EMPIRICAL DETERMINATION OF THE VERY-HIGH-ENERGY HEAVY-QUARK CROSS-SECTION FROM NONACCELERATOR DATA

To cosmic rays incident near the horizon the Earth's atmosphere repres ents a beam dump with a slant depth reaching 36 000 g cm-2 at 90-degre es. The prompt decay of a heavy quark produced by very high energy cos mic ray showers will leave an unmistakable signature in this dump. We translate the failure of experiments to detect such a signal into an u pper limit on the heavy quark hadroproduction cross section in the ene rgy region beyond existing accelerators. Our results disfavor any rapi d growth of the cross section or the gluon structure function beyond c onservative estimates based on perturbative QCD.