Aaboud, M.Aad, G.Abbott, B.Abbott, D.C.Abdinov, O.Abeloos, B.Abhayasinghe, D.K.Abidi, S.H.AbouZeid, O.S.Abraham, N.L.Albert, JustinAnelli, Christopher R.Chiu, Y. H.Ghasemi Bostanabad, M.Hamano, KenjiHill, Ewan ChinKeeler, RichardKowalewski, RobertLefebvre, Michelet al.2020-10-262020-10-2620192019Aaboud, M., Aad, G., Abbott, B., Abbott, D. C., Abdinov, O., Abeloos, B., … Zwalinski, L. (2019). Study of the rare decays of B0 s and B0 mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector. Journal of High Energy Physics, 2019(4). https://doi.org/10.1007/JHEP04(2019)098https://doi.org/10.1007/JHEP04(2019)098http://hdl.handle.net/1828/12261A study of the decays B 0 s → μ+μ− and B0 → μ+μ− has been performed using 26.3 fb−1 of 13 TeV LHC proton-proton collision data collected with the ATLAS detector in 2015 and 2016. Since the detector resolution in μ+μ− invariant mass is comparable to the B 0 s -B0 mass difference, a single fit determines the signal yields for both decay modes. This results in a measurement of the branching fraction B(B0s→μ+μ−)=(3.2+1.1−1.0)×10−9 and an upper limit B(B0→μ+μ−)<4.3×10−10 at 95% confidence level. The result is combined with the Run 1 ATLAS result, yielding B(B0s→μ+μ−)=(2.8+0.8−0.7)×10−9 and B(B0→μ+μ−)<2.1×10−10 at 95% confidence level. The combined result is consistent with the Standard Model prediction within 2.4 standard deviations in the B(B0→μ+μ−)−B(B0s→μ+μ−) plane.enHadron-Hadron scattering (experiments)Article