![]() ![]() NUCLEAR PHYSICS LECTURES PPT PLUSThere appear to exist approximate "lepton-type" conservation laws: the number of e − plus the number of ν e minus the number of the corresponding antiparticles e + and ¯ ν e is conserved in weak reactions, and similarly for the muon and tau-type leptons. ![]() These particles all have antiparticles, in accordance with the predictions of relativistic quantum mechanics (see CPT Theorem). There are three well-defined lepton pairs, the electron (e −) and the electron neutrino (ν e), the muon (µ −) and the muon neutrino (ν µ), and the (much heavier) charged lepton, the tau (τ), and its tau neutrino (ν τ). The charged lep-tons have electromagnetic as well as weak interactions the neutral ones only interact weakly. There are the leptons (see Electron, Leptons, Neutrino, Muonium), all of which have spin 1 2. Classification of Particles The particles that have been identified in high-energy experiments fall into distinct classes. There are also speculative but encouraging developments in the attempt to unify these interactions into a simple underlying framework, and even to incorporate quantum gravity in a parameter-free "theory of everything." In this article we shall attempt to highlight the ways in which information has been organized, and to sketch the outlines of the standard model and its possible extensions. These theories, which are collectively known as the standard model, are almost certainly the correct description of Nature, to first approximation, down to a distance scale 1/1000th the size of the atomic nucleus. Highly successful mathematical theories of the electromagnetic, weak, and strong interactions have been devised and tested. ![]() In the past several decades an enormous amount of experimental information has been accumulated, and many patterns and systematic features have been observed. Elementary-particle physics deals with the fundamental constituents of matter and their interactions. ![]()
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