Threshold pion photoproduction of nucleons in the chiral quark model

Journal Article · Mon Oct 31 23:00:00 EST 1994 · Physical Review, D (Particles Fields); (United States)

DOI:https://doi.org/10.1103/PhysRevD.50.5639· OSTI ID:6962639

Li, Z ^[1]

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1. Physics Department, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213-3890 (United States)

In this paper, we show that the low energy theorem (LET) of threshold pion photoproduction can be fully recovered in the quark model. An essential result of this investigation is that the quark-pion operators are obtained from the effective chiral Lagrangian, and the low energy theorem does not require constraints on the internal structures of the nucleon. Changing from pseudovector to pseudoscalar quark-pion couplings generates an additional term at order [mu]=[ital m][sub [pi]]/[ital M] only in the isospin amplitude [ital A][sup ([minus])]. The role of the transitions between the nucleon and the resonance [ital P][sub 33](1232) or [ital P]-wave baryons is also discussed; we find that the leading contributions to the isospin amplitudes at [ital O]([mu][sup 2]) are from the transition between the [ital P]-wave baryons and the nucleon, and from the charge radius of the nucleon. The leading contribution from the [ital P]-wave baryons only affects neutral pion production, and improves the agreement with data significantly. The transition between the resonance [ital P][sub 33](1232) and the nucleon only gives an order [mu][sup 3] correction to [ital A][sup ([minus])].

• OSTI ID: 6962639
• Journal Information: Physical Review, D (Particles Fields); (United States), Journal Name: Physical Review, D (Particles Fields); (United States) Vol. 50:9; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
BARYONS
BASIC INTERACTIONS
BOSONS
CHIRAL SYMMETRY
COMPOSITE MODELS
COUPLING
ELECTROMAGNETIC INTERACTIONS
ELEMENTARY PARTICLES
FERMIONS
FUNCTIONS
HADRONS
INTERACTIONS
LAGRANGIAN FUNCTION
LOW-ENERGY THEOREM
MATHEMATICAL MODELS
MESONS
NUCLEONS
P WAVES
PARTIAL WAVES
PARTICLE INTERACTIONS
PARTICLE MODELS
PARTICLE PRODUCTION
PHOTOPRODUCTION
PIONS
PSEUDOSCALAR MESONS
QUARK MODEL
SYMMETRY