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

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• 作者：P.-A. Amaudruz^k ; M. Batygov¹ ; ^c ; B. Beltran^a ; J. Bonatt^g ; K. Boudjemline^b ; M.G. Boulay ; ^b ; ^g ; ^{mark.boulay@carleton.ca" class="auth_mail" title="E-mail the corresponding author} ; B. Broerman^g ; J.F. Bueno^a ; A. Butcher^h ; B. Cai^g ; T. Caldwell^f ; M. Chen^g ; R. Chouinard^a ; B.T. Cleveland^c ; ⁱ ; D. Cranshaw^g ; K. Dering^g ; F. Duncan^c ; ⁱ ; N. Fatemighomi^h ; R. Ford^c ; ⁱ ; R. Gagnon^g ; P. Giampa^g ; F. Giuliani^d ; M. Gold^d ; V.V. Golovko² ; ^g ; P. Gorel^a ; E. Grace^h ; K. Graham^b ; D.R. Grant^a ; R. Hakobyan^a ; A.L. Hallin^a ; M. Hamstra^b ; P. Harvey^g ; C. Hearns^g ; J. Hofgartner³ ; ^c ; C.J. Jillings^c ; ⁱ ; M. Kuźniak ; ¹ ; ^g ; ^{kuzniak@owl.phy.queensu.ca" class="auth_mail" title="E-mail the corresponding author} ; I. Lawson^c ; ⁱ ; F. La Zia^h ; O. Liⁱ ; J.J. Lidgard^g ; P. Liimatainenⁱ ; W.H. Lippincott⁴ ; ^l ; R. Mathew^g ; A.B. McDonald^g ; T. McElroy^a ; K. McFarlaneⁱ ; D.N. McKinsey^l ; R. Mehdiyev^b ; J. Monroe^h ; A. Muir^k
• 关键词：Dark matter ; WIMPs ; Liquid noble gas detector ; Liquid argon ; Pulse-shape discrimination ; DEAP
• 刊名：Astroparticle Physics
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：85
• 期：Complete
• 页码：1-23
• 全文大小：4975 K

文摘

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 down to an electron-equivalent energy of 20 keV_ee.

In the surface dataset using a triple-coincidence tag we found the fraction of β   events that are misidentified as nuclear recoils to be <1.4×¹⁰⁻⁷$<1.4\times {10}^{-7}$ (90% C.L.) for energies between 43–86 keV_ee 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 to be done with only a double-coincidence tag.

The combined data set contains 1.23 × 10⁸ 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 level of electronic recoil contamination is e3075292af39f2d236" title="Click to view the MathML source"><2.7×¹⁰⁻⁸$<2.7\times {10}^{-8}$ (90% C.L.) between 44–89 keV_ee 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 pulse-shape-discrimination 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 approximately ¹⁰⁻¹⁰${10}^{-10}$ for an electron-equivalent energy threshold of 15 keV_ee for a detector with 8 PE/keV_ee 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${10}^{-46}$ cm², assuming negligible contribution from nuclear recoil backgrounds.