Test of lepton flavor universality in semileptonic B⁺꜀ meson decays in proton-proton collisions at √s = 13 TeV

Abstract

A measurement of the ratio of branching fractions 𝑅⁢(𝐽/𝜓) =ℬ⁡(B⁺꜀ →𝐽/𝜓⁢𝜏+⁢𝜈𝜏)/ℬ⁡(B⁺꜀ →𝐽/𝜓⁢𝜇+⁢+𝜈𝜇) in the 𝐽/𝜓 →𝜇+⁢𝜇−, 𝜏+→𝜇+⁢𝜈𝜇⁢¯𝜈𝜏 decay channel is presented. This measurement uses a sample of proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment in 2018, corresponding to an integrated luminosity of 59.7 fb⁻¹. The measured ratio, 𝑅⁢(𝐽/𝜓) = 0.1⁢7+0.18−0.17⁢(stat)+0.21−0.22⁢(syst)+0.19−0.18⁢(theo) =0.17 ±0.33, agrees with the value of 0.2582 ±0.0038 predicted by the standard model, which assumes lepton flavor universality. By testing lepton flavor universality, this measurement is a probe of new physics using 𝐵+𝑐 mesons, which are currently only produced at the LHC.