The Underground Argon Project: procurement and purification of Argon for dark matter searches and beyond Provisionally Accepted

Paolo Agnes¹ Walter Bonivento² Nicola Canci³ Mauro Caravati^1* Susana Cebrian⁴ Valentina Cocco² Daniel Diaz Mairena⁵ Davide Franco⁶ Devidutta Gahan^{2, 7} Cristian Galbiati^{1, 8} Pablo Garcia Abia⁵ Adamo Gendotti⁹ Timotee Hessel⁶ Sosuke Horikawa¹⁰ Rodrigo Lopez Manzano⁵ Ludovico Luzzi⁵ Maria Martinez⁴ Vicente Pesudo⁵ Marco Razeti² Luciano Romero⁵ André Rubbia⁹ Roberto Santorelli⁵ Marino Simeone^{3, 11} Riccardo Stefanizzi^{2, 7} Arianna Steri^{2, 7} Sara Sulis^{2, 12}

• ¹Gran Sasso Science Institute, Italy
• ²National Institute of Nuclear Physics of Cagliari, Italy
• ³National Institute of Nuclear Physics of Naples, Italy
• ⁴Centro de Astropartìculas y Fìsica de Altas Energìas, Universidad de Zaragoza, Spain
• ⁵Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Spain
• ⁶APC, Université de Paris, CNRS, Astroparticule et Cosmologie, France
• ⁷Dipartimento di Fisica, Facoltà di Scienze, Università di Cagliari, Italy
• ⁸Princeton University, United States
• ⁹Institute for Particle Physics and Astrophysics, Department of Physics, ETH Zurich, Switzerland
• ¹⁰Dipartimento di Ingegneria industriale e dell'informazione e di economia, University of L'Aquila, Italy
• ¹¹Chemical, Materials, and Industrial Production Engineering Department, Universit\`a degli Studi ``Federico II'' di Napoli, Italy
• ¹²Department of Electrical and Electronic Engineering, Faculty of Engineering and Architecture, University of Cagliari, Italy

The existence of dark matter in the Universe is inferred from abundant astrophysical and cosmological observations. The Global Argon Dark Matter Collaboration (GADMC) searches for dark matter in the form of weakly interacting massive particles (WIMPs), whose collisions with argon nuclei would produce nuclear recoils with tens of keV energy.Argon has been considered an excellent medium in the direct detection of WIMPs as argonbased scintillation detectors can make use of pulse shape discrimination (PSD) to separate WIMP-induced nuclear recoil signals from electron recoil backgrounds with extremely high efficiency.However, argon-based direct dark matter searches must confront the presence of intrinsic 39 Ar as the predominant source of electron recoil background (it is a beta emitter with an endpoint energy of 565 keV and half-life of 269 years). Even with PSD, the 39 Ar activity in atmospheric argon, mainly produced and maintained by cosmic ray induced nuclear reactions, limits the ultimate size of argon-based detectors and restricts their ability to probe very low energy events.The discovery of argon from deep underground well with significantly less 39 Ar than atmospheric argon was an important step in the development of direct dark matter detection experiments using argon as the active target.