Eur. Phys. J. C (2025) 85: 728
https://doi.org/10.1140/epjc/s10052-025-14289-5

Regular Article - Experimental Physics

Direct measurement of the $_{}^{39}$Ar half-life from 3.4 years of data with the DEAP-3600 detector

¹ Department of Physics, University of Alberta, T6G 2R3, Edmonton, AB, Canada
² AstroCeNT, Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Rektorska 4, 00-614, Warsaw, Poland
³ Physics Department, Università degli Studi di Cagliari, 09042, Cagliari, Italy
⁴ Canadian Nuclear Laboratories, K0J 1J0, Chalk River, ON, Canada
⁵ Department of Physics and Astronomy, University of California, 92521, Riverside, CA, USA
⁶ Department of Physics, Carleton University, K1S 5B6, Ottawa, ON, Canada
⁷ Centro de Investigaciones Energénticas, Medioambientales y Tecnológicas, 28040, Madrid, Spain
⁸ Physics Department, Università degli Studi “Federico II” di Napoli, 80126, Napoli, Italy
⁹ INFN Cagliari, 09042, Cagliari, Italy
¹⁰ INFN Napoli, 80126, Napoli, Italy
¹¹ School of Natural Sciences, Laurentian University, P3E 2C6, Sudbury, ON, Canada
¹² Nuclear Science Division, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
¹³ Instituto de Física, Universidad Nacional Autónoma de México, A. P. 20-364, 01000, Ciudad de Mexico, Mexico
¹⁴ BP2, National Centre for Nuclear Research, ul. Pasteura 7, 02-093, Warsaw, Poland
¹⁵ National Research Centre Kurchatov Institute, 123182, Moscow, Russia
¹⁶ National Research Nuclear University MEPhI, 115409, Moscow, Russia
¹⁷ PRISMA+ Cluster of Excellence, Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, 55128, Mainz, Germany
¹⁸ Department of Physics, Engineering Physics and Astronomy, Queen’s University, K7L 3N6, Kingston, ON, Canada
¹⁹ Royal Holloway University London, Egham Hill, TW20 0EX, Egham, Surrey, UK
²⁰ SNOLAB, P3Y 1M3, Lively, ON, Canada
²¹ TRIUMF, V6T 2A3, Vancouver, BC, Canada
²² Department of Physics, Technische Universität München, 80333, Munich, Germany
²³ Arthur B. McDonald Canadian Astroparticle Physics Research Institute, Queen’s University, K7L 3N6, Kingston, ON, Canada
²⁴ Astronomical Observatory of Capodimonte, Salita Moiariello 16, I-80131, Napoli, Italy
²⁵ University of Oxford, OX1 3PU, Oxford, UK
²⁶ University of Amsterdam, Science Park, 1098XG, Amsterdam, Netherlands

^a deap-papers@snolab.ca

Received: 22 January 2025
Accepted: 7 May 2025
Published online: 2 July 2025

Abstract

The half-life of $_{}^{39}$Ar is measured using the DEAP-3600 detector located 2 km underground at SNOLAB. Between 2016 and 2020, DEAP-3600 used a target mass of (3269 ± 24) kg of liquid argon distilled from the atmosphere in a direct-detection dark matter search. Such an argon mass also enables direct measurements of argon isotope properties. The decay of $_{}^{39}$Ar in DEAP-3600 is the dominant source of triggers by two orders of magnitude, ensuring high statistics and making DEAP-3600 well-suited for measuring this isotope’s half-life. Use of the pulse-shape discrimination technique in DEAP-3600 allows powerful discrimination between nuclear recoils and electron recoils, resulting in the selection of a clean sample of $_{}^{39}$Ar decays. Observing over a period of 3.4 years, the $_{}^{39}$Ar half-life is measured to be $(302\pm 8_{\text{stat}}\pm 6_{\text{sys}})$ years. This new direct measurement suggests that the half-life of $_{}^{39}$Ar is significantly longer than the accepted value, with potential implications for measurements using this isotope’s half-life as input.