Observation of the decay D-0 -> rho - mu + nu(mu)

Abstract

By analyzing an e(+)e(-) annihilation data sample corresponding to an integrated luminosity of 2.93 fb(- 1) collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure the branching fraction of the D-0 ->rho(-) mu(+)nu(mu) decay for the first time. We obtain BD0 ->rho(-) mu(+)nu(mu) = (1.35 +/- 0.09(stat) +/- 0.09(syst)) x 10(-3). Using the world average of BD0 ->(rho)- epsilon(+)nu(epsilon), we find a branching fraction ratio of BD0 ->rho(-) mu(+)nu(mu)/ BD0 ->rho(-)e(+) nu(epsilon) = 0.90 +/- 0.11, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. Combining the world average of BD+->rho(0)mu+(.nu)(mu) and the lifetimes of D0(+), we obtain a partial decay width ratio of Gamma D-0 ->rho(-)mu(+)nu mu/2 Gamma D-0 ->rho(0)mu(+)nu(mu) ) = 0.71 +/- 0.14, which is consistent with the isospin symmetry expectation of unity within 2.1s. For the reported values of BD0 ->rho(-) mu(+)nu(mu)/BD0 ->rho(-)e+nu(e) and Gamma D-0 ->rho(-) mu(+nu)(mu) /2 Gamma(+)(D) ->rho(0)mu(+) nu(mu), the uncertainty is the quadratic sum of the statistical and systematic uncertainties.