Dark Rumors

By Sean Carroll | December 9, 2009 12:10 pm

All the physics blogosphere is abuzz about rumors that the CDMS experiment might have collected evidence for the direct detection of dark matter, and is going to announce their results on December 18. The original source was Resonaances, where you can read the basic story; see also New Scientist. It’s to the point where it’s more suspicious if we don’t mention it than if we do, so here you are.

Not too much point in speculating — we’ll find out next week! There was some misplaced excitement about a Nature paper, but it is true that CDMS has scheduled simultaneous talks at CERN, Fermilab, SLAC, and elsewhere. Steinn did the citizen-journalist detective work and dug up the abstract for Priscilla Cushman’s talk at CERN:

I will present new results from the recent blind analysis of 612-kg days (before cuts) of data using the CDMS germanium detectors at Soudan. CDMS uses ionization and athermal phonon signals to discriminate between candidate (nuclear recoil) and background (electron recoil) events in Ge crystals cooled to ~ 50 mK. Timing, yield and position information allows us to tune our expected background leakage into the signal region to 0.5 events. I will report on what we saw when we “opened the box”, whether we have seen WIMPs or not, and implications for future dark matter direct experiments.

It would seem unlikely to me that CDMS would be able to announce a cut-and-dried discovery of dark matter; that would require collecting an awful lot of data. (But what do I know?) It’s more plausible that they would see some kind of provocative signal, but without quite enough significance to be definitive. With many different competing experiments, several of which have been working for quite some time now, it seems like the kind of result that you would gradually sneak up on, rather than dramatically capture in one fell swoop. Or maybe they’re just updating us on their best limits, and some rumor-mongering has spiraled a bit out of control. We’ll see.

  • onymous

    Talks are also scheduled at LBL and the KITP, at least.

    Seeing two or three interesting events seems like the worst possible outcome (and, perhaps, most likely, given the rumors), since it really tells us almost nothing (I suppose this depends a bit on what the recoil energies are). XENON-100, the world of physics turns its desperate eyes to you….

  • Marc

    I understand that there will be a paper submitted to the arXiv that day. The question is, will it be submitted and appear on the listings for Friday, or will we all have to wait until Monday to see it?
    Prisca’s talk is at 11:00 at CERN, so if there’s no arXiv paper for that day, that will be the first we will here (unless CDMS is giving a talk at FNAL at 4:00 AM…)

  • http://www.flamencoandarabicpop.com Adam Solomon

    Interestingly (or maybe not), the conference is about three days after Berkeley’s grad apps are due :)

    I wonder if, had it been a week earlier, there would have been a curious spike in essays claiming to be really really interested in CDMS.

    Also, Sean, if you do hear anything before the 18th, a spoiler alert would be common courtesy.

  • http://pleion.blogspot.com Bjørn Østman

    What does “612-kg days” mean?

  • John

    Probably it’s the product of the mass of germanium detectors in kilograms with the length of time that the experiment was run and thus events could occur in days?

  • John

    (I’m Sean’s co-blogger John; the previous John is not…)

    If CDMS expects 0.5 events from background (with a bit of uncertainty, say, 0.1 events) then it will take about 5 events to claim a 3-sigma observation of WIMPs, and about 8 events to claim a 5-sigma discovery, by my calculations.

    The thing is, in the last major update from CDMS, they saw zero events with about 0.6 plus or minus 0.5 expected background events, with an exposure of 121 kg-days. With five times more exposure now, and clearly improved analysis (the expected background stayed the same even with more exposure) then it is not completely nuts to imagine a 3-sigma tantalizing observation. But 5-sigma would start to be inconsistent with observing zero last time.

    See http://xxx.lanl.gov/pdf/0802.3530 for the previous result.

  • Brian137

    I thought that CDMS would get blown out of the tank by the xenon experiments, and eventually it may, but I’m game for some fun after years of null observations. I’m up for something interesting. I don’t need no five sigmas – just enough to spice up the stew.

  • John

    In this game, three sigma would be spicy indeed…

  • Robert Frost

    Has science become theatrics, or a circus perhaps? The clowns are amusing.

