Evidence for an anomalous like-sign dimuon charge asymmetry

We present a measurement of the like-sign dimuon asymmetry in semileptonic b-hadron decays, performed using 6.1 fb−1 of collisions recorded with the D0 detector at a center-of-mass energy at the Fermilab Tevatron collider. This measured value is , which disagrees with the Standard Model prediction at a statistical level of 3.2 σ, and provides the first evidence of anomalous CP violation in the mixing of neutral B mesons.