Study of $B_s \rightarrow \eta_c(4h) \phi(K^+K^-)$ pre-selection at LHCb

The LHCb experiment is designed to carry out precision measurements in beauty and charm sectors. One of the core physics programs at LHCb is the determination of CP-violating phase $\phi_s$ in the transition $b\rightarrow c\overline{c}s$. The $B_s \rightarrow \eta_c\phi$ decay is such process, and has never been studied before. A multivariate analysis based pre-selection has been developed for $B_s \rightarrow \eta_c\phi$, with $\eta_c\to 4h$, and $\phi \to K^+ K^-$. The efficiency of pre-selection has been improved by a factor of 4, compared to previous work.