No Dark Matter Seen by XENON

By Sean Carroll | April 14, 2011 9:11 am

Here in the Era of (Attempted) Dark Matter Detection, new results just keep coming in. Some are tantalizing, some simply deflating. Count this one in the latter camp.

The XENON100 experiment is a detector underneath the Gran Sasso mountain in Italy (NYT article). It’s a very promising experiment, and they’ve just released results from their most recent run. Unlike some other recent announcement, this one is pretty straightforward: they don’t see anything.

Here we see the usual 2-dimensional dark matter parameter space: mass of the particle is along the horizontal axis, while its cross-section with ordinary matter is along the vertical axis. Anything above the blue lines is now excluded. This improves upon previous experimental limits, and calls into question the possible claimed detections from DAMA and CoGeNT. (You can try to invent models that fit these experiments while not giving any signal at XENON, but only at the cost of invoking theoretical imagination.) See Résonaances or Tommaso Dorigo for more details.

No need to hit the panic button yet — there’s plenty of parameter space yet to be explored. That grey blob in the bottom right is a set of predictions from a restricted class of supersymmetric models (taking into account recent LHC limits). So it’s not like we’re finished yet. But it is too bad. This run of XENON had a realistic shot of actually finding the dark matter. It could be harder to detect than we had hoped, or it could very well be something with an extremely small cross-section, like an axion. The universe decides what’s out there, we just have to dig in and look for it.

  • sterile neutrinos

    It seems to me there is now a distinct possibility that sterile neutrinos could be dark matter, rather than something supersymmetric or axionic, if one takes the recent hints of excitement from the MINOS collaboration at face value…

    Question: how do sterile neutrinos jive with cold dark matter models — presumably, they aren’t very cold?

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  • Ellipsis
  • Cody

    My arm-chair speculation money is on dark matter being the new aether. (At least concerning exotic DM–offer excludes neutrino and baryonic “stuff”.)

  • Paul

    I’d like the theory of antimatter quark nuggets to be true, if only because capturing microscopic multi-ton antimatter chunks zipping through the solar system might eventually become feasible — and useful as an energy source.

  • George Musser

    If you look at a higher-dimensional parameter space, is DAMA still such an outlier?

  • D R Lunsford

    Two words – Cooperstock, Tieu.


  • Chris


    You need to listen to Feynman.

    Doesn’t matter what you would like. Nature is what it is.

  • dg

    Seems like the Xe Leff issue that caused all that ruckus last year is still unresolved. They don’t really seem to address it in the current paper.

    Extrapolating is still extrapolating. Model-dependent predictions are still model-dependent.

    (And to boot, the model they’re based on – SUSY – is much less well-motivated than the evidence for dark matter)

    My takeaways:
    weakly-interacting massive particle (lowercase) – still very much possible.
    SUSY Weakly-Interacting Massive Particle (uppercase) – less likely than before.
    MONDers – not much of a victory.


  • Jimbo

    It’s disappointing, but not discouraging. Look at LIGO/VIRGO. Now That is discouraging, with no detection of grav waves after a decade of science runs, yet they continue to place limits having seen Nothing. Sort of like the sparticle people:”They must be just a bit heavier”, ad nauseam.
    What is disturbing here is that all the prior searches are effectively excluded by one. No Way. Regardless of it’s signal to noise ratio being the highest of all the others, I think the jury is still out, & it would be `CoGent’ to keep an open mind. As Shelly Glashow admonished the stringers,
    “Please heed our advice that you too are not smitten; The book’s not finished, the last word is not Witten.”

  • Noah

    Or there could be some weird crap like MOND or something going on, and no dark matter.

  • Loren Amacher

    Still waiting for some religious website to state: “Search for answered prayer still negative.’

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  • Lab Lemming

    This is a bit of a tangent, but is the recent Fukushima disaster going to put enough radioactive Xe and Kr isotopes into the atmosphere to make future bigger Xe experiments difficult?

  • Shantanu

    Sterile neutrino, as I understand sterile neutrinos are warm dark matter candidates and WDM
    is no longer favored.

  • Roger

    Is dark matter the new Phlogiston (or aether as Cody suggested)? Observable phenomena that are real, but the theoretical postulated mystery substance to explain the phenomena is just wrong.

  • Albert Zweistein

    The evidence for physical dark matter objects appears to be quite strong.

    But do these dark matter objects have to be subatomic particles?

    Black holes of about 1 solar mass formed in the early universe are stable against Hawking radiation and do not conflict with metal abundance constraints.

    They are nonbaryonic, stable, and quite fundamental objects that interact with normal matter gravitationally, but do not emit a lot of radiation if undisturbed in the galactic halo.

    Should we not pay some consistent lip service, or even some serious thought, to such a natural dark matter candidate? After all, there is considerably more observational evidence for “primordial” black holes than there is for WIMPs, sparticles, axions, sterile neutrinos, etc.

