Pulseshape discrimination against low-energy Ar-39 beta decays in liquid argon with 4.5 tonne-years of DEAP-3600 data
Creators: name: The DEAP Collaboration
name: Adhikari, P.
name: Ajaj, R.
name: Alpízar-Venegas, M.
name: Amaudruz, P. -A.
name: Auty, D. J.
name: Batygov, M.
name: Beltran, B.
name: Benmansour, H.
name: Bina, C. E.
name: Bonatt, J.
name: Bonivento, W.
name: Boulay, M. G.
name: Broerman, B.
name: Bueno, J. F.
name: Burghardt, P. M.
name: Butcher, A.
name: Cadeddu, M.
name: Cai, B.
name: Cárdenas-Montes, M.
name: Cavuoti, S.
name: Chen, M.
name: Chen, Y.
name: Cleveland, B. T.
name: Corning, J. M.
name: Cranshaw, D.
name: Daugherty, S.
name: DelGobbo, P.
name: Dering, K.
name: DiGioseffo, J.
name: Di Stefano, P.
name: Doria, L.
name: Duncan, F. A.
name: Dunford, M.
name: Ellingwood, E.
name: Erlandson, A.
name: Farahani, S. S.
name: Fatemighomi, N.
name: Fiorillo, G.
name: Florian, S.
name: Flower, T.
name: Ford, R. J.
name: Gagnon, R.
name: Gallacher, D.
name: Abia, P. García
name: Garg, S.
name: Giampa, P.
name: Goeldi, D.
name: Golovko, V.
name: Gorel, P.
name: Graham, K.
name: Grant, D. R.
name: Grobov, A.
name: Hallin, A. L.
name: Hamstra, M.
name: Harvey, P. J.
name: Hearns, C.
name: Hugues, T.
name: Ilyasov, A.
name: Joy, A.
name: Jigmeddorj, B.
name: Jillings, C. J.
name: Kamaev, O.
name: Kaur, G.
name: Kemp, A.
name: Kochanek, I.
name: Kuźniak, M.
name: Lai, M.
name: Langrock, S.
name: Lehnert, B.
name: Leonhardt, A.
name: Levashko, N.
name: Li, X.
name: Lidgard, J.
name: Lindner, T.
name: Lissia, M.
name: Lock, J.
name: Longo, G.
name: Machulin, I.
name: McDonald, A. B.
name: McElroy, T.
name: McGinn, T.
name: McLaughlin, J. B.
name: Mehdiyev, R.
name: Mielnichuk, C.
name: Monroe, J.
name: Nadeau, P.
name: Nantais, C.
name: Ng, C.
name: Noble, A. J.
name: O'Dwyer, E.
name: Oliviéro, G.
name: Ouellet, C.
name: Pal, S.
name: Pasuthip, P.
name: Peeters, S. J. M.
name: Perry, M.
name: Pesudo, V.
name: Picciau, E.
name: Piro, M. -C.
name: Pollmann, T. R.
name: Rand, E. T.
name: Rethmeier, C.
name: Retière, F.
name: Rodríguez-García, I.
name: Roszkowski, L.
name: Ruhland, J. B.
name: Sánchez-García, E.
name: Santorelli, R.
name: Sinclair, D.
name: Skensved, P.
name: Smith, B.
name: Smith, N. J. T.
name: Sonley, T.
name: Soukup, J.
name: Stainforth, R.
name: Stone, C.
name: Strickland, V.
name: Stringer, M.
name: Sur, B.
name: Tang, J.
name: Vázquez-Jáuregui, E.
name: Viel, S.
name: Walding, J.
name: Waqar, M.
name: Ward, M.
name: Westerdale, S.
name: Willis, J.
name: Zuñiga-Reyes, A.
Publisher: name: arXiv
Year: 2021
Subjects: subject: Instrumentation and Detectors (physics.ins-det)
subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The DEAP-3600 detector searches for the scintillation signal from dark matter particles scattering on a 3.3 tonne liquid argon target. The largest background comes from $^{39}$Ar beta decays and is suppressed using pulseshape discrimination (PSD). We use two types of PSD algorithm: the prompt-fraction, which considers the fraction of the scintillation signal in a narrow and a wide time window around the event peak, and the log-likelihood-ratio, which compares the observed photon arrival times to a signal and a background model. We furthermore use two algorithms to determine the number of photons detected at a given time: (1) simply dividing the charge of each PMT pulse by the charge of a single photoelectron, and (2) a likelihood analysis that considers the probability to detect a certain number of photons at a given time, based on a model for the scintillation pulseshape and for afterpulsing in the light detectors. The prompt-fraction performs approximately as well as the log-likelihood-ratio PSD algorithm if the photon detection times are not biased by detector effects. We explain this result using a model for the information carried by scintillation photons as a function of the time when they are detected.
description: 14 pages, 9 figures