The existence of dark matter is known from gravitational effects, but its nature remains a deep mystery. One possibility motivated by other considerations in elementary particle physics is that dark matter consists of undiscovered elementary particles. Axions and Weakly Interacting Massive Particles (WIMPs) are two possibilities. The thermal motion of the WIMPS comprising the dark matter halo surrounding the galaxy and the earth should result in WIMP-nuclear collisions of sufficient energy to be observable by sensitive laboratory apparatus.
This award is to develop and deploy a small liquid argon detector that has high sensitivity for direct detection of WIMP collisions. This detector, DarkSide-50, builds on past experience and introduces innovative features that will allow it to operate in a background-free mode and thereby achieve a significant science result in spite of its relatively small size. At the same time, this detector will serve as a prototype for a future multi-ton detector. The main innovations being introduced: - Underground argon depleted in radioactive 39Ar; - Low background, high-quantum-efficiency QUPID photo-detectors; and - A compact high-efficiency external veto for neutrons. These innovations, together with the powerful two-parameter background rejection features of argon will result in a detector of unprecedented background-free performance. DarkSide-50 will either detect WIMP dark matter or exclude a substantial fraction of the favored parameter space. DarkSide-50 will benefit from the facility for extraction and refinement of depleted argon, independently funded by the NSF through a grant to Princeton University.
Broader Impacts: this activity will advance the development of astroparticle physics and its scientific and educational mission in a variety of ways: (1) it will offer an excellent opportunity for the training of students, who will have a chance to contribute to the success of a cutting edge project in fundamental science and advanced engineering; (2) it will benefit society by developing techniques that could find application in areas ranging from national security to medical imaging; (3) it will support continued development of successful E&O programs such as the Princeton-Abruzzo-South Dakota summer school for high school students.
The DarkSide program has sucessfully demostrated the operation of a low background dual phase time projection chamber for the use in a direct dark matter search. The UCLA group successfully delivered major components for the HHV and cryogenic systems, and succesffuly commissioned and operated the subsystem with stunning stability. This enabled the detector to run over a long period of time without an y background events making their way past the final analysis cuts. Members of the UCLA group also played a role in the commissioning of the veto detector and calibration of the dector systems. Using the FNAL's art framework for rare event searches as the basis of the analysis framework, the UCLA group has played the leading role in the further development and maintainance of the code. The group also played lead roles in many aspects of the DarkSide data analysis, and have made significant contributions to the understanding of the working detector. Finally, the group at UCLA continues to work on many imprtant R&D projects, all pushing to advance the liquid noble detector technology and it application in the field of physics and beyond. First results from the DarkSide-50 detector have shown the advantages of using liquid argon TPCs for the use in rare event searches, and strongly supports the continued advancement and use of these types of detectors in future experiments.
