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

TL;DR

This paper reports on the measurement and limits of rare B meson decays into muon pairs using ATLAS data from LHC Run 1, providing results consistent with the Standard Model predictions.

Contribution

First measurement of $B^0_s$ decay into muon pairs with ATLAS, setting upper limits and observing results compatible with the Standard Model.

Findings

Upper limit on $B^0$ decay branching fraction: < 4.2 x 10^{-10}

Measured $B^0_s$ decay branching fraction: (0.9^{+1.1}_{-0.8}) x 10^{-9}

Results consistent with Standard Model expectations

Abstract

A study of the decays $B^0\to \mu^+\mu^-$ and $B^0_s\to \mu^+\mu^-$ 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 $B^0$, an upper limit on the branching fraction is set at ${\cal B}(B^0 \to \mu^+\mu^-) < 4.2 \times 10^{-10}$ at $95\%$ confidence level. For $B^0_s$, the branching fraction ${\cal B}(B^0_s \to \mu^+\mu^-) = \left( 0.9^{+1.1}_{-0.8} \right) \times 10^{-9}$ is measured. The results are consistent with the Standard Model expectation with a $p$-value of $4.8\%$, corresponding to $2.0$ standard deviations.