Parton models

Abstract

We discuss the successes and failures of the naive quark and Parton models and offer a possible remedy for the resonance symmetry versus vertex symmetry dilemma. Using the concept of current and constituent quarks related by a general Melosh-type transformation, we calculate matrix elements for excitation of the baryon octet ground state by weak and electromagnetic currents and find that the theory compares well with experiment except in the low ῲ region. Here some further SU (6) breaking mechanism is necessary for a good fit. An alternative to the current and constituent quarks idea is to attempt a relativistic treatment of quarks, assuming current and constituent quarks to be fundamentally identical. Several models are discussed and a new model for mesons is presented. The solutions are similar to those obtained in other models apart from the inclusion of spin-orbit coupling terms, which have not previously appeared naturally in relativistic wave functions. We calculate some decay widths and find reasonable agreement with the data.