Measurement of the $CP$ asymmetry in $B_s^0-\overline{B}{}_s^0$ mixing

TL;DR

This paper reports the most precise measurement to date of the $CP$ asymmetry in $B_s^0$ meson mixing, using proton-proton collision data from the LHCb experiment, consistent with Standard Model predictions.

Contribution

First precise measurement of the $CP$ asymmetry in $B_s^0$ mixing using 3.0 fb$^{-1}$ of LHCb data, improving constraints on new physics models.

Findings

Measured $a_{sl}^s = (0.39 \pm 0.26 ext{(stat)} \pm 0.20 ext{(syst)}) ext{ extperthousand}$

Result is consistent with Standard Model predictions

Provides tighter constraints on new physics models affecting $B_s^0$ mixing.

Abstract

The $CP$ asymmetry in the mixing of $B_s^0$ and $\overline{B}{}_s^0$ mesons is measured in proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Semileptonic $B_s^0$ and $\overline{B}{}_s^0$ decays are studied in the inclusive mode $D_s^{\mp} \mu^{\pm} \nu_{\mu} X$ with the $D_s^{\mp}$ mesons reconstructed in the $K^+ K^- \pi^{\mp}$ final state. Correcting the observed charge asymmetry for detection and background effects, the $CP$ asymmetry is found to be $a_{\text{sl}}^s = (0.39 \pm 0.26 \pm 0.20) \% $, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $a_{\text{sl}}^s$ to date. It is consistent with the prediction from the Standard Model and will constrain new models of particle physics.