K± → π±γγ Studies at NA48/2 and NA62-RK Experiments at CERN

Bob Velghe

doi:10.1016/j.nuclphysbps.2015.10.042

Abstract

Final results from an analysis of about 400K±→π±γγ rare decay candidates collected by the NA48/2 and NA62-RK experiments at CERN during low intensity runs with minimum bias trigger configurations are presented. The results include a model-independent decay rate measurement and fits to Chiral Perturbation Theory (ChPT) description. The data support the ChPT prediction for a cusp in the di-photon invariant mass spectrum at the two pion threshold.

Highlights

The study of K± → π±γγ decay kinematic properties is a good test of the Chiral Perturbation Theory (ChPT) description of weak low energy processes
The model-independent decay rate is obtained from partial measurements of the branching ratio in eight independent z bins above 0.2
A log-likelihoof fit was performed to obtain the cvalue from the reconstructed z spectrum which agrees with ChPT expectations

Summary

Introduction

The study of K± → π±γγ decay kinematic properties is a good test of the Chiral Perturbation Theory (ChPT) description of weak low energy processes. A fit of the data to the ChPT prediction[3] is presented. In addition the model-independent branching ratio is computed. The data used in this work were recorded in 2003 and 2004 by NA48/2 experiment[1] and in 2007 by the NA62-RK experiment[2]. A total of 381 K± → π±γγ candidates were stored on disk. The NA48/2 and NA62RK data sets were analysed separately but with the same software stack. Due to limited space the plots presented are derived from the NA62-RK data set.

Experimental Setup

Experimental Method

Conclusion