Hadronic and Electromagnetic Interactions at Large Transverse Momentum

The scaling laws of inclusive and exclusive processes at large transverse momentum are reviewed. Their theoretical interpretation in terms of composite models for the hadrons is then discussed. The observed inverse power-law behavior of the invariant cross sections at fixed invariant ratios is found to agree with the degrees of freedom suggested by the simple dimensional counting in the quark model. Such counting is characteristic of renormalizable quark field-theoretic models with asymptotically scale-invariant constituent interactions and finite Bethe-Salpeter wavefunctions. However, as sug- gested by the parton interchange model, elementary gluon interactions between quarks of different hadrons must be sup- pressed in order to understand (1) the scaling, but not scale- invariant behavior of the inclusive hadronic cross section for meson production at large transverse momentum, and (2) the effective Regge behavior at large t and angular distribution of exclusive hadronic and electromagnetic processes.