Measurement of the Branching Fraction for the Semileptonic Decay D0 (+) →π- (0)μ+νμ and Test of Lepton Flavor Universality

Abstract

Using a data sample corresponding to an integrated luminosity of 2.93 fb-1 taken at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we perform an analysis of the semileptonic decays D0(+)→π-(0)μ+νμ. The branching fractions of D0→π-μ+νμ and D+→π0μ+νμ are measured to be (0.272±0.008stat±0.006syst)% and (0.350±0.011stat±0.010syst)%, respectively, where the former is of much improved precision compared to previous results and the latter is determined for the first time. Using these results along with previous BESIII measurements of D0(+)→π-(0)e+νe, we calculate the branching fraction ratios to be R0≡BD0→π-μ+νμ/BD0→π-e+νe=0.922±0.030stat±0.022syst and R+≡BD+→π0μ+νμ/BD+→π0e+νe=0.964±0.037stat±0.026syst, which are compatible with the theoretical expectation of lepton flavor universality within 1.7σ and 0.5σ, respectively. We also examine the branching fraction ratios in different four-momentum transfer square regions, and find no significant deviations from the standard model predictions.