New Measurement of the Cosmic-Ray Positron Fraction from 5 to 15 GeV

J. J. Beatty, A. Bhattacharyya, C. Bower, S. Coutu, M. A. DuVernois, S. McKee, S. A. Minnick, D. Müller, J. Musser, S. Nutter, A. W. Labrador, M. Schubnell, S. Swordy, G. Tarlé, and A. Tomasch

Phys. Rev. Lett. 93, 241102 – Published 9 December 2004

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- $e^{\pm}$ 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.

Received 2 July 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.241102

Authors & Affiliations

J. J. Beatty^1,*, A. Bhattacharyya², C. Bower², S. Coutu¹, M. A. DuVernois^1,†, S. McKee³, S. A. Minnick^1,‡, D. Müller⁴, J. Musser², S. Nutter⁵, A. W. Labrador^4,§, M. Schubnell^3,∥, S. Swordy⁴, G. Tarlé³, and A. Tomasch³

¹Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
²Department of Physics, Indiana University, Bloomington, Indiana 47405, USA
³Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
⁴Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637, USA
⁵Department of Physics & Geology, Northern Kentucky University, Highland Heights, Kentucky 41099, USA

^*Now at Department of Physics, The Ohio State University, Columbus, OH 43210.
^†Now at School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455.
^‡Now at Department of Physics, Kent State University Tuscarawas Campus, New Philadelphia, OH 44663.
^§Now at CA Institute of Technology, Space Radiation Laboratory, Pasadena, CA 91125.
^∥Corresponding author. Email address: schubnel@umich.edu

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Vol. 93, Iss. 24 — 10 December 2004

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