Measurement of the 𝐵0 𝑠→𝜇+⁢𝜇− Branching Fraction and Search for 𝐵0→𝜇+⁢𝜇− with the CMS Experiment

S. Chatrchyan, H. Castilla-Valdez, E. De La Cruz-Burelo, I. Heredia-de La Cruz, R. Lopez-Fernandez, A. Sanchez-Hernandez, et al. (CMS Collaboration)

Abstract

Results are presented from a search for the rare decays 𝐵0𝑠→𝜇+⁢𝜇− and 𝐵0→𝜇+⁢𝜇− in 𝑝⁢𝑝 collisions at √𝑠=7 and 8 TeV, with data samples corresponding to integrated luminosities of 5 and 20  fb−1, 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⁡(𝐵0𝑠→𝜇+⁢𝜇−)=(3.0+1.0−0.9)×10−9, where the uncertainty includes both statistical and systematic contributions. An excess of 𝐵0𝑠→𝜇+⁢𝜇− events with respect to background is observed with a significance of 4.3 standard deviations. For the decay 𝐵0→𝜇+⁢𝜇− an upper limit of ℬ⁡(𝐵0→𝜇+⁢𝜇−)<1.1×10−9 at the 95% confidence level is determined. Both results are in agreement with the expectations from the standard model.

DOI: 10.1103/PhysRevLett.111.101804