07/06/2021 : Measurement of the very rare K+→π+νν¯ decay from NA62

Indico

The ultra-rare decay K+→π+νν¯, with a very precisely predicted branching ratio of less than 10−10, is one of the best candidates to reveal indirect effects of new physics at the highest mass scales. The NA62 experiment at CERN SPS is designed to measure Br(K+→π+νν¯) with a decay-in-flight technique, novel for this channel. NA62 took data in 2016, 2017 and 2018. Statistics collected in 2016 and 2017 allows NA62 to reach the Standard Model sensitivity for the K+→π+νν¯ search. The analysis of the 2018 data led to the most precise measurement ever performed, with more than 3σ significance in terms of process observation. A statistical reinterpretation of the analysis gives also the possibility to set limits on Br(K+→π+X), where X is a scalar or pseudo-scalar particle. The context of the measurement will be presented, the details of the analysis will be described, the results and the prospects will be illustrated.