Axions coupled to nucleons might be copiously emitted from core-collapse supernovae (SNe). If the axion-nucleon coupling is strong enough, then axions would be emitted from the SN as a burst and, reaching Earth, may excite the oxygen nuclei in water Čherenkov detectors (${}^{16}\mathrm{O}+a\to {}^{16}\mathrm{O}^{*}$). This process will be followed by decay(s) of the excited state resulting in an emission of photons and thus providing a possibility for a direct detection of axions from a galactic SN in large underground neutrino Čherenkov detectors. Motivated by this possibility, we present an updated calculation of axion-oxygen cross section obtained by using self-consistent continuum random-phase approximation. We calculate the branching ratio of the oxygen nucleus deexcitation into $\gamma$ rays, neutrons, protons, and $\alpha$ particles and also consider photon emission from secondary nuclei to compute a total $\gamma$ spectrum created when axions excite ${}^{16}\mathrm{O}$. These results are used to revisit the detectability of axions from SN 1987A in Kamiokande-II.

• Received 10 July 2023
• Accepted 27 November 2023

DOI:https://doi.org/10.1103/PhysRevC.109.015501