First observation of CP violation in the decays of Bs0 mesons

Using pp collision data corresponding to an integrated luminosity of 1.0 fb ^-1 and collected by LHCb in 2011 at a center-of-mass energy of 7 TeV, we report the measurement of direct CP violation in Bs0→K ^-π ⁺ decays, A _CP(Bs0→K ^-π ⁺)=0.27±0.04 (stat)±0.01 (syst), with significance exceeding 5 standard deviations. This is the first observation of CP violation in the decays of Bs0 mesons. Furthermore, we provide an improved determination of direct CP violation in B0→K ⁺π ^- decays, A _CP(B0→K ⁺π ^-)=-0.080±0. 007 (stat)±0.003 (syst), which is the most precise measurement of this quantity to date.