Analysis of the $B_{s} rightarrow mu^{+}mu^{-}$ Decay with the Reoptimized LHCb Detector

The current status of the $B_{s}^0 rightarrow mu^{+}mu^{-}$ analysis is presented. Results on annual yields and B/S ratio are given based on studies of signal and background samples. The background is assumed to be dominated by inclusive $bar b$ events, in particular events where the two b-hadrons decay semileptonically ($b ightarrow muar u_{mu}X,ar b ightarrow mu u_{mu}X$). According to the Standard Model predictions the total number of $B_{s}^{0} ightarrowmu^{+}mu^{-}$ events produced in one year of data taking of the LHCb experiment will be $sim 700$ and 17 signal events are expected to be selected inside the LHCb detector. No background event passes the final cuts in a sample of 11M simulated events and the upper limit on B/S ratio for $b ightarrowmu u_{mu} X;ar b ightarrowmu u_{mu} X$ is estimated to be 5.7.