Discrimination of Electron and Nuclear Recoils by Varying Luke-Neganov Phonon Gain in Semiconductor Detectors

Abstract Amplifying the phonon signal in a semiconductor dark matter detector can be accomplished by operating at high voltage bias and converting the elec-trostatic potential energy into Luke-Neganov phonons. This amplification method has been validated at up to |E | = 40 V/cm without producing leakage in CDM-SII Ge detectors, allowing sensitivity to a benchmark WIMP with mass Mχ = 8 GeV/c2 and σ = 1.8×10−42 cm2 (with significant sensitivity forMχ> 2 GeV/c2) assuming flat electronic recoil backgrounds near threshold. Furthermore, for the first time we show that differences in Luke-Neganov gain for nuclear and elec-tronic recoils can be used to discriminate statistically between low-energy back-ground and a hypothetical WIMP signal by operating at two distinct voltage bi-ases. Specifically, 99 % of events have p-value < 10−8 for a simulated 20 kg-day experiment with a benchmark WIMP signal with Mχ = 8 GeV/c2 and σ = 3.3×10−41 cm2. PACS numbers: 95.35.+d,07.57.Kp, 95.55.Rg, 07.85.Fv, 29.40.-n