Impact of Low-Energy Response to Nuclear Recoils in Dark Matter Detectors

TL;DR

This paper provides an absolute energy response function for germanium and liquid xenon detectors, demonstrating low-energy thresholds for nuclear recoil detection crucial for dark matter searches.

Contribution

It introduces a precise energy response calibration for germanium and xenon detectors, enabling detection of nuclear recoils at thresholds as low as a few keV.

Findings

Detection threshold of ~2.15 keV for germanium detectors.

Nuclear and electronic recoil Fano factors differ, affecting discrimination.

Energy response function established for dual-phase xenon detectors.

Abstract

We report an absolute energy response function to electronic and nuclear recoils for germanium and liquid xenon detectors. As a result, we show that the detection energy threshold of nuclear recoils for a dual-phase xenon detector can be a few keV for a given number of detectable photoelectrons. We evaluate the average energy expended per electron-hole pair to be $\sim$3.32 eV, which sets a detection energy threshold of $\sim$2.15 keV for a germanium detector at 50 mini-Kelvin at 69 volts with a primary phonon frequency of 1 THz. The Fano factors of nuclear and electronic recoils that constrain the capability for discriminating nuclear recoils below 2-3 keV recoil energy for both technologies are different.