Precise Measurement of the Form Factors in D0 →k∗ (892)-μ+νμ, and Test of Lepton Universality with D0 →k∗ (892)-l+νl Decays

We report a study of the semileptonic decay D0→K̄0π-μ+νμ based on a sample of 7.9 fb-1 of e+e- annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured for the first time to be B(D0→K̄0π-μ+νμ)=(1.373±0.020stat±0.023syst)%, where the first uncertainty is statistical and the second is systematic. Based on the investigation of the decay dynamics, we find that the decay is dominated by the K∗(892)- resonance with the branching fraction measured to be B(D0→K∗(892)-μ+νμ)=(1.948±0.033stat±0.036syst)%. We also determine the hadronic form factors for the D0→K∗(892)-μ+νμ decay to be rV=V(0)/A1(0)=1.46±0.11stat±0.04syst, r2=A2(0)/A1(0)=0.71±0.08stat±0.03syst, and A1(0)=0.609±0.008stat±0.008syst, where V(0) is the vector form factor and A1,2(0) are the axial-vector form factors evaluated at q2=0. The A1(0) is measured for the first time in D0→K∗(892)-μ+νμ decay. Averaging the form factor parameters that we reported previously in D0→K∗(892)-(→K̄0π-)e+νe and D0→K∗(892)-(→K-π0)μ+νμ decays, we obtain rV=1.456±0.040stat±0.016syst, r2=0.715±0.031stat±0.014stat, and A1(0)=0.614±0.005stat±0.004syst. This is the most precise determination of the form factor parameters to date measured in D→K∗(892) transitions, which provide the most stringent test on various theoretical models.