Thursday, August 14, 2008

Could PAMELA Have Detected "Dark Matter"?

That seems to be the anticipation and rumors spreading in the astrophysics community.

Nature News is reporting (link open for free only for a limited time) an highly-anticipated report out of the PAMELA collaboration that detected an anomalous surplus of high-energy positrons whizzing through space.

Nature has learned that the PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) mission — a collaboration between Italy, Russia, Germany and Sweden — has detected a surplus of high-energy antielectrons whizzing through space. The antielectrons, also called positrons, could be the clearest signature yet of the dark matter lurking in the Milky Way, according to Dan Hooper, a theoretical physicist at Fermilab in Batavia, Illinois. “If it's true, it's a major discovery,” he says.

Previous space and balloon missions saw hints of the same positron surplus in the 1990s. But their energy range was limited and their measurements had high uncertainty. PAMELA is, in principle, capable of detecting higher-energy positrons with far better accuracy than any other mission to date.

Now, it doesn't mean that these positrons are the dark matter itself, because it is widely believed that dark matter candidates are neutral, and react very weakly with other particles. But these electrons could come from such dark-matter interactions:

PAMELA's positron surplus could come from dark matter particles described by the supersymmetry theory. This predicts the existence of super-heavy counterparts to everyday particles. The lightest supersymmetric particles are expected to be both massive and stable — making them prime candidates for dark matter. Occasionally, theorists believe, two of these particles will smash together and annihilate each other in a burst of energy. The annihilation will create a stream of more conventional particles that will eventually decay, leaving energetic electrons and positrons. In other words, the positrons detected by PAMELA could be the direct result of dark-matter annihilations.

Of course, there is a very long way to go before something like this gets confirmed, and even longer for it to be accepted as a valid evidence. So let's not jump the gun just yet.


No comments: