Charged-current scattering off the ¹⁶O nucleus as a detection channel for supernova neutrinos

Event spectra of neutrino-¹⁶O charged-current reactions at Super-Kamiokande are evaluated for a future supernova neutrino burst. Since these channels are expected to be useful for diagnosing a neutrino spectrum with high average energy, the evaluations are performed not only for an ordinary supernova neutrino model but also for a model of neutrino emission from a black-hole-forming collapse. Using shell model results, whose excitation energies are consistent with the experimental data, the cross sections of the ¹⁶O(ν_e, e⁻)X and ¹⁶O(ν¯_e, e⁺)X reactions for each nuclear state with a different excitation energy are employed in this study. It is found that, owing to the components of the reaction with higher excitation energy, the event spectrum becomes 4-7 MeV softer than in the case without considering the excitation energies. In addition, a simplified approach to evaluating the event spectra is proposed for convenience, and its validity is examined.