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

A sensitivity study of the search for heavy sterile neutrinos (νH) in the MeV mass range using solar neutrino experiments is presented. νH, with masses ranging from a few MeV up to around 15 MeV, can be produced in the Sun through ⁸B decay and subsequently decay into νₑ e⁺ e⁻. Its flux and lifetime strongly depend on the mixing parameter |UeH|² and mass mνH. The νH signal can be detected via its decay products, either the e⁺e⁻ pair or νₑ, depending on whether νH decays inside or outside the detector. Expected signal yields for both detection methods (detecting e⁺e⁻ or νₑ signal) are presented across the full |UeH|² and mνH parameter space. These two methods are found to be complementary in different regions of the |UeH|² and mνH 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 < |UeH|² < 1 and 2 MeV < mνH < 14 MeV, assuming a 500-ton solar neutrino experiment operating for one year. Key variables, such as the energy spectra and opening angle of νₑ or e⁺e⁻ and the solar angle of νₑ and its scattered electron, are also discussed to help distinguish signal from major backgrounds, such as solar neutrino events. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.