An investigation of the very rare Kpinn decay

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Colleges, School and Institutes


The NA62 experiment reports an investigation of the Kpinn mode from a sample of K+ decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0.389 ± 0.024) × 10−10, corresponding to 2.2 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of 1.78 × 10−10 for the Kpinn branching ratio at 90% CL. This, together with the corresponding 68% CL measurement, are currently the most precise results worldwide, and are able to constrain some New Physics models that predict large enhancements still allowed by previous measurements.


Original languageEnglish
Article number42
Publication statusPublished - 10 Nov 2020