Measurement of the nuclear enhancement in high-Etand jet event production

Abstract
Properties of events produced with high values of transverse energy (Et) in 800-GeV/c proton-nucleus collisions are presented. Both full-azimuth and limited-aperture high-Et triggers were used to select events from six targets (H, Be, C, Al, Cu, and Pb). The events were collected using the large-acceptance Fermilab multiparticle spectrometer that recorded almost 95% of the incoming beam energy. The A dependence of the cross sections at a given Et was parametrized as Aα. The value of α increases from 0.7 at low Et to a plateau at high Et of approximately 1.6. The high-Et value of α is slightly smaller for the limited-aperture triggers. A strong dependence of α on the event structure is observed; ‘‘jetlike’’ events exhibit an A dependence consistent with α≊1.0, while for more isotropic events α is much larger. This observation is consistent with the expected behavior for jet production in pA collisions.