We find a significant excess of ultrahigh-energy cosmic-ray events at large transverse moments with respect to the prediction by standard perturbative /CD at E&~b~10 -10 TeV, an energy regime beyond the reach of existing colliders but vnthin the range of future hadron coOiders. Such a large deviation cannot be accounted for by a compositeness model of quarks arith a characteristic energy scale A, & 1.4 TeV allured by current collider experiments, pointing towards neer physics.PACS numbers: 13.85. Tp, 12.38. gk, 12.60.Re, 96.40.De Efforts have been made to search for signals of departures from the standard model in current high-energy studies. For instance, the proliferation of quarks and leptons has naturally inspired the speculation that they are composite bound states of more fundamental constituents called preons [1]. The basic assumption that underlines almost all composite model building is that preons interact by means of a new strong gauge interaction called metacolor. Compositeness of quarks would manifest itself as an effective four-fermion contact interaction which would be visible at momentum transfers well above a characteristic energy scale, A, . Among various ways suggested so far to test the hypothesis, it is particularly interesting to study the behavior of jet inclusive cross sections at large transverse momentum, p2, where effects of a hypothetical quark substructure could result in a deviation from /CD prediction [2]. At existing accelerators, several experiments have been carried out and have yielded null results [3,4]. In the latest experiment at the Fermilab Tevatron pp collider (v/s = 1.8 TeV), no excess of events at large pr with respect to the standard /CD prediction has been observed and the most stringent lower limit of 1.4 TeV has been placed on A, [4].Various limits on the substructure of quarks and leptons have been obtained by studying e+e + e+e, @+is r+r, and qq, KLn, -+ p, e, Kc-K or Ds-D mixing, and the anomalous magnetic moment of muons [1,5].It is of interest to look for such a deviation in jet production cross section in cosmic-ray interactions at even higher energies. We have examined cosmic-ray doublecore events with large p2 observed in emulsion chamber experiments. Extending the leading-order /CD jet calculations for hadron-hadron collisions to hadron-nucleus collisions by including nuclear effects, we have simulated cosmic-ray particle production and propagation in the atmosphere in order to understand quantitatively the double-core events. In this Letter, we report a significant deviation in the jet cross section at large~derived from cosmic-ray data with respect to the calculation by perturbative /CD. Atmospheric cosmic-ray events observed in emulsion chambers installed on mountains at high altitudes provide information about characteristics of the strong interaction at ultrahigh energies. Several such experiments have been carried out for more than a decade, with the goals of searching for new phenomena and studying the mechanism of nuclear collisions in an energy r...
