Evidence for an anomalous like-sign dimuon charge asymmetry

TL;DR

This paper reports a measurement of like-sign dimuon charge asymmetry in $b$-hadron decays, revealing a significant deviation from the Standard Model and providing first evidence of anomalous CP violation in neutral $B$ meson mixing.

Contribution

It presents the first measurement indicating anomalous CP violation in neutral $B$ mesons, challenging Standard Model predictions.

Findings

Measured asymmetry $A^b_{sl} = -0.957 ext{ extpm}0.251 ext{(stat)} ext{ extpm}0.146 ext{(syst)}$

Disagrees with Standard Model at 3.2 sigma

Provides first evidence of anomalous CP violation in $B$ meson mixing

Abstract

We present a measurement of the like-sign dimuon asymmetry in semileptonic $b$-hadron decays, performed using 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. This measured value is $A^b_{\rm sl} = [-0.957\pm0.251\thinspace({\rm stat})\pm0.146\thinspace({\rm syst})]$ %, which disagrees with the Standard Model prediction at a statistical level of 3.2 $\sigma$, and provides the first evidence of anomalous CP violation in the mixing of neutral $B$ mesons.