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Title: Photoproduction of positive parity baryons in the 1/Nc expansion of QCD

Abstract

We analyze the photoproduction helicity amplitudes for non-strange positive parity excited baryons in the context of the 1/N{sub c} expansion of QCD. Our results strongly suggest that, although one-body transition operators provide the dominant contributions, two-body transition operators are definitely required in order to get good fits to the presently known empirical amplitudes. The significance of this result for quark model calculations is briefly discussed.

Authors:
;
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
896664
Report Number(s):
JLAB-THY-06-601; DOE/ER/40150-4171
TRN: US0700815
DOE Contract Number:
AC05-84ER40150
Resource Type:
Journal Article
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; AMPLITUDES; BARYONS; HELICITY; PARITY; PHOTOPRODUCTION; QUANTUM CHROMODYNAMICS; QUARK MODEL

Citation Formats

Jose L. Goity, and Norberto N. Scoccola. Photoproduction of positive parity baryons in the 1/Nc expansion of QCD. United States: N. p., 2006. Web.
Jose L. Goity, & Norberto N. Scoccola. Photoproduction of positive parity baryons in the 1/Nc expansion of QCD. United States.
Jose L. Goity, and Norberto N. Scoccola. Thu . "Photoproduction of positive parity baryons in the 1/Nc expansion of QCD". United States. doi:. https://www.osti.gov/servlets/purl/896664.
@article{osti_896664,
title = {Photoproduction of positive parity baryons in the 1/Nc expansion of QCD},
author = {Jose L. Goity and Norberto N. Scoccola},
abstractNote = {We analyze the photoproduction helicity amplitudes for non-strange positive parity excited baryons in the context of the 1/N{sub c} expansion of QCD. Our results strongly suggest that, although one-body transition operators provide the dominant contributions, two-body transition operators are definitely required in order to get good fits to the presently known empirical amplitudes. The significance of this result for quark model calculations is briefly discussed.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Dec 21 00:00:00 EST 2006},
month = {Thu Dec 21 00:00:00 EST 2006}
}
  • We analyze the photoproduction helicity amplitudes for non-strange positive parity excited baryons in the context of themore » $$1/N_c$$ expansion of QCD. Our results strongly suggest that, although one-body transition operators provide the dominant contributions, two-body transition operators are definitely required in order to get good fits to the presently known empirical amplitudes. The significance of this result for quark model calculations is briefly discussed.« less
  • We analyze the photoproduction helicity amplitudes for positive-parity excited baryons in the context of the 1/N{sub c} expansion of QCD. The results show that subleading corrections in 1/N{sub c} are important and that, while one-body effective operators are dominant, there is some evidence for the need for two-body effects.
  • The decays of non-strange positive parity baryons via emission of a pseudo-scalar meson are studied in the framework of the 1/Nc expansion to order 1/Nc. In particular, the pionic decays of the l=0 Roper baryons and of the l=2 baryons in the mass interval 1680-1950 MeV are analyzed using the available partial decay widths. Decay widths by emission of an eta meson are shown to be suppressed by a factor 1/Nc{sup 2} with respect to the pionic ones.
  • The decays of non-strange negative parity baryons via the emission of single {pi} and {eta} mesons are analyzed in the framework of the 1/N{sub c} expansion. A basis of spin-flavor operators is established to that order, and with this basis the different partial wave decay amplitudes are obtained. The unknown effective coefficients are determined by fitting to the S- and D-wave partial widths as provided by the PDG. A full set of relations between widths that result at the leading order, i.e. order N{sub c0}, is given and tested with the data. The rather large errors of the input partialmore » widths, that result from the often discrepant results for the resonance parameters from different analyses of the data, lead to a rather good fit at the leading order N{sub c0}. The next to leading order fit fails for that reason to pin down with satisfactory accuracy the effective sub leading effective constants.« less
  • We study the photoproduction helicity amplitudes of negative parity baryons in the context of the 1/Nc expansion of QCD. A complete analysis to next-to-leading order is carried out. The results show sub-leading effects to be within the magnitude expected from themore » $$1/N_c$$ power counting. They also show significant deviations from the quark model, in particular the need for 2-body effects.« less