First Measurement of the Form Factors in $D^+_{s}\rightarrow K^0 e^+\nu_e$ and $D^+_{s}\rightarrow K^{*0} e^+\nu_e$ Decays

Abstract

We report on new measurements of Cabibbo-suppressed semileptonic Ds+ decays using 3.19fb−1 of e+e− annihilation data sample collected at a center-of-mass energy of 4.178 GeV with the BESIII detector at the BEPCII collider. Our results include branching fractions B(Ds+→K0e+νe) = [ 3.25 ± 0.38 ( stat ) ± 0.16 ( syst ) ] × 10−3 and B(Ds+→K∗0e+νe) = [2.37 ± 0.26 (stat) ± 0.20 (syst)] × 10−3, which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For Ds+→K0e+νe, we obtain f+(0) = 0.720 ± 0.084 (stat) ± 0.013 (syst), and for Ds+→K∗0e+νe, we find form-factor ratios rV=V(0)/A1(0) = 1.67 ± 0.34 ( stat ) ± 0.16 (syst) and r2 = A2(0)/A1(0) = 0.77 ± 0.28 (stat) ± 0.07 (syst).