Precise measurement of the decay ${K_{L}\to\pi^0\gamma\gamma}$

TL;DR

This paper reports a precise measurement of the decay rate of the rare kaon decay $ ext{K}_L o ext{pi}^0 ext{gamma} ext{gamma}$ using the NA48 detector, providing key parameters and implications for CP violation effects.

Contribution

The paper presents the first high-precision measurement of the $ ext{K}_L o ext{pi}^0 ext{gamma} ext{gamma}$ decay rate and related parameters, improving understanding of CP violation in kaon decays.

Findings

Branching ratio measured as (1.36 ± 0.03)×10^{-6}.

Vector coupling constant a_v determined as -0.46 ± 0.03.

Upper limit set for decay rate with $m_{ ext{γγ}}<m_{ ext{π}^0}$.

Abstract

The decay rate of $\klpgg$ has been measured with the NA48 detector at the CERN SPS. A total of 2558 $\klpgg$ candidates have been observed with a residual background of 3.2%. The branching ratio is determined to be $(1.36 \pm0.03_{(stat)} \pm0.03_{(syst)}\pm 0.03_{(norm)})\times10^{-6}$ and the vector coupling constant $a_v = -0.46 \pm0.03_{(stat)} \pm0.04_{(syst)}$. This result suggests that the CP-violation effects are dominating in the $\klpee$ decay. An upper limit for the $\klpgg$ decay rate in the two photon mass region $m_{\gamma\gamma}<m_{\pi^0}$ is also given.