Speaker
Description
Searches for the decays $K^{+}\rightarrow\pi^{+}X$ and $\pi^{+}\rightarrow e^{+}N$ are presented using data collected by the NA62 experiment at CERN in 2016--2022 and 2017--2024, respectively. Results are interpreted to constrain a range of new physics scenarios covering all four portal model scenarios. Upper limits on the $K^{+}\rightarrow\pi^{+}X$ branching ratio are established at the $10^{-11}$ level, providing constraints on dark photon, scalar and ALP couplings. From the search for heavy neutral lepton production in $\pi^{+}\to e^+N$ decays of beam pions, upper limits of the extended neutrino mixing matrix element $|U_{e4}|^2$ are established at the $10^{-8}$ level over the heavy neutral lepton mass range 95--126~MeV/$c^2$. The NA62 experiment has the capability to collect data in a beam-dump mode, where 400~GeV protons are dumped on an absorber. In this configuration, new physics particles may be produced in the absorber and decay in an instrumented volume beginning approximately 80 m downstream of the dump. Preliminary results from a search for heavy neutral leptons decaying in flight to semi-leptonic final states are reported, based on an analysis of a sample of $6.2 \times 10^{17}$ protons on dump collected by NA62 in 2021, 2023, and 2024.
