New experimental information is presented about the effect of a nucleus on patrons which have undergone a hard scatter. We have observed clear dijet events from 400 GeV/c p-nucleus interactions and compared them to dijets from pp interactions. Our results show that the angular width of the individual jets is only slightly affected by the presence of the nucleus, but the acoplanarity of the jet pairs is sharply increased.

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The production of high-p, direct photons is studied using quantum chromodynamics. The theoretical predictions are shown to be compatible with the existing data over the energy interval 20 < fi< 63 GeV. In addition, the possibility of using a high-p, direct-photon trigger in hadronic-jet experiments is studied. By simultaneously triggering on a direct photon and on the away-side hadronic jet it is possible to obtain more precise information concerning the underlying dynamical subprocesses than if a two-jet trigger is used. In particular, one can, by using a combination of n * , p , and p beams, measure both the pion quark and gluon distribution functions as well as the gluon distribution function for the proton. Furthermore, if particle identification is available for the away-side jet, one can separately measure various quark and gluon fragmentation functions. A method of measuring the Q 2 dependences of these various functions is also discussed.

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We have measured inclusive e + e -production in 17-GeV/c P-p collisions and find anomalously large cross sections for pair masses below 0.6 GeV/cZ and Feynman x 1 0 . 5 . Charged particles and photons produced in association with e +e -were measured. Decays of known resonances are not capable of explaining the effect. No excess of photons or charged particles associated with the anomalous pairs is detected. Implications of our results for various models and for direct single-electron and photon production are discussed.