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Two topics in elementary particle physics: 1) The reaction γ + N → π + N [photon + nucleon going to pion + nucleon] at high energies. 2) K leptonic decay and partially conserved currents


Zweig, George (1964) Two topics in elementary particle physics: 1) The reaction γ + N → π + N [photon + nucleon going to pion + nucleon] at high energies. 2) K leptonic decay and partially conserved currents. Dissertation (Ph.D.), California Institute of Technology.


1. γ + N → π + N

The process γ + N → π + N is studied at high energies in both the forward and backward directions. The helicity formalism is used. Contributions from the ρ, ω, φ and π trajectories in the t channel and from the N*3+/2, N1+/2, and N*1-/2 trajectories in s‾ channel are included. Polarization formulae for the final state nucleon are given. If we may neglect cuts in the angular momentum plane, then at high energies for momentum transfers -t >> μ2π the ρ trajectory should dominate charged pion photoproduction in the forward direction. A curde estimate of the cross section yields dσ/dt ~ s2jρ(0)-2 ≈ 1/s. However, the pion trajectory is expected to be important for small momentum transfers up to very high energies. For forward neutral pion photoproduction both the ρ and ω trajectories should be important. The cross section is estimated to be dσ/dt ~ 1/s. For photoproduction in the backward direction, the situation is much more complex with at least three trajectories contributing to dσ/ds‾. However, since the same set of trajectories are to be used in πN scattering, backward πN scattering and backward photoproduction are expected to have the same energy dependence. Assuming that the N*3+/2 trajectory dominates with jN*3+/2(0) ≈ 0, we obtain dσ/ds‾ ~ s2jN*3+/2(0)-2 ≈ 1/s2.

2. K Leptonic Decay and Partially Conserved Currents

An operational definition for the partial conservation of the strangeness changing vector current is given and applied to leptonic K+ and K°2 decay. The K* resonance is explicitly included in the calculation and quantitative agreement with experiment is obtained. A detailed comparison with the K+ data of Brown et. al. and Dobbs et al. is given. Because of rapid variations of a form factor, it is found that the data of these two groups are not in contradiction. From the K°2 experiment of Luers et. al., I = 1/2 and 3/2 currents are seen to exist. Λβ-decay is briefly considered. It is found that an explanation for the slowness of K leptonic decay and the vector part of Λβ-decay may be connected with the partial conservation of the strangeness changing vector current.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics. Reggie poles and photoproduction, Partially conserved currents, suppression of kaon decay
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Feynman, Richard Phillips (advisor)
  • Tollestrup, Alvin V. (advisor)
Thesis Committee:
  • Feynman, Richard Phillips (chair)
  • Walker, Robert Lee
  • Mathews, Jon
Defense Date:May 1963
Non-Caltech Author Email:zweig (AT)
Additional Information:Richard Feynman was George Zweig's thesis advisor. The author defended his thesis in May 1963, but is listed in the 1964 commencement program. He also went to CERN as a NAS-NRC postdoctoral fellow in summer 1963.
Funding AgencyGrant Number
U.S. Atomic Energy CommissionUNSPECIFIED
Record Number:CaltechETD:etd-12112002-091415
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4937
Deposited By: Imported from ETD-db
Deposited On:19 Dec 2002
Last Modified:26 May 2017 19:25

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