European Physical Journal C: Particles and Fields (Sep 2021)

Pulse-shape discrimination against low-energy Ar-39 beta decays in liquid argon with 4.5 tonne-years of DEAP-3600 data

  • P. Adhikari,
  • R. Ajaj,
  • M. Alpízar-Venegas,
  • P.-A. Amaudruz,
  • D. J. Auty,
  • M. Batygov,
  • B. Beltran,
  • H. Benmansour,
  • C. E. Bina,
  • J. Bonatt,
  • W. Bonivento,
  • M. G. Boulay,
  • B. Broerman,
  • J. F. Bueno,
  • P. M. Burghardt,
  • A. Butcher,
  • M. Cadeddu,
  • B. Cai,
  • M. Cárdenas-Montes,
  • S. Cavuoti,
  • M. Chen,
  • Y. Chen,
  • B. T. Cleveland,
  • J. M. Corning,
  • D. Cranshaw,
  • S. Daugherty,
  • P. DelGobbo,
  • K. Dering,
  • J. DiGioseffo,
  • P. Di Stefano,
  • L. Doria,
  • F. A. Duncan,
  • M. Dunford,
  • E. Ellingwood,
  • A. Erlandson,
  • S. S. Farahani,
  • N. Fatemighomi,
  • G. Fiorillo,
  • S. Florian,
  • T. Flower,
  • R. J. Ford,
  • R. Gagnon,
  • D. Gallacher,
  • P. García Abia,
  • S. Garg,
  • P. Giampa,
  • D. Goeldi,
  • V. Golovko,
  • P. Gorel,
  • K. Graham,
  • D. R. Grant,
  • A. Grobov,
  • A. L. Hallin,
  • M. Hamstra,
  • P. J. Harvey,
  • C. Hearns,
  • T. Hugues,
  • A. Ilyasov,
  • A. Joy,
  • B. Jigmeddorj,
  • C. J. Jillings,
  • O. Kamaev,
  • G. Kaur,
  • A. Kemp,
  • I. Kochanek,
  • M. Kuźniak,
  • M. Lai,
  • S. Langrock,
  • B. Lehnert,
  • A. Leonhardt,
  • N. Levashko,
  • X. Li,
  • J. Lidgard,
  • T. Lindner,
  • M. Lissia,
  • J. Lock,
  • G. Longo,
  • I. Machulin,
  • A. B. McDonald,
  • T. McElroy,
  • T. McGinn,
  • J. B. McLaughlin,
  • R. Mehdiyev,
  • C. Mielnichuk,
  • J. Monroe,
  • P. Nadeau,
  • C. Nantais,
  • C. Ng,
  • A. J. Noble,
  • E. O’Dwyer,
  • G. Oliviéro,
  • C. Ouellet,
  • S. Pal,
  • P. Pasuthip,
  • S. J. M. Peeters,
  • M. Perry,
  • V. Pesudo,
  • E. Picciau,
  • M.-C. Piro,
  • T. R. Pollmann,
  • E. T. Rand,
  • C. Rethmeier,
  • F. Retière,
  • I. Rodríguez-García,
  • L. Roszkowski,
  • J. B. Ruhland,
  • E. Sánchez-García,
  • R. Santorelli,
  • D. Sinclair,
  • P. Skensved,
  • B. Smith,
  • N. J. T. Smith,
  • T. Sonley,
  • J. Soukup,
  • R. Stainforth,
  • C. Stone,
  • V. Strickland,
  • M. Stringer,
  • B. Sur,
  • J. Tang,
  • E. Vázquez-Jáuregui,
  • S. Viel,
  • J. Walding,
  • M. Waqar,
  • M. Ward,
  • S. Westerdale,
  • J. Willis,
  • A. Zuñiga-Reyes,
  • DEAP Collaboration

DOI
https://doi.org/10.1140/epjc/s10052-021-09514-w
Journal volume & issue
Vol. 81, no. 9
pp. 1 – 13

Abstract

Read online

Abstract 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 $$^{39}\text{ Ar }$$ 39 Ar beta decays and is suppressed using pulse-shape discrimination (PSD). We use two types of PSD estimator: 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 mean single-photoelectron charge, 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 pulse shape 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.