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. 2010
2. 2009
3. 2007

Current projects

The status and plan of EBAC can be found here. The on-going core projects for achieving NSAC milestones HP3 and HP7 by 2012 are briefly desciribed below:


1. Dynamical coupled-channels analysis of π N reactions

As a first step to analyze the data of electromagnetic production of πN, ππN, ηN, KΛ, KΣ, and ωN, it is necessary to first determine the hadronic parameters of the EBAC dynamical coupled-channels model (EBAC-DCC) by analyzing the available πN reaction data. This was achieved [1] with accurate descriptions of all available πN elastic scattering data. The model has also given good descriptions of πN → ππN [2] and πN → ηN [3] reactions. Currently, we are refining the parameters by performing a combined fit of all of the world data of πN → πN, ππN, ηN. Efforts are also being made to improve the parameterization of the model by using hadron structure calculations.

[1] B. Julia-Diaz, T.-S. H. Lee, A. Matsuyama, T. Sato, Phys. Rev. C76, 065201 (2007) [arXiv:0704.1615]
[2] H. Kamano, B. Julia-Diaz, T.-S. H. Lee, A. Matsuyama, T. Sato, Phys. Rev. C79, 025206 (2009) [arXiv:0807.2273]
[3] J. Durand, B. Julia-Diaz, T.-S. H. Lee, B. Saghai, T. Sato, Phys. Rev. C78, 025204 (2008) [arXiv:0804.0347]


2. Dynamical coupled-channels analysis of electromagnetic meson production reactions

With the hadronic parameters determined in our analysis of πN reactions, the only freedom in our investigation of electromagnetic π production is the γN → N* parameters. By only adjusting these parameters, we are able to obtain good description of all of the available data of γN → πN [1] and N(e,e'π)N [2] at invariant mass W < about 1.65 GeV. We have also obtained [3] good description of 2π photoproduction at W < about 1.4 GeV, but overestimate the data in higher W region. We have found that the difficulties are mainly from the non-resonant interactions of the model and are making improvements. Investigation of η photoproduction is being carried in a collaboration with Saclay Group. The code for investigating KY and ωN photoproduction have also been developed.

[1] B. Julia-Diaz, T.-S. H. Lee, A. Matsuyama, T. Sato, L.C. Smith, Phys. Rev. C77, 045205 (2007) [arXiv:0712.2283]
[2] B. Julia-Diaz, H. Kamano, T.-S. H. Lee, A. Matsuyama, T. Sato, N. Suzuki, Phys. Rev. C80, 025207 (2009) [arXiv:0904.1918]
[3] H. Kamano, B. Julia-Diaz, T.-S. H. Lee, A. Matsuyama, T. Sato, Phys. Rev. C80, 065203 (2009) [arXiv:0909.1129]


3. Extraction of nucleon resonances from dynamical coupled-channels model

An analytic continuation method has been developed [1] to extract nucleon resonance parameters from the EBAC-DCC model. We have determined [2] 14 resonances and have shown that the Roper (1440) and the next higher mass resonance in P11 originate from the same bare state. The focus of our current efforts is to investigate the stability of our P11 solutions and to extract the γ* N → N* form factors from the multipole amplitudes of electromagnetic π production predicted by EBAC-DCC.

[1] N. Suzuki, T. Sato, T.-S. H. Lee, Phys. Rev. C79, 025205 (2009) [arXiv:0806.2043]
[2] N. Suzuki, B. Julia-Diaz, H. Kamano, T.-S. H. Lee, A. Matsuyama, T. Sato, Phys. Rev. Lett. 104, 042302 (2010) [arXiv:0909.1356]


4. Determination of KΛ photoproduciton amplitudes from over-complete experiments

Jointly with experimentalists of Hall B, we have developed methods for extracting multipole amplitudes as model independently as possible from the forthcoming over-complete experiments on KΛ photoproduction by CLAS [1]. The resulting multipole amplitudes will be analyzed within the EBAC-DCC model in order to search for new resonances which are only assessable to KΛ channel.

[1] A. M. Sandorfi, S. Hoblit, H. Kamano, T.-S. H. Lee, J.Phys.G 38 053001 (2011) [arXiv:1010.4555]


5. Meson resonances in 3π production reactions

As a new direction, we are making an application of the dynamical coupled-channels approach of EBAC, based on the formulation of [1], to meson physics. With this approach which maintains both 2-body and 3-body unitarity consistently, we examine the extent to which methods used in the experimental analyses such as the isobar model are valid, aiming at developing an unitary approach to identify excited mesons from the experiments to be conducted under the GlueX project.

[1] A. Matsuyama, T. Sato, T.-S. H. Lee, Phys. Rep. 439, 193 (2007) [nucl-th/0608051]