CHAPTER 1 - Preliminary Concepts

Abstract

With the knowledge of high-energy physics the reactions of subnuclear particles can be described by four or five different interactions—the strong interactions of baryons and mesons, the electromagnetic interactions mediated by photons, the weak interactions observed mainly in slow decay processes and neutrino reactions, and gravitation. This chapter discusses the concept of different interactions based on two classes of phenomena. In cross-sections, decay rates, and mass-differences the characteristic orders of magnitude can be found for the effects of each interaction. Universal coupling constants have been identified for the electromagnetic and weak interactions, the electric charge and the Fermi coupling constant. For strong interactions the pion-nucleon coupling constant represents the order of magnitude, but no universal role is ascribed to it. Gravitation coupling is universal at the macroscopic level, but it is too weak to be tested with subnuclear particles. Baryons and mesons take part in all interactions; of the leptons, electrons and muons participate in electromagnetic and weak interactions, neutrinos only in weak interactions. The interactions have different symmetries and conservation laws. Relativistic invariance in respected by all interactions, and the product operation CPT (charge conjugation, space reflexion, time reversal) is taken to be a universal symmetry. Absolute conservation laws have been found for the baryon number, lepton number, and electric charge.