Searching for a solar relaxion/scalar with XENON1T and LUX

TL;DR

This paper uses data from liquid xenon dark matter detectors to search for a light scalar particle produced in the Sun, setting new bounds on its coupling to electrons and its mixing with the Higgs.

Contribution

It provides the first direct experimental bounds on a solar-produced scalar particle coupling to electrons using XENON1T and LUX data.

Findings

Bounds on scalar-electron coupling: $g_{\phi ee} < 7 \times 10^{-15}$ (S1) and $2 \times 10^{-15}$ (S2)

Bounds on Higgs mixing angle: $\sin \theta < 2 \times 10^{-9}$ (relaxion case)

Results are a few times weaker than stellar evolution bounds.

Abstract

We consider liquid xenon dark matter detectors for searching a light scalar particle produced in the solar core, specifically one that couples to electrons. Through its interaction with the electrons, the scalar particle can be produced in the Sun, mainly through Bremsstrahlung process, and subsequently it is absorbed by liquid xenon atoms, leaving prompt scintillation light and ionization events. Using the latest experimental results of XENON1T and Large Underground Xenon, we place bounds on the coupling between electrons and a light scalar as $g_{\phi ee} < 7 \times 10^{-15}$ from S1-only analysis, and as $g_{\phi ee} < 2 \times 10^{-15}$ from S2-only analysis. These can be interpreted as bounds on the mixing angle with the Higgs, $\sin \theta < 2 \times 10^{-9} \, \left(7 \times 10^{-10}\right)$, for the case of a relaxion that couples to the electrons via this mixing. The bounds are a factor few weaker than the strongest indirect bound inferred from stellar evolution considerations.