NEW MEASUREMENTS OF COSMIC RAY POSITRONS

Abstract

Cosmic ray electrons consists of mostly negative electrons and a relatively smaller flux of positrons. A simple interpretation is that all the positrons, together with an approximately equal flux of negative electrons, are decay products of pions created in the interaction of cosmic ray protons with the interstellar medium, and the remaining negative electrons are produced in primary cosmic ray sources. However, the existing data on the positron fraction (e+/e++e−) does not support this simple picture. While the positron flux around a few GeV can be explained by the secondary production, there are apparently excesses of positrons both at lower and higher energies. This has stimulated many interpretation and conjectures of new astrophysical sources of positrons. Recently, there are new measurements from four different balloon experiments. They begin to show some discrepancy with the old data. A brief summary of the new results and their impact is given here.