Long-term study of backgrounds in the DRIFT-II directional dark matter experiment

TL;DR

This study analyzes background events, especially radon progeny recoils, in the DRIFT-II dark matter detector over 5.5 years, leading to improved understanding and mitigation of backgrounds in directional dark matter searches.

Contribution

It provides a detailed long-term analysis of background sources in a directional dark matter detector and develops new strategies to suppress radon-related backgrounds.

Findings

Identification of four background populations and their origins.

Development of new mitigation strategies for radon progeny recoils.

Long-term data analysis enhances background understanding in dark matter detection.

Abstract

Low-pressure gas Time Projection Chambers being developed for directional dark matter searches offer a technology with strong particle identification capability combined with the potential to produce a definitive detection of Galactic Weakly Interacting Massive Particle (WIMP) dark matter. A source of events able to mimic genuine WIMP-induced nuclear recoil tracks arises in such experiments from the decay of radon gas inside the vacuum vessel. The recoils that result from associated daughter nuclei are termed Radon Progeny Recoils (RPRs). We present here experimental data from a long-term study using the DRIFT-II directional dark matter experiment at the Boulby Underground Laboratory of the RPRs, and other backgrounds that are revealed by relaxing the normal cuts that are applied to WIMP search data. By detailed examination of event classes in both spatial and time coordinates using 5.5 years of data, we demonstrate the ability to determine the origin of 4 specific background populations and describe development of new technology and mitigation strategies to suppress them.