title: New measurement of the cosmic-ray positron fraction from 5 to 15 GeV.
abstract: 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 nonstandard 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.
authors.affiliation: Department of Physics, Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Beatty
authors.forename: A
authors.initials: A
authors.lastname: Bhattacharyya
authors.forename: C
authors.initials: C
authors.lastname: Bower
authors.forename: S
authors.initials: S
authors.lastname: Coutu
authors.forename: M A
authors.initials: MA
authors.lastname: Duvernois
authors.forename: S
authors.initials: S
authors.lastname: McKee
authors.forename: S A
authors.initials: SA
authors.lastname: Minnick
authors.forename: D
authors.initials: D
authors.lastname: Müller
authors.forename: J
authors.initials: J
authors.lastname: Musser
authors.forename: S
authors.initials: S
authors.lastname: Nutter
authors.forename: A W
authors.initials: AW
authors.lastname: Labrador
authors.forename: M
authors.initials: M
authors.lastname: Schubnell
authors.forename: S
authors.initials: S
authors.lastname: Swordy
authors.forename: G
authors.initials: G
authors.lastname: Tarlé
authors.forename: A
authors.initials: A
authors.lastname: Tomasch