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

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.

Comments: 9 pages, 12 figures. Submitted to CPC