Axionlike particle searches in short-baseline liquid scintillator neutrino detectors

Abstract

Short-baseline reactor neutrino experiments using large organic liquid scintillator detectors provide an experimentally rich environment for precise neutrino physics. Neutrino detection is done through inverse beta decay and relies on prompt and delayed signals, which enable powerful background discrimination. In addition to their neutrino program, they offer an ideal experimental environment for other physics searches. Here we discuss the case of axionlike particles (ALPs) produced by either Primakoff-like or Compton-like processes. Their detection relies on the corresponding inverse processes, axio-electric absorption and ALP decays to photon or electron pairs. Assuming experimental parameter values broadly representative of JUNO-TAO or CLOUD we show that scattering ALP processes involve a prompt photon signal component followed by a delayed photon signal about 5 ns after. We point out that if these signals can be resolved, this might allow for efficient ALP signal discrimination against radioactive background. Likewise, coincident events from ALP decays and scintillation light followed by Auger electrons from axio-electric absorption might as well allow for background discrimination. We determine sensitivities in both the nuclear and electron channels using as a benchmark case an experimental setup resembling that of the CLOUD or JUNO-TAO detectors. Our findings demonstrate that with efficient background discrimination these type of technology has the capability to test regions in parameter space not yet explored. In particular, the cosmological triangle can be fully tested and regions of MeV ALP masses with ALP-electron couplings of the order of $10^{-8}$ can be entirely explored.