Single-Pion Photoproduction in a Model of Higher Baryon Couplings

Rashmi Mehrotra and A. N. Mitra
Phys. Rev. D 5, 1803 – Published 1 April 1972
PDFExport Citation

Abstract

Pion photoproduction off nucleons via s-channel resonances up to a total c.m. energy of ∼ 2 GeV, and also the electromagnetic decay widths of such resonances, are investigated in a recently proposed unified model of B¯BLP and B¯BLV couplings. In this phenomenological model, which uses the "quark" language only formally, the couplings B¯BLP of baryon resonance (BL) with pseudoscalar (P) mesons in broken SU(6) × O(3) are extended to incorporate electromagnetic interactions through "partial symmetry" for B¯BLV couplings, together with the principle of vector-meson dominance. These supermultiplet LP0+ transitions are characterized by an empirical but relativistically invariant multiplying form factor, for which two different forms are considered. The calculated electromagnetic decay widths for the baryon resonances Y*(1520) and Δ(1238) are in extremely good agreement with experiment. For the other resonances no direct experimental data are available, and comparison has been made with other contemporary analyses. The results for the reactions γpπ0p, γpπ+n, and γnπp are also presented with reference to the following types of data: (i) total cross sections, (ii) the angular distribution of the differential cross sections, (iii) the energy dependence of the cross sections at fixed angles (especially θ=0, π), and (iv) recoilproton polarization. The agreement with the experimental data in all these respects is extremely good, thus suggesting that the direct s channel makes a large and dominant contribution to the amplitude in the intermediate-energy region. The only discrepancy lies in the forward direction for charge-exchange processes, where the t-channel pion pole is known to be important, yet a partial simulation of duality seems to be indicated by our results. Also, the qualitative features of pionic photoproduction are reasonably well reproduced by our model. The Moorhouse selection rule for spin quartet states and a "charge" selection rule proposed recently by Copley et al. are satisfied in the limit of mρ=mω in our model. The most prominent resonances turn out to be P11, P33, D13, F15, and F37.

  • Received 23 October 1970

DOI:https://doi.org/10.1103/PhysRevD.5.1803

©1972 American Physical Society

Authors & Affiliations

Rashmi Mehrotra and A. N. Mitra

  • Department of Physics and Astrophysics, University of Delhi, Delhi-7, India.

References (Subscription Required)

Click to Expand
Issue

Vol. 5, Iss. 7 — 1 April 1972

Reuse & Permissions
Access Options
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review D

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×