Simultaneous measurement of KS and KL decays into π+π-γ

With the E731 apparatus at Fermilab, we have simultaneously collected 6859 K L and K S decays into π + π - γ. Using our sample of over 370000 π + π - decays for normalization we have determined that the ratio Γ(K 0 →π + π - γ)/Γ(K 0 →π + π - ) is (23.0±0.7)×10 -3 for K L and (7.10±0.22)×10 -3 ) for K S , for photon energies greater than 20 MeV in the kaon center of mass. After removing the inner-bremsstrahlung contribution, we find that the photon energy spectrum of the direct emission decay of the K L is consistent with the presence of a vector meson propagator in the form factor