Measurement of the decay rate of the radiative K-e3(0) decay

Data from the NA31 experiment at CERN have been used to measure the decay KL → π±e∓vy (K0e3γ). 1384 ± 53 events of this decay type have been observed. The decay rate relative to K0e3 is found to be Γ(K0e3γ, E(Black star)γ ≥ 30 MeV, Θ(Black star)e-γ ≥ 20°)/Γ(K0e3) = (0.934 ± 0.036 (stat.) +0.055-0.039 (syst.))% which corresponds to a branching ratio of BR(K0e3γ, E(Black star)γ ≥ 30 MeV, Θ(Black star)e-γ ≥ 20°) = (0.361 ± 0.014(stat.) +0.021-0.015 (syst.))%. The result is in good agreement with theoretical predictions. The decay KL → π±e∓vγ is found to be dominated by internal bremsstrahlung

A measurement of the decay KL→π0γγ

The full data set of the experiment NA31 at CERN has been used to analyse the decay mode KL→π0γγ. A signal of 63 events has been observed with an estimated background of 6.0±1.7 events, corresponding to a branching ratio of (1.7±0.3) × 10-6 consistent with our previous result based on partial statistics. The invariant mass spectrum of the two photons is found to be consistent with chiral perturbation theory, and the decay is dominated by the J = 0 two-photon state

Measurement of the decay KL → e+e-γγ

The full data set of the NA31 experiment at CERN has been used to analyse the decay mode KOL → e+ e-γγ. A signal of 47 events has been observed with an estimated background of 6.9 events. The total number of kaon decays in the decay volume was determined to be (2.1 ± 0.1stat) · 109. This corresponds to a branching ratio of (8.0 ± 1.5+1.4-1.2)· 10-7. © 1998 Published by Elsevier Science B.V

Measurement of the decay K-L -> e(+)e(-)gamma gamma

The full data set of the NA31 experiment at CERN has been used to analyse the decay mode $K^{0}_{L} \to e^{+}e^{−}\gamma\gamma$. A signal of 47 events has been observed with an estimated background of 6.9 events. The total number of kaon decays in the decay volume was determined to be $(2.1 \pm 0.1_{stat}) \times 10^{9}$. This corresponds to a branching ratio of $8.0 \pm 1.5^{+1.4}_{-1.2} \times 10^{-7}$

Search for the decay KL → π0π0γ

Data from the NA31 experiment at CERN have been used for a search for the decay mode KL → π0π0γ. After all cuts, three events remain in the signal region with an estimated background of 2.2 ± 0.9 events. The upper limit for the branching ratio of KL→π0π0γ is 5.6×10-6 at the 90% confidence level