In theories with extra dimensions, the standard QCD axion has excited states with higher mass. These Kaluza-Klein (KK) axions would have a significantly shorter de- cay time and, when produced by the Sun, would remain gravitationally trapped in our Solar System. In these theories, the local axion decay rate could be boosted high enough to solve the Solar Corona heating problem.
A low density detector would be able to distinguish such decays from background, by identifying the separate location of the capture of the two resulting photons. The NEWS-G collaboration uses low-pressure Spherical Proportional Counters, gas-filled metallic spheres with a high voltage electrode in their centre. The presented work aims to set exclusion limits on the solar KK axion model based on data from NEWS-G detectors.
