DEAP
A first-generation detector (DEAP-1) with a 7 kg target mass was operated at Queen's University to test the performance of pulse-shape discrimination at low recoil energies in liquid argon.
[2] Research and development efforts are working towards a next generation detector (ARGO) with a multi-hundred tonne liquid argon target mass designed to reach the neutrino floor, planned to operate at SNOLAB due to its extremely low-background radiation environment.
The recoiling argon nuclei undergo recombination or self-trapping, ultimately resulting in the emission of 128 nm vacuum ultra-violet (VUV) photons.
It is expected that WIMP-nucleon interactions also produce a nuclear recoil type signal due to the elastic scattering of the dark matter particle with the argon nucleus.
The first stage of the DEAP project, DEAP-1, was designed in order to characterize several properties of liquid argon, demonstrate pulse-shape discrimination, and refine engineering.
[7] The acrylic vessel is surrounded by 255 high quantum efficiency photomultiplier tubes (PMTs) to detect the argon scintillation light.
The acrylic vessel is housed in a stainless steel shell submerged in a 7.8m diameter shield tank filled with ultra-pure water.
The outside of the steel shell has additional 48 veto PMTs to detect Cherenkov radiation produced by incoming cosmic particles, primarily muons.
The first dark matter search results with an exposure of 4.44 live days from the initial fill were published in August 2017, giving a cross-section limit of 1.2×10−44 cm2 for a 100 GeV/c2 WIMP mass.
[10] Improved sensitivity to dark matter was achieved in February 2019, with an analysis of data collected over 231 live days from the second fill in 2016-2017, giving a cross-section limit of 3.9×10−45 cm2 for a 100 GeV/c2 WIMP mass.
[11] This updated analysis demonstrated the best performance ever achieved in liquid argon at threshold, for the pulse-shape discrimination technique against beta and gamma backgrounds.
The collaboration also developed new techniques to reject rare nuclear recoil backgrounds, using the observed distribution of light in space and time after a scintillation event.
