Improved measurement of the semileptonic decay $D_s^{+}\to K^0{e}^{+}{\nu }_e$

Analyzing $e^{+}{e}^{-}$ collision data corresponding to an integrated luminosity of $7.33{\mathrm{f}\mathrm{b}}^{-1}$ collected at center-of-mass energies between 4.128 and 4.226~GeV with the BESIII detector, we measure the branching fraction of the semileptonic decay $D_s^{+}\to K^0{e}^{+}{\nu }_e$ to be $(2.98\pm 0.23\pm 0.12)\times {10}^{-3}$. The $D_s^{+}\to K^0$ hadronic form factor is determined from the differential decay rate of $D_s^{+}\to K^0{e}^{+}{\nu }_e$ to be $f_{+}^{K^0}(0)=0.636\pm 0.049\pm 0.013$. For both measurements, the first uncertainty is statistical and the second systematic. The branching fraction and form factor measurements are factors of 1.6 and 1.7 more precise than the previous world averages, respectively.