Abstract
Final results from an analysis of about 400 K± → π±γγ rare decay candidates collected by the NA48/2 and NA62 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) descriptions. The data support the ChPT prediction for a cusp in the di-photon invariant mass spectrum at the two pions threshold.
Highlights
Experimental studies of radiative non-leptonic decays allow crucial tests of Chiral PerturbationTheory (ChPT) describing weak low energy processes
The rare decay K ± → π ± γγ (Kπγγ ) was first observed by the BNL E787 experiment in 1997 [1]: 31 K + decay candidates were reported in the kinematic region 100 MeV/c < p∗π < 180 MeV/c, where p∗π is the π + momentum in the
The NA48/2 experiment used simultaneous K + and K − beams produced by 400 GeV/c primary SPS protons impinging on a beryllium target, the NA62 experiment used K + and K − beams either alternately or simultaneously
Summary
Experimental studies of radiative non-leptonic decays allow crucial tests of Chiral Perturbation. Theory (ChPT) describing weak low energy processes. The rare decay K ± → π ± γγ (Kπγγ ) was first observed by the BNL E787 experiment in 1997 [1]: 31 K + decay candidates were reported in the kinematic region 100 MeV/c < p∗π < 180 MeV/c, where p∗π is the π + momentum in the. A related decay mode K ± → π ± γe+ e− (Kπγee ) has been measured from 120 candidates in the kinematic region mγee > 260 MeV/c2 at the NA48/2 experiment [2]. A measurement of the Kπγγ decay based on the combination of data collected by the NA48/experiment in 2003 and 2004 and from the NA62 experiment in 2007 is reported here
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