Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy beta and nuclear recoils in liquid argon with DEAP-1
Creators: name: Amaudruz, P. -A.
name: Batygov, M.
name: Beltran, B.
name: Bonatt, J.
name: Boudjemline, K.
name: Boulay, M. G.
name: Broerman, B.
name: Bueno, J. F.
name: Butcher, A.
name: Cai, B.
name: Caldwell, T.
name: Chen, M.
name: Chouinard, R.
name: Cleveland, B. T.
name: Cranshaw, D.
name: Dering, K.
name: Duncan, F.
name: Fatemighomi, N.
name: Ford, R.
name: Gagnon, R.
name: Giampa, P.
name: Giuliani, F.
name: Gold, M.
name: Golovko, V. V.
name: Gorel, P.
name: Grace, E.
name: Graham, K.
name: Grant, D. R.
name: Hakobyan, R.
name: Hallin, A. L.
name: Hamstra, M.
name: Harvey, P.
name: Hearns, C.
name: Hofgartner, J.
name: Jillings, C. J.
name: Kuźniak, M.
name: Lawson, I.
name: La Zia, F.
name: Li, O.
name: Lidgard, J. J.
name: Liimatainen, P.
name: Lippincott, W. H.
name: Mathew, R.
name: McDonald, A. B.
name: McElroy, T.
name: McFarlane, K.
name: Mehdiyev, R.
name: McKinsey, D. N.
name: Monroe, J.
name: Muir, A.
name: Nantais, C.
name: Nicolics, K.
name: Nikkel, J.
name: Noble, A. J.
name: O'Dwyer, E.
name: Olsen, K.
name: Ouellet, C.
name: Pasuthip, P.
name: Peeters, S. J. M.
name: Pollmann, T.
name: Rau, W.
name: Retière, F.
name: Ronquest, M.
name: Seeburn, N.
name: Skensved, P.
name: Smith, B.
name: Sonley, T.
name: Tang, J.
name: Vázquez-Jáuregui, E.
name: Veloce, L.
name: Walding, J.
name: Ward, M.
Publisher: name: arXiv
Year: 2009
Subjects: subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The DEAP-1 low-background liquid argon detector was used to measure scintillation pulse shapes of electron and nuclear recoil events and to demonstrate the feasibility of pulse-shape discrimination (PSD) down to an electron-equivalent energy of 20 keV. In the surface dataset using a triple-coincidence tag we found the fraction of beta events that are misidentified as nuclear recoils to be $&lt;1.4\times 10^{-7}$ (90% C.L.) for energies between 43-86 keVee and for a nuclear recoil acceptance of at least 90%, with 4% systematic uncertainty on the absolute energy scale. The discrimination measurement on surface was limited by nuclear recoils induced by cosmic-ray generated neutrons. This was improved by moving the detector to the SNOLAB underground laboratory, where the reduced background rate allowed the same measurement with only a double-coincidence tag. The combined data set contains $1.23\times10^8$ events. One of those, in the underground data set, is in the nuclear-recoil region of interest. Taking into account the expected background of 0.48 events coming from random pileup, the resulting upper limit on the electronic recoil contamination is $&lt;2.7\times10^{-8}$ (90% C.L.) between 44-89 keVee and for a nuclear recoil acceptance of at least 90%, with 6% systematic uncertainty on the absolute energy scale. We developed a general mathematical framework to describe PSD parameter distributions and used it to build an analytical model of the distributions observed in DEAP-1. Using this model, we project a misidentification fraction of approx. $10^{-10}$ for an electron-equivalent energy threshold of 15 keV for a detector with 8 PE/keVee light yield. This reduction enables a search for spin-independent scattering of WIMPs from 1000 kg of liquid argon with a WIMP-nucleon cross-section sensitivity of $10^{-46}$ cm$^2$, assuming negligible contribution from nuclear recoil backgrounds.
description: Accepted for publication in Astroparticle Physics