Extending the sensitivity of heavy sterile neutrino searches with solar neutrino experiments

TL;DR

This study explores how solar neutrino experiments can be used to detect heavy sterile neutrinos in the MeV range, proposing two complementary detection methods and analyzing their effectiveness across parameter space.

Contribution

It introduces a sensitivity analysis for heavy sterile neutrino detection using solar neutrino experiments, combining decay product detection methods to enhance search capabilities.

Findings

Expected to observe signals across a broad parameter space with a 500-ton detector.

Both detection methods are complementary, covering different regions of parameter space.

Analysis of energy spectra and angles aids in distinguishing signals from backgrounds.

Abstract

A sensitivity study of the search for heavy sterile neutrinos ($\nu_H$) in the MeV mass range using solar neutrino experiments is presented. $\nu_H$, with masses ranging from a few MeV up to around 15 MeV, can be produced in the Sun through $^8$B decay and subsequently decay into $\nu_e e^+ e^-$. Its flux and lifetime strongly depend on the mixing parameter $|U_{eH}|^2$ and mass $m_{\nu_H}$. The $\nu_H$ signal can be detected via its decay products, either the $e^+e^-$ pair or $\nu_e$, depending on whether $\nu_H$ decays inside or outside the detector. Expected signal yields for both detection methods (detecting $e^+e^-$ or $\nu_e$ signal) are presented across the full $|U_{eH}|^2$ and $m_{\nu_H}$ parameter space. These two methods are found to be complementary in different regions of the $|U_{eH}|^2$ and $m_{\nu_H}$ phase space. By combining both approaches, we anticipate observing at least a handful of signal events across most of the parameter space of $10^{-6} < |U_{eH}|^2 < 1$ and 2 MeV $< m_{\nu_H} < $ 14 MeV, assuming a 500-ton solar neutrino experiment operating for one year. Key variables, such as the energy spectra and opening angle of $\nu_e$ or $e^+e^-$ and the solar angle of $\nu_e$ and its scattered electron, are also discussed to help distinguish signal from major backgrounds, such as solar neutrino events.