The Cosmic Positron Fraction: Implications of a New Measurement

Abstract

The first balloon flight of the HEAT instrument in 1994 yielded results on the cosmic ray positron fraction with good statistical and systematic accuracy over the range 4.5-50 GeV. These results do not confirm the distinct increase in the positron fraction above 10 GeV that was reported in several other experiments. This seems to rule out a number of models that were proposed to explain the apparent positron excess. In the context of the leaky box model, we conclude from our data that at most 2-3% of the total electron flux (e + + e \Gamma ) arriving near Earth could consist of positrons from primary sources. 1 Introduction Electrons and positrons are distinguished from the nuclear cosmic rays by their low mass and the absence of hadronic interactions. Therefore, at high energies their propagation through the galaxy becomes dominated by radiative energy losses. Different mechanisms may also contribute to the sources of these particles, but are difficult to identify on the basis o..