Discrimination of Recoil Backgrounds in Scintillating Calorimeters

TL;DR

This paper investigates alpha decay backgrounds in scintillating calorimeters used for rare event detection, demonstrating methods to discriminate lead recoil backgrounds via pulse shape analysis to improve experimental sensitivity.

Contribution

It introduces a novel pulse shape discrimination technique using scintillating foil to effectively identify lead recoil backgrounds in cryogenic calorimeters.

Findings

Lead nuclei show a specific scintillation light yield of 0.0142 relative to electrons.

Scintillating foil enables discrimination of lead recoil events from electron recoils.

Pulse shape differences in phonon detectors can be exploited for future background suppression.

Abstract

The alpha decay of $\n{{}^{210}Po}$ is a dangerous background to rare event searches. Here, we describe observations related to this alpha decay in the Cryogenic Rare Event Search with Superconducting Thermometers (CRESST). We find that lead nuclei show a scintillation light yield in our $\n{CaWO_4}$ crystals of $0.0142\pm0.0013$ relative to electrons of the same energy. We describe a way to discriminate this source of nuclear recoil background by means of a scintillating foil, and demonstrate its effectiveness. This leads to an observable difference in the pulse shape of the light detector, which can be used to tag these events. Differences in pulse shape of the phonon detector between lead and electron recoils are also extracted, opening the window to future additional background suppression techniques based on pulse shape discrimination in such experiments.