CP Violation and Flavor Mixing

Abstract

This is the text of the Nobel Lecture delivered on December 8, 2008, at Aula Magna, Stockholm University. §1. IntroductionWe know that ordinary matter is made of atoms. An atom consists of the atomic nucleus and the electrons. The atomic nucleus is made of a number of the protons and the neutrons. The proton and the neutron are further made of two kinds of quarks, u and d. Therefore the fundamental building blocks of ordinary matter are the electron and two kinds of quarks, u and d.The standard model, which gives comprehensive description of current understanding of the elementary particle phenomena, however, tells us that the number of species of quarks is six. The additional quarks are called s, c, b and t. The reason why we do not find them in the ordinary matter is that they are unstable in the usual environment. Similarly, the electron belongs to a family of six members called leptons. Three types of the neutrinos are included among these six.Another important ingredient of the standard model is the fundamental interac-Fig. 1. The standard model.)