eta_{c} pi^{+}pi^{-}$ decays is performed using $pp$ collision data corresponding to an integrated luminosity of 3.0$,rm fb^{-1}$, collected with the LHCb detector in Run~1 of the LHC. The observation of the decay $B^{0}_{s} to eta_{c} phi$ is reported, where the $eta_{c}$ meson is reconstructed in the $pbar p$, $K^+K^-pi^+pi^-$, $pi^+pi^-pi^+pi^-$ and $K^+K^-K^+K^-$ decay modes and the $phi(1020)$ in the $K^+ K^-$ decay mode. The decay $B^{0}_{s} to J/psi phi$ is used as a normalisation channel. Evidence is also reported for the decay $B^{0}_{s} to eta_{c} pi^{+}pi^{-}$, where the $eta_{c}$ meson is reconstructed in the $pbar p$ decay mode, using the decay $B^{0}_{s} to J/psi pi^+ pi^-$ as a normalisation channel. The measured branching fractions are begin{eqnarray*} {mathcal B (B^{0}_{s} to eta_{c} phi)} &=& left(5.01 pm 0.53 pm 0.27 pm 0.63 right) times 10^{-4} ,, onumber {mathcal B (B^{0}_{s} to eta_{c} pi^+ pi^-)} &=& left(1.76 pm 0.59 pm 0.12 pm 0.29 right) times 10^{-4} ,, end{eqnarray*} where in each case the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions.