Reactor-based Search for Axion-Like Particles using CsI(Tl) Detector

TL;DR

This study uses a CsI(Tl) detector near a nuclear reactor to search for axion-like particles, achieving low background levels and exploring new parameter space for ALP couplings in the MeV mass range.

Contribution

First application of a reactor-based CsI(Tl) detector to search for ALPs with sensitivity to previously unexplored coupling regions.

Findings

Achieved sub-100 DRU background level in MeV range

Sensitive to ALPs with specific axion-photon and axion-electron couplings

Can probe the cosmological triangle in ALP parameter space

Abstract

The absence of conclusive signals in weakly interacting massive particle (WIMP) searches has motivated increased interest in alternative dark matter candidates such as axions and axion-like particles (ALPs), which also provide a solution to the strong CP problem. In this work, we employ a $\sim100~\mathrm{kg}$ scale CsI(Tl)-based detector operated in proximity to a nuclear reactor to achieve a sub-100 DRU (differential rate unit, expressed in counts/keV/kg/day) background level in the MeV energy range through a combination of active veto and passive shielding techniques. Such a low-background environment enables sensitivity to ALPs with axion--photon coupling $g_{a\gamma\gamma} \gtrsim 10^{-6}$ and axion--electron coupling in the range $10^{-8} < g_{aee} < 10^{-4}$ for ALP masses between 1~keV and 10~MeV. These results demonstrate that the experiment has the potential to probe previously unexplored regions of parameter space, including the so-called cosmological triangle in the ALP--photon coupling for MeV-scale ALPs.