EBAC is an international effort which incorporates researchers from institutes around the world.

Research Projects

The main objective of the Excited Baryon Analysis Center (EBAC) is to develop dynamical reaction models for extracting and interpreting the nucleon resonance (N*) parameters by using the very extensive data of electromagnetic production of pseudoscalar mesons, vector mesons, and also two pions.

Anual Reports

1. 2007

Current projects

1. Dynamical coupled-channel analysis at EBAC
(B. Julia-Diaz, T.-S. H. Lee, A. Matsuyama, M. Paris, T. Sato, K. Tsushima)

A dynamical coupled-channel model has been developed [1] and being applied at EBAC to analyze the data of and production, aiming at verifing and interpreting the gamma N → N* form factors for a number of known N* states which are extracted recently by the CLAS collaboration and other empirical amplitude analysis groups. The model is an extension of a well-developed dynamical model [2] in the Δ region to include higher mass N* states and more reaction channels including the N continuum. An extension of the analysis to include N channel is being pursued, as a step toward performing a complete dynamical anaysis with all reaction channels. This effort is also providing theoretical input to the data analyses by the experimental groups, especially by the CLAS collaboration at JLab.

[1] A. Matsuyama, T. Sato, and T.-S. H. Lee, to appear in Phys. Rept. (2007) [nucl-th/0608051]
[2] T. Sato and T.-S. H. Lee, Phys. Rev. C54, 2660 (1996); 63, 055201 (2001) [nucl-th/9606009 ]


2. Analysis of CLAS data with Julich model
(J. Haidenbauer, C. Hanhart, S. Krewald, Ulf-G. Meißner, A. Sibirtsev, K. Nakayama, H. Haberzettl )

The Julich coupled-channel model [1] has been extended [2] recently to analyze pion photoproduction data in the Δ region. As part of the effort at EBAC, this model is being refined [3] to match with the chiral perturbation theory and Regge phenomenology. It is also being extended to include K, KΣ, N and N channels to analyze the CLAS data. Effort is being made to improve the treatment of the N unitary cut. The electroproduction processes are to be calculated in the next stage.

[1] A. M. Gasparyan, J. Haidenbauer, C. Hanhart, and J. Speth, Phys. Rev. C 68, 045207 (2003) [nucl-th/0307072 ], and earier works therein.
[2] H. Haberzettl, K. Nakayama, S. Krewald, Phys. Rev. C74, 045202 (2006) [nucl-th/0605059 ]
[3] J. Haidenbauer, C. Hanhart, S. Krewald, Ulf-G. Meiβner, A. Sibirtsev, K. Nakayama, H. Haberzettl [PS ]


3. EBAC-Saclay coupled-channel analysis of N and KY photoproduction
(J.-C. David, J. Durand, Jun He, B. Julia-Diaz, T.-S. H. Lee, B. Saghai, T. Sato)

An effort is being made by appling EBAC's coupled-channel code to perform a comprehensive analysis of all of available data of N→ N and gamma N → N data. Progress is also being made to extend the work of Ref.[1] to include more reaction channels in extracting the N* parameters from KY photoproduction data.

[1] B. Julia-Diaz, B. Saghai, T.-S. H. Lee, F. Tabakin, Phys. Rev. C73, 055204 (2006) [nucl-th/0601053 ]