THE ASTROPHYSICAL JOURNAL, 565 280296, 2002 January 20

High-energy collisions of cosmic-ray nuclei with interstellar gas are believed to be the mechanism producing the majority of cosmic-ray antiprotons. Because of the kinematics of the process, they are created with a nonzero momentum ; the characteristic spectral shape with a maximum at D2 GeV and a sharp decrease toward lower energies makes antiprotons a unique probe of models for particle propagation in the Galaxy and modulation in the heliosphere. On the other hand, accurate calculation of the secondary antiproton ux provides a "" background for searches for exotic signals from the annihilation of supersymmetric particles and primordial black hole evaporation. Recently, new data with large statistics on both low- and high-energy antiproton uxes have become available which allow such tests to be performed. We use our propagation code GALPROP to calculate interstellar cosmic-ray propagation for a variety of models. We show that there is no simple model capable of accurately describing the whole variety of data : boron/carbon and sub-iron/iron ratios, spectra of protons, helium, antiprotons, positrons, electrons, and di+use c-rays. We nd that only a model with a break in the di+usion coefficient plus convection can reproduce measurements of cosmic-ray species, and the reproduction of primaries (p, He) can be further improved by introducing a break in the primary injection spectra. For our best-t model we make predictions of proton and antiproton uxes near the Earth for di+erent modulation levels and magnetic polarity using a steady state drift model of propagation in the heliosphere