Germanium Detector Response to Nuclear Recoils in Searching for Dark Matter

TL;DR

This paper develops a new model for ionization efficiency in germanium detectors at low energies, crucial for improving dark matter search sensitivity, by analyzing nuclear stopping power contributions.

Contribution

It introduces a correction to existing models by incorporating a fraction of the ZBL nuclear stopping power, enhancing the accuracy of ionization efficiency predictions at sub-10 keV energies.

Findings

The model aligns well with previous measurements of germanium ionization efficiency.

It reveals that a fraction of nuclear stopping power contributes to ionization at low energies.

Application to CDMS II and CoGeNT thresholds improves understanding of nuclear recoil detection.

Abstract

The discrepancies in claims of experimental evidence in the search for weakly interacting massive particle (WIMP) dark matter necessitate a model for ionization efficiency (the quenching factor) at energies below 10 keV. We have carefully studied the physics processes that contribute to the ionization efficiency through stopping power. The focus of this work is the construction of a model for the ionization efficiency in germanium by analyzing the components of stopping power, specifically that of the nuclear stopping power, at low energies. We find a fraction of the ZBL nuclear stopping power can contribute to ionization efficiency. We propose a model that corrects the missing contribution to ionization efficiency from the ZBL nuclear stopping power. The proposed model is compared to previous measurements of ionization efficiency in germanium as well as that of other theoretical models. Using this new model, the thresholds of both CDMS II and CoGeNT are analyzed and compared in terms of the nuclear recoil energy.