First measurement of the D s + → K * ( 892 ) 0 μ + ν μ decay, study of dynamics and test of lepton universality with D s + → K * ( 892 ) 0 ℓ + ν ℓ decays

We report the first measurement of the semileptonic decay D⁺ₛ → K^*(892)⁰μ⁺ν_μ and an improved measurement of the decay D⁺ₛ → K^*(892)⁰ e⁺νₑ using a sample of 7.33~fb⁻¹ of e⁺e⁻ annihilation data collected at center-of-mass energies between 4.128 to 4.226~GeV with the BESIII detector at the BEPCII collider. We measure the branching fractions to be B(D⁺ₛ→ K^*(892)⁰ μ⁺ν_μ)=(2.07±0.22ₛₜₐₜ±0.10syst)×10⁻³ and B(D⁺ₛ→ K^*(892)⁰ e⁺νₑ)=(2.14±0.18ₛₜₐₜ±0.10syst)×10⁻³. Based on a simultaneous study of the dynamics in two semileptonic decays, the hadronic form factor parameters in the D⁺ₛ→ K*(892)⁰ transition are determined to be rV = V(0)/A₁(0) = 1.63 ± 0.14ₛₜₐₜ ± 0.08syst, r₂ = A₂(0)/A₁(0) = 0.60 ± 0.13ₛₜₐₜ ± 0.06syst, and A₁(0)=0.56 ± 0.02ₛₜₐₜ ± 0.01syst, where $V(0)$ is the vector form factor and A1,2(0) are the axial-vector form factors evaluated at q²=0. The precision of rV and r₂ is improved by twofold and A₁(0) is measured for the first time. We also report the first model-independent measurements of the differential decay rates and the lepton forward-backward asymmetries for D⁺ₛ→ K*(892)⁰⁺ν_ decays. Based on these measurements, we perform a test of lepton flavor universality in full and separate q² intervals with D⁺ₛ→ K*(892)⁰⁺ν_ decays. No violation is found within uncertainties. Our results present for the first time a complete study of the dynamics in the Dₛ⁺→ K^*(892)⁰ transition, and provide stringent tests of various non-perturbative theoretical calculations.