Study of the rare decays of B^0_s and B^0 into muon pairs from data collected during the LHC Run 1 with the ATLAS detector

A study of the decays B0?µ+µ- and B0s?µ+µ- has been performed using data corresponding to an integrated luminosity of 25 fb-1 of 7 TeV and 8 TeV proton--proton collisions collected with the ATLAS detector during the LHC Run 1. For B0, an upper limit on the branching fraction is set at B(B0?µ+µ-)<4.2×10-10 at 95% confidence level. For B0s, the branching fraction B(B0s?µ+µ-)=(0.9+1.1-0.8)×10-9 is measured. The results are consistent with the Standard Model expectation with a p-value of 4.8%, corresponding to 2.0 standard deviations.