First measurement of the form factors in $D_s^{+}\to K^0{e}^{+}\hat{I}{½}_e$ and $D_s^{+}\to K^{\ast 0}{e}^{+}\hat{I}{½}_e$ decays

Abstract

We report on new measurements of Cabibbo-suppressed semileptonic $D_s^{+}$ decays using $3.19{\mathrm{fb}}^{-1}$ 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 $\mathcal{B}(D_s^{+}\to K^0{e}^{+}\hat{I}{½}_e)=(3.25\pm 0.38(stat.)\pm 0.16(syst.))\times 10^{-3}$ and $\mathcal{B}(D_s^{+}\to K^{\ast 0}{e}^{+}\hat{I}{½}_e)=(2.37\pm 0.26(stat.)\pm 0.20(syst.))\times 10^{-3}$ which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For $D_s^{+}\to K^0{e}^{+}\hat{I}{½}_e$, we obtain $f_{+}(0)=0.720\pm 0.084(stat.)\pm 0.013(syst.)$, and for $D_s^{+}\to K^{\ast 0}{e}^{+}\hat{I}{½}_e$, we find form-factor ratios $r_V=V(0)/A_1(0)=1.67\pm 0.34(stat.)\pm 0.16(syst.)$ and $r_2=A_2(0)/A_1(0)=0.77\pm 0.28(stat.)\pm 0.07(syst.)$.

7 pages, 3 figures