Current Status of EBAC Project

1
Current Status of EBAC Project

• Hiroyuki Kamano
• Excited Baryon Analysis Center, Jefferson Lab
• in collaboration with
• B. Julia-Diaz, T.-S. H. Lee, A. Matsuyama,
• T. Sato, K. Tsushima

2
Approaches to determining N-N form factors
Reaction Data
N-N form factor
Lattice QCD
Hadron Models
QCD
3
Coupled-channels model _at_ EBAC
For details see Matsuyama, Sato, Lee, Phys. Rep.
439,193 (2007)

• Partial wave (LSJ) amplitude of a ? b reaction
• Reaction channels
• Potential

c.c. effect
Impose minimal number of bare N state at
present 15 of 23 (3 and 4 from PDG)
meson exchange
bare N state
4
Strategy for analysis _at_ EBAC
Feedback
Application
Pass hadronic parameters
Pass hadronic parameters
Feedback
Refit electro-magnetic part of parameters
Fit electro-magnetic part of parameters
Application
5
Pion-nucleon elastic scattering
Julia-Diaz, Lee, Matsuyama, Sato, PRC76 065201
(2007)

• Five coupled-channels are considered
• Fitted to the SAID pN partial wave amplitudes up
  to 2GeV.

6
Pion-nucleon elastic scattering
Julia-Diaz, Lee, Matsuyama, Sato, PRC76 065201
(2007)
1340 MeV
1440 MeV
1540 MeV
1680 MeV
1760 MeV
1860 MeV
Polarization
?N
7
Single pion photoproduction reaction
Julia-Diaz, Lee, Matsuyama, Sato, Smith, PRC77
045205 (2008)
Includes 1st and 2nd resonance region

• Fitted to the data up to 1.65 GeV.
• Only N? g N bare helicity amps. are varied for
  the fitting.

?
8
Single pion photoproduction reaction
Julia-Diaz, Lee, Matsuyama, Sato, Smith, PRC77
045205 (2008)
1154 MeV
1232 MeV
1285 MeV
1417 MeV
1513 MeV
0
0 90
180
0 90
180
1
1
0
0
-1
-1
0 90
180
0 90
180
9
pi N ? pi pi N reaction
Kamano, Julia-Diaz, Lee, Matsuyama, Sato,
submitted to PRC
full result c.c. effect off
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pi N ? pi pi N reaction
Kamano, Julia-Diaz, Lee, Matsuyama, Sato,
submitted to PRC
invariant mass distributions
full result phase space
Data handled with the help of D. Arndt
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Outlook
end of 2008
Combined analysis of p N ? p N, p p N and g N ? p
N
(Julia-Diaz, Kamano, Lee, Matsuyama, Sato)

• Retune parameters using the data of all three
  reactions.
• Extends energy region of g N ? p N up to 2 GeV

12
Back up
13
gamma N ? pi pi N reaction
W 1420 MeV
W 1780 MeV
invariant mass distributions (preliminary)
In most energy,

• Shape is reasonable.
• Magnitude
• overestimates the data.

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Dynamical coupled-channels model for double pion
production reactions
All ingredients already prepared in 2-body
calculation !!
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Dynamical coupled-channels model for double pion
production reactions

2 ? 3 effective potential




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Approximate treatment of direct term


part of V23
part of
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Dynamical coupled-channels modelfor double pion
production reactions
To obtain g N ? p p N amplitude, just make
replacement below
where
18
Results
full c.c. effect off res. only nonres. only
19
Results
full res. only nonres. only
W 1790 MeV
20
Results
full res. only nonres. only
W 1440 MeV
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EBAC _at_ JLab
Excited Baryon Analysis Center (EBAC) at
Jefferson Lab
http//ebac-theory.jlab.org/
Explore nature of the nucleon resonances from
analyzing world data of meson production
reactions on the nucleon target pN, ?N,
? N ? pN, ppN, ?N, ?N, fN, KY,

• Pole position of N states on the complex
  energy plane
• Transition form factors of N states
• Search for new N states

Closely related to the quark-gluon substructure
of N states
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Contribution of V23
PRC result PRC result V23
23
Single pion photoproduction reaction
Julia-Diaz, Lee, Matsuyama, Sato, Smith, PRC77
045205 (2008)
1154 MeV
1232 MeV
1285 MeV
1417 MeV
1513 MeV
1603 MeV
0
0 90
180
0 90
180
1
1
0
0
-1
-1
0 90
180
0 90
180