Precise measurements of the KS->gamma gamma and KL->gamma gamma decay rates

TL;DR

This paper reports precise measurements of the decay rates of KS and KL particles into two photons, revealing significant deviations from theoretical predictions and providing valuable data for particle physics models.

Contribution

The study provides the first high-precision measurements of KS->gamma gamma decay rate and the ratio of KL->gamma gamma to KL->3pi0, challenging existing theoretical predictions.

Findings

Measured BR(KS->gamma gamma) = (2.78 +- 0.06(stat) +- 0.04(syst)) x 10^-6

BR(KL->gamma gamma)/BR(KL->3pi0) = (2.81 +- 0.01(stat) +- 0.02(syst)) x 10^-3

Observed decay rates are significantly higher than Chiral Perturbation Theory predictions.

Abstract

The KS->gamma gamma decay rate has been measured with the NA48 detector using a high intensity short neutral beam from the CERN SPS. The measured branching ratio BR(KS->gamma gamma)=(2.78+-0.06(stat)+-0.04(syst))x10-6, obtained from 7461+-172 KS->gamma gamma events, is significantly higher than the O(p^4) prediction of Chiral Perturbation Theory. Using a KL beam the ratio BR(KL->gamma gamma)/BR(KL->3pi0)=(2.81+-0.01(stat)+-0.02(syst))x10-3 has been measured.