1. N* electromagnetic transition form factors from CLAS data on 2p production off proton.
presented by V.I.Mokeev
First comprehensive data on N* electromagnetic transition amplitude
evolution with photon virtuality Q2<1.5 GeV2 for proton states with masses
less then 2.0 GeV, extracted from the analysis of p+p-p exclusive channel.
2p electro- production:
M.Ripani et. al. Phys. Rev. Lett.91,
(2003);
preliminary data L.Elouadrhiri, G.Fedotov,
et. al.
preliminary data on 2p photo- production:
M.Bellis. Proc. of NSTAR04 Workshop
Data analyzed:
(full data sets are
available in
Analysis was carried out within the framework of phenomenological model,
developed in collaboration between JLAB & MSU 05’ version - JM05.

2. Why N* studies have key importance.
Why the studies of N* have key importance.
Why N* studies have key importance.
Comprehensive data on the evolution of N* electromagnetic form factors
A1/2,3/2, S1/2 with Q2 will allow us to access non-perturbative strong
interaction mechanisms, responsible for baryon formation from
quarks and gluons. In particular:
establish leading symmetry for confinement potential;
determine N* wave functions in terms of contributing 3q configurations;
eventually fit to the data the shape of confinement potential and
confront it to the expectation from Lattice QCD.
Matrix elements between ground state nucleon and i-configuration,
contributing to the N* state may be expressed, under particular
symmetry assumption, through few parameters fitted to the data.
Alternatively, they may be calculated for particular shape of binding
potential, providing an opportunity to determine its shape from
the data.
Relative contributions from various configuration ai should be fitted to the
data, providing information on N*’s wave functions.

3. JLAB-MSU model for 2-p electroproduction (JM03-version).
Quasi-2-body mechanisms included
3-body processes
All well established N* with pD decays +P33(1600)&P11(1710)&P13(1720)&P33(1920) 3-star states.
Minimal set of Reggetized gauge invariant Born terms
Effective treatment of couplings with other open channels
All well established N* with rp decays
+P11(1710)&P13(1720) 3-star states.
Diffractive ansatz for non-resonant rp
production.
3/2+(1720) candidate state from analysis of CLAS
2p electroproduction data.

4. c2 for best CLAS data fit averaged over W
con’d
3-body processes
Quasi-2-body mechanisms included
Minimal set of Born terms similar to what was
used for pD states, except an additional g5 matrix
to account for the opposite parities of D and
D13(1520)
c2 for best CLAS data fit averaged over W
Q2, GeV2
0.65
0.95
1.30
pD13(1520) included
4.01
3.29
1.61
substituted by 3b ph. space
7.58
5.74
2.17
Residual mechanisms, beyond shown on the plots, were parameterized
either as 3-body phase space C(W,Q2) or through a set of partial waves
with J<13/2. Both lead to a similar description.

5. Evidences for direct 2p production mechanisms.
W=1.45 GeV, Q2=0. GeV2
JM03 fit
fit with direct 2p production mechanisms
contribution from
direct 2p production
Preliminary CLAS data from:
M.Bellis, et. al.,
(CLAS Collaboration) Proc of
NSTAR2004 Workshop
Q2=0. GeV2
G.Fedotov, L.Elouadrhiri, et.al.,
CLAS Meeting June 05’
Q2=0.275 GeV2
W=1.485 GeV, Q2=0.275 GeV2

6. cont’d W=1.49 GeV fit with direct 2p production mechanisms JM03 fit
Q2=0.65 GeV2
Q2=0.95 GeV2
JM03 fit
contribution from
direct 2p production
CLAS data from:
M.Ripani et. al. ,
(CLAS Collaboration),
Phys. Rev. Lett.91,
(2003).

7. Direct 2p production mechanisms and an additional contact terms in pD channels needed to fit data.
2 = 1.64 GeV2

8. Evidences for complementary contact terms in pD channels.
W=1.78 GeV Q2=0. GeV2
W=1.84 GeV Q2=0.65 GeV2
p+D0
JM05
JM03+direct 2p production
W=1.84 GeV Q2=0.95 GeV2
Structure around D0 peak in
p-p and high mass part in p+p
mass distributions are better
described, implementing an
additional contact terms in
pD chanels

9. Evidence for gpp+F015(1685) and gpp-P++33(1600) channels.

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

11. Fit of p+p-p single differential cross-sections in JM05 and the contributions from particular mechanisms.
Full calculations
gpp-D++
gpp+D0
gpp+D13(1520)
gprp
gpp-P++33(1600)
gpp+F015(1685)
direct 2p production
Combined fit of various 1-diff.
cross-sections allowed to
establish all significant
mechanisms.

