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 DA Phi DNE, similar to 6500 each of K-S -> pi(+)e(-)(v) over bar and K-S -> pi(-)e(+)v decays have been observed with the KLOE detector. From these, the ratio Gamma(K-S -> pi ev)/Gamma(K-S -> pi(+)pi(-)) = (10.19 +/- 0.13) x 10(-4) is obtained, improving the accuracy on BR(K-S -> pi ev) by a factor of four and providing the most precise test of the Delta S = Delta Q rule. From the partial width F(K-S -> pi ev), a value for f(+)(K0) (0) x V-us is obtained that is in agreement with unitarity of the quark-mixing matrix. The lepton charge asymmetry A(S) = (1.5 +/- 9.6(stat) 2.9(syst)) x 10(-3) is compatible with the requirements of CPT invariance. The form-factor slope agrees with recent results from semileptonic K-L and K+ decays. These are the first measurements of the charge asymmetry and form-factor slope for semileptonic K-S decays. (c) 2006 Elsevier B.V. All rights reserved.