Supernova Bursts as a Probe of Neutrino Nature via $CEνNS$ Coherent Scattering

TL;DR

This work analyzes Resonant Spin-Flavor Precession (RSFP) of core-collapse supernova neutrinos through a quantum density-matrix framework, revealing that SN1987A cooling argues against core RSFP for Dirac neutrinos but a safe outer-envelope window ($r>1000$ km) allows adiabatic RSFP for $\mu_\nu$ in $[10^{-14},10^{-12}]\,\mu_B$, yielding helicity inversion without shortening the burst. The authors predict distinct observable signatures in Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS): Dirac neutrinos show a suppressed total flux (a dimmed standard candle) while Majorana neutrinos conserve flux but distort the spectral recoil distribution due to flavor-to-antiflavor conversions. They propose a normalization strategy leveraging the high-energy tail near $E_\nu \sim 1$ GeV, which RSFP suppresses, to cancel astrophysical uncertainties and enable robust discrimination between Dirac and Majorana neutrinos with sensitivity to $\mu_\nu$ down to $10^{-14}\,\mu_B$. This multi-messenger approach turns a galactic SN into a precision laboratory for neutrino properties, potentially surpassing solar and terrestrial limits by over two orders of magnitude and shedding light on the fundamental nature of neutrinos.

Abstract

The Resonant Spin-Flavor Precession (RSFP) of core-collapse supernova neutrinos within the framework of the quantum density matrix formalism is studied. The cooling duration of SN1987A severely constraints standard RSFP models for Dirac Neutrinos. Using the properties of the outer stellar envelope where resonant conversion could occur after thermal decoupling, we show that for neutrino magnetic moments in the range $μ_ν\sim 10^{-14} - 10^{-12} μ_B$, adiabatic conversion in the envelope ($R > 1000$ km) leads to macroscopic helicity inversion without violating cooling bounds.This RSFP neutrino helicity change induces different signatures for Dirac or Majorana neutrinos in Coherent Elastic Neutrino-Nucleus Scattering (CE$ν$NS) detectors. For Dirac neutrino, a massive flux deficit for Dirac neutrinos due to sterile conversion should be seen. For Majorana neutrinos, the flux will not change but a modification to its spectral decomposition of the cross section should be seen due to the transition from left-handed electron neutrinos to right-handed $μ$ or $τ$ anti-neutrinos. An experimental strategy is proposed to minimize the astrophysical uncertainties using the high-energy neutrino tail ($E \approx 1$ GeV) which evades RSFP to normalize the signal. This ratio-based approach effectively cancels astrophysical uncertainties, allowing future detectors to distinguish the fundamental nature of the neutrino and probe magnetic moments down to $10^{-14} μ_B$, two orders of magnitude beyond current solar limits.

Figures (1)

• Figure 1: Dependence of the final helicity parameter $S_{\parallel}$ on the neutrino magnetic moment $\mu_\nu$ for a Dirac neutrino traversing the supernova envelope. The vertical green dashed line marks the minimal Standard Model prediction ($\mu_\nu \sim 10^{-20} \mu_B$). The orange shaded region highlights the transition window ($\mu_\nu \sim 10^{-14} - 10^{-12} \mu_B$) where the interaction with envelope magnetic fields ($B \sim 10^7$ G) is adiabatic.