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 argon-based 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 39Ar 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 39Ar 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 39Ar than atmospheric argon was an important step in the development of direct dark matter detection experiments using argon as the active target. Thanks to pioneering research and to successful R&D, in 2012 a first 160 kg batch of underground argon (UAr) was extracted from a CO2 well in Cortez, Colorado. The DarkSide-50 experiment at Gran Sasso National Laboratory (LNGS) in Italy, the first liquid argon detector ever operated with an UAr target, demonstrated a ~ 1400 suppression of the 39Ar activity with respect to the atmospheric argon. A even larger suppression is expected for 42Ar (another intrinsic beta emitter with 42K daughter isotope, also beta emitter), as its production is expected mainly in the upper atmosphere.. Following DarkSide-50's results the GADMC initiated the UAr Project for extraction from underground and cryogenic purification of 100 t of argon to be used as target in the next generation experiment, DarkSide-20k. This paper contains a description of the Urania plant in Cortez, Colorado, where the UAr is extracted; of the Aria plant in Sardinia, Italy, an industrial scale plant comprising a 350 m state-of-the-art cryogenic isotopic distillation column, designed for further purification of the extracted argon and further reduction of the isotopic abundance of 39Ar; and DArT, a facility for UAr radiopurity qualification at Canfranc Underground Laboratory (LSC), Spain. Moreover the high radiopurity of UAr leads to other possible applications, for instance for those neutrinoless double beta decay experiments using argon as shielding material or, more generally, for all those activities on argon-based detectors in high-energy physics or nuclear physics, which will be briefly discussed.
The underground argon project: procurement and purification of argon for dark matter searches and beyond
Agnes, P.;Caravati, M.
;Galbiati, C.;Horikawa, S.;
2024-01-01
Abstract
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 argon-based 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 39Ar 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 39Ar 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 39Ar than atmospheric argon was an important step in the development of direct dark matter detection experiments using argon as the active target. Thanks to pioneering research and to successful R&D, in 2012 a first 160 kg batch of underground argon (UAr) was extracted from a CO2 well in Cortez, Colorado. The DarkSide-50 experiment at Gran Sasso National Laboratory (LNGS) in Italy, the first liquid argon detector ever operated with an UAr target, demonstrated a ~ 1400 suppression of the 39Ar activity with respect to the atmospheric argon. A even larger suppression is expected for 42Ar (another intrinsic beta emitter with 42K daughter isotope, also beta emitter), as its production is expected mainly in the upper atmosphere.. Following DarkSide-50's results the GADMC initiated the UAr Project for extraction from underground and cryogenic purification of 100 t of argon to be used as target in the next generation experiment, DarkSide-20k. This paper contains a description of the Urania plant in Cortez, Colorado, where the UAr is extracted; of the Aria plant in Sardinia, Italy, an industrial scale plant comprising a 350 m state-of-the-art cryogenic isotopic distillation column, designed for further purification of the extracted argon and further reduction of the isotopic abundance of 39Ar; and DArT, a facility for UAr radiopurity qualification at Canfranc Underground Laboratory (LSC), Spain. Moreover the high radiopurity of UAr leads to other possible applications, for instance for those neutrinoless double beta decay experiments using argon as shielding material or, more generally, for all those activities on argon-based detectors in high-energy physics or nuclear physics, which will be briefly discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
