$K^+ \to \pi^+ \nu \bar \nu$ first NA62 results

The K+ → π+νν ̄ decay is characterised by a very precise prediction in the Standard Model (SM). Its branching ratio, which is expected to be less than 10−10 is one of the best candidates to indicate indirect effects of new physics beyond SM at the highest mass scales. The NA62 experiment at CERN SPS is designed to measure the branching ratio of the K+ → π+νν ̄ decay with an in-fight technique, never used before for this measurement. NA62 is taking data since in 2016 with the goal to reach the SM sensitivity, an accuracy of the order of 10%. In 2017 it has then collected 10 times more statistics and a similar amount of data is expected from the 2018 run. The preliminary result on K+ → π+νν ̄ from the full 2016 data set and prospects for future developments are presented.