Solar Kaluza-Klein axion search with NEWS-G

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 $g_{a{\hat{I}}^3{\hat{I}}^3}<8.99\cdot 10^{-13}Ge{V}^{-1}$ is set on the axion-photon coupling for a KK axion density on Earth of $n_a=4.07\cdot 10^{13}{m}^{-3}$ and two extra dimensions of size $R=1e{V}^{-1}$.

19 pages, 11 figures. Updated with additional details requested during review for publication in PRD and mild relaxation of final constraint