The authors observed a new neutral kaon decay mode, KL → ?±e∓$ar{v}$e+e- for the first time. Based on the 20225 events including 1018 ± 25 background events, they determined the branching ratio, B(KL → ?±e∓$ar{v}$e+e-; Me+e- > 5 MeV/c2, E*+e- > 30 MeV) = (1.281 ± 0.041) x 10 -5. This branching ratio agrees with a theoretical prediction based on the chiral perturbation theory (XPT) calculation at ?(p4). Most of the kinematical distributions agree with the XPT ?(p4) calculation. They also measured one of the low energy coupling constants for the XPT ?(p4), L$rtop{9}$= (8.0 ± 1.6) x 10-3. The Me+e- distribution below 100 MeV showed a 3 ? deviation from the XPT O(p4) calculation. This requires further studies in theory and experiments.

The authors observed a new neutral kaon decay mode, K{sub L} {yields} {pi}{sup {+-}}e{sup {-+}}{bar {nu}}e{sup +}e{sup -} for the first time. Based on the 20225 events including 1018 {+-} 25 background events, they determined the branching ratio, B(K{sub L} {yields} {pi}{sup {+-}}e{sup {-+}}{bar {nu}}e{sup +}e{sup -}; M{sub e{sup +}e{sup -}}> 5 MeV/c{sup 2}, E*{sub e{sup +}e{sup -}}> 30 MeV) = (1.281 {+-} 0.041) x 10{sup -5}. This branching ratio agrees with a theoretical prediction based on the chiral perturbation theory ({chi}PT) calculation at {Omicron}(p{sup 4}). Most of the kinematical distributions agree with the {chi}PT {Omicron}(p{sup 4}) calculation. They also measured one of the low energy coupling constants for the {chi}PT {Omicron}(p{sup 4}), L{sub 9}{sup r} = (8.0 {+-} 1.6) x 10{sup -3}. The M{sub e{sup +}e{sup -}} distribution below 100 MeV showed a 3 {sigma} deviation from the {chi}PT {Omicron}(p{sup 4}) calculation. This requires further studies in theory and experiments.