Speaker
Description
The decay K+→π+ νν ̅, with a very precisely predicted branching ratio of less than 10-10, is among
the best processes to reveal indirect effects of new physics.
The NA62 experiment reports the branching ratio measurement BR(K+→π+νν¯) =
(10.6+4.0−3.4|stat ± 0.9syst) × 10−11 at 68% CL, based on the observation of 20 signal candidates
with an expected background of 7.0 events from the total data sample collected at the CERN SPS
during 2016-2018. This provides evidence for the very rare K+→π+νν¯ decay, observed with a
significance of 3.4σ. The experiment achieves a single event sensitivity of (0.839±0.054) × 10−11,
corresponding to 10.0 events assuming the Standard Model branching ratio of (8.4±1.0) × 10−11.
This measurement is also used to set limits on BR(K+→π+X), where X is a scalar or pseudo-scalar
particle. Details are given of the analysis of the 2018 data sample, which corresponds to about
80% of the total data sample.
Future NA62 plans and prospects are also reviewed.
