Effective-Lagrangian approach to the theory of pion photoproduction in the. Delta. (1232) region

Journal Article · Tue Jan 01 00:00:00 EST 1991 · Physical Review, D (Particles Fields); (USA)

DOI:https://doi.org/10.1103/PhysRevD.43.71· OSTI ID:6052570

Davidson, R M; Mukhopadhyay, N C; Wittman, R S ^[1]

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1. Physics Department, Rensselaer Polytechnic Institute, Troy, New York 12180-3590 (US)

We investigate theoretical uncertainties and model dependence in the extraction of the nucleon-{Delta}(1232) electromagnetic transition amplitudes from the multipole data base. Our starting point is an effective Lagrangian incorporating chiral symmetry, which includes, at the tree level, the pseudovector nucleon Born terms, leading {ital t}-channel vector-meson exchanges, and {ital s}- and {ital u}-channel {Delta} exchanges. We express the nucleon-{Delta} transition magnetic dipole ({ital M}1) and electric quadrupole ({ital E}2) amplitudes in terms of two independent gauge couplings at the {gamma}{ital N}{Delta} vertex, and fit these to various multipole data sets. We find a large sensitivity to the method used in unitarizing the amplitude, and extract the {ital E}2/{ital M}1 ratio (EMR) to be {ital negative}, with a magnitude of around 1.5%. The resonant amplitudes in this work are of interest to the test of topical hadron models inspired by QCD: the sign of the EMR, extracted by us, is in accord with that predicted by most realistic models, and its magnitude lies between the predictions of the quark shell model and the Skyrmion model. Finally, our work provides a phenomenologically satisfying unitary amplitude for pion photoproduction off nucleons, which can be used as a realistic starting point for theoretical studies of this process in complex nuclei.

• DOE Contract Number: AC02-83ER40114; FG02-88ER40448
• OSTI ID: 6052570
• Journal Information: Physical Review, D (Particles Fields); (USA), Vol. 43:1; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
PIONS
PHOTOPRODUCTION
CHIRAL SYMMETRY
DELTA-1232 BARYONS
E2-TRANSITIONS
LAGRANGIAN FUNCTION
M1-TRANSITIONS
QUANTUM CHROMODYNAMICS
QUARK MODEL
S CHANNEL
SHELL MODELS
STANDARD MODEL
T CHANNEL
U CHANNEL
BARYONS
BASIC INTERACTIONS
BOSONS
COMPOSITE MODELS
DELTA BARYONS
ELECTROMAGNETIC INTERACTIONS
ELEMENTARY PARTICLES
ENERGY-LEVEL TRANSITIONS
FERMIONS
FIELD THEORIES
FUNCTIONS
HADRONS
INTERACTIONS
MATHEMATICAL MODELS
MESONS
MULTIPOLE TRANSITIONS
N BARYONS
NUCLEAR MODELS
PARTICLE MODELS
PARTICLE PRODUCTION
PSEUDOSCALAR MESONS
QUANTUM FIELD THEORY
SYMMETRY
UNIFIED GAUGE MODELS
645202* - High Energy Physics- Particle Interactions & Properties-Theoretical- Electromagnetic Interactions & Properties