New Result on K+ → φ+v v from the NA62 Experiment

Abstract

The NA62 experiment at the CERN SPS is designed to measure the branching ratio of the K+ → φ+v v with a decay-in-ight technique and took data in 2016{2018. The statistics collected in 2017 allows NA62 to achieve the best up{to{date single event sensitivity for K+ → φ+v v corresponding to more than 2 Standard Model K+ → φ+v v expected events. The analysis of the 2017 data has revealed 2 candidate K+ → φ+v v events, while 1.5 background were expected. Together with the candidate found on the 2016 data, this result leads to 1:85 × 10-10 as preliminary upper limit at 90% C.L. on the branching ratio of the K+ → φ+v v decay. The 2017 data also allow NA62 to achieve the best up{to{date sensitivity on the search for the φ0 → invisible decay