Alpha radioactivity deep-underground as a probe of axion dark matter

Abstract

We propose to investigate the time modulation of radioisotope decays deep underground as a method to explore axion dark matter. In this work, we focus on the $\hat{I}\pm$-decay of heavy isotopes and develop a theoretical description for the $\hat{I}¸$-dependence of $\hat{I}\pm$-decay half-lives, which enables us to predict the time variation of $\hat{I}\pm$-radioactivity in response to an oscillating axion dark matter background. To probe this scenario, we have recently constructed and installed a setup deep underground at the Gran Sasso Laboratory, based on the $\hat{I}\pm$-decay of Americium-241. This prototype experiment, named RadioAxion-$\hat{I}\pm$, will allow us to explore a broad range of oscillation's periods, from a micro-second up to one year, thus providing competitive limits on the axion decay constant across 13 orders of magnitude in the axion mass, ranging from $10^{-9}$ eV to $10^{-20}$ eV after one month of data collection, and down to $10^{-22}$ eV after three years.

7 pages, 3 figures. Added an Appendix providing an analytical treatment of the theta dependence of alpha decay. Version to appear in Physics Letters B