  This dissertation investigated selected processes involving baryons and
nuclei in hard scattering reactions. Through these processes, this work
explored the constituent structure of baryons and the mechanisms through which
the interactions between these constituents ultimately control the selected
reactions. First, hard nucleon-nucleon elastic scattering was studied
considering the quark exchange (QE) between the nucleons to be the dominant
mechanism of interaction in the constituent picture. It was found that an
angular asymmetry exhibited by proton-neutron (pn) elastic scattering data is
explained within this framework if a quark-diquark picture dominates the
nucleon's structure instead of a more traditional SU(6) model. The latter
yields an asymmetry around 90 deg center of mass scattering with a sign
opposite to what is experimentally observed. The second process is the hard
breakup by a photon of a nucleon-nucleon system in light nuclei. Proton-proton
(pp) and pn breakup in 3He, and double Delta-isobars production in deuteron
breakup were analyzed in the hard rescattering model (HRM), which in
conjunction with the QE mechanism provides a QCD description of the reaction.
Cross sections for both channels in 3He photodisintegration were computed
without the need of a fitting parameter. The results presented here for pp
breakup show excellent agreement with recent experimental data. In double
Delta-isobars production in deuteron breakup, HRM angular distributions for the
two double Delta channels were compared to the pn channel and to each other. An
important prediction from this study is that the Delta++ Delta- channel
consistently dominates Delta+Delta0, which is in contrast with models that
unlike the HRM consider a double Delta system in the initial state of the
interaction. For such models both channels should have the same strength.
