1. Analysis of 2p Production
presented by V.I.Mokeev
gp→2pN exclusive channels in N* studies.
modeling of 2p photo- and electroproduction by tree level meson-baryon diagrams.
phenomenological analysis within the framework of JLAB-MSU model.
N* studies in combined analysis of major exclusive channels. Argonne-Osaka coupled channel approach.
Conclusions.

2. The p-p+p electroproduction amplitudes are needed for credible evaluation of N* parameters in coupled channel analysis.
Exclusive channels in pN
scattering responsible for
ISI&FSI in meson electro-
production
CLAS data on meson electroproduction
at Q2<4.0 GeV2
p(e,e’)X (trigger)
p(e,e’p)p0
p(e,e’p+)n
p(e,e’pp+)p-
p(e,e’pp+)X

3. Why the studies of 2p electroproduction are important.
D33(1700) electrocouplings
from world data on 1p electroproduction
from CLAS data on 2p electroproduction
combined analysis of 1p/2p CLAS data

4. Meson-baryon (MB) models (partial list of references).
L. Luke, P. Soding, Springer Tracts in Modern Physics 59 (1971) 39.
L.Y. Murphy, J.-M. Laget, DAPNIA-SPHN
J.A. Gomez Tejedor, E. Oset, Nucl. Phys. A571 (1994) 667.
J.A. Gomez Tejedor, E. Oset, Nucl. Phys. A600 (1996) 413.
J.C. Nacher, et. al., Nucl. Phys. A695 (2001) 295.
S. Ong, J. Van de Wiele, Phys. Rev. C63 (2001)
W. Roberts, A.Rakotovao, hep-ph/
W. Roberts, T.Oed, Phys. Rev. C71 (2005)
M. Hirata, K. Ochi, T. Takaki, Phys. Rev. C56 (1997) 1472.
M. Hirata, N. Katagiri, T. Takaki, Phys. Rev. C67 (2003)
M. Ripani, V.I. Mokeev, et. al., Nucl. Phys. A672 (2000) 220.
V.I. Mokeev, et. al., Phys. of Atom. Nucl. 64 (2001)
V. Bernard, N .Kaiser, U.G. Meissner, Eur. Phys. J. A11 (2001) 209.
A. Fix, H. Arenhovel, Eur. Phys. J. A25 (2005) 115.

5. Valencia group approach. (applicable at W<1.6 GeV)
M=p,r; B=p,D,P11(1440),D13(1520),
D33(1700); relevant for W<1.6 GeV
Isobar channels: pD, rp, pP11(1440)
& pN background
non fully relativistic description
(resolved in ref. 6 at p.5);
c-numbers instead of vertex functions
(in part resolved in ref. 6 at p.5) ;
no ISI&FSI effects
The contributions:
-pD Born terms
- to pD extra terms of JM06
- to direct 2p production of JM06
-s-channel N* excitation

6. Fully relativistic description. W.Roberts approach.
p,V-mesons and all N*,D* of 1/2, 3/2 spin are included. A general framework for most comprehensive MB description in N* excitation region. r g N
N*,D* p
Open problems:
reliability of effective MB lagrangians→test against data on N* LS partial decay widths;
vertex functions, most of them are still unknown;
ISI&FSI should be implemented

7. A.Fix and H.Arenhövel approach.
M=p,r,s, B=N,D
All N*,D* with masses less then 1.8 GeV are included to s-channel amplitudes.
Effective description of ISI&FSI within the framework of diffractive absorptive ansatz
Open problems:
completeness of mechanisms at high W;
credibility of approximations for ISI&FSI, considering huge absorptive effects

8. How well MB approaches working?
Reasonable description of fully integrated cross-sections in all approaches, BUT huge ad hoc absorptive corrections at W>1.6 GeV.
ABBHHM, TAPS data in comparison with A.Fix, H.Arenhovel model
gp→p0p0p

9. gp→p0p0p gp→p+p0n TAPS data E.Oset,et.al. model E.Oset,et.al. model
Cont’d
gp→p0p0p
gp→p+p0n
TAPS data
E.Oset,et.al. model
E.Oset,et.al. model
Discrepancies
Due to problems with description of 1-diff cross-sections neither of MB approaches was ever used to extract N* parameters from the 2p photo and electroproduction data.

