Atmospheric axion-like particles at Super-Kamiokande

by Po-Yen ‍Tseng (National Tsing Hua University, Department of Physics)

Thursday 27 Jun 2024, 16:00 → 17:00 Australia/Sydney

We consider a muonphilic axion-like-particle (ALP), denoted as $a$, lighter than twice the muon mass. ALPs of this mass range dominantly decay into a pair of photons, induced by a triangular muon loop. Such light muonphilic ALPs are naturally long-lived. At the atmosphere, the ALPs are copiously produced from charged-meson decays in air showers, such as $\pi^\pm\to \mu^\pm \nu a$, via the ALP-muon coupling gaμμ. After propagating tens of kilometers, the ALPs decay with $a\to \gamma\gamma$ inside large-volume Cherenkov detectors near the Earth’s surface, such as Super-Kamiokande (SK). We find the present SK observation constrains on muonphilic ALPs of mass range [1 MeV, 30 MeV] and ALP-muon coupling $[10^{−3}, 10^2]$, assuming the proper decay length $c\tau_a$ in [$10^{−3}$ km, $10^6$ km] either dependent on or independent of $g_{a\mu\mu}$. We conclude that atmospheric searches of such exotic states can be complementary to collider and beam-dump experiments as well as astrophysical probes.