Solar Kaluza-Klein axion search with NEWS-G

TL;DR

This paper reports on a search for Kaluza-Klein axions using the NEWS-G detector, setting new upper limits on axion-photon coupling and contributing to understanding axion properties in theories with extra dimensions.

Contribution

First experimental search for KK axions with the NEWS-G detector, establishing upper limits on axion-photon coupling for specific extra-dimensional models.

Findings

Set a 90% C.L. upper limit of $g_{aetaeta}<8.99\times10^{-13}\,GeV^{-1}$

Observed a single axion-like event in 42 days

Constrained axion density and properties in extra-dimensional theories

Abstract

Kaluza-Klein (KK) axions appear in theories with extra dimensions as higher mass, significantly shorter lifetime, excitations of the Peccei-Quinn axion. When produced in the Sun, they would remain gravitationally trapped in the solar system, and their decay to a pair of photons could provide an explanation of the solar corona heating problem. A low-density detector would discriminate such a signal from the background, by identifying the separation of the interaction point of the two photons. The NEWS-G collaboration uses large volume Spherical Proportional Counters, gas-filled metallic spheres with a spherical anode in their centre. After observation of a single axionlike event in a 42 day long run with the SEDINE detector, a $90\%$ C.L. upper limit of $g_{a\gamma\gamma}<8.99\cdot10^{-13}\,GeV^{-1}$ is set on the axion-photon coupling for a KK axion density on Earth of $n_{a}=4.07\cdot10^{13}\,m^{-3}$ and two extra dimensions of size $R = 1\,eV^{-1}$.