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<b>High Energy-Astrophysics</b><br><i>Cosmic-Ray Electrons and Positrons</i>

Monday, October 26, 2009
4:00 AM
335 West Hall

Speaker: Michael Schubnell (U-M Physics)

Direct measurements of cosmic-ray electrons and positrons were first made in the early 1960s and since then a number of instruments were built to study this component of the cosmic radiation. The precise measurement of the intensities of CR electrons and positrons are key to our understanding of cosmic-ray origin and propagation and in addition the locally observed abundance of cosmic ray electrons and/or positrons may exhibit interesting spectral features. The recent report by the PAMELA team of the observed rise in the cosmic-ray positron fraction above a few GeV and the report of an excess of cosmic-ray electrons around a few hundred GeV by the ATIC collaboration has resulted in a flurry of publications interpreting these observations either as a possible signature from the decay of dark matter or as a contribution from isolated astrophysical sources. While those interpretations are scientifically exciting, the possibility that measurements are contaminated by mis-identified cosmic-ray protons cannot be ignored. Upcoming observations by new instruments such as AMS (at GeV energies) and CREST (at TeV) energies have the potential to improve upon current measurements and to further our understanding of galactic cosmic rays.