Precision measurement of the $B_s^0$-${\bar{B}}_s^0$ oscillation frequency with the decay $B^{0}_{s}\rightarrowD^{-}_{s}π^{+}$

Abstract

A key ingredient to searches for physics beyond the Standard Model in $B_s^0$ mixing phenomena is the measurement of the $B_s^0$-${\bar{B}}_s^0$ oscillation frequency, which is equivalent to the mass difference $\hat{I}”m_s$ of the $B_s^0$ mass eigenstates. Using the world's largest $B_s^0$ meson sample accumulated in a dataset, corresponding to an integrated luminosity of 1.0 fb${}^{-1}$, collected by the LHCb experiment at the CERN LHC in 2011, a measurement of $\hat{I}”m_s$ is presented. A total of about 34,000 $B^{0}_{s}\rightarrowD^{-}_{s}π^{+}$ signal decays are reconstructed, with an average decay time resolution of 44 fs. The oscillation frequency is measured to be \mbox{$\hat{I}”m_s$ = 17.768 $\pm$ 0.023 (stat) $\pm$ 0.006 (syst) ps${}^{-1}$}, which is the most precise measurement to date.