UNIV OREGON,DEPT PHYS,EUGENE,OR 97403
; ACAD SINICA,INST HIGH ENERGY PHYS,COSM RAY LAB,BEIJING 100039,PEOPLES R CHINA
; UNIV CALIF BERKELEY,DEPT PHYS,BERKELEY,CA 94720
; UNIV CALIF BERKELEY,SPACE SCI LAB,BERKELEY,CA 94720
; UNIV CALIF BERKELEY,LAWRENCE BERKELEY LAB,DIV NUCL SCI,BERKELEY,CA 94720
; UNIV CALIF BERKELEY,LAWRENCE BERKELEY LAB,INST NUCL & PARTICLE ASTROPHYS,BERKELEY,CA 94720
We present a detailed account of our analysis on ultrahigh-energy cosmic-ray double-core 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 Lambda(c)>1.4 TeV or a possible value of Lambda(c) similar or equal to 1.6 TeV from the CDF at the Fermilab Tevatron. We discuss possible onset of new physics indicated by the large discrepancy at E(lab)similar to 10(4)-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.