Solar Kaluza-Klein axion search with NEWS-G

Kaluza-Klein 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 ga gamma gamma < 8.99 x 10-13 GeV-1 is set on the axion-photon coupling for the benchmark of a Kaluza-Klein axion density on Earth of na = 4.07 x 1013 m-3 and two extra dimensions of size R = 1 eV-1.