Eur. Phys. J. C (2020) 80: 303
https://doi.org/10.1140/epjc/s10052-020-7789-x

Regular Article - Experimental Physics

The liquid-argon scintillation pulseshape in DEAP-3600

¹ Department of Physics, University of Alberta, Edmonton, AB, T6G 2R3, Canada
² AstroCeNT, Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, Rektorska 4, 00-614, Warsaw, Poland
³ Canadian Nuclear Laboratories Ltd, Chalk River, ON, K0J 1J0, Canada
⁴ Department of Physics, Carleton University, Ottawa, ON, K1S 5B6, Canada
⁵ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, 28040, Madrid, Spain
⁶ Physics Department, Università degli Studi “Federico II” di Napoli, 80126, Napoli, Italy
⁷ INFN Napoli, 80126, Napoli, Italy
⁸ INFN Laboratori Nazionali del Gran Sasso, 67100, Assergi, AQ, Italy
⁹ Department of Physics and Astronomy, Laurentian University, Sudbury, ON, P3E 2C6, Canada
¹⁰ Instituto de Física, Universidad Nacional Autónoma de México, A. P. 20-364, Mexico, D. F. 01000, Mexico
¹¹ National Research Centre Kurchatov Institute, Moscow, 123182, Russia
¹² National Research Nuclear University MEPhI, Moscow, 115409, Russia
¹³ PRISMA Cluster of Excellence and Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, 55128, Mainz, Germany
¹⁴ Physics Department, Princeton University, Princeton, NJ, 08544, USA
¹⁵ Department of Physics, Engineering Physics, and Astronomy, Queen’s University, Kingston, ON, K7L 3N6, Canada
¹⁶ Royal Holloway University London, Egham Hill, Egham, Sy, TW20 0EX, UK
¹⁷ Rutherford Appleton Laboratory, Harwell Oxford, Didcot, OX11 0QX, UK
¹⁸ SNOLAB, Lively, ON, P3Y 1N2, Canada
¹⁹ University of Sussex, Sussex House, Brighton, ES, BN1 9RH, UK
²⁰ TRIUMF, Vancouver, BC, V6T 2A3, Canada
²¹ Department of Physics, E15, Technische Universität München, 85748, Garching, Germany

^* e-mail: deap-papers@snolab.ca

Received: 20 January 2020
Accepted: 27 February 2020
Published online: 4 April 2020

Abstract

DEAP-3600 is a liquid-argon scintillation detector looking for dark matter. Scintillation events in the liquid argon (LAr) are registered by 255 photomultiplier tubes (PMTs), and pulseshape discrimination (PSD) is used to suppress electromagnetic background events. The excellent PSD performance of LAr makes it a viable target for dark matter searches, and the LAr scintillation pulseshape discussed here is the basis of PSD. The observed pulseshape is a combination of LAr scintillation physics with detector effects. We present a model for the pulseshape of electromagnetic background events in the energy region of interest for dark matter searches. The model is composed of (a) LAr scintillation physics, including the so-called intermediate component, (b) the time response of the TPB wavelength shifter, including delayed TPB emission at (ms) time-scales, and c) PMT response. TPB is the wavelength shifter of choice in most LAr detectors. We find that approximately 10% of the intensity of the wavelength-shifted light is in a long-lived state of TPB. This causes light from an event to spill into subsequent events to an extent not usually accounted for in the design and data analysis of LAr-based detectors.