Why PAMELA may not have found dark matter


This is the one we’ve been waiting for. For months, the astrophysical world has been abuzz with rumors that the orbiting observatory PAMELA has found evidence of dark matter.

Various people have speculated on the nature of this dark matter but the PAMELA team has been cautious, refusing to release the data until they are happy with it. (Although that hasn’t stopped data being smuggled out of private presentations using digital cameras to capture slides).

Now the wait is over. The PAMELA team has put its data on the arXiv and the evidence looks interesting but far from conclusive
Here’s the deal: PAMELA has seen more positrons above a certain energy (10GeV) than can be explained by known physics. This excess seems to match what dark matter particles would produce if they were annihilating each other at the center of the galaxy. That’s what has got everybody excited

But there’s a fly in the ointment in the form of another explanation: positrons of this kind of energy can also be generated by nearby pulsars.

So PAMELA isn’t the smoking gun for dark matter that everybody hoped. At least not yet.

For that, we’ll need some way to distinguish between the positron signature of dark matter annihilation and the positron signature of pulsars.

That means a whole lot more data and some refreshing new ideas. You can be sure that more than a few  astrobods are onto the case.

Ref: arxiv.org/abs/0810.4995: Observation of an Anomalous Positron Abundance in the Cosmic Radiation

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