Observation of the rare $B^0_s\to\mu^+\mu^-$ decay from the combined analysis of CMS and LHCb data

TL;DR

This paper reports the first observation of the rare decay $B^0_s o\mu^+\mu^-$ and evidence for $B^0 o\mu^+\mu^-$, using combined CMS and LHCb data, confirming SM predictions and constraining new physics models.

Contribution

It provides the first observation of the $B^0_s o\mu^+\mu^-$ decay and improves measurements of its branching fraction using combined data from CMS and LHCb.

Findings

First observation of $B^0_s o\mu^+\mu^-$ decay with >6 sigma significance.

Evidence for $B^0 o\mu^+\mu^-$ decay at 3 sigma significance.

Branching fraction measurements compatible with Standard Model predictions.

Abstract

A joint measurement is presented of the branching fractions $B^0_s\to\mu^+\mu^-$ and $B^0\to\mu^+\mu^-$ in proton-proton collisions at the LHC by the CMS and LHCb experiments. The data samples were collected in 2011 at a centre-of-mass energy of 7 TeV, and in 2012 at 8 TeV. The combined analysis produces the first observation of the $B^0_s\to\mu^+\mu^-$ decay, with a statistical significance exceeding six standard deviations, and the best measurement of its branching fraction so far. Furthermore, evidence for the $B^0\to\mu^+\mu^-$ decay is obtained with a statistical significance of three standard deviations. The branching fraction measurements are statistically compatible with SM predictions and impose stringent constraints on several theories beyond the SM.