Measurement of CP violation in $\mathrm{B_s} \rightarrow $ J$/\psi \phi$ decays with the CMS experiment

The CP violating weak phase $\phi_s$ and the decay width difference $\Delta \Gamma_s$ of the $\mathrm{B_s}$ light and heavy mass eigenstates are measured with the CMS detector at the LHC using a data sample of $\mathrm{B_s}$ $\to$ $J/\psi \phi(1020) \to \mu^{+} \mu^{-} \mathrm{K}^{+} \mathrm{K}^{-}$ decays. The analysed data correspond to an integrated luminosity of 19.7 fb$^{-1}$ and it is collected in pp collisions at a centre-of-mass energy of 8 TeV. A total of 49 200 reconstructed $\mathrm{B_s}$ candidates are used in the analysis. The weak phase is measured to be $\phi_\mathrm{s} = -0.075 \pm 0.097 ~\mathrm{(stat)} \pm 0.031 ~\mathrm{(syst)}$ rad, and the decay width difference is $\Delta\Gamma_\mathrm{s} = 0.095 \pm 0.013~\mathrm{(stat)} \pm 0.007~\mathrm{(syst)}$ ps$^{-1}$.