Dark matter or background noise? Results intriguing but not conclusive

Feb 11, 2010

Physicists may have glimpsed a particle that is a leading candidate for mysterious dark matter but say conclusive evidence remains elusive.

A 9-year search from a unique observatory in an old iron mine 2,000 feet underground has yielded two possible detections of weakly interacting massive particles, or WIMPs. But physicists, who include two University of Florida researchers, say there is about a one in four chance that the detections were merely background noise -- meaning that a worldwide hunt involving at least two dozen different observatories and hundreds of scientists will continue.

"With one or two events, it's tough. The numbers are too small," said Tarek Saab, a UF assistant professor and one of dozens of physicists participating in the Cryogenic Dark Matter Search II, or CDMS II, experiment based in the Soudan mine in Northern Minnesota.

A paper about the results is set to appear Thursday in , the journal Science's Web site for selected papers that appear in advance of the print publication.

Scientists recognized decades ago that the rotational speed of galaxies and the behavior of galaxy clusters could not be explained by the traditional forces of gravity due to the mass of visible stars alone. Something else -- something invisible, undetectable yet extremely powerful -- had to exert the force required to cause the galaxies' more-rapid-than-expected rotational speed and similar anomalous observations.

What came to be known as "dark matter" - dark because it neither reflects nor absorbs light in any form, visible or other - is now estimated to comprise as much as 23 percent of the universe. But despite abundant evidence for its influence, no one has ever observed dark matter directly.

There are several possibilities for the composition of this mysterious, omnipresent matter. Particle physics theory points toward WIMPs as one of the most likely candidates.

WIMPs are "weakly interacting" because, although their masses are thought to be comparable to the masses of standard atomic nuclei, they have little or no effect on ordinary matter.

Among other things, that makes them extremely difficult to detect.

However, scientists believe WIMPs should occasionally "kick" or bounce off standard atomic nuclei, leaving behind a small amount of energy that should be possible to detect.

The CDMS II observatory is located a half-mile underground beneath rock that blocks most particles, such as those accompanying cosmic rays. At the observatory's heart are 30 hockey-puck-sized germanium and silicon detectors cryogenically frozen to negative 459.58 Fahrenheit, just shy of absolute zero. In theory, WIMPs would be among the few particles that make it all the way through the earth and rock. They would then occasionally kick the atoms on these detectors, generating a tiny amount of heat, a signal that would be observed and recorded on the experiment's computers.

Durdana Balakishiyeva, a postdoctoral associate in physics at UF, and Saab have participated in the analysis of data produced by the experiment as well as simulations of the detectors' response. Beginning in 2007 they have helped to test many of the detectors at the UF campus in Gainesville which are being used in the successor SuperCDMS experiment. The UF tests involved cooling and operating the detectors just as they are operated in Minnesota to verify that they were up to par.

The 15 institutions participating in CDMS II gathered data from 2003 to 2009. Observers recorded the two possible events in 2007, one on Aug. 8 and the second on Oct. 27. Scientists had estimated that five detections would be sufficient to confirm WIMPs -- meaning that the two fell short, according to the CDMS. But while the two detections may not be conclusive, they do help to set more stringent values on the WIMPs' interaction with subatomic particles.

"Up until now, not only us, but everybody was operating without statistics -- we were blind in that sense," Balakishiyeva said. "But now we can speak of statistics in some way."

At the very least, the finding helps to eliminate some theories about -- raising the profile of the WIMP and potentially accelerating the race to detect it.

"Many people believe we are extremely close -- not just us, but other experiments," Saab said. "It is expected or certainly hoped that in the next five years or so, someone will see a clear signal."

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User comments : 13

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seneca
2 / 5 (4) Feb 11, 2010
Science is about publishing of confirmed results - or at least it should be. Now the article with two events is generating another bunch of articles, which are disputing its relevancy and/or speculating about extrapolations and freelance writers have their job. But does it mean anything for real? BTW cold fusion results of the same significance level would be ignored, because they don't fit some theory well.
axemaster
5 / 5 (3) Feb 11, 2010
BTW cold fusion results of the same significance level would be ignored, because they don't fit some theory well.


My favorite physics professor (and employer, I work as an undergraduate at a research university), told me a story about how he and an entire lab tried to confirm results for cold fusion back when it was first reported. They tried for nearly a year to reproduce the results (from another lab), with absolutely no success. They finally gave up in disgust. His words:

"They saw neutrons because they were chemists, and they didn't know how to use the neutron detectors correctly."

And btw, the theory that cold fusion doesn't agree with is... all of classical and quantum physics. Basically science in general.

Sorry to burst your bubble.
dan42day
5 / 5 (2) Feb 12, 2010
But does it mean anything for real?


