Measurement of the K-L ->pi mu nu form factor parameters with the KLOE detector

Using 328 pb−1of data collected at DA©NE corresponding to ∼1.8 million KL → πμν decays, we have measured the Kμ3 form factor parameters. The structure of the K−π vector-current provides information about the dynamics of the strong interaction; its knowledge is necessary for evaluation of the phase-space integral required for measuring the CKM matrix element Vus and for testing lepton universality in kaon decays. Using a new parametrization for the vector and scalar form factors, we find λ+=(25.7±0.6)×10−3 and λ0=(14.0 ± 2.1) × 10−3. Our result for λ0, together with recent lattice calculations of f¼, fK and f(0), satisfies the Callan-Treiman relation.