A new experiment may have found the first direct evidence of dark matter particles, a discovery that could begin to unravel one of the biggest mysteries in physics.

Theorists believe that dark matter, made up of of weakly-interacting massive particles, composes 23 percent of the universe, but no one has ever directly detected one of these WIMPs.



Now, physicists have announced they've spotted electrons with just about the amount of energy they would have expected to be made by a particular kind of WIMP entering the visible world.

John Wefel of Louisiana State University and colleagues report in Nature Wednesday that they could have detected "Kaluza-Klein" electron-positron pairs resulting from the annihilation of these WIMPS.

The KK particles are predicted by multiple-dimension theories of the universe and have long-been a leading candidate as the substance of dark matter. The new discovery then, if confirmed, would provide evidence that the fabric of space-time has many "compact" dimensions beyond the four that humans perceive.

"If the Kaluza–Klein annihilation explanation proves to be correct, this will necessitate a fuller investigation of such multidimensional spaces, with potentially important implications for our understanding of the Universe," the authors conclude.

Dozens of teams are working to understand the invisible dark matter and dark energy that when combined astrophysicists believe make up 95 percent of the universe. Most of the evidence for the dark stuff's existence comes through indirect observations: as physicist Myungkook James Jee put it last year, "We can't see a wind, but we can see it blow." So, the first direct detection of dark matter would be a landmark discovery.

Wefel's team sent a balloon carrying the "ATIC" particle detector aloft over Antarctica, where it measured the telltale charges and energies of electrons.

But the new detection isn't a sure indication of the existence of KK

particles. Harvard astrophysicist Yousaf Butt argued that other astronomical objects could explain the creation of these high-energy electrons, in an editorial that accompanied the original paper. The leftovers from supernovas, spinning pulsars, or microquasars could all be responsible for the observations, or things could get even stranger.

"And let’s not forget that a completely new type of astrophysical object could also produce the detected electron excess; after all, pulsars were discovered only in 1967, and until 1992 we were blissfully unaware of microquasars," he wrote.

Further experiments seem likely to reveal the true source of this cosmic electron anomaly. With longer observation times or better detectors, scientists should be able to puzzle out whether the spectral signature of the detected electrons fits the dark matter thesis.

See Also:

Image: *1. Two trucks carrying helium gas cylinders are used to inflate this 30 million cubic foot balloon / Joachim B. Isbert /

Nature. 2. "Content of the Universe"/ NASA. 3. The balloon awaits release from the launch vehicle / T. Gregory Guzik / Nature.__ __ *

*Citations: *

"An excess of cosmic ray electrons at energies of

300–800 GeV" *

J.

Chang, J. H. Adams Jr, H. S. Ahn, G. L. Bashindzhagyan, M. Christl, O.

Ganel, T. G. Guzik, J. Isbert, K. C. Kim, E. N. Kuznetsov, M. I.

Panasyuk, A. D. Panov, W. K. H. Schmidt, E. S. Seo, N. V. Sokolskaya,

J. W. Watts, J. P. Wefel, J. Wu & V. I. Zatsepin

doi:10.1038/nature07477* "A message from the dark side"

Yousaf M. Butt

News & Views: NATURE|Vol 456|20 November 2008

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