12. Total p+p-p cross-sections off protons.
s, mcbn
s, mcbn
Q2=0.65 Gev2
no 3/2+(1720)
Q2=0.95 Gev2
full calculation
Q2=0 Gev2
Background
Q2=1.30 Gev2
Resonances
W, GeV
W, GeV

13. Improvements in the fit of the 2p CLAS electroproduction data within the framework of JM05.
Q2, GeV2
0.65
0.95
1.30
c2/d.p. JM03
version
3.91
3.30
2.26
c2/d.p. JM05
2.83
1.90
2.01
c2 was estimated from
comparison between
calculated and measured
1-diff. cross-sections
for entire set of data in
particular Q2-bin
Quality of CLAS data allowed to establish all significant mechanisms of 2p
production at W<1.9 GeV and Q2<1.5 GeV2. Good description of all
available CLAS/world 2p unpolarized data was achieved without any need
for remainig mechanisms of unknown dynamics.
Essentials of JM05 model may be found in:
V.Mokeev et. al., hep-ph/ , to be published in NSTAR05 Proceedings.

14. Does resonant part, determined in JM05, depend on the way non-resonant mechanisms are modeled ?
N* part was estimated for two different ways of non-resonant process modeling, both comparable to the data:
JM05 calculation with phenomenological description for complementary contact terms in pD channels, when peculiar dynamic features were incorporated to the contact term vertex functions, fitted to the data.
Implementing particular meson-baryon diagrams for complementary mechanisms in pD channels, using as a guide gauge invariance for entire set of pD Born quasi-two-body amplitudes.
Successful data description with the same N* electrocouplings for both ways of non-resonant mechanism modeling represents evidence for reliable evaluation of resonant part in JM05.

15. Contact term ~A(W) (see p.7) Contact term ~B(W) (see p.7)
Minimal set of complementary Born terms needed for gauge invariance of complementary non-resonant processes in  channels.
Contact term ~A(W) (see p.7)
Contact term ~B(W) (see p.7)
Complementary contact terms may be obtained from conventional, applying substitutions:
Set of Born diagrams beyond contact with amplitudes obtained as described below:
WTS identity, insured gauge invariance, will be fulfilled for complementary Born terms, obtained from conventional ones, substituting gmn by Gmn in their hadronic vertices.

16. JM05&description with extra Born terms on slide 15.
Full calculations:
After
implementation
of additional
Born terms
JM05
Non-resonant contibutions:
After
implementation
of additional
Born terms
JM05

17. Cont’d
The data are described
reasonably well with the
same values of
N* electrocouplings for
both ways of non-resonant
mechanisms modeling. .
JM05 allowed us to
estimate unambiguously
N* part from CLAS data
fit.

18. Combined analysis of the CLAS data on 1p and 2p electroproduction
Data at Q2=0.65 GeV2 were analyzed. It is only photon
virtuality for which both 1p and 2p CLAS data exist so far.
Single pion data: ds/dW differential cross-sections:
p+ at W between GeV,
p0 at W between GeV;
beam asymmetries:
p+ and p0 at W between GeV
9870 data points
CLAS 1p data
K.Joo, L.C.Smith, et.al
Double pion data: p+p-, p+p, p-p mass and
CM p- angular distributions at
W between GeV
680 data points
The data are available in CLAS Physics DB:
CLAS 2p data
M.Ripani, V.D.Burkert,
et.al.
CLAS 1-p data (K.Joo, L.C.Smith, et.al.)
1p analysis models : I.G. Aznauryan, et. al., Phys. Rev. C71,
(2005).
Combined 1p/2p analysis was publised in I.G. Aznauryan, et.al.,
Phys. Rev. C72, (2005).

19. -The states with considerable 1p decays
N* electrocouplings (in 10-3 GeV-1/2) extracted in analyses of 1p/2p exclusive channels at Q2=0.65 GeV2 N*
1p-2p analysis
1p analysis
2p analysis
A1/2
A3/2
S1/2
P11(1440)
21±4
33± 6
4± 4
(23±4)
40± 4
21± 9
35± 6
D13(1520)
-65± 4
62± 5
-35± 3
-67± 3
62± 4
-38± 3
-63± 12
62± 11
-40± 7
S31(1620)
16± 4
-28± 3
31± 3
13± 3
-25± 4
S11(1650)
43± 7
-6± 3
43± 2
-15± 2
44± 16
-8± 2
F15(1680)
-32± 5
51± 4
-15± 3
-38± 4
56± 2
-18± 2
-31± 8
52± 10
-14± 3
D33(1700)
44± 4
36± 4
-7± 4
58± 5
29± 3
-15± 5
49± 8
36± 8
-11± 4
D13(1700)
-21± 2
10± 1
-6± 8
-55± 7
0±8
-19± 3
11± 2
P13(1720)
55± 3
-68 ±4
45± 6
-48± 7
0±7
56± 6
-62± 9
(…) result from dispersion relations. Roper is only state with
A1/2 dependent from model for 1p analysis
-The states with considerable 1p decays

20. 1p data description with N
1p data description with N* photocouplings from combined analysis of 1p/2p channels.
W=1.52 GeV
gvp→p0p
W=1.68 GeV

