First observation of the decay D0→K−π+μ+μ−in the ρ0–ωregion of the dimuon mass spectrum

Abstract

A study of the decay D0→K−π+μ+μ−is performed using data collected by the LHCb detector in proton–proton collisions at a centre-of-mass energy of 8TeV, corresponding to an integrated luminosity of 2.0fb−1. Decay candidates with muon pairs that have an invariant mass in the range 675–875MeV/c2are considered. This region is dominated by the ρ0and ωresonances. The branching fraction in this range is measured to be B(D0→K− π + μ + μ − ) = (4.17±0.12 (stat)±0.40 (syst))×10−6. This is the first observation of the decay D0→K−π+μ+μ−. Its branching fraction is consistent with the value expected in the Standard Model.