Dynamical Coupled-channels Effects on Pion Photoproduction

Journal Article · Tue Dec 18 04:00:00 EST 2007

OSTI ID:921049

Julia-Diaz, B; Lee, T -S. H.; Matsuyama, A; Sato, T; Smith, L C

The electromagnetic pion production reactions are investigated within the dynamical coupled-channels model developed in {\bf Physics Reports, 439, 193 (2007)}. The meson-baryon channels included in this study are $$\gamma N$$, $$\pi N$$, $$\eta N$$, and the $$\pi\Delta$$, $$\rho N$$ and $$\sigma N$$ resonant components of the $$\pi\pi N$$ channel. With the hadronic parameters of the model determined in a recent study of $$\pi N$$ scattering, we show that the pion photoproduction data up to the second resonance region can be described to a very large extent by only adjusting the bare $$\gamma N \rightarrow N^*$$ helicity amplitudes, while the non-resonant electromagnetic couplings are taken from previous works. It is found that the coupled-channels effects can contribute about 10 - 20 $$\%$$ of the production cross sections in the $$\Delta$$ (1232) resonance region, and can drastically change the magnitude and shape of the cross sections in the second resonance region. The importance of the off-shell effects in a dynamical approach is also demonstrated. The meson cloud effects as well as the coupled-channels contributions to the $$\gamma N \rightarrow N^*$$ form factors are found to be mainly in the low $Q^2$ region. For the magnetic M1 $$\gamma N \rightarrow \Delta$$ (1232) form factor, the results are close to that of the Sato-Lee Model. Necessary improvements to the model and future developments are discussed.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA
• Sponsoring Organization: USDOE - Office of Science (SC)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 921049
• Report Number(s): JLAB-THY-07-765; DOE/OR/23177-0238
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
AMPLITUDES
CLOUDS
CROSS SECTIONS
FORM FACTORS
HELICITY
MESONS
PHOTOPRODUCTION
PHYSICS
PIONS
PRODUCTION
RESONANCE
SCATTERING
SHAPE