ABSTRACT
This chapter describes the fundamental particles known as leptons and quarks. The three generations of leptons include the negatively charged electron, muon, and tau particle, as well as the corresponding three flavours of neutrino: electron neutrino, muon neutrino, and tau neutrino, each of which has zero electric charge. Recently discovered flavour oscillations in solar neutrinos confirm that they possess non-zero masses. The three generations of quarks include up, charm, and top with a positive charge of 2/3 that of the proton, and down, strange, and bottom with a negative charge of 1/3 that of the electron. Each lepton and quark has an associated antimatter particle with opposite electric charge. Quarks combine in triplets to make baryons, and quark–antiquark pairs form mesons. These are collectively referred to as hadrons. Protons and neutrons are baryons composed of up and down quarks, whilst pions are mesons composed of up and down quarks and antiquarks. In high-energy reactions, energy may be converted into the mass of new particles, as long as mass-energy and charge are conserved.
