Study of hadrons at the cores of extensive air showers and the elemental composition of cosmic rays at 1015 eV

An experiment was done near sea level at College Park, Maryland, to study hadrons near the cores of air showers resulting from primary cosmic rays of 100--10 000 TeV per nucleon. The parameters studied were (1) the rate of events which exceed a minimum shower density cut and specific hadronic calorimeter signal cuts and (2) the rate of events with hadrons delayed with respect to the shower front. Extensive computer simulations of the experiment were done using several particle-interaction and primary-composition models as well as details of the detector response. It is found that interaction models which include scaling or only modest scaling violation will fit the data only with primary spectra that are rich in heavy nuclei in the 100--10 000-TeV total-energy range. A proton-dominated flux will fit the data only when an extreme scale-breaking model is used, in disagreement with extrapolations of accelerator data