Study of the branching ratio and charge asymmetry for the decay KS->πeν with the KLOE detector

Among some 400 million KSKL pairs produced in e+e- annihilations at DAΦNE, ∼6500 each of KS->π+e-ν-bar and KS->π-e+ν decays have been observed with the KLOE detector. From these, the ratio Γ(KS->πeν)/Γ(KS->π+π-)=(10.19+/-0.13)x10-4 is obtained, improving the accuracy on BR(KS->πeν) by a factor of four and providing the most precise test of the ΔS=ΔQ rule. From the partial width Γ(KS->πeν), a value for f+K0(0)xVus is obtained that is in agreement with unitarity of the quark-mixing matrix. The lepton charge asymmetry AS=(1.5+/-9.6stat+/-2.9syst)x10-3 is compatible with the requirements of CPT invariance. The form-factor slope agrees with recent results from semileptonic KL and K+ decays. These are the first measurements of the charge asymmetry and form-factor slope for semileptonic KS decays