Measurement of the Decay KL -> Pi0 Gamma Gamma
We report on a new measurement of the decay KL -> pi0 gamma gamma by the KTeV experiment at Fermilab. We determine the KL -> pi0 gamma gamma branching ratio to be (1.68 +/- 0.07 +/- 0.08)x10**-6. Our data shows the first evidence for a low-mass gamma gamma signal as predicted by recent O(p**6) chiral perturbation calculations that include vector meson exchange contributions. From our data, we extract a value for the effective vector coupling aV = -0.72 +/- 0.05 +/- 0.06.