Dark Matter Search with the DEAP-3600 Detector using the Profile Likelihood Ratio Method

TL;DR

This paper reports a search for WIMP dark matter using the DEAP-3600 detector with a profile likelihood ratio method, setting new upper limits on WIMP-nucleon interactions based on extensive liquid argon data.

Contribution

The study introduces an improved analysis technique using the profile likelihood ratio method to enhance sensitivity in dark matter searches with liquid argon detectors.

Findings

Set new upper limits on WIMP-nucleon cross section for 20-100 GeV/c² WIMPs.

Achieved a 90% confidence level limit of 3.4 × 10⁻⁴⁵ cm² at 100 GeV/c².

Identified alpha decays from dust as the main background limiting sensitivity.

Abstract

We present here a search for WIMP dark matter using 790.8 live-days of data collected with 3269 kg of liquid argon (1266 kg fiducial) by the DEAP-3600 detector at SNOLAB, using the Profile Likelihood Ratio method. The likelihood model is based on three parameters: estimated energy, pulse-shape discrimination parameter, and reconstructed position within the detector. Using this method, the expected signal sensitivity of DEAP-3600 benefits from an increased fiducial volume and improved event selection acceptance. Alpha-decays from a small number of dust particulates circulating within the liquid argon target are the dominant source of background events and limit the sensitivity of this search. This result provides improved exclusion upper limits on the WIMP-nucleon spin-independent cross section on liquid argon for WIMP masses between 20 GeV/$c^{2}$ and 100 GeV/$c^{2}$. At 100 GeV/$c^{2}$ the observed limit is 3.4 $\times$ 10$^{-45}$ cm$^2$ at 90% confidence level.