Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy β and nuclear recoils in liquid argon with DEAP-1

Amaudruz, P -A, Batygov, M, Beltran, B, Bonatt, J, Boudjemline, K, Boulay, M G, Broerman, B, Bueno, J F, Butcher, A, Cai, B, Caldwell, T, CHEN, M, Chouinard, R, Cleveland, B T, Cranshaw, D, Dering, K, Duncan, F, Fatemighomi, N, Ford, R, Gagnon, R, Giampa, P, Giuliani, F, Gold, M, Golovko, V V, Gorel, P, Grace, E, Graham, K, Grant, D R, Hakobyan, R, Hallin, A L, Hamstra, M, Harvey, P, Hearns, C, Hofgartner, J, Jillings, C J, Kuźniak, M, Lawson, I, La Zia, F, Lipski, O, Lidgard, J J, Liimatainen, P, Lippincott, W H, Mathews, R, McDonald, A B, McElroy, T, McFarlane, K, McKinsey, D N, Mehdiyev, R, Monroe, J, Muir, A, Nantais, C, Nicolics, K, Nikkel, J, Noble, A J, O’Dwyer, E, Olsen, K, Ouellet, C, Pasuthip, P, Peeters, S J M, Pollmann, T, Rau, W, Retière, F, Ronquest, M, Seeburn, N, Skensved, P, Smith, B, Sonley, T, Tang, J, Vázquez-Jáuregui, E, Veloce, L, Walding, J and Ward, M (2016) Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy β and nuclear recoils in liquid argon with DEAP-1. Astroparticle Physics, 85. pp. 1-23. ISSN 0927-6505

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Abstract

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 <1.4×10 −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 1.23×10 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 <2.7×10 −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.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Research Centres and Groups: Experimental Particle Physics Research Group
Subjects: Q Science > QC Physics
Depositing User: Richard Chambers
Date Deposited: 25 Nov 2016 11:55
Last Modified: 08 Mar 2017 06:43
URI: http://sro.sussex.ac.uk/id/eprint/65661

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Project NameSussex Project NumberFunderFunder Ref
Liquid Argon Detector Calibration R&D for Dark Matter and Neutrino PhysicsG0972STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/K002473/1