The first observation of the K± → π±π0e+e− rare decay by the NA48/2 experiment at CERN SPS is reported, based on ∼ 2 ×1011 K± decays recorded in 2003-2004. From a sample of 4919 candidates with 4.9% background the branching ratio in the full kinematic region is measured to be BR(K± → π±π0e+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. The CP-violating asymmetry between K+ → π+π0e+e− and K− → π−π0e+e− decay rates has been measured, providing an upper limit |ACP| < 4.82 ×10−2 at 90% CL. The NA48/2 combined measurement of the charged kaon semileptonic form factors, based on 4.4 million K± → π0e±νe and 2.3 million K± → π0µ±νµ events collected in 2004, is presented. This result represents the most precise form factor measurement from a combined Kl±3 analysis.
|Original language||English (US)|
|Journal||Proceedings of Science|
|State||Published - 2019|
|Event||27th International Workshop on Deep-Inelastic Scattering and Related Subjects, DIS 2019 - Torino, Italy|
Duration: Apr 8 2019 → Apr 12 2019
ASJC Scopus subject areas