    Albert Z

  • Brian137

    Goodbye, Ruiz et al.

    Hello, Buchmueller et al.

  • Alan L

    Let’s see now. What characteristics of Invisible DM have we found so far, Watson?

    1. Invisible DM strongly in evidence around all galaxies and exerts a powerful gravitational influence on the rotational speed of every part of those galaxies.

    2. Cannot be found anywhere near massive bodies such as planet surfaces, let alone deep mines.

    This is a little bit more complex than a 2 + 2 brain teaser.

    Perhaps every particle of Invisible DM in the universe is emitting tiny gravitational waves from Lisa Randall’s tetra space ‘brane’ and ‘bulk’ to help us all keep our baryonic feet on the baryonic ground, in a le Sage type of way.

    Just a non peer reviewed thought.

  • Phillip Helbig

    “Black holes of about 1 solar mass formed in the early universe are stable against Hawking radiation and do not conflict with metal abundance constraints.

    They are nonbaryonic, stable, and quite fundamental objects that interact with normal matter gravitationally, but do not emit a lot of radiation if undisturbed in the galactic halo.”

    If such objects were to make up most of the dark matter, they would have a much stronger microlensing signal than is observed.

    Good idea, but ruled out by observations.

  • PTM

    Personally I suspect dark matter to be some conceptual problem in the foundations of physics.

    As an example of the type of problems i have in mind consider Lorentz Symmetry, we believe Nature obeys this symmetry, but is that really the case? Perhaps LS is not really an universal symmetry of Nature but rather a consequence of the way we observe it. There could be other fields/entities out there which do not obey LS and which are too fleeting and chaotic to interact with normal matter in any other way then by gravitation (quantum interactions mediated by particles require a certain spatio-temporal synchronization which could very well be impossible for fields violating Lorentz invariance).

  • Martin g

    Not really surprising that no Dark Matter was found. It’s pretty clear that it’s spectacularly absent from our part of the cosmos. If it were here it would affect everything from the orbits of planets and satellites to the paths of laser beams. Considering that only 5% or so of the universe is ‘normal’ matter (according to the theory) isn’t it just a touch bizarre that we’re surrounded by nothing but that?
    My guess is that there is no ‘Dark Matter’ or ‘Dark Energy’ – a much more credible explanation would be variations in ‘constants’ such as gravity, lightspeed etc etc.

  • Thorny

    @20 Phillip Helbig: “If such objects were to make up most of the dark matter, they would have a much stronger microlensing signal than is observed.

    Good idea, but ruled out by observations.”

    Because we know what microlensing looks like, and would know it when we see it? Seriously, what’s the object weight limit that we’ve got from experiment?

  • Thomas Larsson

    The current generation of physicists will of course never consider any null result as evidence against susy. Progress only happens from funeral to funeral.

  • Peter Fred

    Dark matter is like Count Dracula. It will take more than a few nails in the coffin to put this neo-aether idea to rest. Fortunately, there are now three studies linking the temperature of a test mass to its gravitational weight. These studies suggest the possibility that luminosity is the source of gravitational attraction. Astronomers all know that luminosity emanates from all gravitationally bound bodies in the universe such as binary stars, planetary systems, galaxies and clusters. My studies show a 1.9%, 8.9%, 9.6% and a 16% increase in the weight of the test mass when these test masses were placed between a 1000 W hot source and a cold source. Such unexpected anomalous results challenge the principle of equivalence upon which General Relativity depends and Einstein’s interpretation of E = mc^2. But go a ahead and ignore them. Maybe someday they will find that dark matter (and dark energy).

  • spaceman


    You mentioned axions as a possible dark matter candidate; however, I was under the impression that the parameter space for axions has been even more tightly constrained than it has for WIMPs.

    This time period seems to be a crisis in cosmology in the Thomas Kuhn framework of scientific revolutions, no? None of the ideas currently on the table seem to be working: MOND has its problems, so does LCDM, so does LWDM, so do theories that posit extra dimensions, etc. It makes me wonder when there are so many people with 140+ IQs and billions of dollars of funding, why there seems to be no resolution in sight when it comes to establishing an accurate description of most of the Universe!

  • John R Ramsden

    Has any observational evidence been found yet for when all this supposed dark matter first appeared?

    In particular, do the most distant galaxies whose peripheral rotational red shifts can be meaured show the same anomalouslty fast rotation as nearby galaxies?

    I gather at one time it was thought that clumps of dark matter promoted the initial formation of galaxies. But hasn’t that idea now been supplanted by the notion of this being achieved by polar jets of primordial black holes concentrating vast clouds of gas? In that case dark matter could have turned up later than the Big Bang.

