A Measurement of The Response of A High Purity Germanium Detector to Low-Energy Nuclear Recoils

Abstract

The Standard model process of Coherent Elastic Neutrino-Nucleus Scattering (CEvNS), which was first predicted by Freedman in 1974, has recently been observed by the COHERENT collaboration on CsI and liquid argon targets. The result is a new way to build a compact neutrino detector which unlocks new channels to test the Standard Model. A semiconductor germanium detector, a technology that has been developed by many dark matter direct detection experiments due to its excellent energy resolution and low-energy thresholds, will also be deployed to ORNL in order to detect CEvNS as part of the next phase of the COHERENT experiment. One of the challenges is to understand the signature of neutrino-induced low-energy nuclear recoils in germanium. A measurement was carried out at the Triangle Universities Nuclear Laboratory (TUNL) to characterize the it response to low-energy nuclear recoils. A quenching factor of 14-20% for nuclear recoil energies between 0.8-4.9 keV in Ge was established. A long predicted smearing effect due to quenching was observed for the first time and estimated to be 0.024 at ~2 keVnr. Finally, the impact of this effect and the quenching factor on the expected CEvNS spectrum of the future Ge deployment is presented.