Abstract
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 \(K^{+}\rightarrow\pi^{+}\nu\bar{\nu}\) decay, based on 20 candidates, and presented in 2021. In this talk the NA62 experiment reports new results from analyses of \(K^{+}\rightarrow\pi^{+}\mu^{+}\mu^{-}\) and \(K^{+}\rightarrow\pi^{+}\gamma\gamma\) decays, using a data sample recorded in 2017–2018. The \(K^{+}\rightarrow\pi^{+}\mu^{+}\mu^{-}\) —sample comprises about 27k signal events with negligible background contamination, and the analysis results presented include the most precise determination of the branching ratio and the form factor. The \(K^{+}\rightarrow\pi^{+}\gamma\gamma\) 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 \(10^{17}\) protons on target have been collected in this way during a week-long data-taking campaign. We report on new results from analysis of this data, with a particular emphasis on Dark Photon and Axion-like particle Models.