10. CLAS electroproduction data.
New prospects for N* studies in 2p production. Effective lagrangians + phenomenological parametrization hybrid approach.
ELSA, MAMI, GRAAL photo- and CLAS electroproduction data extended amount of measured observables considerably.
CLAS electroproduction data.
For unpolarized beam/target, the final state, gr,v→p-p+p reaction offers 9 independent 1-differential cross-sections in each (W&Q2) bin. All these cross-sections are available from CLAS for the first time.
Contributing mechanisms may be established in phenomenological analysis of all available data combined. It is joint JLAB/MSU effort.

11. JLAB-MSU model (JM05) for 2-p electroproduction. V. I. Mokeev, V. D
JLAB-MSU model (JM05) for 2-p electroproduction. V.I. Mokeev, V.D.Burkert et.al., Proc. of the Workshop NSTAR2005, World scientific, p.47
3-body processes
Quasi-2-body mechanisms included
All well established N* with pD decays +P33(1600)&P11(1710)&P13(1720)&P33(1920) 3-star states and 3/2+(1720) candidate.
Reggetiezed Born terms & effective FSI&ISI treatment (Ref. 11 p.5).
extra pD contact term
All well established N* with rp decays
+P11(1710)&P13(1720) 3-star states and 3/2+(1720) candidate.
Diffractive ansatz for non-resonant part & r-line shrinkage in N* region.

12. con’d Direct 2p production. 3-body processes
Quasi-2-body mechanisms included
(p-)
for p+D013(1520) set of Born terms similar
to what was used for pD isobar channels.
for p+F015(1685), p-P++33(1640) 3-body contact term with exponential propagators of isobars in 2 body intermediate states.
(P++33(1640))
(p+)
F015(1685)
Direct 2p production.
Exchange processes,
parameterized as:

13. CLAS data M.Ripani, V.D.Burkert, et. al.
Evidences for processes beyond isobar channel superposition in 2p production.
CLAS data M.Ripani, V.D.Burkert, et. al.
Q2=0.95 GeV2
2p direct mechanisms
The contributions from all isobar channels combined still underestimate 2p cross-sections. 2p direct mechanisms are needed to reproduce CLAS/world data.

14. Evidences for exchange mechanisms in direct 2p production from the CLAS data.
E CLAS data fit with remaining mechanisms:
W=1.49 GeV
Q2=0.65 GeV2
Q2=0.95 GeV2
exchange processes
3-body phase space
remaining mechanisms
shown on slide 6

15. CLAS data M.Ripani, V.D.Burkert, et. al.
p+p-p cross-sections off protons from the fit of mass and p- angular distributions within the framework of JM05.
s, mcbn
CLAS data M.Ripani, V.D.Burkert, et. al.
Q2=0.65 Gev2
Q2=0.95 Gev2
Q2=1.30 Gev2
Reasonable description of invariant mass and p- angular distributions were achieved without any need for an additional mechanisms beyond implemented to JM05.
W, GeV

16. Preliminary JM06 full p-D++ p+D0 2p direct
Global fit of complete set of unpolarized 1-differential cross-sections within the framework of JM06 model (1.3<W<1.6 GeV & 0.25<Q2<0.60 GeV2) .
JM06 full
p-D++
p+D0
2p direct
ai-angular distributions were
calculated with parameters of
JM06 fitted to 6 other 1-diff.
cross-sections.
Preliminary
Successful description of all E94-005
data was achieved.
Complete data on unpolarized
1-differential cross-sections for the
first time available from CLAS
allowed us to establish all
significant mechanisms contributing
to the 2p electroproduction.

