Nuclear Recoil Discrimination Through Solely Phonon Signal in Cryogenic Semiconductor Dark Matter Detectors

The Super Cryogenic Dark Matter Search (SuperCDMS) is a direct-detection experiment focused on searching for WIMP-like dark matter in the 1-5 GeV mass range. SuperCDMS is currently in commission at SNOLAB, a deep underground Canadian laboratory that will provide shielding from high energy cosmic rays and radioactive decay byproducts. SuperCDMS is a modular collection of cryogenically cooled crystal target masses, primarily silicon and germanium, that rely on a variety of detector designs to demonstrate sensitivity to nuclear and/or electronic recoil events within the crystals. Characterization of detectors' design performance has been ongoing to evaluate their efficacy. A silicon "hybrid" style detector that can perform event-by-event discrimination of recoil interactions using Neganov-Luke phonon amplification has undergone initial characterization studies. The detector is composed of two acoustically isolated regions; a low voltage (LV) region that measures the primary phonon energy from the initial recoil, and a high voltage (HV) region that amplifies the ionization from the initial recoil to induce secondary phonons. Discrimination between nuclear and electronic recoil is achieved through indirectly measuring the Lindhard suppression of nuclear recoil's ionization yield. In addition to a larger germanium version of this detector, a 2nd generation redesign has been in development to improve charge transport, increase fiducial volume, and improve the acoustic isolation between the LV and HV regions.