An investigation of the very rare K+ to π+ νν- decay

Carmignani, Joe and Jones, Roger William Lewis and Ruggiero, Giuseppe and Dainton, John (2020) An investigation of the very rare K+ to π+ νν- decay. Journal of High Energy Physics, 2020: 42. ISSN 1029-8479

Text (2007.08218)
2007.08218.pdf - Accepted Version
Available under License Creative Commons Attribution.
Download (2MB)

Abstract

The NA62 experiment reports an investigation of the K+ to π+ νν- 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 K+ to π+ νν- branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of (0.48+0.72−0.48) × 10−10, 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.