    Another in a long string of HEP false positives?

    Or perhaps the ‘Lone Magnetic Monopole of the Cosmos’.


  • Nick

    I last saw a talk on CDMS at a conference in march. They had a very clear separation between signal and background regions, and absolutely nothing inside the signal region.

    It’ll be interesting to see what has changed in such a short amount of time.

  • http://vixra.org/osky PhilG

    If they really had nothing they may be able to announce that they have ruled out some classes of WIMP as CDM

  • Anonymous

    I have no idea what CDMS is going to say, but in many people’s opinion they are the gold standard of dark matter experiments, and I will take whatever they say very seriously. Their background rejection is unparalleled by competing technologies.

  • Sili

    Isn’t there an adage that when the title of a paper is in the form of a question, the answer is invariably no?

    I think this counts:

    I will report on what we saw when we “opened the box”, whether we have seen WIMPs or not, and implications for future dark matter direct experiments.

  • Marc

    Sili–From a paper in 1995:

    Boris Peon

    Hinchliffe has asserted that whenever the title of a paper
    is a question with a yes/no answer, the answer is always no.
    This paper demonstrates that Hinchliffe’s assertion is false,
    but only if it is true.

  • Robert Frost

    Most likely answer: yet another brilliant “discovery” of a null result.

    Wimps found = 0
    Lower Limits Briliantly Established = MANY

    Another commanding lead!

    Attaway HEP; you go pseudoscientists!

  • John

    Robert Frost, how do you make the leap from “null result implies limits on hypothetical models” to “pseudoscience” exactly?

  • A. Ewing

    Is anyone else thinking :
    “Al Capone’s Safe”.

    I didn’t think so.


  • http://norwegianshooter.blogspot.com/ Norwegian Shooter

    Both sources cited above have posted updates denying the rumors.

  • Gabe

    fyi… there’s an update on the CDMS website


    “The collaboration is working hard to complete the first scientific publication about these new results and plans to submit the manuscript to arXiv.org (http://arXiv.org) before the two primary CDMS talks scheduled for Thursday, December 17, 2009 at Fermilab and at SLAC. “

  • chris


    how can they reduce the relative error on the expected background by a factor 6 while keeping the expectation value constant with just a factor of 2 in statistics? better theoretical understanding?

    that seems to contradict everything i think i know about statistics.

  • John

    chris, the only way they could reduce the background while maintaining the same efficiency for the signal is to use additional information about each event, something that distinguishes the background events from the real ones. I am not an expert in their analysis, though I have followed it at a general level for some time now. It’s entirely possible, though, that they got better at discriminating signal and background. I would expect no less – CDMS has a bunch of very talented experimentalists.

  • Roman

    Dear scientists
    Please speculate more as this is sooo exciting reading. Please.

  • General Omar Windbottom

    Robert Frost answered John’s question in a quite definitive manner.

    Alas, the powers that be decided to suppress the answer because it threatened their sense of intellectual security.

    “Something’s happening here, but you don’t know what it is. Do you Mr. Jones.”

  • http://www.shaky.com Timon of Athens

    Robert Frost said: “Wimps found = 0
    Lower Limits Briliantly Established = MANY

    Another commanding lead!

    Attaway HEP; you go pseudoscientists!”

    That’s pretty funny, but there is still a great difference between being a pseudoscientist and being a real scientist who pumps up a non-result because of funding difficulties… but I guess we are all rather sick of papers of the form, “hey we looked for something and didn’t find it, isn’t that wild eh?”

  • BF

    Robert Frost, the electric universe crank, is calling people pseudoscientists. Too funny!

  • http://scienceblogs.com/startswithabang/ Ethan Siegel
  • Pingback: And the Eagerly-Awaited Dark Matter Result Is… | Cosmic Variance | Discover Magazine()

  • Pingback: Dark Matter Detected, or Not? Live Blogging the Seminar | Cosmic Variance | Discover Magazine()

  • Pingback: CDMS’ Endresultat: Wie die Dunkle Materie wieder nicht entdeckt wurde « Skyweek Zwei Punkt Null()


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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] cosmicvariance.com .


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