The NA62 experiment at CERN collected the world’s largest dataset of charged
kaon decays in 2016-2018, leading to the first measurement of the branching
ratio of the ultra-rare K+ → π+ν ̄ν decay, based on 20 candidates, and presented
in 2021. In this talk the NA62 experiment reports new results from analyses
of K+ → π+μ+μ− and K+ → π+γγ decays, using a data sample recorded in
2017–2018. The K+ → π+μ+μ− sample comprises about 27k signal events with
negligible background contamination, and the presented analysis results include
the most precise determination of the branching ratio and the form factor. The
K+ → π+γγ sample contains about 4k signal events with 10% background
contamination, and the analysis improves the precision of the branching ratio
measurement by a factor of 3 with respect to the previous measurements.
The NA62 experiment can also be run as a “beam-dump experiment” by
removing the Kaon production target and moving the upstream collimators
into a “closed” position. More than 1017 protons on target have been collected
in this way during a week-long data-taking campaign by the NA62 experiment.
We report on new results from analysis of this data, with a particular emphasis
on Dark Photon and Axion-like particle Models.