In this era of precision cosmology, measurements suggest that ordinary matter (protons and neutrons) makes up a mere 15% of the total matter density in the Universe. The rest, whose effect we can only see gravitationally, appears to be dark. The goal of detecting and identifying dark matter is widely recognized as one of the most important problems in 21st century cosmology. Current particle physics models suggest that dark matter might be 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 which mimic expected dark matter signals. Fortunately, a number of unique dark matter signatures exist which, if exploited, can be used to discriminate against backgrounds. These are based on the predicted behavior of the WIMP flux as the Sun-Earth system moves through the galaxy. The largest and most robust of these signatures is a day-night modulation of nuclear recoil directions in the lab frame. Of current experimental searches for dark matter only one, Directional Recoil Identification From Tracks (DRIFT), is equipped to detect this directionality signature.
The main subject of this proposal is to experimentally study novel detectors for future directionally sensitive dark matter detectors. These studies will focus on improving DRIFT's sensitivity for measuring directionality by taking full advantage of the directional signature from halo WIMPs while maintaining DRIFT's good background rejection capabilities, intrinsic low-maintainability, and low cost per unit mass. The goals of this research are to quantify the advantages and disadvantages of the new technologies by measuring their performance in the laboratory, and to assess the feasibility of employing these new technologies in future, large mass directional dark matter experiments.
Broader impacts of this work include the training of undergraduate and graduate students (including underrepresented minorities). Additionally, a targeted Outreach Program for the professional development of middle- and high-school teachers will be developed. As part of this program, each year a 1-day workshop will be offered, followed by a 2-week intensive course, with graduate credit towards a M.A. in Education, for teachers across New Mexico. This will take place in collaboration with and support from the Lodestar Astronomy Center and the Science Education Institute of the Southwest.
Intellectual merit In this era of precision cosmology, we now know the age of the Universe, the geometry of space, its total energy density and contributions to it from various types of matter and energy. Measurements suggest that ordinary matter (protons and neutrons) is a mere 15% of the total mass density in the Universe. The rest, whose effect we can only see gravitationally, appears to be dark. The goal of detecting and identifying dark matter is widely recognized as the most important problem in 21st century cosmology. Current particle physics models suggest that dark matter might be 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 which mimic expected dark matter signals. Fortunately, a number of unique dark matter signatures exist which, if exploited, can be used to discriminate against backgrounds. These are based on the predicted behavior of the WIMP flux as the Sun-Earth system moves through the galaxy. The largest and most robust of these signatures is a day-night modulation of nuclear recoil directions in the lab frame. Although there are many clever technologies being employed to discriminate backgrounds from potential dark matter signals, many astrophysicists still consider directionality to be necessary for proof of the discovery of dark matter. There are now several experiments that have developed techniques and deployed experiments to detect this directionality signature. Of these searches the Directional Recoil Identification From Tracks (DRIFT, on which the PI is a collaborator) has operated underground the longest and has the best spin dependent limit on WIMPs on protons. The main research goals of this proposal were two-fold. The first was to study the fundamental properties of low energy nuclear (the signal) and electronic (the background) recoils to assist in designing optimal directional detectors. The second was to study novel detector readouts, such as GEMs (Gas Electron Multipliers), that have excellent tracking resolution and signal-to-noise. Both of these qualities are desired from the perspective of detecting the small, feeble signals expected from dark matter all the while distinguishing them from the copious signals from the pernicious radioactivity backgrounds. It was hoped that the outcome of this work would feedback into the design of better, more optimal future directional detectors. Our results indicate that both the good spatial resolution and high signal-to-noise achieved with appropriate novel detectors (e.g. GEMs) are indeed crucial in improving the sensitivity of directional detectors. Our test detector was used to show that large improvements in sensitivity to the dark matter signals could be achieved with high signal-to-noise and high spatial resolution readouts. Such readouts enable clear identification of the gamma- and beta-induced backgrounds (i.e., the electronic recoils), thereby demonstrating that directional dark matter detectors could employ lower energy thresholds than current experiments employ. The same high-resolution, high-signal-to-noise readouts also maintain the good directional sensitivity that is an essential requirement. Broader impacts During the period of this grant we performed 3 weeklong summer K-12 teacher workshops which were held at UNM and in the field at various sites in dark-sky regions of New Mexico. These workshops had classroom components where the PI gave lectures in modern cosmology, focusing on modern problems such as dark matter and dark energy. In the field component we demonstrated the use of simple Dobsonian telescopes over a period of 2-3 nights in very dark sky locations. The goal here was to teach the participants how to use the telescopes to find objects in the sky such as double stars, nebula, and galaxies, i.e., concrete materials for them to take back to their schools to seed astronomy clubs and other field based activities. During the same period, the PI also gave several public lectures on cosmology, dark matter and dark energy to a wide range of audiences ranging from elementary school students to senior citizens, as well as several seminars and colloquia at colleges, universities and national laboratories. On the technical side, our studies with the new technologies could have applications in other fields such as medical imaging, homeland defense and other rare searches.
