Diffuse Supernova Neutrino Background Search at Super-Kamiokande

TL;DR

This paper reports the most sensitive search to date for the diffuse supernova neutrino background using Super-Kamiokande data, setting stringent upper limits and discussing future prospects with gadolinium and Hyper-Kamiokande.

Contribution

It introduces improved background reduction and neutron tagging techniques, achieving the world's best sensitivity and upper limits on the DSNB flux.

Findings

Set the world's most stringent upper limit on the DSNB $ar{ u}_e$ flux below 31.3 MeV.

Combined data from all SK phases to enhance sensitivity, reaching limits around 2.7 cm$^{-2}$ sec$^{-1}$.

Discussions on future detection prospects with gadolinium and Hyper-Kamiokande.

Abstract

A new search for the diffuse supernova neutrino background (DSNB) flux has been conducted at Super-Kamiokande (SK), with a $22.5\times2970$-kton$\cdot$day exposure from its fourth operational phase IV. The new analysis improves on the existing background reduction techniques and systematic uncertainties and takes advantage of an improved neutron tagging algorithm to lower the energy threshold compared to the previous phases of SK. This allows for setting the world's most stringent upper limit on the extraterrestrial $\bar{\nu}_e$ flux, for neutrino energies below 31.3 MeV. The SK-IV results are combined with the ones from the first three phases of SK to perform a joint analysis using $22.5\times5823$ kton$\cdot$days of data. This analysis has the world's best sensitivity to the DSNB $\bar{\nu}_e$ flux, comparable to the predictions from various models. For neutrino energies larger than 17.3 MeV, the new combined $90\%$ C.L. upper limits on the DSNB $\bar{\nu}_e$ flux lie around $2.7$ cm$^{-2}$$\cdot$$\text{sec}^{-1}$, strongly disfavoring the most optimistic predictions. Finally, potentialities of the gadolinium phase of SK and the future Hyper-Kamiokande experiment are discussed.