DOI: 10.1140/epjc/s10052-025-14289-5 ISSN: 1434-6052

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

P. Adhikari, R. Ajaj, M. Alpízar-Venegas, P.-A. Amaudruz, J. Anstey, D. J. Auty, M. Batygov, B. Beltran, M. A. Bigentini, C. E. Bina, W. M. Bonivento, M. G. Boulay, J. F. Bueno, M. Cadeddu, B. Cai, M. Cárdenas-Montes, S. Cavuoti, Y. Chen, S. Choudhary, B. T. Cleveland, R. Crampton, S. Daugherty, P. DelGobbo, P. Di Stefano, G. Dolganov, L. Doria, F. A. Duncan, M. Dunford, E. Ellingwood, A. Erlandson, S. S. Farahani, N. Fatemighomi, G. Fiorillo, R. J. Ford, D. Gahan, D. Gallacher, A. Garai, P. García Abia, S. Garg, P. Giampa, A. Giménez-Alcázar, D. Goeldi, V. V. Golovko, P. Gorel, K. Graham, A. Grobov, A. L. Hallin, M. Hamstra, S. Haskins, J. Hu, J. Hucker, T. Hugues, A. Ilyasov, B. Jigmeddorj, C. J. Jillings, A. Joy, G. Kaur, A. Kemp, M. Khoshraftar Yazdi, M. Kuźniak, F. La Zia, M. Lai, S. Langrock, B. Lehnert, J. LePage-Bourbonnais, N. Levashko, M. Lissia, L. Luzzi, I. Machulin, A. Maru, J. Mason, A. B. McDonald, T. McElroy, J. B. McLaughlin, C. Mielnichuk, L. Mirasola, A. Moharana, J. Monroe, A. Murray, C. Ng, G. Oliviéro, M. Olszewski, S. Pal, D. Papi, B. Park, M. Perry, V. Pesudo, T. R. Pollmann, F. Rad, C. Rethmeier, F. Retière, I. Rodríguez García, L. Roszkowski, R. Santorelli, F. G. Schuckman II, S. Seth, V. Shalamova, P. Skensved, T. Smirnova, K. Sobotkiewich, T. Sonley, J. Sosiak, J. Soukup, R. Stainforth, M. Stringer, J. Tang, R. Turcotte-Tardif, E. Vázquez-Jáuregui, S. Viel, B. Vyas, M. Walczak, J. Walding, M. Ward, S. Westerdale, R. Wormington, A. Zuñiga-Reyes,
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Abstract

The half-life of

$$^{39}$$ 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
$$^{39}$$ 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
$$^{39}$$ 39
Ar decays. Observing over a period of 3.4 years, the
$$^{39}$$ 39
Ar half-life is measured to be
$$(302 \pm 8_\textrm{stat} \pm 6_\textrm{sys})$$ ( 302 ± 8 stat ± 6 sys )
years. This new direct measurement suggests that the half-life of
$$^{39}$$ 39
Ar is significantly longer than the accepted value, with potential implications for measurements using this isotope’s half-life as input.

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