Phonon-Based Position Determination in SuperCDMS iZIP Detectors

TL;DR

This paper presents a phonon-based method for accurately determining the position of particle interactions in SuperCDMS germanium detectors, improving surface event rejection and extending position sensitivity to lower energies.

Contribution

It introduces a novel phonon signal analysis technique for position reconstruction in cryogenic germanium detectors, enhancing background rejection capabilities.

Findings

Achieved surface event rejection of (4.5 +/- 0.9) x 10^-4 with 46% nuclear recoil acceptance.

Demonstrated efficient identification of events near the detector sidewall using phonon channels.

Extended position reconstruction to lower energies than ionization-based methods.

Abstract

SuperCDMS is currently operating a 10-kg array of cryogenic germanium detectors in the Soudan underground laboratory to search for weakly interacting massive particles, a leading dark matter candidate. These detectors, known as iZIPs, measure ionization and athermal phonons from particle interactions with sensors on both sides of a Ge crystal. The ionization signal can be used to efficiently tag events at high radius and near the top and bottoms surfaces, where diminished charge collection can cause events to mimic WIMP-induced nuclear recoils. Using calibration data taken with a 210Pb source underground at Soudan, we demonstrate rejection of surface events of (4.5 +/- 0.9) x 10^-4 with 46% acceptance of nuclear recoils using the phonon signal only. We also show with 133Ba calibration data underground that the phonon channels can efficiently identify events near the sidewall. This phonon-based approach can also be extended to lower energies than the ionization-based position reconstruction.