Results on direct CP violation in B decays in LHCb

Abstract

I present three studies from the LHCb experiment on the subject of direct CP violation in $B^0$ and $B_s$ decays. First, we measure the CP asymmetry in $B^\pm\to\psi K^\pm$ decays, with $\psi=J/\psi, \psi(2S)$, using 0.35 $fb^{-1}$ of $pp$ collisions at $\sqrt{s}=7 TeV$. We find no evidence for CP violation. Second, using the same data sample, we see the first evidence of CP violation in the decays of $B_s$ mesons to $K^\pm\pi^-\pi^+$ pairs, $A_{CP}(B_s\to K\pi) = 0.27 \pm 0.08 {\rm (stat)}\pm 0.02 {\rm (syst)}$ ($3.3\sigma$). Third, using 1.0 $fb^{-1}$ of data, measurements of CP sensitive observables of the $B^\pm\to D K^\pm$ system are presented. They include the first observation of the suppressed mode $B^\pm\to[\pi^\pm K^\mp]_D K^\pm$. Combining several $D$ final states, CP violation in $B^\pm\to D K^\pm$ decays is observed with a significance of $5.8\sigma$.