First observation and study of the K ± → π ± π 0 e + e − decay

The NA48/2 Collaboration (2019) First observation and study of the K ±  → π ± π 0 e + e − decay. Physics Letters B, 788. pp. 552-561. ISSN 0370-2693

Abstract

The NA48/2 experiment at CERN reports the first observation of the K ± →π ± π 0 e + e − decay from an exposure of 1.7×10 11 charged kaon decays recorded in 2003–2004. A sample of 4919 candidates with 4.9% background contamination allows the determination of the branching ratio in the full kinematic region, BR(K ± →π ± π 0 e + e − )=(4.24±0.14)×10 −6 . The study of the kinematic space shows evidence for a structure dependent contribution in agreement with predictions based on chiral perturbation theory. Several P- and CP-violating asymmetries are also evaluated.