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

TL;DR

This paper reports the most precise measurement to date of the semileptonic $CP$ asymmetry in $B^0-ar{B}^0$ mixing using LHCb data, confirming consistency with the Standard Model.

Contribution

It provides a new, highly precise measurement of $a_{sl}^d$, improving the experimental constraints on $CP$ violation in $B^0$ mixing.

Findings

Measured $a_{sl}^d = (-0.02 ext{±} 0.19 ext{(stat)} ext{±} 0.30 ext{(syst)}) ext{%}

Result is the most precise to date and aligns with Standard Model predictions.

Used proton-proton collision data at 3.0 fb$^{-1}$ from LHCb.

Abstract

The semileptonic $CP$ asymmetry in $B^0-\overline{B}{}^0$ mixing, $a_{\rm sl}^d$, is measured in proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb experiment. Semileptonic $B^0$ decays are reconstructed in the inclusive final states $D^-\mu^+$ and $D^{*-}\mu^+$, where the $D^-$ meson decays into the $K^+\pi^-\pi^-$ final state, and the $D^{*-}$ meson into the $\overline{D}{}^0(\rightarrow K^+\pi^-)\pi^-$ final state. The asymmetry between the numbers of $D^{(*)-}\mu^+$ and $D^{(*)+}\mu^-$ decays is measured as a function of the decay time of the $B^0$ mesons. The $CP$ asymmetry is measured to be $a_{\rm sl}^d = (-0.02 \pm 0.19 \pm 0.30)\%$, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $a_{\rm sl}^d$ to date and is consistent with the prediction from the Standard Model.