Results on direct CP violation in B decays in LHCb

TL;DR

This paper reports on three studies from LHCb investigating direct CP violation in B meson decays, including measurements of asymmetries and the first evidence of CP violation in certain decay modes, with some results confirming CP violation.

Contribution

The paper presents new measurements of CP asymmetries in B meson decays, including the first evidence of CP violation in $B_s$ decays and the first observation of CP violation in $B^\pm o D K^\pm$ decays.

Findings

No evidence for CP violation in $B^\pm o \psi K^\pm$ decays.

First evidence of CP violation in $B_s o K \pi$ decays ($3.3\sigma$).

CP violation observed in $B^\pm o D K^\pm$ decays ($5.8\sigma$).

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 $5.8\sigma$.