What can we learn on supernova neutrino spectra with water Cherenkov detectors?

TL;DR

This study assesses how precisely water Cherenkov detectors like Hyper-Kamiokande can reconstruct supernova neutrino spectra, demonstrating significant improvements over previous capabilities, especially for electron antineutrinos, through comprehensive likelihood analyses.

Contribution

The paper introduces a detailed likelihood analysis approach to accurately reconstruct supernova neutrino spectra using water Cherenkov detectors, including multiple detection channels and theoretical uncertainties.

Findings

Electron antineutrino average energy can be measured with ~2% accuracy.

Pinching parameter for electron antineutrinos can be determined with ~7% precision.

Muon and tau neutrino parameters can be measured with ~7% accuracy.

Abstract

We investigate the precision with which the supernova neutrino spectra can be reconstructed in water Cherenkov detectors, in particular the large scale Hyper-Kamiokande and Super-Kamiokande. To this aim, we consider quasi-thermal neutrino spectra modified by the Mikheev-Smirnov-Wolfenstein effect for the case of normal ordering. We perform three 9 degrees of freedom likelihood analyses including first inverse-beta decay only, then the combination of inverse beta decay and elastic scattering on electrons and finally a third analysis that also includes neutral scattering neutrino-oxygen events. A tenth parameter is added in the analyses to account for the theoretical uncertainty on the neutral current neutrino-oxygen cross section. By assuming a 100\% efficiency in Hyper-Kamiokande, we show that one can reconstruct the electron antineutrino average energy and pinching parameter with an accuracy of $\sim2\%$ and $\sim7\%$ percent respectively, while the antineutrino integrated luminosity can be pinned down at $\sim3\%$ percent level. As for the muon and tau neutrinos, the average energy and the integrated luminosity can be measured with $\sim7\%$ precision. These results represent a significant improvement with respect Super-Kamiokande, particularly for the pinching parameter defining the electron antineutrino spectra. As for electron neutrinos, the determination of the emission parameters requires the addition of supplementary detection channels.