Using 328 pb(-1) of data collected at DA phi NE corresponding to similar to 1.8 million K-L -> pi mu nu decays, we have measured the K-mu 3 form factor parameters. The structure of the K-pi 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 V-us and for testing lepton universality in kaon decays. Using a new parametrization for the vector and scalar form factors, we find lambda(+)=(25.7 +/- 0.6) x 10(-3) and lambda(0) = (14.0 +/- 2.1) x 10(-3). Our result for lambda(0), together with recent lattice calculations of f pi, fK and f(0), satisfies the Callan-Treiman relation.
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