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 a new gas system to run with CS2-CF4 mixtures and the R&D for fiducializing DRIFT and retrofitting the present DRIFT detector with such a system.
The Broader impacts of this work include the training of undergraduates in increasingly rare small-scale experiments, giving them exposure to a wide range of hardware and software experience. Finally, 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. Occidental college took primary responsibility for limits mentioned above. An automated gas-mixture system was needed to set these limits, to add a spin-dependent target nucleus. That system was designed and assembled at our lab here in Los Angeles. We also maintain a duplicated DRIFT detector in our lab and that detector was used to calibrate the gas mixture. Occidental College also took primary responsibility for the analysis of the data which eventually set the aforementioned limits. The primary challenge there was to figure out a way to separate the signal from the noise. Using knowledge of the physics of the detector allowed us to separate the prevalent background from our central cathode from the expected signal in the detector volume. Finally in order to set limits one must be able to predict what a dark matter signal would look like. We accomplished this by using a neutron source, which produces recoils very much like those predicted to be produced by WIMPs, calibrating a simulation off of it and then extrapolating to the predicted WIMP response. Finally Occidental College took on the responsibility of writing up the final paper. In the summer of 2011 a team of 5 students, the PI and his research assistant undertook the task of building a set of new DRIFT detectors called DRIFT-IIe detectors. By the end of the summer 6 were made and those will be deployed this summer in the Boulby Underground Facility. Broader impacts The primary impact of this research, outside of the research, is on undergraduates. Occidental College is solely an undergraduate college; we do not have a graduate program. Students interested in physics, though, have the opportunity to get involved in cutting-edge research at the forefront of physics. Over the course of this proposal 9 different undergraduates were hired to work on this project. Some of them for 3 summers in a row. One student wrote code which has now been widely adapted by the collaboration. 5 of them, one summer, built 6 new DRIFT detectors. The PI has given a number of seminars about dark matter and DRIFT to a wide range of audiences. Finally, the DRIFT detector technology has promising applications to double-beta decay experiments, KK Axion searches and tracking at the Next Linear Collider.
