Heavy Neutral Lepton Decay Searches using Solar Neutrinos

TL;DR

This paper explores the potential to detect heavy neutral lepton decays into electron-positron pairs using solar neutrinos, proposing new methods and predicting significant improvements over current bounds.

Contribution

It provides a detailed differential cross section including interference effects and forecasts enhanced sensitivity in future detectors for heavy neutral lepton decay searches.

Findings

Over two orders of magnitude improvement in mixing angle sensitivity.

Revised bounds from Borexino are considered.

Predictions for future detector sensitivities.

Abstract

We study the sensitivity to the decay of a heavy neutral lepton into $e^+e^-$-pairs using the solar boron-8 neutrino flux as source. We provide a fully differential cross section for this process including the interference of neutral and charged current amplitudes. We revisit a previous bound from Borexino and make predicitions for the expected sensitivity in future large liquid noble gas detectors, like XLZD, Argo and DUNE, as well as high-resolution scintillator detectors based on the LiquidO technology. We find that more than two orders of magnitude improvement in mixing angle reach is possible relative to existing bounds.