Physics & Astronomy ETDs

Bruce Goplen

Publication Date

12-2-1974

Abstract

The nonradiative absorption of positive pi-mesons by deuterons is studied within the framework of Lagrangian formalism and the impulse approximation. The pi-nucleon absorption interaction is taken to be pseudovector; however, the reaction is believed to be dominated by pi­nucleon scattering. Thus, the main thrust of the investigation is directed at three different approaches to the scattering interaction. First, the Hamiltonian formalism of Koltun and Reitan is extended to include energetic pions. An off-shell form is chosen for p-wave scattering which at low energy reduces to the field-theoretical result of Klein. In the second approach, the S-matrix formalism of Lazard, Ballot and Becker is adapted for use with phenomenological nucleon­nucleon wave functions. Here the scattering interaction off-shell is given by the on-shell amplitudes. Finally, a pion optical model formalism is presented in which scattering graphs are included through modification of the external pion wave function. A new second-order optical model for the deuteron is given. In all three approaches calculations are performed using phenomenological nuclear potentials, including the Boundary Condition Model and the Hamada-Johnston. Calculated results for total and differential cross sections are compared with experimental data from 2 to 240 MeV pion kinetic energy. The S-matrix approach and two forms of the Hamiltonian method are successful in representing the data, while the Kisslinger optical model produces a resonance below the experimental peak. Results are also presented for pi-deuteron elastic scattering calculations using the pion optical model, which gives reasonable agreement with the experimental data. In conclusion, it does not appear possible to confirm the Galilean­invariant absorption term with this reaction. However, differential cross section results exhibit some sensitivity to nuclear models and to the D-state fraction in the deuteron. An experiment now under way at LAMPF may allow selection of preferred nuclear models. While use of an on-shell scattering Hamiltonian gives the desired total cross section, this result is not credible since calculations show great sensitivity to the off-shell behavior. The pi-deuteron absorption reaction offers a good means of measuring this off-shell behavior. Finally, a separable Hamiltonian interaction density is recommended for the investigation of nuclear structure using pi-meson absorption.

Degree Name

Physics

Level of Degree

Doctoral

Department Name

Physics & Astronomy

First Committee Member (Chair)

Christopher Pratt Leavitt

Second Committee Member

Illegible

Third Committee Member

Roy Thomas

Fourth Committee Member

Howard Carnes Bryant

Language

English

Document Type

Dissertation

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