PoS - Proceedings of Science
Volume 405 - 7th Symposium on Prospects in the Physics of Discrete Symmetries, DISCRETE 2020-2021 (DISCRETE2020-2021) - Parallel sessions Tuesday
Search for $K^+$ decays to a lepton and invisible particles
R. Volpe
Full text: Not available
The NA62 experiment at CERN reports searches for
$K^+ \to e^+ N$, $K^+ \to \mu^+ N$ and $K^+ \to \mu^+ X$ decays,
where $N$ and $X$ are massive invisible particles, using the 2016-2018 data set.
The $N$ particle is assumed to be a heavy neutral lepton, and the results are expressed as upper limits
of $O(10^{-9})$ and $O(10^{-8})$ on the neutrino mixing parameter $|U_{e4}|^2$ and $|U_{\mu 4}|^2$,
improving on the earlier searches for heavy neutral lepton production and decays in the kinematically accessible mass range.
The $X$ particle is considered a scalar or vector hidden sector mediator decaying to an invisible final
state, and upper limits of the decay branching fraction for $X$ masses in the range 10-370 MeV/c$^2$ are
reported for the first time, ranging from $O(10^{-5})$ to $O(10^{-7})$.
An upper limit of
$1.0 \cdot 10^{-6}$
is established
at 90\% CL on the
$K^+\to \mu^+ \nu \nu \bar{\nu}$ branching fraction.
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