PEBS - Positron Electron Balloon Spectrometer
The PEBS program aims at a precise measurement of the cosmic-ray positron fraction using a balloon-borne spectrometer. Measurements performed by balloon-borne and space experiments in the past decade have shown an intriguing and unexpected rise of the fraction of positrons compared to electrons in the cosmic rays. This observation has been confirmed and intensified recently by the PAMELA detector which has shown the positron fraction to rise further, up to energies of 100 GeV. Fascinating explanations for this excess have been proposed, ranging from the fingerprint of a nearby pulsar to exotic dark matter particles annihilating in the halo of our Galaxy.
Additional science goals include a measurement of the high-energy electron sky map, which might hold clues to nearby sources of these particles, the study of charge-sign dependent solar modulation, and a measurement of the antiproton flux at high energies.
A proposal has been submitted to NASA in spring 2009. This page contains information about the physics that PEBS seeks to explore and the program of detector design and construction. For a recent review of experimental techniques in the field of cosmic-ray positron/electron and antiproton measurements, see this talk by Luca Baldini that also shows how PEBS fits into the general picture.
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Mechanical drawing of the PEBS-2 spectrometer.
| Projected positron fraction as measured by PEBS-2 compared to experimental data from PAMELA and the weighted mean of HEAT, AMS-1, TS-93 and CAPRICE.
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