Germanium response to sub-keV nuclear recoils: a multipronged experimental characterization

TL;DR

This study systematically measures the germanium detector's response to sub-keV nuclear recoils using multiple experimental techniques, revealing deviations from existing models and informing future dark matter and neutrino detection efforts.

Contribution

It provides the first comprehensive experimental characterization of germanium's quenching factor at sub-keV energies, challenging the Lindhard model predictions.

Findings

Deviations from Lindhard model at sub-keV energies

Experimental data compatible with low-energy processes like Migdal effect

Implications for future dark matter and neutrino searches

Abstract

Germanium is the detector material of choice in many rare-event searches looking for low-energy nuclear recoils induced by dark matter particles or neutrinos. We perform a systematic exploration of its quenching factor for sub-keV nuclear recoils, using multiple techniques: photo-neutron sources, recoils from gamma-emission following thermal neutron capture, and a monochromatic filtered neutron beam. Our results point to a marked deviation from the predictions of the Lindhard model in this mostly unexplored energy range. We comment on the compatibility of our data with low-energy processes such as the Migdal effect, and on the impact of our measurements on upcoming searches.