Constraints on millicharged neutrinos via analysis of data from atomic ionizations with germanium detectors at sub-keV sensitivities

TL;DR

This paper investigates the electromagnetic properties of neutrinos, specifically their possible millicharge, using atomic ionization data from germanium detectors with sub-keV sensitivities, setting new limits on neutrino charge.

Contribution

The study provides the first ab-initio calculations of millicharged neutrino interactions with atoms and applies these to reactor data to set stringent new limits on neutrino charge.

Findings

No evidence of millicharged neutrinos found in the data.

Established an upper limit on neutrino charge fraction of |q| < 1.0 x 10^{-12} at 90% CL.

Atomic ionization enhances sensitivity to neutrino electromagnetic properties.

Abstract

With the advent of detectors with sub-keV sensitivities, atomic ionization has been identified as a promising avenue to probe possible neutrino electromagnetic properties. The interaction cross-sections induced by millicharged neutrinos are evaluated with the ab-initio multi-configuration relativistic random-phase approximation. There is significant enhancement at atomic binding energies compared to that when the electrons are taken as free particles. Positive signals would distinctly manifest as peaks at specific energies with known intensity ratios. Selected reactor neutrino data with germanium detectors at analysis threshold as low as 300 eV are studied. No such signatures are observed, and a combined limit on the neutrino charge fraction of | \numq | < 1.0 X 10^{-12} at 90% confidence level is derived.