Of Particular Significance

Dark News

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 09/05/2011

Well, just as if we didn’t have enough to keep track of in particle physics, along comes another claim that dark matter has been detected, by looking for extremely rare and faint signals of collisions of dark matter particles with atomic nuclei in a special type of crystal.

The abstract from the paper http://arxiv.org/PS_cache/arxiv/pdf/1109/1109.0702v1.pdf says (paraphrasing when necessary to make it somewhat lay-person-interpretable)

The CRESST-II Dark Matter search, aiming at detection of “WIMPs” (hypothetical dark-matter particles that feel the weak nuclear force)  through their scattering off atomic nuclei in CaWO4 crystals, [presents] data collected with eight detector modules, which can detect  the energy deposited when a dark matter particle strikes a nucleus, and distinguish (on average) a real dark matter particle collision from various backgrounds that could fake a signal.  Sixty-seven events are found.  We estimate background contributions to this observation from four sources, but find, at a high statistical signi ficance, 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 mass and interaction strength of such a WIMP that would be required.

How excited should we get?  The subject is murky.  This is not the first dark matter experiment to claim a detection of this type, yet no two experiments that have made such claims have ever seen evidence of the same thing.  And a first glance at this paper shows it is very complicated, and not particularly clear.   Moreover, this experimental collaboration has been somewhat obscure about its previous results.  And finally, the effect they see would appear, naively, already to have been excluded by some other experiments (you can even see this in figure 13 of this very paper.)

These are very tough measurements; estimating the various backgrounds, which they claim are too small to explain what they observe, is very difficult.  It would be hard to be confident of their results until another experiment, or an upgrade of this one, sees the same result.  With any hint of a discovery, healthy skepticism is warranted, but perhaps a bit more than usual is needed here initially, at least until the super-experts have looked this one over.

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7 Responses

  1. Very illuminative comments are given in a paper arxiv.org/abs/1006.5255.
    It contains a sound discussion of the complicated neutron backgrounds
    which are probably underestimated by DM detection experiments.

  2. The M2 region is not too far from the DAMA and Cogent observations, both in terms of mass ~ 10GeV and cross section. What do you think about this?

    1. No opinion yet … For instance, how strongly do DAMA and Cogent actually exclude the M2 region? and how strongly does CRESST exclude the DAMA and Cogent regions? In other words, is there a compromise that would actually satisfy all three experiments? I doubt it, but I don’t have the knowledge to answer those questions and so must defer to experts.

  3. I would appreciate a lot a slight extension of this article containing some (Feynman ?) diagrams explaining in some more detail the processes they were looking at in this experiment 😉 …

    1. Certainly I need to create a preliminary dark matter page — though this will have to wait until later in the week. For the next 36 hours I’m committed to doing full-time LHC-research-related activities, pulling 14 hour days, so there’s no time to do anything detailed until that’s over. I will glance around for a decent existing on-line resource, which in the case of dark matter probably exists. [Suggestions, readers?]

      1. Dear Prof. Strassler,
        I did not mean to be impatient, I just enjoy every new article or update as they come in 🙂
        Anyway it is remarkable to me that You find time beside Your “regular” work to produce these nicely illustrated articles which explain things about particle physics in such a clear way that just everybody has to understand it.
        Doing this for us is very kind of You 🙂


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