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.
Recent results on Kaon decays from NA48/2 / Bizzeti A., Anzivino G., Arcidiacono R., Baldini W., Balev S., Batley J.R., Behler M., Bi-Fani S., Biino C., Bizzeti A., Bloch-Devaux B., Bocquet G., Cabibbo N., Calvetti M., Cartiglia N., Ceccucci A., Cenci P., Cerri C., Cheshkov C., Cheze J.B., et al.. - In: POS PROCEEDINGS OF SCIENCE. - ISSN 1824-8039. - ELETTRONICO. - 352:(2019), pp. 1-1.
Recent results on Kaon decays from NA48/2
Bizzeti A.
;Calvetti M.
;Collazuol G.
;Lenti M.
;Ruggiero G.
;
2019
Abstract
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.
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