Relativistic descriptions of polarization transfer observables for quasielastic proton scattering

Hillhouse, G. C.(Gregory Campbell) (1999)

Thesis (Ph.D.) -- University of Stellenbosch, 1999.

Thesis

ENGLISH ABSTRACT: This thesis is devoted to the development of relativistic Dirac-based models for describing complete sets of quasielastic (p,p') and (p, ii) polarization transfer observables at medium energies. The original relativistic-plane-wave-impulse-approximation (RPWIA) model of Horowitz and Murdock is modified to include the phenomenological Horowitz-Love-Franey meson-exchange (HLF) model for the NN amplitudes, and new HLF parameter sets are generated between 80 and 200 MeV. Medium effects are incorporated by replacing free nucleon masses in the Dirac plane waves with more refined effective projectile and target nucleon masses. For a 4°Ca target at a fixed momentum transfer of 1.97 fm-1, and incident energies between 135 and 300 MeV, the sensitivity of complete sets of quasielastic (P,p') and (P, ii) polarization transfer observables is investigated with respect to nuclear medium effects, ambiguities in 1rNN coupling, exchange contributions to NN amplitudes, and spin-orbit distortions. It is seen that, (1) compared to (p,p 1 ) scattering, the (p, ii) polarization transfer observables are more sensitive to pseudoscalar versus pseudovector forms of the 1rNN coupling, (2) as the incident proton energy is lowered, nuclear medium effects and spin-orbit distortions become more important, (3) nuclear medium effects are extremely sensitive to the type of pion coupling, (4) contrary to the original RPWIA, exchange contributions cannot be neglected at energies as high as 500 MeV. For an optimal study of nuclear medium effects, this investigation stresses the urgent need for measurements of complete sets of quasielastic polarization transfer observables for both (p,p') and (p, n) reactions at energies lower than 200 MeV. Comparison of RPWIA predictions with the small amount of available data yields an inconsistent picture: The (P, p') data favour a pseudoscalar coupling for the pion, whereas the limited (P, n) data suggest a pseudovector form. Our poor treatment of distortions is considered to be the main source for this inconsistency. The issue of distortion effects on polarization transfer observables is addressed by developing the theoretical framework for the relativistic distorted wave impulse approximation. As an additional improvement over the RPWIA, models of nuclear structure (relativistic Fermi-gas model, relativistic mean-field approximation, and local-density-approximation) are developed, whereby the nuclear structure information is contained in a large set of nuclear respon

AFRIKAANSE OPSOMMING: Hierdie proefskrif handel oor die ontwikkeling van relatiwistiese modelle, gebaseer op die Diracformalisme, vir volledige stelle parameters vir spinpolarisasie-oordrag in die geval van kwasielastiese (p, p ') en (p, ii) verstrooiing by medium energiee. Die oorspronklike Relatiwistiese Vlakgolf-Impulsbenadering (RVI) van Horowitz en Murdock is gewysig om ook die fenomenologiese meson-uitruilmodel van Horowitz, Love en Franey (HLF-model) vir die nuckleon-nukleon (NN) amplitudes in te sluit. Hiervoor is 'n nuwe stel HLF-parameters vir die energiegebied 80- 100 MeV bereken. Om effekte van die omringende kernmedium in te sluit, is effektiewe nukleon massas tans vir beide die projektiel- en die teikennukleon op 'n nuwe, verfynde wyse bereken. Vir die kwasi-elastiese reaksies (p,p ') en (p, ii) met 4°Ca as teikenkern, invallende energiee tussen 135 en 500 MeV en 'n (vaste) momentum-oordrag van 1,97 fm-1, is volledige stelle polarisasie-parameters bereken. Laasgenoemde se gevoeligheid is ondersoek ten opsigte van effekte van die kernmedium, dubbelsinnighede ten opstigte van die 1r NN-interaksie, die bydraes van uitruilterme tot die NN-interaksie en die golfvervorming as gevolg van spin-baan koppeling. Die volgende is bevind: (1) Die polarisasieveranderlikes van die (p, ii)-reaksie is meer gevoelig ten opsigte van die keuse tussen 'n pseudoskalare of 'n pseudovektor term in die 1rNN-interaksie, as die van die (P,p ') reaksie; (2) Effekte van die kernmedium en spin-baan vervorming word belangrik by lae energiee; (3) Die effekte van die kernmedium is uiters gevoelig vir die tipe pion-koppeling; ( 4) In teenstelling met die oorspronklike RVI, kan uitruileffekte nie by hoer energiee, byvoorbeeld 500 MeV, verontagsaam word nie. Hierdie ondersoek beklemtoon dat, vir 'n behoorlike studie van effekte van die kernmedium, veral vir energiee laer as 200 MeV, volledige stelle van polarisasie-veranderlikes van beide (P,p') en (if, ii) reaksies gemeet moet word. Vergelykings met die beperkte beskikbare data (hoofsaaklik vanaf onvolledige stelle veranderlikes) lewer 'n onsamehangende prentjie: Die (p, ii)polarisasieveranderlikes gee voorkeur aan 'n pseudovektor term in die 1rNN-interaksie, waar die (if, p ') veranderlikes egter 'n pseudoskalare-term verkies. Die oorsaak van hierdie niekonsistensie kan moontlik aan die weglating van vervorming van die invallende golf deur die kernmedium gewyt word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/51408
This item appears in the following collections: