STUDYING NEW PHYSICS USING ULTRAHIGH-ENERGY COSMIC-RAY GAMMA-FAMILY DATA

This review discusses some recent developments in the study of ultrahi gh-energy interactions using cosmic-ray gamma-family data obtained wit h emulsion chambers at mountain altitudes. The apparent excess of the event rate at large transverse momenta with respect to the prediction based on perturbative QCD indicates new interaction mechanisms at E(la b)similar or equal to 10(4)-10(5) TeV, an energy regime beyond the rea ch of existing colliders. To reconcile the data with a compositeness m odel of quarks, the characteristic energy scale would have to be as lo w as Lambda(c) less than or equal to 0.1 TeV, in conflict with the low er limit of Lambda(c)>1.4 TeV or a possible value of Lambda(c) similar or equal to 1.6 TeV obtained by the CDF experiment at Tevatron. Possi ble new physics beyond the standard model, together with future experi ments at the LHC, are also discussed.