Neutrino oscillation signatures of oxygen-neon-magnesium supernovae

TL;DR

This paper analyzes neutrino flavor conversions from oxygen-neon-magnesium supernovae, identifying unique signatures in neutrino fluxes that can reveal core composition and shock wave dynamics.

Contribution

It provides the first detailed simulation of neutrino flavor evolution in ONeMg-core supernovae, highlighting distinctive observational signatures.

Findings

Electron neutrino survival probability differs significantly before shock hits the density step.

Shock wave passage causes a decrease in neutrino oscillation amplitude.

Unique time-dependent signatures can test supernova shock speed and core composition.

Abstract

We discuss the flavor conversion of neutrinos from core collapse supernovae that have oxygen-neon-magnesium (ONeMg) cores. Using the numerically calculated evolution of the star up to 650 ms post bounce, we find that, for the normal mass hierarchy, the electron neutrino flux in a detector shows signatures of two typical features of an ONeMg-core supernova: a sharp step in the density profile at the base of the He shell and a faster shock wave propagation compared to iron core supernovae. Before the shock hits the density step (t ~ 150 ms), the survival probability of electron neutrinos is about 0.68, in contrast to values of 0.32 or less for an iron core supernova. The passage of the shock through the step and its subsequent propagation cause a decrease of the survival probability and a decrease of the amplitude of oscillations in the Earth, reflecting the transition to a more adiabatic propagation inside the star. These changes affect the lower energy neutrinos first; they are faster and more sizable for larger theta_13. They are unique of ONeMg-core supernovae, and give the possibility to test the speed of the shock wave. The time modulation of the Earth effect and its negative sign at the neutronization peak are the most robust signatures in a detector.