Cryogenic pure CsI as a probe for neutrino electromagnetic interactions

TL;DR

Cryogenic pure CsI detectors can effectively probe neutrino-electron interactions and electromagnetic properties at reactors, offering significant improvements over current limits due to their low thresholds and stable backgrounds.

Contribution

This work introduces a novel cryogenic CsI detector design for neutrino-electron scattering, enabling enhanced sensitivity to neutrino electromagnetic properties.

Findings

Order-of-magnitude improvements over current limits on neutrino magnetic moment.

Effective suppression of nuclear recoil detection, focusing on neutrino-electron interactions.

Feasibility of scalable, low-background neutrino probes using cryogenic CsI.

Abstract

Searches for neutrino electromagnetic interactions at reactor sites require an unusual combination of ultra-low thresholds and a stable low-background environment. It is shown here that cryogenic undoped cesium iodide (CsI) naturally satisfies these conditions in a way prior detectors have not. Although suppression of nuclear recoil ionization efficiency at low energies limits the use of this scintillator for coherent elastic neutrino-nucleus scattering, that same property renders the detector effectively blind to those nuclear recoils from MeV-scale reactor antineutrinos. This leaves the low-energy regime free to expose neutrino-electron ($\bar{\nu}_{e} -e^{-}$) scattering as the dominant observable channel and converts cryogenic CsI into a targeted probe of electromagnetic couplings. This work presents a conceptual design based on pure CsI crystals immersed in an active xenon-doped liquid argon veto evaluated under realistic intrinsic and environmental backgrounds. Under present detector capabilities, order-of-magnitude improvements over current reactor limits on the neutrino magnetic moment and millicharge are achievable. Cryogenic pure CsI therefore offers a distinctive and scalable route to leading studies of $\bar{\nu}_{e} -e^{-}$ physics.