17. + Modification of parameterization for direct 2 amplitudes JM05 JM06

18. P11(1440) and D13(1520) electrocouplings.
Preliminary
from analysis of E CLAS 2p
data within the framework of JM06
from analysis of 1p CLAS data
from analysis of E CLAS 2p
data within the framework of JM05
combined analysis of 1p/2p
CLAS data

19. “bare’ amplitudes from other electroproduction channels
Combined analysis of major exclusive electroproduction channels within the framework of the coupled channel (cc) approach, using phenomenological input from JM06
Argonne-Osaka approach (T-S.H.Lee, et.al.) is only available worldwide, capable to account for full complexity of FSI in the ppN final states.
resulting AO amplitudes
“bare” amplitudes, established within the framework of JM06
“bare’ amplitudes from other electroproduction channels
ppN unitarity cut

20. Current efforts in combined 1p/2p analysis
Current efforts in combined 1p/2p analysis. Hall B group & EBAC collaboration.
The amplitudes of all significant mechanisms in the 1p/2p exclusive channels were determined in phenomenological analysis of the CLAS data
(I. Aznauryan for 1p, JM06 for 2p). Modification of these amplitudes by FSI, is under evaluation, using AO approach at 0.25< Q2<1.5 GeV2 and W<1.5 GeV, where only 1p/2p channels contribute
1p/2p CLAS electroproduction data will be re-fitted, using non-resonant amplitudes accounting for FSI. Clobal fit of observables from major exclusive channels, accounting for unitarity, will be gradually extended up to 2.0 GeV W, allowing us to extract most reliable data on electrocouplings for an entire excited nucleon spectrum.
Studies of underlying MB/partonic mechanisms for remaining JM06 phenomenological terms will be carried out.
Expected outcome:
MB vertex off-shell behavior → input for lattice simulation(?);
Understanding of the transition from MB mechanisms to pD rp GPD’s,/other partonic processes needed for N* studies at high Q2.

21. What mechanisms behind JM06 phenomenological terms?
JM06 phenomenological terms will be replaced by MB amplitudes, derived from modern effective Lagrangians of the outlined approach +
residual phenomenological contributions, if any.
S.Capstick, T.-S.H.Lee, A. Kiswandhi model
For particular mechanisms isolated in JM06 the sum is rather limited

22. Conclusions.
Considerable extension of the data on 2p photo- and electro- production from recent experiments, carried out worldwide on continues beams with 4p detectors, open up new opportunities for N* studies. Global analysis of full set of unpolarized observables for the first time available from CLAS, allowed us to develop the JM06 model with most complete accounting for all significant mechanisms. These studies demonstrated capability to map-out all sizeable mechanisms from the fit of various observables combined. The amplitudes, determined for all contributing mechanisms, provide necessary input for extraction of N* parameters in the cc analyses.
Global analysis of observables from major photo- / electro- production channels combined, implementing unitarity within the framework of most advanced Argonne-Osaka approach, offers promising way for credible N*/non-resonant processes separation. Therefore, all necessary tools are available to extract reliable values of N* electrocouplings, at various photo virtualities Q2 and to improve knowledge of N* hadronic parameters.
2p exclusive channels offer very reach information both on resonant and non-resonant processes, vital for modern hadronic physics. Wealthy of this information may be accessed only in combined efforts, including phenomenological mapping of contributing mechanisms, comprehensive FSI treatment and the studies of actual mechanisms behind phenomenology within the framework of meson-baryon and partonic degrees of freedom.

23. BACK-UP

24. Modeling of 2p production by tree level meson-baryon diagrams.
Set of tree level meson-baryon diagrams. Particular meson and baryon states were implemented based on:
manifestation of unstable particles in invariant mass distributions;
established in analysis 1p production and experiments with pion beams;
needs to improve description of particular data features.
Full sets of diagrams were created, applying all possible permutations for meson/baryon legs

25. Fit of E94-005 CLAS 2p data (L. Elouadrhiri, G. Fedotov, et. al
Fit of E CLAS 2p data (L.Elouadrhiri, G.Fedotov, et. al.) collected at low W&Q2 within the framework of JM05 model.
full
p-D++
p+D0
2p direct
JM05 succeeded to describe p+p, p-p+
p-p mass and p- angular distributions,
Preliminary
Failure in description of p+ and
pf angular distributions, revealed necessity to modify direct 2p production mechanisms.

