The $K^+\to \pi^+ \nu \bar\nu$ decay: First results from the NA62 experiment

NA62 is a fixed target experiment installed in the CERN North Area that studies the physics of the $K^+$ meson. Its main purpose is to carry out a precision test of the Standard Model, measuring the branching ratio of the ultra-rare $K^+\to \pi^+ \nu \bar\nu$ decay with a 10% precision, then probing New Physics evidence. NA62 collected data in 2016 and 2017, and the 2018 run is going on. The full 2016 data sample has been analysed. It shows that the new in flight technique for the study of the $K^+\to \pi^+ \nu \bar\nu$ decay works, and 1 signal candidate event has been observed.