Why the Antiproton-to-Proton Ratio Stays Flat, and What Its Flatness Excludes

This paper presents a computed study of cosmic-ray antimatter, carried out with a transparent analytic treatment whose every numerical output is produced by deposited code. The computed ratio climbs through the threshold region, settles near the published plateau value by 20 GeV, and then drifts by only a small percentage between 20 and 300 GeV. The headline outputs of the computation are: r20 = 2.11e-04; r100 = 2.03e-04; r300 = 1.99e-04; spread_pct = 5.8. All values are computed from the stated assumptions and published reference data; the study is simulated, not measured, and its conclusions are stated at the size the propagated input uncertainties permit. The calculation is designed so that each input can be varied independently, making clear which assumptions each conclusion depends on and which it survives.