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

TL;DR

This study searches for annual modulation signals from solar Kaluza-Klein axions using the XMASS-I detector, setting the first experimental constraints on their photon coupling and providing insights into extra-dimensional theories.

Contribution

First experimental search for annual modulation of solar KK axions with XMASS-I, constraining their photon coupling and exploring extra-dimensional models.

Findings

No significant annual modulation detected.

Set upper limit on KK axion-photon coupling at 4.8 x 10^{-12} GeV^{-1}.

Provided the first experimental constraints on KK axions in this context.

Abstract

In theories with the large extra dimensions beyond the standard 4-dimensional spacetime, axions could propagate in such extra dimensions, and acquire Kaluza-Klein (KK) excitations. These KK axions are produced in the Sun and could solve unexplained heating of the solar corona. While most of the solar KK axions escape from the solar system, a small fraction is gravitationally trapped in orbits around the Sun. They would decay into two 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 $832\times 359$ kg$\cdot$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 $4.8 \times 10^{-12}\, \mathrm{GeV}^{-1}$ at 90% confidence level for a KK axion number density of $\bar{n}_\mathrm{a} = 4.07 \times 10^{13}\, \mathrm{m}^{-3}$, the total number of extra dimensions $n = 2$, and the number of extra dimensions $\delta = 2$ that axions can propagate in.