Commissioning Of The Worlds First Water Cherenkov Neutron Veto And First Wimp Dark Matter Search Results Of The Xenonnt Experiment

Author : H. Nelson
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (316 download)

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Download or read book Deep Underground Science and Engineering Lab written by H. Nelson and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this report we have described the broad and compelling range of astrophysical and cosmological evidence that defines the dark matter problem, and the WIMP hypothesis, which offers a solution rooted in applying fundamental physics to the dynamics of the early universe. The WIMP hypothesis is being vigorously pursued, with a steady march of sensitivity improvements coming both from astrophysical searches and laboratory efforts. The connections between these approaches are profound and will reveal new information from physics at the smallest scales to the origin and workings of the entire universe. Direct searches for WIMP dark matter require sensitive detectors that have immunity to electromagnetic backgrounds, and are located in deep underground laboratories to reduce the flux from fast cosmic-ray-muon-induced neutrons which is a common background to all detection methods. With US leadership in dark matter searches and detector R & D, a new national laboratory will lay the foundation of technical support and facilities for the next generation of scientists and experiments in this field, and act as magnet for international cooperation and continued US leadership. The requirements of depth, space and technical support for the laboratory are fairly generic, regardless of the approach. Current experiments and upgraded versions that run within the next few years will probe cross sections on the 10{sup -45}-10{sup -44} cm{sup 2} scale, where depths of 3000-4000 m.w.e. are sufficient to suppress the neutron background. On the longer term, greater depths on the 5000-6000 level are desirable as cross sections down to 10{sup -46} cm{sup 2} are probed, and of course, if WIMPs are discovered then building up a statistical sample free of neutron backgrounds will be essential to extracting model parameters and providing a robust solution to the dark matter problem. While most of the detector technologies are of comparable physical scale, i.e., the various liquid and solid-state detector media under consideration have comparable density, a notable exception is the low-pressure gaseous detectors. These detectors are very likely to play a critical role in establishing the galactic origin of a signal, and so it is important to design the lab with this capability in mind. For example, for a WIMP-nucleon cross section of 10{sup -43} cm{sup 2} (just below the present limit [20]), 100 of the current DRIFT-II modules of 1 m{sup 3} at 40 torr CS{sub 2} [63] would require a two-year exposure [61] to get the approximately 200 events [64] required to establish the signal's galactic origin. While detector improvements are under investigation, a simple scaling for the bottom of the MSSM region at 10{sup -46} cm{sup 2} would require a 100,000 m{sup 3} detector volume. If a factor of 10 reduction in required volume is achieved (e.g., higher pressure operation, more detailed track reconstruction, etc.) then an experimental hall of (50 m){sup 3} could accommodate the experiment. Because the WIMP-nucleon cross section is unknown, it is impossible to make a definitive statement as to the ultimate requirements for a directional gaseous dark matter detector, or any other device, for that matter. What is clear, however, is that whatever confidence one gives to specific theoretical considerations, the foregoing discussion clearly indicates the high scientific priority of, broad intellectual interest in, and expanding technical capabilities for increasing the ultimate reach of direct searches for WIMP dark matter. Upcoming experiments will advance into the low-mass Supersymmetric region and explore the most favored models in a complementary way to the LHC, and on a similar time scale. The combination of astrophysical searches and accelerator experiments stands to check the consistency of the solution to the dark matter problem and provide powerful constraints on the model parameters. Knowledge of the particle properties from laboratory measurements will help to isolate and reduce the astrophysical uncertainties, which will allow a more complete picture of the galactic halo and could eventually differentiate between, say, infall versus isothermal models of galaxy formation. The scientific landscape of dark matter, which spans particle physics, astrophysics and cosmology, is very rich and interwoven. Exploring this exciting program following an initial detection will need many observables and hence a range of capabilities for followup experiments including different targets to sort out the mass and coupling of the WIMP, and directional sensitivity to confirm its galactic origin and open the age of WIMP astronomy. Clearly, this broad and fascinating program is ideally suited to the multi-decade span of DUSEL.