26. General problems of MB approaches.
Available MB models are unable to establish all significant mechanisms contributing to the 2p production due to lack of guidance from fundamental theory and insufficient amount of analyzed observables to determine complexity of contribution processes from the data fit.
Most of MB vertex function are unknown and may be only fitted to the data.
FSI were either neglected or treated in oversimplified approximations. Comprehensive approach for description of FSI complexity in the 3 body ppN final state was needed. Such approach has been developed just recently by Argonne-Osaka collaboration (see T-S.H.Lee talk, hep-th/ ).
Neither of MB approaches was ever used to extract N* parameters from the 2p photo and electroproduction data.

27. An additional contact terms in pD channels needed to fit data.
2 = 1.64 GeV2

28. The amplitudes for gpp+F015(1685) and gpp-P++33(1600) channels.

29. Fit of single differential cross-sections from E93-006 experiment within the framework of JM05.
Full calculations
gpp-D++
gpp+D0
gpp+D13(1520)
gprp
gpp-P33++(1640)
gpp+F150(1685)
direct 2p production

30. Selected p-p+p cross-sections calculated within the framework of JM05, most closed to the E CLAS data.
p+ p, p- p+, p -p invar. masses and p- angular
distributions were fitted within the framework
of JM05 (V.Mokeev et.al. , Proc. of NSTAR2005
Workshop, p.47)
experimetal data from M.Ripani et. al. ,
Phys. Rev. Lett.91, (2003)
Q2=0 65GeV2
W-interv., GeV
2 thresh.
2.45
2.19
2.04
2.06
Yes
Q2=0 95GeV2
Q2=1 30 GeV2

31. Evidence for complementary contributions to pD isobar channels.
JM05 full:
W=1.76 GeV Q2=0.95 GeV2
extra contact term in pD
channels
p+D0 on
off
ds/dM, mcbn/GeV
gp→p+D0:
extra contact term in pD
channels
off on
W=1.81 GeV Q2=0.95 GeV2
p+p mass, GeV
p-p mass, GeV

32. Manifestation of gp→p-P33++(1640) and gp→p+F15(1685) isobar channels.
W=1.89 GeV
Q2=0.95 GeV2
JM05 full
gp→p+F15(1685)
p-P33++(1640) and
p+F15 (1685) isobar
channels off
gp→p-P 33(1640)
Contribution from
isobar channels:
p-P33++(1640)
p+F15 (1685)

33. Resonant/non-resonant mechanism separation.
full JM06 calculations
non-resonant part
resonant part
Preliminary
Combined fit of all unpolarized
1-diff. cross-sections allows us
to isolate resonant/non-resonant
parts, exploiting difference in shapes
of their cross-sections.

34. Total p-p+p cross-sections calculated within the framework of JM06, most closed to the preliminary CLAS data at 0.25<Q2<0.60 GeV2 and W<1.57 GeV.
preliminary CLAS data,
exper. E94-005,
L.Elouadrhiri, G.Fedotov, et.al.
Q2-interv., GeV2
2 thresh.
2.80
1.80
1.70
Preliminary

35. High lying N* electrocouplings.
D33(1700), P13(1720)
resonances mostly
decay with 2p
emission. 1p data do
not have enough
sensitivity to these
states.
D33(1700)
D33(1700)
First preliminary data on
Q2 -evolution of
S31(1620), D13(1700),
D33(1700), P13(1720)
electromagnetic form
factors were obtained
from analysis of CLAS
E experiment on
2p electroproduction.
P13(1720)
P13(1720)
No?Yes