Hadronic Interactions with High Transverse Energy.

Properties of events produced with high values of transverse energy (E_{T}) in 800 GeV/c proton-nucleus (pA) collisions are presented. The events were collected using the large acceptance Fermilab multiparticle spectrometer that detected particles containing nearly 95% of the available beam energy. Six nuclear targets (H, Be, C, Al, Cu, and Pb) were used to establish A-dependent trends in the data. High E_{T} events were collected using both full-azimuth and limited aperture high E_{T} triggers. The A-dependence of the cross sections at a given E_{T} is parametrized as A^{alpha}. The value of alpha increases from 0.7 at low E_{T} to a plateau at high E_{T} of approximately alpha ~eq 1.6. A strong dependence of alpha on the event structure is observed; events dominated by narrow "jets" of particles, expected to arise from hard scattering, exhibit an A-dependence consistent with alpha ~eq 1.0. Jet clusters are reconstructed using a standard jet-finding algorithm so that cross sections and event structures for single jet and dijet events can be measured. The pp data measurements are consistent with results from hard scattering experiments done at other energies. Nuclear effects in jet production are extracted from comparisons of pp and pA data. Jet structures in the pA data become less pronounced for heavier nuclei. Cross sections at a given jet transverse momentum (p_{T }) or dijet E_{T} are well described by the A^{ alpha} parametrization. Values of alpha for jet p_{T} > 7 GeV/c or dijet E_ {T} > 15 GeV are consistent with alpha ~eq 1.6. This value of alpha indicates that a significant amount of jet rescattering occurs within the nucleus.