Measurement of K0e3 form factors

The semileptonic decay of the neutral K meson, K0L → π± e∓ ν (Ke3 ), 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+(q2)), scalar (fS) and tensor (fT) interactions were measured. The linear slope of the vector form factor λ+ = 0.0284 ± 0.0007 ± 0.0013 and values for the ratios |fS/f+(0)| = 0.015 +0.007-0.010 ± 0.012 and |fT/f+(0)| = 0.05 +0.03-0.04 ± 0.03 were obtained. The values for fS and fT 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

Measurement of the radiative Ke3 branching ratio

We present a measurement of the relative branching ratio of the decay K0 → π± e± νγ (Ke3γ) with respect to K0 → π± e± ν (Ke3 + Ke3γ ) decay. The result is based on observation of 19 000 Ke3γ and 5.6 × 10^6 Ke3 decays. The value of the branching ratio is BR(K0e3γ , E∗γ > 30 MeV, θ∗eγ > 20◦)/ Br(K0e3 ) = (0.964 ± 0.008+0.011-0.009)%. This result agrees with theoretical predictions but is at variance with a recently published result

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First measurement of the rate K-L(0)->pi mu nu gamma

In a preliminary version of the NA48 experiment at the CERN SPS, in which an iron-scintillator sandwich calorimeter was used as a photon detector, the ratio of K-L --> pi mu nu gamma and K-L --> pi mu nu decays was measured. The branching ratio BR(K-L --> pi mu nu gamma,E-gamma*greater than or equal to 30 MeV)/(K-L --> pi mu nu) is found to be (2.08+/-0.17(-0.21)(+0.16)x10(-3), where the first error is statistical and the second systematic. The result is in agreement with theoretical predictions