First observation and study of the $K^{\pm} \rightarrow \pi^{0} \pi^{0} \mu^{\pm} \nu$ decay

TL;DR

This paper reports the first observation of a rare kaon decay involving two neutral pions, a muon, and a neutrino, measuring its branching ratio and confirming theoretical predictions.

Contribution

It provides the first experimental observation and measurement of the $K^{ ightarrow} ightarrow ightarrow ightarrow$ decay, validating chiral perturbation theory.

Findings

First observation of the decay with 2437 candidates

Measured branching ratio in restricted kinematic region

Extrapolated full kinematic branching ratio agrees with theory

Abstract

The NA48/2 experiment at CERN reports the first observation of the $K^{\pm} \rightarrow \pi^{0} \pi^{0} \mu^{\pm} \nu$ decay based on a sample of 2437 candidates with 15% background contamination collected in 2003--2004. The decay branching ratio in the kinematic region of the squared dilepton mass above $0.03$~GeV$^2/c^4$ is measured to be $(0.65 \pm 0.03) \times 10^{-6}$. The extrapolation to the full kinematic space, using a specific model, is found to be $(3.45 \pm 0.16) \times 10^{-6}$, in agreement with chiral perturbation theory predictions.