The answer lies in this quote from the article:

"It is expected or certainly hoped that in the next five years or so, someone will see a clear signal."

Translation:

"We want 5 more years of funding....FOR REAL!"

broglia
2 / 5 (1) Feb 12, 2010
Sorry to burst your bubble
Arata's cold fusion experiments were confirmed both in Japan, both in Italia independently. There exist many neutronless channels of cold fusion and it's not so easy to fake experimental evidence, like this one: There's a video of hot spots, created by nuclear reaction, as observed in thermocamera.

http://www.lenr-c...Navy.htm

You see: not just some one or two events - but many of them, in fact... With such number of events the evidence of WIMPS or dark matter would be discussed in every local newspaper. And theory of WIMPS doesn't agree with contemporary theories better, then the theory of cold fusion - in fact, both these phenomena could be even related as a manifestation of supersymmetry.
Noumenon
5 / 5 (45) Feb 12, 2010
"Science is about publishing of confirmed results - or at least it should be"

What do you mean by confirmed? How are others supposed to recreate the same results or find correlations without anyone publishing.
newsreader
5 / 5 (2) Feb 12, 2010
"Science is about publishing of confirmed results - or at least it should be"

You realize, of course, that not detecting as many particles as expected could be just as important as actually detecting the particles.
seneca
1 / 5 (1) Feb 12, 2010
..not detecting as many particles as expected could be just as important as actually detecting the particles..
I've no problem with such approach - my question "only" was, why it is not applied consistently to different phenomena. For example to homeopathy or various psychic phenomena. It's all just about consistency of scientific method.

BTW If Higgs particle is unparticle, then the WIMPS should be unparticles too, because they're both predicted by supersymmetry.
seneca
not rated yet Feb 12, 2010
What do you mean by confirmed?
Does it mean, science is about publishing of whatever results ASAP for not to lose the eventual priority? What the peer-review process is supposed to be for, after then?

Again, I've no problem with such approach, I'm just trying to find consistent, inter-subjectively acceptable criteria of it.

BTW There is apparent similarity in experimental arrangement during finding of WIMPS and neutrinoless double beta decay. Is it possible to distinguish each of other?

http://www.physor...542.html
Quantum_Conundrum
Feb 12, 2010
This comment has been removed by a moderator.
Nik_2213
5 / 5 (1) Feb 12, 2010
I remember the epic struggle over the first neutrino detection results, that 'dry cleaning fluid tank' stuff, and the persistent problem that the workers were only catching 1/3 of the predicted SNU flux.

Now, the battle is on to determine neutrino mass using germanium detectors.

One researcher's error bars may be another's breakthrough-- Or not.
tkjtkj
not rated yet Feb 13, 2010
Science is about publishing of confirmed results - or at least it should be. Now the article with two events is generating another bunch of articles, which are disputing its relevancy and/or speculating about extrapolations and freelance writers have their job. But does it mean anything for real? BTW cold fusion results of the same significance level would be ignored, because they don't fit some theory well.


Yes! definitely! Let's not have scientists be sooo loquacious as to communicate with each other except concerning validated discoveries!

Are you for real? Is that what you believe science ought to require???? If so, i'd suggest you find some other field!

tkjtkj@gmail.com
mayan
1 / 5 (4) Feb 14, 2010
There is already Dark Matter on earth, only some Physicists are aware of the Super Metals on Earth that produce Anti Gravity, Tractor beams, energy...visit the links
http://www.youtub...=related
http://www.youtub...=related
SEE PROPERTIES OF THESE METALS IN COMMENT SECTION OF LINK BELOW
http://www.physor...94.html#
seneca
not rated yet Feb 14, 2010
Let's not have scientists be sooo loquacious as to communicate with each other except concerning validated discoveries!
Of course, at the case of PUBLIC communication it's the basic quality assurance policy of the job, which they're taking PUBLIC money for. Do you remember the misconduct affairs of Hendrik Schon or Hwang Woo-Suk? But as we can see at case of recent "climategate" affair, even private communication isn't completely out of public control.

If scientists would experiment for their OWN money like Faraday or Tesla, then they could indeed choose whatever policy for their PRIVATE OR PUBLIC communication without problem.
jsa09
not rated yet Feb 17, 2010
What came to be known as "dark matter" - dark because it neither reflects nor absorbs light in any form, visible or other - is now estimated to comprise as much as 23 percent of the universe. But despite abundant evidence for its influence, no one has ever observed dark matter directly


How come the amount of dark matter keeps changing. In other physorg articles it says something like 95% - in this one 23%. It seems to me that we should be saying there is as much dark matter as we want whenever we want it. And how ever much that is, it was predicted accurately.