Search for dark matter with a 231-day exposure of liquid argon using DEAP-3600 at SNOLAB

Abstract

DEAP-3600 is a single-phase liquid argon (LAr) direct-detection dark matter experiment, operating 2 km underground at SNOLAB (Sudbury, Canada). The detector consists of 3279 kg of LAr contained in a spherical acrylic vessel. This paper reports on the analysis of a 758 tonne .day exposure taken over a period of 231 live-days during the first year of operation. No candidate signal events are observed in the WIMP-search region of interest, which results in the leading limit on the WIMP-nucleon spin-independent cross section on a LAr target of 3.9 ×10<SUP>-45</SUP> cm<SUP>2</SUP> (1.5 ×10<SUP>-44</SUP> cm<SUP>2</SUP> ) for a 100 GeV /c<SUP>2</SUP> (1 TeV /c<SUP>2</SUP> ) WIMP mass at 90% C.L. In addition to a detailed background model, this analysis demonstrates the best pulse-shape discrimination in LAr at threshold, employs a Bayesian photoelectron-counting technique to improve the energy resolution and discrimination efficiency, and utilizes two position reconstruction algorithms based on the charge and photon detection time distributions observed in each photomultiplier tube.