Analysis of neutral $B$-meson decays into two muons

TL;DR

This paper reports precise measurements of the rare decay $B_s^0 o \mu^+\mu^-$, including its branching fraction and lifetime, and sets upper limits on related decay modes, confirming consistency with the Standard Model.

Contribution

First measurement of the $B_s^0 o \\mu^+\\mu^-$ branching fraction and lifetime using LHCb data across multiple energies, with new upper limits on related decay modes.

Findings

Measured ${\\mathcal{B}}(B_s^0 o \\mu^+\\mu^-)$ as $(3.09^{+0.46+0.15}_{-0.43-0.11}) imes 10^{-9}$

Effective lifetime of $B_s^0 o \\mu^+\\mu^-$ is $(2.07 \\pm 0.29 \\pm 0.03)$ ps

No significant signals for $B^0 o \\mu^+\\mu^-$ and $B_s^0 o \\mu^+\\mu^- \\gamma$, with upper limits set.

Abstract

Branching fraction and effective lifetime measurements of the rare decay $B^0_s\to\mu^+\mu^-$ and searches for the decays $B^0\to\mu^+\mu^-$ and $B^0_s\to\mu^+\mu^-\gamma$ are reported using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of $7$ TeV, $8$ TeV and $13$ TeV, corresponding to a luminosity of $9$ fb$^{-1}$. The branching fraction ${\mathcal{B}}(B^0_s\to\mu^+\mu^-)=\left(3.09^{+0.46+0.15}_{-0.43-0.11}\right)\times 10^{-9}$ and the effective lifetime $\tau(B^0_s\to\mu^+\mu^-)=(2.07\pm 0.29\pm 0.03)$ are measured, where the first uncertainty is statistical and the second systematic. No significant signal for $B^0\to\mu^+\mu^-$ and $B^0_s\to\mu^+\mu^-\gamma$ decays is found and upper limits $\mathcal{B}(B^0\to\mu^+\mu^-)<2.6\times 10^{-10}$ and $\mathcal{B}(B^0_s\to\mu^+\mu^-\gamma)<2.0\times 10^{-9}$ at the 95% CL are determined, where the latter is limited to the range $m_{\mu\mu} > 4.9$ GeV$/c^2$. The results are in agreement with the Standard Model expectations.