Measurement of the B(s) to mu+ mu- branching fraction and search for B0 to mu+ mu- with the CMS Experiment

TL;DR

This paper reports the measurement of the rare B(s) to mu+ mu- decay, observing an excess consistent with the Standard Model, and sets an upper limit on B0 to mu+ mu- decay using CMS data from the LHC.

Contribution

First measurement of B(s) to mu+ mu- branching fraction with a 4.3 sigma significance and an improved upper limit on B0 to mu+ mu- using CMS data at 7 and 8 TeV.

Findings

B(B(s) to mu+ mu-) = (3 +1.0/-0.9) x 10^-9

Observed excess with 4.3 sigma significance

Upper limit B(B0 to mu+ mu-) < 1.1 x 10^-9 at 95% CL

Abstract

Results are presented from a search for the rare decays B(s) to mu+ mu- and B0 to mu+ mu- in pp collisions at sqrt(s) = 7 and 8 TeV, with data samples corresponding to integrated luminosities of 5 and 20 inverse femtobarns, respectively, collected by the CMS experiment at the LHC. An unbinned maximum-likelihood fit to the dimuon invariant mass distribution gives a branching fraction B(B(s) to mu+ mu-) = (3 +1.0/-0.9)E-9, where the uncertainty includes both statistical and systematic contributions. An excess of B(s) to mu+ mu- events with respect to background is observed with a significance of 4.3 standard deviations. For the decay B0 to mu+ mu- an upper limit of B(B0 to mu+ mu-) < 1.1E-9 at the 95% confidence level is determined. Both results are in agreement with the expectations from the standard model.