Darkside -astronomical observations have provided strong evidence that the known matter accounts for only a small fraction of the observed total mass-energy of the universe

A leading dark matter candidate is the so-called weakly interacting massive particle, or wimp, a predicted relic particle of the big bang. Direct (non-gravitational) detection of dark matter would be a transformational discovery of fundamental importance broadly to the sciences, opening new investigations of the dark universe. Such first measurements of dark matter may be possible via wimp-nucleus collisions detectable at low-background, low-energy threshold detectors capable of distinguishing a small number of nuclear recoils from wimp collisions over a long exposure period. Liquid argon has been identified to have unique light emission properties that provide excellent sensitivity for such wimp collisions while providing strong background suppression. This award provides support for the fabrication of a next-generation wimp dark matter experiment, darkside-20K. The darkside international collaboration has pioneered the use of liquid argon with high radiopurity to search for rare wimp interactions. The darkside-20K detector, with a designed fiducial exposure volume of approximately 20KT of low-background liquid argon, will operate in the infn laboratori nazionali DEL gran sasso deep underground lab. The US NSF darkside team is supported via this award to build the central dark matter detector liquid argon time-projection chamber, including the associated high-voltage delivery, cryogenic, purification and calibration systems. The awarded activities involve transferable technologies that include: the production of low-radioactivity underground argon for the experiment as well as for nuclear test BAN verification and radiometric dating; studies of underground gas sources; development of low-background, large-area, single-photon cryogenic silicon photomultiplier photosensors; liquid argon-based time-of-flight positron emission tomography system for enhanced cancer screening, and; the world?s tallest cryogenic distillation tower to improve availability of stable rare isotopes for medical and energy applications. Also included are training and education opportunities, including a summer school experience in the cortez-durango region that will offer increased access to underrepresented groups in stem. The US darkside program led the darkside-50 experimental program that demonstrated the viability of background-free searches in liquid argon. The darkside-20K experiment will extend the sensitivity of wimp dark matter searches in the cross-section VS. Mass range to 4.6E-48 CM-squared for the 90% confidence limit exclusion, and to 1.5E-47 CM-squared 5 sigma discovery significance for a 1 TEV/c-squared wimp mass after a 500T-YR exposure. Unique US expertise in the construction of noble liquid detectors is leveraged to ensure the success of this next generation detector. The scale of project, and its resultant sensitivity, exceeds that of detectors currently operating, leading to discovery, confirmation, or exclusion of the wimp dark matter hypothesis to the level where coherent scatters from atmospheric neutrinos become an irreducible background. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the foundation's intellectual merit and broader impacts review criteria.