New Measurement of the Cosmic-Ray Positron Fraction from 5 to 15 GeV
  We present a new measurement of the cosmic-ray positron fraction at energies between 5 and 15 GeV with the balloon-borne HEAT-pbar instrument in the spring of 2000. The data presented here are compatible with our previous measurements, obtained with a different instrument. The combined data from the three HEAT flights indicate a small positron flux of non-standard origin above 5 GeV. We compare the new measurement with earlier data obtained with the HEAT-e+- instrument, during the opposite epoch of the solar cycle, and conclude that our measurements do not support predictions of charge sign dependent solar modulation of the positron abundance at 5 GeV. 
J. J. Beatty, A. Bhattacharyya, C. Bower, S. Coutu, M. A. DuVernois,   S. McKee, S. A. Minnick, D. Muller, J. Musser, S. Nut...