Study of the rare decays of B 0 s Bs0 and B 0 B0 into muon pairs from data collected during the LHC Run 1 with the ATLAS detector

A study of the decays B 0 s →μ + μ − Bs0→μ+μ− and B 0 →μ + μ − B0→μ+μ− has been performed using data corresponding to an integrated luminosity of 25 fb −1 −1 of 7 and 8 TeV proton–proton collisions collected with the ATLAS detector during the LHC Run 1. For the B 0 B0 dimuon decay, an upper limit on the branching fraction is set at B(B 0 →μ + μ − )<4.2×10 −10 B(B0→μ+μ−)<4.2×10−10 at 95 % confidence level. For B 0 s Bs0, the branching fraction B(B 0 s →μ + μ − )=(0.9 +1.1 −0.8 )×10 −9 B(Bs0→μ+μ−)=(0.9−0.8+1.1)×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