Cosmic-ray double-coreγ-family events at ultrahigh energies

Abstract

We present a detailed account of our analysis on ultrahigh-energy cosmic-ray double-core $\ensuremath{\gamma}$-family events observed in emulsion chambers at mountain levels. Extending the leading-order perturbative QCD jet calculations for hadron-hadron collisions to hadron-nucleus collisions by including nuclear effects, we performed a Monte Carlo simulation of cosmic-ray particle interaction and propagation in the atmosphere. We find a significant excess of event rates at large transverse momenta with respect to our prediction based on perturbative QCD. The excess cannot be accounted for by a compositeness model of quarks with a characteristic energy scale lower limit ${\ensuremath{\Lambda}}_{c}>1.4$ TeV or a possible value of ${\ensuremath{\Lambda}}_{c}\ensuremath{\simeq}1.6$ TeV from the CDF at the Fermilab Tevatron. We discuss possible onset of new physics indicated by the large discrepancy at ${E}_{\mathrm{lab}}\ensuremath{\sim}{10}^{4}\ensuremath{-}{10}^{5}$ TeV, an energy region beyond the reach of existing colliders but within the range of future hadron colliders such as the proposed Large Hadron Collider at CERN.