title: Measurement of the cosmic-ray antiproton-to-proton abundance ratio between 4 and 50 GeV.
abstract: We present a new measurement of the antiproton-to-proton abundance ratio, pbar/p, in the cosmic radiation. The HEAT-pbar instrument, a balloon borne magnet spectrometer with precise rigidity and multiple energy loss measurement capability, was flown successfully in Spring 2000, at an average atmospheric depth of 7.2 g/cm(2). A total of 71 antiprotons were identified above the vertical geomagnetic cutoff rigidity of 4.2 GV. The highest measured proton energy was 81 GeV. We find that the pbar/p abundance ratio agrees with that expected from a purely secondary origin of antiprotons produced by primary protons with a standard soft energy spectrum.
authors.affiliation: Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Beach
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: A W
authors.initials: AW
authors.lastname: Labrador
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: 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