Recent NA48/2 and NA62 results

TL;DR

This paper presents new measurements of rare kaon decays from NA48/2 and NA62 experiments, improving branching fraction data and testing Chiral Perturbation Theory with high-statistics samples.

Contribution

It provides the first detailed form factor analysis of $K_{e4}$ decays and new decay rate measurements for $K^ ightarrow o \pi^ ightarrow \gamma \gamma$ using extensive data.

Findings

Improved branching fraction measurements for $K_{e4}$ decays.

First detailed form factor analysis of $K_{e4}$ modes.

Decay rate measurement consistent with ChPT predictions.

Abstract

The NA48/2 Collaboration at CERN has accumulated and analysed unprecedented statistics of rare kaon decays in the $K_{e4}$ modes: $K_{e4}(+-)$ ($K^\pm \to \pi^+ \pi^- e^\pm \nu$) and $K_{e4}(00)$ ($K^\pm \to \pi^0 \pi^0 e^\pm \nu$) with nearly one percent background contamination. It leads to the improved measurement of branching fractions and detailed form factor studies. New final results from the analysis of 381 $K^\pm \to \pi^\pm \gamma \gamma$ rare decay candidates collected by the NA48/2 and NA62 experiments at CERN are presented. The results include a decay rate measurement and fits to Chiral Perturbation Theory (ChPT) description.