COSMIC rays that zip into our atmosphere from deep space may have provided evidence of “supersymmetry”. This theory predicts a new, corresponding particle for each of those we currently know, and is a possible successor to today’s Standard Model.
During experiments in the upper atmosphere in 1994 and 1995, the High Energy Antimatter Telescope (HEAT) detected more positrons – the antimatter partners of electrons – than theorists expected. And a revamped detector which collected more data last year confirmed the excess, says Stephane Coutu of Pennsylvania State University in University Park.
Cosmic-ray positrons are thought to originate from collisions between atomic nuclei drifting through space. Calculations predict that HEAT should see about four positrons for every 100 electrons among high energy cosmic rays. But HEAT found roughly six positrons for every 100 electrons.
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It’s not a huge excess, but Gordon Kane and Lian-Tao of the University of Michigan in Ann Arbor and James Wells of the University of California at Davis think the extra positrons are evidence for supersymmetry. They believe the positrons come from rare collisions between the lightest particle predicted by supersymmetry and its antimatter partner. “If the signal is real, I don’t see how it could be anything else,” says Kane.
But Coutu says supersymmetry is just one of several possible explanations. “I think they are getting a little overenthusiastic about the interpretation of the data,” he says. “What causes [the excess] is still open to debate.”
If Kane and the others are right, it may help solve one of the biggest mysteries in astrophysics. The motion of galaxies implies that they contain huge amounts of unseen dark matter. The new particles predicted by supersymmetry fit the bill for this dark matter very well. But Jonathan Feng of the Massachusetts Institute of Technology says the number of supersymmetric particles allowed by the positron data is too small to account for all of the dark matter.
More at: www.arxiv.org/abs/hep-ph/0108138
