Measurement of form factors

The semileptonic decay of the neutral K meson, K-L(0) --> pi+/-e-/+upsilon (K-e3), was used to study the strangeness-changing weak interaction of hadrons. A sample of 5.6 million reconstructed events recorded by the NA48 experiment was used to measure the Dalitz plot density. Admitting all possible Lorentz-covariant couplings, the form factors for vector (f+(q(2))), scalar (f(S)) and tensor (f(T)) interactions were measured. The linear slope of the vector form factor lambda(+) = 0.0284 +/- 0.0007 +/- 0.0013 and values for the ratios |f(S)/f(+)(0)| = 0.015(-0.010)(+0.007) +/- 0.012 and |f(T)/f(+)(0)| = 0.05(-0.04)(+0.03) +/- 0.03 were obtained. The values for f(S) and f(T) are consistent with zero. Assuming only vector-axial-vector couplings, lambda(+) = 0.0288 +/- 0.0004 +/- 0.0011 and a good fit consistent with pure V-A couplings were obtained. Alternatively, a fit to a dipole form factor yields a pole mass of M = 859 +/- 18 MeV, consistent with the K*(892) mass. (C) 2004 Elsevier B.V. All rights reserved.