Measurement of CP Violation in $\mathrm{B}^{0}_{\mathrm{s}} \! \to \mathrm{J} / \psi\,\phi$ decays with the CMS detector

The CP-violating weak phase $\phi_\mathrm{s}$ and the decay width difference $\Delta\Gamma_{\mathrm{s}}$ of $\mathrm{B}^{0}_{\mathrm{s}}$ mesons are measured by the CMS experiment at the LHC using a data sample of $\mathrm{B}^{0}_{\mathrm{s}} \! \to \mathrm{J} / \psi\,\phi$ decays. The analysed dataset corresponds to an integrated luminosity of about $20~\mathrm{fb}^{-1}$ collected in $pp$ collisions at a centre-of-mass energy $\sqrt{s} = 8~\mathrm{TeV}$. A total of $49\,000$ reconstructed $\mathrm{B}^{0}_{\mathrm{s}}$ decays are used to extract the values $\phi_\mathrm{s}$ and $\Delta\Gamma_\mathrm{s}$ by performing a time-dependent and flavour-tagged angular analysis of the $\mu^+\mu^-\mathrm{K}^+\mathrm{K}^-$ final state.The weak phase is measured to be $\phi_\mathrm{s} = -0.03 \pm 0.11~\mathrm{(stat.)} \pm 0.03~\mathrm{(syst.)}~\mathrm{rad}$, and the decay width difference between the $\mathrm{B}^{0}_{\mathrm{s}}$ mass eigenstates is $\Delta\Gamma_\mathrm{s} = 0.096 \pm 0.014~\mathrm{(stat.)} \pm 0.007~\mathrm{(syst.)}~\mathrm{ps}^{-1}$.