Measurement of K-mu 3(0) form factors

This Letter reports on a new high precision measurement of the form factors of the K-L -> pi(+/-) mu(-/+) nu(mu) decay. The data sample of about 2.3 x 10(6) events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, lambda(+)' = (20.5 +/- 2.2(stat) +/- 2.4(syst)) x 10(-3), and a quadratic, lambda(+)''(2.6 +/- 0.9(stat) +/- 1.0(syst)) x 10(-3) term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be lambda(o) = (9.5 +/- 1.1(stat) +/- 0.8(syst)) x 10(-3). Using a linear fit our results were: lambda(+) = (26.7 +/- 0.6(stat) +/- 0.8(syst)) x 10(-3) and lambda(o) = (11.7 +/- 0.7(stat) +/- 1.0(syst)) x 10(-3). A pole fit of the form factors yields: M-V = (905 +/- 9(stat) +/- 17(syst)) MeV/c(2) and m(S) = (1400 +/- 46(stat) +/- 53(syst)) Mev/c(2). (c) 2007 Elsevier B.V. All rights reserved.