More Hints of Dark Matter

By Sean Carroll | September 5, 2011 7:27 pm

Also known as, “scientific progress goes boink.”

One of the benefits of being a Master of Time and Space is that I get to see the future. For example, cosmologically-inclined folks have been wondering for a few weeks about this press release from the TAUP conference in Munich, which includes the lines “Latest results from the CRESST Experiment provide an indication of dark matter. The press conference will be held on 6. September 2011 starting at 2:00 pm.” Suspense! But I know what they’re going to say.

As Neal Weiner points out, we don’t have to wait for the press conference; the friendly folks at the CRESST experiment have ambitiously decided to write a paper as well as giving a press conference, and that paper appeared on the arxiv this evening. (You remember Neal as a distinguished guest blogger; re-read that post to get your bearings in this complicated game.) Very short version: they claim to see some signal that is statistically significantly greater than background, consistent with a WIMP dark-matter particle with a mass of around 20-40 GeV. Slightly longer version:

Results from 730 kg days of the CRESST-II Dark Matter Search

G. Angloher, M. Bauer, I. Bavykina, A. Bento, C. Bucci, C. Ciemniak, G. Deuter, F. von Feilitzsch, D. Hauff, P. Huff, C. Isaila, J. Jochum, M. Kiefer, M. Kimmerle, J.-C. Lanfranchi, F. Petricca, S. Pfister, W. Potzel, F. Pröbst, F. Reindl, S. Roth, K. Rottler, C. Sailer, K. Schäffner, J. Schmaler, S. Scholl, W. Seidel, M. von Sivers, L. Stodolsky, C. Strandhagen, R. Strauß, A. Tanzke, I. Usherov, S. Wawoczny, M. Willers, A. Zöller

The CRESST-II cryogenic Dark Matter search, aiming at detection of WIMPs via elastic scattering off nuclei in CaWO$_4$ crystals, completed 730 kg days of data taking in 2011. We present the data collected with eight detector modules, each with a two-channel readout; one for a phonon signal and the other for coincidently produced scintillation light. The former provides a precise measure of the energy deposited by an interaction, and the ratio of scintillation light to deposited energy can be used to discriminate different types of interacting particles and thus to distinguish possible signal events from the dominant backgrounds. Sixty-seven events are found in the acceptance region where a WIMP signal in the form of low energy nuclear recoils would be expected. We estimate background contributions to this observation from four sources: 1) “leakage” from the e/gamma-band 2) “leakage” from the alpha-particle band 3) neutrons and 4) Pb-206 recoils from Po-210 decay. Using a maximum likelihood analysis, we find, at a high statistical significance, that these sources alone are not sufficient to explain the data. The addition of a signal due to scattering of relatively light WIMPs could account for this discrepancy, and we determine the associated WIMP parameters.

Or if you like pictures:

Taken at face value, what we have is yet another indication — joining results from DAMA and CoGeNT, although not completely consistent with them — of a dark matter signal that is (1) lower mass than most theorists would have expected, and (2) nominally ruled out by other experiments such as XENON and CDMS. So either the universe is really messing with us by making dark matter more complicated than we might have thought (but still accessible to our experiments), or searching for dark matter is really hard and the experiments are still fighting with unknown sources of error. Or both!

So this might be extremely exciting, but at the moment we’re still stuck saying: patience until it all gets figured out. We can take our time to get it right, the universe will still be there tomorrow.

CATEGORIZED UNDER: arxiv, Science, Top Posts
  • Al

    Haven’t we been through this about 343 times before?

  • Lab Lemming

    What is so special about CaWO4, that makes it a good dark matter detector?

  • Marc

    So, of CRESST, DAMA, COGENT and CDMSII, we can see that at least two of them must be wrong. DAMA and COGENT are inconsistent, CDMSII and CRESST are inconsistent. And if XENON is right, then all four of those are wrong. Sigh….

