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

Adhikari, P.; Ajaj, R.; Alpizar-Venegas, M.; Amaudruz, P. -A.; Auty, D. J.; Batygov, M.; Beltran, B.; Benmansour, H.; Bina, C. E.; Bonatt, J.; Bonivento, W.; Boulay, M. G.; Broerman, B.; Bueno, J. F.; Burghardt, P. M.; Butcher, A.; Cadeddu, M.; Cai, B.; Cardenas-Montes, M.; Cavuoti, S.; Chen, M.; Chen, Y.; Cleveland, B. T.; Corning, J. M.; Cranshaw, D.; Daugherty, S.; Delgobbo, P.; Dering, K.; Digioseffo, J.; Di Stefano, P.; Doria, L.; Duncan, F. A.; Dunford, M.; Ellingwood, E.; Erlandson, A.; Farahani, S. S.; Fatemighomi, N.; Fiorillo, G.; Florian, S.; Flower, T.; Ford, R. J.; Gagnon, R.; Gallacher, D.; Garcia Abia, P.; Garg, S.; Giampa, P.; Goeldi, D.; Golovko, V.; Gorel, P.; Graham, K.; Grant, D. R.; Grobov, A.; Hallin, A. L.; Hamstra, M.; Harvey, P. J.; Hearns, C.; Hugues, T.; Ilyasov, A.; Joy, A.; Jigmeddorj, B.; Jillings, C. J.; Kamaev, O.; Kaur, G.; Kemp, A.; Kochanek, I.; Kuzniak, M.; Lai, M.; Langrock, S.; Lehnert, B.; Leonhardt, A.; Levashko, N.; Li, X.; Lidgard, J.; Lindner, T.; Lissia, M.; Lock, J.; Longo, G.; Machulin, I.; Mcdonald, A. B.; Mcelroy, T.; Mcginn, T.; Mclaughlin, J. B.; Mehdiyev, R.; Mielnichuk, C.; Monroe, J.; Nadeau, P.; Nantais, C.; Ng, C.; Noble, A. J.; O'Dwyer, E.; Oliviero, G.; Ouellet, C.; Pal, S.; Pasuthip, P.; Peeters, S. J. M.; Perry, M.; Pesudo, V.; Picciau, E.; Piro, M. -C.; Pollmann, T. R.; Rand, E. T.; Rethmeier, C.; Retiere, F.; Rodriguez-Garcia, I.; Roszkowski, L.; Ruhland, J. B.; Sanchez-Garcia, E.; Santorelli, R.; Sinclair, D.; Skensved, P.; Smith, B.; Smith, N. J. T.; Sonley, T.; Soukup, J.; Stainforth, R.; Stone, C.; Strickland, V.; Stringer, M.; Sur, B.; Tang, J.; Vazquez-Jauregui, E.; Viel, S.; Walding, J.; Waqar, M.; Ward, M.; Westerdale, S.; Willis, J.; Zuniga-Reyes, A.

doi:10.1140/epjc/s10052-021-09514-w

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 39Ar 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.

Pulse-shape discrimination against low-energy Ar-39 beta decays in liquid argon with 4.5 tonne-years of DEAP-3600 data / Adhikari, P., Ajaj, R., Alpizar-Venegas, M., Amaudruz, P.-A., Auty, D.J., Batygov, M., Beltran, B., Benmansour, H., Bina, C.E., Bonatt, J., Bonivento, W., Boulay, M.G., Broerman, B., Bueno, J.F., Burghardt, P.M., Butcher, A., Cadeddu, M., Cai, B., Cardenas-Montes, M., Cavuoti, S., et al.. - In: THE EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS. - ISSN 1434-6044. - 81:9(2021), p. 823. [10.1140/epjc/s10052-021-09514-w]