Tuesday, May 17, 2011

Fermi reproduces PAMELA excess

Jester brings us some news from Rome that became the Mecca of the Fermi collaboration. Once again, Fermi didn't disappoint and its new findings could have implications for the "Is Dark Matter Seen" war.

In 2008, PAMELA (TRF) announced its excess of high-energy positrons with energies 1.5-100 GeV in cosmic rays which could be viewed as evidence of annihilation of dark matter. But was that signal real? Many people have harbored doubts. After all, PAMELA could also be a blonde and you don't want to believe everything that a blonde says. ;-)

Click the picture above to zoom in

However, Fermi - who is male, experienced, and renowned (not to mention that he's been dead for decades and he was formerly known as GLAST) - has just mostly eliminated all those doubts.

Unlike PAMELA, Fermi didn't have its own magnetic field but it was able to cleverly borrow the magnetic field of the Earth. This loan allowed Fermi to do something that it couldn't do otherwise: to distinguish electrons and positrons.

Click to zoom in

As you can see, at certain moments and when looking to certain directions, all of the electrons - or all of the positrons - are shielded by the Earth because their trajectories are bent by the geomagnetic field to achieve this goal. Effectively, electrons and positrons may be separated and the result, as you saw at the top, is that PAMELA's excess is confirmed.

Whether the excess is due to dark matter annihilation or a more mundane astrophysical effect remains a somewhat open question but the case for DMIS - "Dark Matter Is Seen" coalition in the war - has strengthened again.

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