Thursday, April 02, 2009
PAMELA: excess of 1.5-100 GeV positrons
Click the picture to see the experiment's website
As you have been already told when we talked about the CDF lepton jets, the PAMELA collaboration has detected an excess of positrons at energies above a few GeV, especially if they approach 100 GeV, their measured maximum.
These positrons can't come from secondary sources. While the theoretical percentage of positrons from secondary sources among electrons and positrons drops from 5% to 2% between 5 GeV and 100 GeV, PAMELA indicates that the fraction increases from 5% to 15%.
They must arise either from primary astrophysical sources (such as pulsars) or from dark matter annihilation (for example from neutralinos, the prime dark matter candidates, or even winos - if our world is supersymmetric).