Measurement of the Bs lifetime difference

A flavour-untagged measurement of the lifetime difference in the $B_s\rightarrow J/\psi \phi$ with $\JPsi \rightarrow \mu ^+ \mu ^-$ and $\phi \rightarrow K ^+ K ^-$ decay is presented. The analyzed dataset corresponds to an integrated luminosity of $5.0\pm0.1~\mbox{fb}^{-1}$ collected in \textrm{pp} collisions at a centre of mass energy $\sqrt{s}= 7$ TeV with the CMS detector at the LHC. A total of 14456 $B_s\rightarrow J/\psi \phi$ decay signal candidates is reconstructed and used to measure the decay width difference $\Delta\Gamma_s$ and the polarization amplitudes, via an angular and proper decay time analysis. Assuming the mixing phase $\phi_s$ to be zero, we obtain a decay width difference $\Delta\Gamma_s = 0.048 \pm 0.024~(\mbox{stat.}) \pm 0.003~(\mbox{syst.})~\mbox{ps}^{-1}$ between the two ${B_s}$ mass eigenstates.