High energy electron sky map | AMS | PEBS |  |  | | Sky coverage of the AMS-2 experiment on board the ISS | Sky coverage of a PEBS balloon experiment launched at the poles |
At energies above 10 GeV, the positron fraction measured by PAMELA exceeds significantly the expectation for purely secondary production. At energies around 500 GeV, the ATIC experiment and PPB-BETS have reported an excess in the combined flux of electrons and positrons. If these features were due to a local source of electrons and positrons, for instance a nearby pulsar, such as Vela and Geminga, an observable anisotropy of TeV electrons might result. If, on the other hand, the origin was dark matter annihilation the distribution of electrons would be isotropic. In order to experimentally test these hypotheses, a full sky map in the TeV electron and positron arrival directions is needed. The GLAST/FERMI experiment will be able to do this only for electrons and it may be challenging for GLAST/FERMI to control the hadronic background to the required precision. The AMS-2 instrument has an opening angle of 50 degrees and covers the sky as shown in the figure. A balloon-borne experiment with a similar opening angle flown at the poles would be complementary to AMS-2. Both experiments together could produce a full sky map. The figure shows why we wish to ultimately fly PEBS in both the north and south polar regions. For reasons discussed in the management section we propose the first flight to take place at the North Pole from Kiruna to Alaska and the second one at the South Pole. The flight at the North Pole would also serve as an engineering flight to test the detector concept for possible further upgrades depending on the available funding for the European groups as outlined below for the PEBS-2 experiment.
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