Two Topics in Particle Physics. I. Tests for Helicity Conservation and Spin-Parity Selection Rules in Diffraction Dissociation. II. Independent Production of Pions

Citation

Silver, Richard Neil (1971) Two Topics in Particle Physics. I. Tests for Helicity Conservation and Spin-Parity Selection Rules in Diffraction Dissociation. II. Independent Production of Pions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2932-DW06. https://resolver.caltech.edu/CaltechTHESIS:06112018-103332658

Abstract

I. Tests for Helicity Conservation and Spin-Parity Selection Rules in Diffraction Dissociation

A phenomenological discussion of diffraction dissociation is presented in which the development of experimental tests for its conjectured properties is emphasized. Of particular interest is the problem of distinguishing between the behavior of resonances and background. Simple tests for the helicity, spin-parity, and internal quantum number selection rules proposed for resonance production would be possible only if the nonresonant background were absent. These would include an isotropy in azimuthal angle test for helicity conservation and a symmetry under parity inversion test for the Chou-Yang and Carlitz-Frautschi-Zweig rules. The more general and realistic case is that in which nonresonant background is present as well as resonances. It is found that a nonresonant pion exchange mechanism can account for the production characteristics of the broad low mass enhancements seen in present diffraction dissociation data. These include the variation of momentum transfer dependence with invariant mass and the spin-parity of the enhancements. It is unlikely that this background obeys the selection rules expected of resonance production. Nevertheless, the rapid variation in phase and possibly high spins of resonance contributions when interfered with the slow variation in phase and predominantly low spins expected of a pion exchange contribution should make possible tests for resonance production selection rules given adequate statistics.

II. Independent Production of Pions

We investigate theoretical limitations on the possibility that multiparticle experiments at high energies are dominated by the independent production of uncorrelated pions. A description of pion production in coherent states is developed in order to systematically study the effects of conservation laws. Charge conservation leads to modifications of Poisson distributions for charged particle production in purely hadronic reactions that agree well with experiment. Other systems such as e⁺ e^- → pions are so limited by charge conjugation considerations that production of uncorrelated pious is ruled out. A formalism for the isospin analysis of pious with identical momentum distributions is developed and applied to coherent states. The fixed phase of a coherent state is important for minimizing the increase of <I²> with <n>. The minimum that can be achieved with independent uncorrelated pious is a random walk in isospace. In this case the dominant contributions at present multiplicites come from the lowest isospins so that independent and coherent pions can be an approximation to experiment. Finally, the role of two pion correlations is studied. Independent emission of isoscalar pairs of pions solves the isospin problem and gives reasonable distributions of charged pions, but leads to negative correlations between charged and neutral pions that seriously disagree with experiment. Emission of charged isovector pairs of pions would improve the agreement with the observed slightly positive correlations. It is concluded that the effects of the many possible correlations may be difficult to resolve in the present analysis of existing data.

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