Measurement of the Decay KL -> Pi0 Gamma Gamma

TL;DR

This paper presents a precise measurement of the rare decay KL -> pi0 gamma gamma, providing evidence for theoretical predictions and extracting key parameters related to vector meson exchange.

Contribution

First experimental evidence for low-mass gamma gamma signal in KL decay and determination of the effective vector coupling aV.

Findings

Branching ratio measured as (1.68 +/- 0.07 +/- 0.08) x 10^-6

Evidence supports recent chiral perturbation theory predictions

Effective vector coupling aV found to be -0.72 +/- 0.05 +/- 0.06

Abstract

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.