Evidence for an anomalous like-sign dimuon charge asymmetry

TL;DR

This paper reports the first evidence of anomalous CP violation in neutral B meson mixing, observed through a significant like-sign dimuon charge asymmetry in proton-antiproton collisions at Fermilab.

Contribution

It provides the first measurement indicating a deviation from the Standard Model prediction of CP violation in B meson mixing.

Findings

Measured like-sign dimuon charge asymmetry $ ext{A}_{ ext{sl}}^b = -0.00957 \

Significantly differs from the Standard Model prediction by 3.2 standard deviations.

Provides evidence for anomalous CP violation in neutral B meson mixing.

Abstract

We measure the charge asymmetry $A\equiv(N^{++} - N^{--})/(N^{++} + N^{--})$ of like-sign dimuon events in 6.1~fb$^{-1}$ of $p\bar{p}$ collisions recorded with the D0 detector at a center-of-mass energy $\sqrt{s}=1.96$~TeV at the Fermilab Tevatron collider. From $A$ we extract the like-sign dimuon charge asymmetry in semileptonic $b$-hadron decays: $\aslb=-0.00957\pm0.00251\thinspace({\rm stat})\pm0.00146\thinspace({\rm sys})$. It differs by 3.2~standard deviations from the standard model prediction $\aslb({\rm SM})=(-2.3^{+0.5}_{-0.6})\times10^{-4}$, and provides first evidence of anomalous $CP$ violation in the mixing of neutral $B$ mesons.