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Dark Matter: Results and Further Planning

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).


Comments on this entry are closed.

  • kurt9 November 4, 2009, 17:24

    My understanding is that “dark matter” is needed in order to explain why galaxies rotate the way that they do. Is this true? If so, can someone remind me why this dark matter has to be something exotic like WIMPs and not more mundane stuff like dust to asteroid-sized objects?

    Also, its my understanding that “dark energy” is necessary in order to make the Big Bang Theory fit certain astronomical observations that appear to be inconsistent with it. Is this correct? If dark energy is real, could it be a manifestation of zero-point energy?

  • Bounty November 4, 2009, 19:15

    I’m not sure I understand the potential link between WIMPs and dark matter. What exactly is the prediction here? I’d guess that a weakly interacting particle wouldn’t be thrown around like regularly interacting particles, so wouldnt’ that change the shape of objects? Basically if I picture the big bang (or other explosions) and everything else, with 2 types of mass…. both with gravity, but can pass through and not effect each other much. Shouldn’t we be able to see gravity drag by the WIMPs?

  • Ron S November 4, 2009, 22:02
  • Adam November 5, 2009, 2:22

    Hi Guys

    “Dark matter” is inferred by the non-Keplerian orbits of galaxies and the odd mass distributions of larger scale objects like galactic clusters, as evidenced by bound clouds of x-ray emitting plasma and gravitational-lens images of other galaxies behind the clusters. It isn’t regular, but dark, matter because it doesn’t absorb light like non-visible matter (e.g. dust, gas) does and doesn’t produce enough micro-lensing events to be in star-sized clumps (i.e. white-dwarfs, red-dwarfs, brown dwarfs etc.)

    So the options are either really small non-electrical particles, like neutrinos, or really heavy non-electrical particles like WIMPs. Galaxy formation simulations indicate that not much can be neutrinos because most of the “Dark Matter” has to be “cold” (i.e. slow-moving) and neutrinos are too quick. Thus a preference for WIMPs.

    Another option is “shadow matter” which is the equivalent of regular matter, but it has a different weak-force chirality. Such “shadow matter” might interact very slightly with regular matter by a leakage between the two kinds of electromagnetism, but otherwise is invisible. There’s a few lines of evidence that “dark matter” might be “shadow matter”, but it’s not a popular option because supersymmetric particles physics theories predict a number of WIMP-type particles and these are considered the best options at present.

    As for “dark energy” it might be an Einsteinian “cosmological constant” – the repulsive energy of space-time itself. It might instead be several different fields that different physics theories predict. Currently there’s not enough data and too many options to say. All the current observational data is consistent with a cosmological constant ala Einstein.

  • spaceman November 5, 2009, 16:33

    Astronomical observations suggest its existence, particle physics theories provide natural candidates for it independent of astronomy– so it sort of surprises me that with all of the effort being put into finding dark matter, no definitive evidence has been uncovered. But maybe I am just being impatient.

  • James M. Essig November 5, 2009, 19:04

    Hi Folks;

    I have just recently started wondering if some of the dark matter might be stable bosonic massive particles comprised of quarks of just the right flavor combinations and relative flavor contributions so that the bosons would be electrically neutral.

    Exotic forms of quark matter have been proposed in the form of stable strangelets and even quark nuggets which might have a density ~ 10 EXP 21 kilograms per cubic meter.

    Perhaps based on any unknown characteristics of the weak force, strong nuclear force, or the electroweak unification, exotic bosons as such might very rarely interact with ordinary baryoic/fermionic matter such as atomic nuclei and electrons.

    I am keeping my fingers crossed regarding the start up of the LHC, the evential operaton of the FRIB within the U.S., the planned 1 – 2 TeV range electron positron LINAC, and even the eventual upgrade of the LHC to a collision energy around 40 TeV for protons. An LHC upgrade has already been a topic of study, but such an upgrade would not likely begin for another decade. Perhaps any of these bad boys will produce SUSY particles, WIMPs, and the like so that we can measure these particles.

  • kurt9 November 6, 2009, 12:50

    Thanks guys. I get it about the dark matter. But I still don’t get it about the dark energy. I’ll have to look this up on my own.

  • ljk November 6, 2009, 13:48

    Is the Higgs boson now sending messages to contemporary birds from the future to stop the LHC?


  • kurt9 November 6, 2009, 15:50

    Doesn’t the MOND theory of gravity provide an explanation for galactic rotation that does not require dark matter?