Towards the Detection of Thermal Solar Neutrinos

Abstract

We show that $\sim$keV thermal solar neutrinos, arising from electroweak processes in the solar plasma, are kinematically accessible to large-volume dark matter direct detection experiments via electron ionization signatures. Using S2-only data from the XENONnT experiment, we place an upper limit on the thermal solar neutrino flux of $\hat{I}\cdot \lesssim 1.2\times 10^8$ times the standard model predicted value, while paired searches from XENONnT, LZ and PandaX give slightly weaker limits. The future XLZD experiment could improve these limits by orders of magnitude. While still far from a detection, this result establishes low-threshold direct detection experiments as a viable probe of the lowest-energy neutrino sources in astrophysics, with important implications for stellar physics and beyond.

15 pages, 13 figures