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 $g_{a\gamma \gamma }<8.99\times {10}^{-13}{\mathrm{GeV}}^{-1}$ is set on the axion-photon coupling for the benchmark of a Kaluza-Klein axion density on Earth of $n_a=4.07\times {10}^{13}{\mathrm{m}}^{-3}$ and two extra dimensions of size $R=1{\mathrm{eV}}^{-1}$.

• Received 13 September 2021
• Accepted 9 December 2021

DOI:https://doi.org/10.1103/PhysRevD.105.012002

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Published by the American Physical Society