  • Doug

    @Thorny: figure 14. Some more recent microlensing studies have been published, but of smaller samples so haven’t updated the percentages yet. Basically if you combine the MACHO and EROS samples, you are left with solar mass scale black holes making up no more than about 20% of the needed halo mass. It’s also very hard to invent a way to make primordial black holes prior to Big Bang Nucleosynthesis time scales without producing axions as a side product.

    @John R Ramsden: Baryon Accoustic Oscillations – hard to get that 100 Mpc peak in the matter power spectrum without the early universe having a lot of dark matter. See for a good description.

  • Low Math, Meekly Interacting

    spaceman: I’ll hazard a guess. The reason very smart people can’t solve the problem is because they have no direct experimental observation of the stuff. They see all kinds of weird things that cry out for an explanation, and they can come up with plausible explanations. But there is no substitute for empirical evidence. None. And no amount of smarts will ever make up for that fact.

  • Albert Zweistein

    Phillip Helbig: “If such objects were to make up most of the dark matter, they would have a much stronger microlensing signal than is observed.”

    Doug: “you are left with solar mass scale black holes making up no more than about 20% of the needed halo mass”

    Yes, dear colleagues, but even IF the microlensing inference of 20% turns out to be valid in the long run, and this inference is far from a final verdict, that is:

    MACHOs = billions

    “WIMPs” = ZERO (as in zilch, nada, goose-egg, nein)

    Tell me. Is billions of “birds” in hand less of a scientific desiderata than a small herd of “unicorns” that might be just around the 1,343rd corner, or the 1,344th, or the 1,345th, or …?

    Albert Z

  • Thorny

    Doug: thanks a lot! I have to wonder though whether a check with other galaxies would be appropriate, just to make sure that there isn’t a coincidence between our orbital velocity and that of the DM halo in the direction of the Magellanic Clouds that’s changing the expected lengths and frequency of microlensing events. Is anything like that done/published yet?

  • Doug

    Thorny: a lot of work has been done on Andromeda, and a few attempts on some more distant galaxies – a summary can be found at

    You run into two problems as you go to other galaxies: 1) the lensing signal is strongest when the lens is half way between us and the object being lensed, but all the possible machos are either in our halo or the target galaxy’s and not between the two, and 2) you can’t resolve individual stars in a ground based observation, so are looking at a blend of stars, one of which is being microlensed during an event (same problem Hubble had in his Cepheid observations that caused him to overestimate H0). This makes you need to model the observations in a more statistical manner and ultimately need many more events to reach the same level of significance as the galactic studies (of course you get more stars per image, which helps).

  • King Cynic

    Calm down, everyone. WIMPs of the sort that XENON and CDMS are sensitive to are simply one of very many possibilities of dark matter. The idea that we are in the middle of some kind of paradigm collapse for dark matter is ludicrous. In fact both cosmology and astronomical constraints (see Bullet Cluster) make the case for dark matter stronger now than it was just a few years ago—-namely, incontrovertible.

    At best we’re getting indications that GeV-scale SUSY-inspired particles may not be the dark matter. If so there’s about 10^2 other possible types of dark matter to be ruled out still.

  • Shantanu

    Sean , I agree there is no need for alarm. However the “WIMP miracle” argument which
    everyone talks about in any pedagogical talk about WIMPs fixes the cross-section
    to be about weak-interaction scale about 10^-43 cm^2 and slowly that space is been ruled out
    over a larger mass range. so people should now be talking about super-wimps or very-WIMPs or ultra-WIMPS.
    Also as someone pointed out even if 2 more orders of magnitude cross-sections are ruled out,
    one can always invent models which evade all bounds, but it becomes fine-tuning

  • Eugenie Samuel Reich

    @14 Lab Lemming. The possibility of atmospheric contamination affecting dark matter experiments was discussed on Nature’s news blog at

  • Lab Lemming

    Thank you Dr. Reich!

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  • JB

    Wow, this post really brought out the quacks. DM isn’t going anywhere. Just because a few possible WIMP models are being ruled out doesn’t mean there aren’t many more where they came from. Everyone should understand that theorists have a tendency to talk up the plausibility of the most detectable versions of WIMPs, inflation fields, etc. to 1.) help experimentalists get funding for not-sensitive-enough instruments, and 2.) to stake out territory predicting something that might actually get detected in their lifetime.

  • m. bora cilek

    hi there everyone,
    finally I have solved the dark matter problem..this is no joke, believe me..
    just good-old (proven) laws of physics from Newton and new models, funny concepts or cumbersome mathematics…I will soon post an article in one of the e-print archives..the important part is only one or two paragraphs, rest will be references etc. as this is the norm for this kind of write-ups.. you will be amazed to see how long humanity have spent in the wrong direction..very embarrassing indeed..
    just note my name and wait for another 2-3 the meantime I need your suggestions for alternative sites, to publish the article online simultaneously..
    please contact me:

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Cosmic Variance

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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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