Measurement of CP asymmetry in $B^0_s \rightarrow D^{\mp}_s K^{\pm}$ decays

TL;DR

This paper measures CP violation in $B^0_s ightarrow D^{ m ext{-}}_s K^{ m ext{+}}$ decays using LHCb data, leading to the first extraction of the CKM angle gamma from these decays.

Contribution

It provides the first measurement of CP asymmetries in these decays and extracts the CKM angle gamma from them.

Findings

Measured CP violating observables with statistical and systematic uncertainties.

First extraction of the CKM angle gamma from $B^0_s ightarrow D^{ m ext{-}}_s K^{ m ext{+}}$ decays.

Results are consistent with the Standard Model expectations.

Abstract

We report on measurements of the time-dependent CP violating observables in $B^0_s\rightarrow D^{\mp}_s K^{\pm}$ decays using a dataset corresponding to 1.0 fb$^{-1}$ of pp collisions recorded with the LHCb detector. We find the CP violating observables $C_f=0.53\pm0.25\pm0.04$, $A^{\Delta\Gamma}_f=0.37\pm0.42\pm0.20$, $A^{\Delta\Gamma}_{\bar{f}}=0.20\pm0.41\pm0.20$, $S_f=-1.09\pm0.33\pm0.08$, $S_{\bar{f}}=-0.36\pm0.34\pm0.08$, where the uncertainties are statistical and systematic, respectively. Using these observables together with a recent measurement of the $B^0_s$ mixing phase $-2\beta_s$ leads to the first extraction of the CKM angle $\gamma$ from $B^0_s \rightarrow D^{\mp}_s K^{\pm}$ decays, finding $\gamma$ = (115$_{-43}^{+28}$)$^\circ$ modulo 180$^\circ$ at 68% CL, where the error contains both statistical and systematic uncertainties.