In this era of precision cosmology, measurements suggest that ordinary matter represents only a fraction of the total matter density in the Universe. The rest, whose effect we can only see gravitationally, appears to be dark. Particle physics models suggest that dark matter is composed of relic weakly interacting massive particles (WIMPs) left over from the Big Bang. Efforts to directly detect WIMPs are hampered by small interaction probabilities and large backgrounds that mimic expected dark matter signals. Fortunately, a number of unique dark matter signatures exist that can be used to discriminate against backgrounds and decisively identify WIMP interactions. The largest and most robust of these signatures, based on the predicted behavior of the WIMP flux as the Sun-Earth system moves through the galaxy, is a day-night modulation of nuclear recoil directions in the lab frame. The intellectual merit of this proposal resides in the Directional Recoil Identification From Tracks (DRIFT) Experiment's unique and powerful capabilities being brought to bear on one of the most important questions in science today.
This award provides funds to support this group and to provide the funds for fiducializing DRIFT and retrofitting the present DRIFT detector in the Boulby (U.K.) Mine with such a system.
Broader impacts of this work include the training of students (including under-represented minorities) in increasingly rare small-scale experiments, giving them exposure to a wide range of hardware and software experience. The UNM DRIFT group has demonstrated this capability with previous NSF funding. The DRIFT detector technology has promising applications to axion searches, Homeland Security and double-beta decay experiments.
Intellectual merit In this era of precision cosmology, measurements suggest that ordinary matter (protons and neutrons) represents only a fraction of the total matter density in the Universe. The rest, whose effect we can only see gravitationally, appears to be dark. Particle physics models suggest that dark matter is composed of relic weakly interacting massive particles (WIMPs) left over from the Big Bang. Efforts to directly detect WIMPs are hampered by small interaction probabilities and large backgrounds that mimic expected dark matter signals. Fortunately, a number of unique dark matter signatures exist that can be used to discriminate against backgrounds and decisively identify WIMP interactions. The largest and most robust of these signatures, based on the predicted behavior of the WIMP flux as the Sun-Earth system moves through the galaxy, is a day-night modulation of nuclear recoil directions in the lab frame. Of current experimental searches for dark matter, the Directional Recoil Identification From Tracks (DRIFT) project has the longest running detectors underground and the best limits on dark matter interaction rates. The intellectual merit of this proposal resides in DRIFT’s unique and powerful capabilities being brought to bear on one of the most important questions in science today. The DRIFT experiment is a multi-institution US (CSU, Occidental and UNM), UK (Boulby, Edinburgh and Sheffield) collaboration with the experiment housed in the UK at a depth of about 1 km in the Boulby Mine. During this grant period we made progress in a number of areas. As a collaboration we set limits on spin dependent dark matter interaction cross sections with protons that are better by a factor ~2000 over other directional dark matter experiments, and that are competitive with the best limits set by non-directional experiments. At UNM we focused largely on developing and implementing technologies to reduce or eliminate backgrounds in our detector that mimic the signals from dark matter. We incorporated one of these techniques in our underground detector and the collaboration undertook a new dark matter search that last several months. Data from this search demonstrated that the background reduction succeeded: we saw a factor ~20 reduction in our main background, which comes from radon in our detector. We continued working on ideas to improve our radon related background suppression with the goal of entirely eliminating it. Because the radon related backgrounds originate at the inner surfaces of our detector, the "holy grail" for identifying and eliminating this type of background is having the ability to localize events in our detector. At UNM we developed a new technique to do this and successfully demonstrated event localization with a small prototype detector. We are continuing to study and optimize this technique with the hope of applying it to the large DRIFT-II detectors. Broader impacts Broader impacts of this work included the training of undergraduate and graduate students (including underrepresented minorities) in increasingly rare small-scale experiments, giving them exposure to a wide range of hardware and software experience. At UNM we also continued our program (funded with an NSF CAREER) of Outreach with a number of workshops for K-12 teachers. In addition, the PI gave numerous public lectures in modern cosmology and astronomy in venues where the audiences ranged from elementary school students to senior citizens, as well as several seminars and colloquia at colleges, universities and national laboratories. Finally, the DRIFT detector technology has promising applications to double-beta decay experiments, KK Axion searches and tracking at the Next Linear Collider.
