A study of the decays Bs0 → 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 Bs0–B0 mass difference, a single fit determines the signal yields for both decay modes. This results in a measurement of the branching fraction B(Bs0 → µ+ µ−) = ( 3.2+−11..10 ) × 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(Bs0 → µ+ µ−) = ( 2.8+−00..87 )× 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(Bs0 → µ+ µ−) plane.
|Original language||English (US)|
|State||Published - Dec 7 2018|
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