If you’re going to snare dark matter, you’d better have incredibly accurate detectors. So the thinking goes at Case Western Reserve, where researchers are planning the most sensitive experiment yet to go after WIMPs (weakly interacting massive particles). WIMPs are almost impossible to detect because they don’t give off radiation and pass through normal matter unimpeded. The CWRU group has received a three year $3.2 million National Science Foundation grant to design a new WIMP detector.
The existence of dark matter is a theory that received support in 2006 when the collision of two distant galaxies was analyzed in ways that seemed to show the effects of dark matter on a cloud of galactic gas. Dark matter could provide the needed mass that keeps galaxies like the Milky Way from flying apart, but we still need a direct detection. The new experiment is a 20-ton liquid xenon detector called LZD. The Case Western group proposes LZD as an experiment for the Deep Underground Science and Engineering Laboratory planned for the abandoned Homestake Gold Mine, to be established almost a mile beneath Lead, South Dakota.
We’ve tracked earlier dark matter efforts in these pages, systems like the XENON 10 prototype in San Grasso, Italy and the Large Underground Experiment (LUX), which also operates in the former Homestake mine. But LZD would be seventy times larger than LUX and a whopping 2,000 times the size of XENON 10. The press materials on the detector claim it would increase the chance of spotting a WIMP by more than 30,000 times over XENON 10 and 150 times over LUX.
A WIMP colliding with a xenon atom should produce a tiny flash of light that LZD could trace and analyze. The experiment is to be lowered underground next year, where the WIMP investigation can proceed without impediment from the charged particles that continually strike the Earth’s surface in their billions. But LUX and a smaller interim detector called LZS will have to duke it out for funding with technologies that use germanium crystals frozen to nearly absolute zero, or liquid argon detectors. Masahiro Morii (Harvard) likes the xenon approach: “Liquid xenon has a distinct advantage: it’s straight forward to scale up,” Morii said. And, “It’s ahead of the other technologies by 3 to 5 years.”
Related: Measurements of the cosmic microwave background (CMB) using data from the QUaD telescope project near the South Pole provide further support for the standard cosmological model of the universe. That model predicts that dark matter and dark energy make up 95 percent of everything, with the ordinary matter we see and interact with accounting for just five percent. The measurements zeroed in on variations in the CMB’s temperature and polarization, which offer clues as to how matter in the early universe was distributed.
Creating a map of CMB polarization allows the researchers to investigate how light became polarized when it struck moving matter, pinpointing not only where matter existed but how it was moving. The results strongly match the predictions of temperature and polarization we derive from the standard cosmological model, which includes the existence of dark matter and dark energy.
Says Walter Gear (Cardiff University):
“Studying the CMB radiation has given us extremely precise pictures of the Universe at just 400,000 years old. When we first started working on this project the polarization of the CMB hadn’t even been detected and we thought we might be able to find something wrong with the theory. The fact that these superb data fit the theory so beautifully is in many ways even more amazing. This reinforces the view that researchers are on the right track and need to learn more about the strange nature of dark energy and dark matter if we are to fully understand the workings of the universe.”
The paper on the CMB work is Brown et al., “Improved Measurements of the Temperature and Polarization of the Cosmic Microwave Background from QUaD,” Astrophysical Journal 705 (November, 2009), pp. 978-999 (abstract).