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  • Greg Campbell

    If WIMP mass is 20-40 GeV/c^2, the choice collision detector for selectivity, total active mass on the cheap, and sensitivity is Juan Collar’s supercritical bubble chamber (arxiv:1008.3518) loaded with CCl_3F, (bp 23.7 C, d 1.49 g/cm^3. Boiling point increases with depth given hydrostatic pressure. Large area somewhat shallow containers will also afford directional information vs. time of day and Earth’s orbital direction. Begin synthesis with natural gas for no C-14, half-life 5715 years. Chlorine from salt dome NaCl for no Cl-36, half-life 3×10^5 years versus 150 million years age, 500 half-lives.

    Collision energy transfer is maximum when the two bodies have equal mass, as in Newton’s cradle. If physics knows where to look, why doesn’t physics look there?

  • gameshowhost

    I hear the Tea Party is already staging a protest.

  • Ben

    A fable to read (or re-read) for the CRESST people: “The Boy Who Cried Wolf” by Aesop (620-564 BCE)

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  • Brian137

    There might be several types of DM particles.

  • Al

    Xenon100 doubles down with a new preprint and new analysis (arxiv, 9/8/11).

    They cast considerable doubt on any “WIMP” sightings.

    No one really believes the CRESST-II “weak signal amid substantial background noise”.

    Nature is not “messing with us”, but some very misguided theoretical physicists might be.

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  • True_Q

    You’re a Time Lord? The Doctor would be happy to meet You

  • forester

    If this is some non-dark matter physical process that CRESST, CoGENT, and DAMA are detecting, then why are both XENON and CDMS not seeing evidence of the same physical process?

    I suspect that there is some background affecting the CRESST etc experiments that the XENON and CDMS teams have been able to block out. The problem with this interpretation is that CRESST, CoGENT, and DAMA teams are run by different people and use different equipment and yet they each seem to be pointing to a new particle in a mass-range that’s compatible with one another. In other words, it is not like DAMA sees evidence of a particle at 300 Gev, CRESST sees evidence at 1 mg, and CoGENT at 100 Gev. They all seem to be more or less compatible with one another from a “mass of particle standpoint.”

  • Tissa Perera

    But Dark Matter is more illusive than Ghosts
    Some people some times have seen ghosts, but not this stuff with a big qualification…”so far”.
    Dark Matter is most cosmologists play putty. It can be invoked if and when necessary and molded conveniently to accommodate and rectify the observed seemingly abnormal behavior of real matter in order to save Newton’s law of gravity. To explain Dark Matter, certain obvious properties are assigned.
    It must be made of some kind of particles not resembling any of the known particles, more akin to neutrinos, but unlike neutrinos, it must have significant mass(hence gravity), must move slow(cold) and hardly interact physically with each other or with real matter(weakly interacting) except via gravity. I do not know why they had to attribute even a weak interaction with real matter, may be they hoped to physically detect it one day like they did with neutrinos. After so many years this stuff still remains to be detected.
    The problem with such tenuous matter properties is that it cannot congregate into any significant structure except by gravity, and gravity is already a very weak force. Computer simulations have produced vast web structures of this stuff where real matter is supposed to gravitate at the web nodes. But the visible composite structures(Galaxies etc) are moving in space at tremendous speeds. I do not see how the dark matter web nodes flow with the real matter at these speeds without separation.
    Nature may not be that way, how about modifying gravity? I have a different theory of the universe in which an extra cosmic size bounded 4th spatial dimension naturally modifies Newton’s law of gravity at cosmic scales to reproduce and modify the now famous empirical MOND theory. Dark energy becomes a natural consequence of this theory and dark matter is not necessary. This theory basically shows that the so called dark matter is a natural consequence of the bounded curvature of the 4th space where real matter by itself is the cause of so called dark matter. Only gravity can venture into the 4th dimension which I call the dark space. After all, MOND is on the right track and MOND becomes a legitimate theory under this hypothesis.

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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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