Particle physics I

Abstract

Particle families (quarks and leptons), their properties and their interactions are introduced. The exchange mechanism and the Yukawa potential are discussed. Natural units are explained. The cross-section for e − + e + → μ‎− + μ‎+ is calculated using a first order Feynman diagram. Comparison with data reveals the existence of the Z0-boson and makes a link between electroweak processes. Higher orders diagrams give divergences and their removal by renormalization is described. Neutrino properties are outlined and the determination of the number of light neutrinos related. The weak interaction is discussed: parity and charge parity are seen to be maximally violated in W-boson exchange, but the product is approximately conserved. Handedness is pursued in an appendix using Dirac spinors. The neutrino mass and weak eigenstates differ and this leads to oscillations between weak eigenstates in flight. Measurements of the neutrino flux from the sun revealing this behaviour are described. Weak and strong eigenstates of quarks also differ by a unitary transformation, the CKM matrix. This difference leads to oscillations of certain neutral mesons from particle to antiparticle. This behaviour is explored for neutral K-mesons and for B0 d mesons. CP violation is observed, which is required for the survival of matter in the universe.