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

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We report a study of the semileptonic decay D^{0}→K[over ¯]^{0}π^{-}μ^{+}ν_{μ} 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(D^{0}→K[over ¯]^{0}π^{-}μ^{+}ν_{μ})=(1.373±0.020_{stat}±0.023_{syst})%, 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(D^{0}→K^{*}(892)^{-}μ^{+}ν_{μ})=(1.948±0.033_{stat}±0.036_{syst})%. We also determine the hadronic form factors for the D^{0}→K^{*}(892)^{-}μ^{+}ν_{μ} decay to be r_{V}=V(0)/A_{1}(0)=1.46±0.11_{stat}±0.04_{syst}, r_{2}=A_{2}(0)/A_{1}(0)=0.71±0.08_{stat}±0.03_{syst}, and A_{1}(0)=0.609±0.008_{stat}±0.008_{syst}, where V(0) is the vector form factor and A_{1,2}(0) are the axial-vector form factors evaluated at q^{2}=0. The A_{1}(0) is measured for the first time in D^{0}→K^{*}(892)^{-}μ^{+}ν_{μ} decay. Averaging the form factor parameters that we reported previously in D^{0}→K^{*}(892)^{-}(→K[over ¯]^{0}π^{-})e^{+}ν_{e} and D^{0}→K^{*}(892)^{-}(→K^{-}π^{0})μ^{+}ν_{μ} decays, we obtain r_{V}=1.456±0.040_{stat}±0.016_{syst}, r_{2}=0.715±0.031_{stat}±0.014_{stat}, and A_{1}(0)=0.614±0.005_{stat}±0.004_{syst}. 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.

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