Test of lepton flavor universality in semileptonic B+c meson decays in proton-proton collisions at V¯s=13 TeV

Abstract

A measurement of the ratio of branching fractions R(J/y)=B(B+c-J/yt+vr)/B(B+c-J/yu+vu) in the J/y-u+u¯,t+-u+vuv¯t decay channel is presented. This measurement uses a sample of proton-proton collision data collected at a ceter-of-mass energy of 13 TeV by the CMS experiment in 2018, corresponding integrated luminosity of 59.7 fb-1. The measured ratio, R(J/y)=0.17+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.