Measurement of Ke30 form factors

Abstract The semileptonic decay of the neutral K meson, K L 0 → π ± e ∓ ν ( K e 3 ), 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 λ + = 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, λ + = 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.