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Short Sharp Science: A New Scientist blog

Dark matter no-show hobbles elegant particle theory

Lisa Grossman, reporter


(Image: Francesco Arneodo LNGS-INFN)

Dark matter stubbornly refuses to come out of the shadows. The latest results from an underground detector show no sign of WIMPs, or weakly interacting massive particles, the still-theoretical particles thought to make up the invisible majority of the universe's mass.

The result puts the strictest limits yet on the particle's properties, and may squeeze out some favourite extensions to the standard model of particle physics.

Dark matter is the mysterious stuff dreamed up by cosmologists to explain why galaxies don't fly apart and why matter in the universe clusters the way it does. To explain the universe we see, dark matter must make up 83 per cent of all matter. But it doesn't emit light or speak to ordinary matter at all, except through gravity.


Physicists try to glimpse these particles by placing detectors deep underground, where they are shielded from cosmic radiation. If a WIMP collides with the nucleus of a heavy atom such as xenon, the collision should produce a telltale light signal, which the physicists can use to reconstruct the properties of the particle responsible.

The new result comes from the Xenon100 experiment (see photo), a tub of cryogenically cooled liquid xenon buried 1400 metres down a mine at the Gran Sasso National Laboratory near L'Aquila, Italy. The project's previous results, presented over a year ago and based on just 100 days of data, came up empty.

The latest results, presented at the DarkAttack2012 conference in Ascona, Switzerland, on 18 July, were based on 225 days of new data. The team used an improved detector that was 3.5 times as sensitive to the skittish particles as before. Still, the result was the same: no WIMPs.

"We have essentially set the most stringent limits of any other experiment" for WIMPs with masses heavier than 8 gigaelectronvolts (GeV), says Antonio Melgarejo of the Xenon team.

That doesn't mean WIMPs aren't real - it just means they may be harder to find than we hoped. Either WIMPs are much lighter than theories originally predicted (Xenon100 was optimised for 100-GeV WIMPs), or they're even more shy of ordinary matter than thought.

This in turn tightens the noose around certain versions of the theory known as supersymmetry, which some hope will extend the standard model, removing its many insufficiencies. The standard model was completed by the discovery of the Higgs boson this month, but it still doesn't explain dark matter. In supersymmetry, every standard particle has a heavier "superpartner" particle, one of which could be a WIMP.

However, the new Xenon results rule out most of the region where some of the simpler supersymmetry models predicted a dark matter WIMP should be.


The Xenon team will keep looking. The next generation of the experiment, called XENON1T, will use a tonne of liquid xenon, and should start construction this year.

Also this year, a detector called LUX (Large Underground Xenon) will start operation at a mine in South Dakota. It promises to be 10 times as sensitive as previous searches.

If WIMPs don't show up soon, though, it may be a sign that physicists are simply on the wrong track.

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Did the scientists stop to think that maybe dark matter doesn't exist? That maybe our understanding of gravity is not quite correct?


Sean: of course they have. Did you read the article? Scientists have to remain open minded, otherwise science can't move forward. They also aren't willing to discard a theory just because it doesn't fit quite right yet until the evidence shows that the theory is fundamentally flawed. We refine based on observation, not based on public opinion.


What about string theory? Does the WIMP no-show problem constrain the almost infinite variety of possible universes the string math seems to permit?


I am all for much of the great science going on in our world these days. It does seem a little forced to pursue this particular tack though. The mathematical model says that there must be all this stuff (invisible and yet acting in reality) in our universe. And they laugh at people who believe in an invisible God derisivly calling Him the God of the gaps. They have the dark matter of their own perception of the gaps.


Dark matter never sat right with me. Science is about forming a hypothesis around observation. Dark matter is forming a (suspected) observation around a hypothesis. If our current equations on gravity don't fit galaxy size observations then perhaps the equations are not correct for galaxy size systems. When quantum observations didn't fit the equations, we made new equations.


Is there any reason that dark matter has to be weakly interacting? Can't it just interact gravitationally?


After 40 years without a single sign of a "WIMP" I think it is quite safe to say that theoretical physicists are obviously on the wrong track in the dark matter search.

MRS Hawkins has a preprint on that is entitled "The case for primordial black holes as dark matter".

Fundamental stellar-mass and planetary-mass black holes are also predicted by Discrete Scale Relativity as the true identity of the galactic dark matter, and the recently launched NuSTAR X-ray telescope may see at least the higher mass members of this population. This new telescope has just started scientific observations.

Time for new ideas in the search for an answer to the long-running dark matter enigma.

"WIMPs" are a dead idea to all but the true believers.


The particles would have existed, but annoyed by the name chosen for them instead choose to remain aloof.


I've said it before and will continue to say it.
There is no such thing as dark matter.
We just haven't got the whole picture of gravity yet.
Dark matter has always sounded to me like a child's imagining of a magical substance to explain something that's not clearly understood.
Like luminiferous Ether.




so called dark matter is ordinary matter. neutrinos have the same characteristics as "dark matter" they are very hard to detect and they dont interact much with the rest of the universe


Dark Matter is Antimatter(gravitationally repulsive to matter) It cannot be detected in an Earth based detector, and does not reside within
the body of matter based galaxies. There is no such thing as Wimps. There is no such thing as Supersymmetry either. LHC has not detected it, nor have any other detectors.


Gravity does all the work of the very small particles you

are looking for. It travels through the Earth but you put

experiments in mines to find a particle that is doing the

same thing disregarding gravity. It travels in a straight

line because the centre of gravity is where the mass is,

its why you can stand up in a mine and not stick to the

walls. When gravity has passed through the Earth it is

fractionaly diminished, by 1G, when it emerges, gravity

at the surface will now have an unequal "pressure" and

any matter in that area will "fall" towards the line of

least resistance. Gravity is everywhere, you just have to

except which direction it is travelling in. It explains

why the universe is moving apart. It explains why

everything falls at the same speed. It explains why

different mass makes for different gravity. Its why you

cant find gravity emiting from mass, its why everything

has gravity.


In dense aether model the neutrinos are solitons of longitudinal waves in supersymmetric way, like the photons are solitons of light wave and they're playing the role of fotinos of supersymmetry model. The problem therefore isn't, that the SUSY is wrong, but that it's misunderstood heavily.


Funny how people dismiss Dark Matter because we haven't found it, when before last week, the same could be argued about the Higgs.


Dark Matter (DM)- A proton is small. Think about the bricks the proton is made of, or the bricks' bricks
Eventually, the smallest bricks are elementary particles
The singularity crushed the space out of matter, creating the smallest uncrushable bricks
The Big Bang/Expansion distributed it, most in the form of what we call "dark matter"
Over billions of years, sub-atomic particles eventually form from dark matter. Hydrogen forms as the sole element, leading to the universe we know through the formation of stars and the creation of all other elements within stars destined to nova... we still have LOTS of residual dark matter
Nobel please!

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