This award provides funds for this Yale University group to contribute to the LUX-350 dark matter experiment. LUX-350 promises substantially improved sensitivity to the existence of Weakly Interacting Massive Particles (WIMPs), a theoretically attractive explanation for the nature of the missing dark matter. LUX-350 is a two-phase (liquid/gas) xenon experiment, with a total liquid xenon (LXe) mass of 350 kg and a fiducial mass of 100 kg. The LUX-350 detector exploits a number of features of LXe to drive backgrounds down. The active detector volume permits the full reconstruction of event energy deposition and position. Crucially, the background rate is heavily suppressed in the fiducial volume due to the active shielding by the surrounding LXe, and decreases with increasing LXe mass. Integration of LUX-350 will take place at a newly renovated surface facility at SUSEL, the Sanford Underground Science and Engineering Laboratory at Homestake before moving underground.
On LUX-350, Yale is responsible for the xenon purification system, the 100 kV cathode high voltage system, slow control electronics, and radioactive source manipulators for detector calibration. The group has also developed a method of calibrating LXe detectors using Kr-83 atoms dissolved in the LXe, and performed a new measurement of the scintillation efficiency and charge yield for nuclear recoils in LXe.
Broader Impact: Development of technology related to LXe will find use in the increasing number of experiments worldwide using noble liquids as detection materials. These projects will also result in technical training in radiation detection, cryogenics, and gas purification for graduate and undergraduate students. LXe has practical applications to gamma ray imaging for astrophysics, Homeland Security, and medical imaging, as well as for fast neutron detection.
This award supported the McKinsey research group at Yale University for contributions to the Large Underground Xenon (LUX) dark matter experiment, which is located a mile underground at the Sanford Underground Research facility in Lead, South Dakota. LUX provides substantially improved sensitivity to weakly interacting massive particles (WIMPs), a theoretically attractive explanation for the nature of the missing dark matter. In the long term, the technology represented by LUX holds great promise for enabling multi-tonne detectors with even better sensitivity to WIMPs. In October 2013, the LUX collaboration announced dark matter results that exceeded the sensitivity of all other direct dark matter searches, worldwide. LUX uses a two-phase (liquid/gas) xenon technology, and has a fiducial mass of about 100 kg. The LUX detector exploits a number of features of LXe to drive down backgrounds. The active detector volume permits the full reconstruction of event energy deposition and position. An inner fiducial volume can be established with < 1 cm uncertainty in position determination. Crucially, the neutron and gamma ray background event rate is heavily suppressed in the fiducial volume due to the active shielding by the surrounding LXe, and the background rate decreases with increasing LXe mass. Based on event charge to light ratio, the electron recoil vs. nuclear recoil discrimination in LUX is measured to be 99.6%. The fiducial volume and electron recoil discrimination cuts work in concert to provide an extraordinarily low background rate. In 2008, project funds for LUX were awarded by the NSF and DOE High Energy Physics, and LUX detector subsystems were constructed at the various collaborating institutions. In late 2011 and early 2012, LUX was successfully operated at a newly renovated surface facility at SURF, the Sanford Underground Research Facility in Lead, South Dakota. Meanwhile, the Davis Cavern at the 4850 ft. level of SURF was outfitted with the necessary shielding, clean room, and other infrastructure for low-background operation. In Summer 2012, immediately following laboratory beneficial occupancy, underground installation of LUX began. Beginning in January 2013, the LUX detector was operated within its water shielding. The LUX detector will continue to be operated through 2015, and is expected to gain another factor of 3 to 5 in sensitivity beyond the results announced in October 2013. On LUX, Yale is responsible for several crucial subsystems, including the xenon purification and gas handling system, the 100 kV cathode high voltage delivery system, the xenon recovery system, and radioactive sources and source manipulators for detector calibration. The Yale group has also developed a method of calibrating LXe detectors using metastable Kr atoms dissolved in the LXe, and has performed a new measurement of the scintillation efficiency and charge yield for nuclear recoils in LXe. The Yale group is highly engaged in LUX data processing and analysis. Dan McKinsey is Co-Spokesperson of LUX. The first scientific results paper was chaired by Dr. Blair Edwards, a postdoctoral associate at Yale, who also served as LUX Analysis Coordinator during the first LUX dark matter search. Development of technology related to LXe will find use in the increasing number of experiments worldwide using noble liquids as detection materials. These projects also result in technical training in radiation detection, cryogenics, and gas purification for graduate and undergraduate students. LXe has practical applications to gamma ray imaging for astrophysics, Homeland Security, and medical imaging.
