Study of the rare decays of B-s(0) and B-0 into muon pairs from data collected during the LHC Run 1 with the ATLAS detector

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