Search

Arguments are presented in favor of the existence of “charm” particles, that is, hadronic states not classifiable in the usual three-quark model of Gellmann and Zweig. The three-triplet scheme of Han-Nambu is the most promising but, far from unique, theoretical structure for such particles. Assuming, for any of these models, that the charm quantum number is conserved in strong and electromagnetic interactions, but not in weak interactions, limits are deduced from past experiments on the possible minimum mass of charm particles and the maximum charm-changing four-fermion coupling constant. Finally several possible experimental methods of searching for charm particles are discussed. Unfortunately none are certain to discover them even if they do exist with masses less than a few GeV.