Search for solar Kaluza-Klein axions by annual modulation with the XMASS-I detector

Abstract

In theories with large extra dimensions beyond the standard 4-dimensional spacetime, axions could propagate in such extra dimensions, and acquire Kaluza-Klein ( KK) excitations. TheseKK axions are produced in the Sun and could solve the unexplained heating of the solar corona. While most of the solar KK axions escape from the solar system, a small fraction are gravitationally trapped in orbits around the Sun. They would decay into 2 photons inside a terrestrial detector. The event rate is expected to modulate annually depending on the distance from the Sun. We have searched for the annual modulation signature using 832 x 359 kg center dot days of XMASS-I data. No significant event rate modulation is found, and hence we set the first experimental constraint on the KK axion-photon coupling of 4.8 x 10(-12) GeV-1 at the 90% confidence level for a KK axion number density of (n) over bara = 4.07x10(13) m(-3), the total number of extra dimensions n = 2, and the number of extra dimensions d = 2 that axions can propagate in.