Pion photoproduction on nucleons in a covariant hadron-exchange model

Journal Article · Sun Aug 01 04:00:00 EDT 2004

OSTI ID:827490

Pascalutsa, Vladimir; Tjon, John A

We present a relativistic dynamical model of pion photoproduction on the nucleon in the resonance region. It offers several advances over the existing approaches. The model is obtained by extending our {pi} N-scattering description to the electromagnetic channels. The resulting photopion amplitude is thus unitary in the {pi}N, {gamma}N channel space, Watson's theorem is exactly satisfied. At this stage we have included the pion, nucleon, {Delta}(1232)-resonance degrees of freedom. The {rho} and {omega} meson exchanges are also included, but play a minor role in the considered energy domain (up to {radical}s = 1.5 GeV). In this energy range the model provides a good description of all the important multipoles. We have allowed for only two free parameters--the photocouplings of the {Delta}-resonance. These couplings are adjusted to reproduce the strength of corresponding resonant-multipoles M{sub 1+} and E{sub 1+} at the resonance position. We then obtain R{sub EM} = 3.8 {+-} 1.6% for the E2/M1 ratio, in a qualitative agreement with other dynamical models.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (US)
• Sponsoring Organization: USDOE Office of Energy Research (ER) (US)
• DOE Contract Number: AC05-84ER40150
• OSTI ID: 827490
• Report Number(s): JLAB-THY-04-249; DOE/ER/40150-2824
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
AMPLITUDES
BOSON-EXCHANGE MODELS
DEGREES OF FREEDOM
ENERGY RANGE
MULTIPOLES
NUCLEONS
PHOTOPRODUCTION
PIONS
RESONANCE