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 232&_mathId=si27.gif&_user=111111111&_pii=S0927650516301232&_rdoc=1&_issn=09276505&md5=c58c520db4087595e1bbdf6b34f56698" title="Click to view the MathML source"><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 232&_mathId=si28.gif&_user=111111111&_pii=S0927650516301232&_rdoc=1&_issn=09276505&md5=d09ca474920f54e3075292af39f2d236" 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 232&_mathId=si29.gif&_user=111111111&_pii=S0927650516301232&_rdoc=1&_issn=09276505&md5=8b21620fcebeefcd998ad1b201b54af2" title="Click to view the MathML source">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 232&_mathId=si30.gif&_user=111111111&_pii=S0927650516301232&_rdoc=1&_issn=09276505&md5=f1d2302d1a7756c5ea83d2ac1f9ca032" title="Click to view the MathML source">¹⁰⁻⁴⁶${10}^{-46}$ cm², assuming negligible contribution from nuclear recoil backgrounds.