21. 2p data description with N
2p data description with N* photocouplings from combined analysis of 1p/2p channels.
W=1.54 GeV Q2=0.65 GeV2
W=1.66 GeV Q2=0.65 GeV2
Bunches of curves correspond to calculated cross-sections with common sets of N* photocouplings

22. N* electromagnetic form factors from analysis of the CLAS 2p data within the framework of JM05.
Fitted data: p+p-, p+p, p-p mass and CM p- angular distributions at 20 W-bins between GeV and photon virtualities Q2: 0., 0.65, 0.95, 1.30 GeV2.
Combined fit of 4 Q2 bins was carried out within a framework of JM05. W-intervals between GeV, GeV, GeV, GeV were fitted independently.
Electromagnetic form factors and poorly known masses, pD and rp couplings of N* were varied and fitted to the data together with parameters of non-resonant mechanisms implemented to the JM05. Hadronic couplings were further constrained, exploiting their Q2-independence. The photocouplings at 4 Q2’s were derived for the states: P11(1440), D13(1520), S31(1620), S11(1650), P33(1600)*), F15(1685), D13(1700), D33(1700), P13(1720), candidate 3/2+(1720), F35(1905), P33(1920), F37(1950).
*)1.65 GeV mass from our analysis
Yes

23. Description of total p+p-p cross-sections with N
Description of total p+p-p cross-sections with N* electrocouplings hadronic and non-resonant mechanism parameters fitted to the data.
Sub-sets of calculated cross-sections most close to the data were isolated, applying restriction 2<2 thresh,
listed in the table
Q2=0 GeV2
Q2=0 65GeV2
W-interv., GeV
2 thresh.
2.45
2.19
2.04
2.06
Yes
Q2=0 95GeV2
Q2=1 30 GeV2

24. N* electromagnetic transition amplitudes, determined from analysis of CLAS 2p data within the framework of JM05.
D13(1520)
CLAS 2p data
analysis
(A1/22+S1/22)1/2, GeV-1/2
A3/2, GeV-1/2
PDG
1p/2p combined
CLAS data analysis
World data
before CLAS,
obtained in
analysis of 1p
electroproduction:
V.D. Burkert, et. al.,
Phys. Rev. C67,
(2003)
Q2 GeV2
Q2 GeV2

25. Cont’d D33(1700), P13(1720) resonances mostly decay with 2p
emission. 1p data
have not enough
sensitivity to these
states.
D33(1700)
D33(1700)
First reliable data on
Q2 -evolution of
S31(1620), D13(1700),
D33(1700), P13(1720).
electromagnetic form
factors were obtained
from analysis of CLAS
experiments on 2p
photo- and electro-
production.
P13(1720)
P13(1720)
No?Yes

26. N*’s heavier than 1.9 GeV. F35(1905) First data on Q2 -evolution of
P33(1920), F35(1905),
F37(1950) electromagnetic
form factors were
obtained from analysis
of CLAS experiments on
2p photo- and electro-
production.

27. Conclusions.
Phenomenological approach was developed for description of 2p production by real and virtual photons in N* excitation region and for the photon virtualities Q2<1.5 GeV2 with most complete treatment of all significant mechanisms. Successful description of all unpolarized observables combined, without any need for remaining mechanisms of unknown dynamics, allowed us to establish all mechanisms with sizeable contributions from data fit. Currently JM05 is the only available approach worldwide for studies of high lying N* (M>1,6 GeV) in p+p-p exclusive channel.
Successful description of all observables measured with CLAS for major exclusive channels in N* excitation region: p+n, p0p, p+p-p, at Q2=0.65 GeV2 with common values of N* electrocouplings strongly supported reliability of non-resonant mechanism description and N*/background separation achieved in JM05. Credibility for resonant part evaluation was also confirmed, applying various approaches for non-resonant mechanism modeling. Therefore, JM05 may be used for evaluation of N* parameters from experimental data fit.
N* electromagnetic form factors in Q2-area between 0 and 1.5 GeV2 were extracted from CLAS 2p photo- and electroproduction data for most excited proton states with masses less then 2.0 GeV. Q2-evolution of electromagnetic form factors for S31(1620), D13(1700), D33(1700), P13(1720), F35(1905), P33(1920), F37(1950) states were determined for the first time.

28. Outlook. Two directions should be pursued:
First comprehensive data on Q2-evolution of electromagnetic transition form factors for many N*’s allow us to establish driving symmetry for quark binding potential in baryons; determine N* structure in terms of contributing configurations, and eventually to fit shape of binding potential to the data. Established in this way binding potential may be confronted to the expectations from Lattice QCD.
Complexity of 2p production mechanisms, established in CLAS data analysis within the framework of JM05, provides necessary input for development of framework for combined studies of nucleon resonances in variety of exclusive electromagnetic and hadronic reactions, aimed to determine N* electromagnetic form factors and hadronic parameters in explicit coupled channel approaches, proposed by T.-S. H. Lee.