On the Observability of Collective Flavor Oscillations in Diffuse Supernova Neutrino Background

TL;DR

This paper investigates whether the signature of collective neutrino oscillations, which depend on the neutrino mass hierarchy, can be observed in the diffuse supernova neutrino background despite flux averaging from multiple sources.

Contribution

The study analyzes how the hierarchy sensitivity of collective oscillations is affected by flux distribution parameters, highlighting the importance of the mean initial luminosity.

Findings

Hierarchy sensitivity depends on the mean initial luminosity.

Increasing flux variance reduces hierarchy sensitivity.

Sensitivity is nearly lost at small mixing angles with certain flux conditions.

Abstract

Collective flavor oscillations are known to bring multiple splits in the supernova (SN) neutrino and antineutrino spectra. These spectral splits depend not only on the mass hierarchy of the neutrinos but also on the initial relative flux composition. Observation of spectral splits in a future galactic supernova signal is expected to throw light on the mass hierarchy pattern of the neutrinos. However, since the Diffuse Supernova Neutrino Background (DSNB) comprises of a superposition of neutrino fluxes from all past supernovae, and since different supernovae are expected to have slightly different initial fluxes, it is pertinent to check if the hierarchy dependent signature of collective oscillations can survive this averaging of the flux spectra. Since the actual distribution of SN with initial relative flux spectra of the neutrinos and antineutrinos is unknown, we assume a log-normal distribution for them. We study the dependence of the hierarchy sensitivity to the mean and variance of the log-normal distribution function. We find that the hierarchy sensitivity depends crucially on the mean value of the relative initial luminosity. The effect of the width is to reduce the hierarchy sensitivity for all values of the mean initial relative luminosity. We find that in the very small mixing angle ($\theta_{13}$) limit considering only statistical errors even for very moderate values of variance, there is almost no detectable hierarchy sensitivity if the mean relative luminosities of $\nu_e$ and $\bar\nu_e$ are greater than 1.