Glossary for new particles and new quantum numbers

Abstract

We give some definitions here for the convenience of non-specialist readers. Many words are used with a technical meaning quite different from their everyday meaning. A number of initials are also defined in the Introduction. Asymptotic freedom . The property which some gauge theories of strong interactions have, that the strong interactions become steadily weaker at high energy and/or momentum transfer, or, equivalently, at short distances. Charm . A fourth quark attribute C , the other quark attributes being baryon number B , charge Q and strangeness s (or hyperchange Y = B + s ). The quarks of SU(3) symmetry have charm C = 0; a charmed quark has C = +1, and the charmed antiquark has C = — 1. The hadronic interactions for quarks and antiquarks are believed to obey (approximately) an SU(4) symmetry. Charmonium . Name given to the bound quark-antiquarke system cc̅, by analogy with the name positronium for the particle-antiparticle system e _ e + well known in electrodynamics. Colour . A three-dimensional attribute of the quark, acting in a parallel ‘ colour space’ for an internal symmetry SU(3) Each quark may exist in three possible states, (fancifully) labelled red, white and blue by M. Gell-Mann. For given ( Q, s, C ) these three quark states have identical properties with respect to the weak and electromagnetic interactions, and their hadronic forces are SU(3)' symmetrical. The wavefunction for a hadronic system is then the sum of terms each consisting of three factors, a wavefunction in colour space, a wavefunction in SU(4) space and a wavefunction describing the spin and orbital motions. This complete wavefunction must be antisymmetric with respect to permutations of the labels attached to the quarks, as the Pauli principle requires for spin-1/2 particles