1. Nucleon resonance electrocouplings from the CLAS data on charge double pion electroproduction
Victor I. Mokeev
Jefferson Lab
Introduction
JM model for evaluation of N* electrocouplings in analyzing the p+p-p electroproduction
New results on N* electrocouplings from our studies on the p+p-p CLAS data
Conclusions and outlook

2. Why p+p-p electroproduction channel is important
CLAS data on meson electroproduction
at Q2 < 4.0 GeV2
Np/Npp channels are the two major contributors in N* excitation region;
these two channels combined are sensitive to almost all excited proton states;
they are strongly coupled by pN→ppN final state interaction;
may substantially affect exclusive channels having smaller cross sections, such as hp,KL, and KS.
Therefore knowledge on Np/Npp electro production mechanisms is key for the entire N* Program

3. Npp electroproduction data from CLAS
The measurements with an unpolarized e- beam onto a proton target: offer nine independent differential cross sections in each (W,Q2) bin.
Number data points > 8200
1.3 < W < 2.1 GeV ;
0.25 < Q2< 1.5 GeV2
M. Ripani et al., PRL,91, (2003);
G. Fedotov et al., PRC 79, (2009). .

4. JLAB-MSU isobar model (JM) for Npp electroproduction.
Isobar channels included:
3-body processes:
p-D++
All well established N*s with pD decays and 3/2+(1720) candidate, seen in CLAS 2p data.
Reggeized Born terms with effective FSI & ISI treatment .
Extra pD contact term. rp
All well established N*s with rp decays and 3/2+(1720) candidate.
Diffractive ansatz for non-resonant part and r-line shrinkage in N* region.

5. continued 3-body processes: Isobar channels included:
p+D013(1520), p+F015(1685), p-P++33(1640) isobar channels; observed for the first time in the CLAS data at W > 1.5 GeV.
(P++33(1640))
(p+)
F015(1685)
Direct 2p production
V. Mokeev, V .Burkert, J. Phys. 69, (2007); V. Mokeev et al., arXiv:0809:4158[hep-ph]

6. Description of the CLAS Npp differential cross sections within the framework of JM model
full JM calc.
p+D0 rp
p+F015(1685)
p-D++
2p direct
p+D013(1520)

7. Resonant & non-resonant parts of Npp cross sections as determined from the CLAS data fit with the framework of JM model
full cross sections
resonant part
non-resonant part

8. P11(1440) electrocouplings from the CLAS data on Np/Npp electroproduction
Light front models:
I. Aznauryan
S. Capstick
hybrid P11(1440)
Good agreement between the electrocouplings obtained from the Np and Npp channels: Reliable measure of the electrocouplings.
The electrocouplings for Q2 > 2.0 GeV2 are consistent with P11(1440) structure as a 3-quark radial excitation.
Zero crossing for the A1/2 amplitude has been observed for the first time, indicating an importance of light-front dynamics.

9. High lying resonance electrocouplings from Npp CLAS data analysis
preliminary
Np world
N(1720)P13
Np world
Q2=0

10. Conclusions and outlook
Phenomenological approach JM has been developed by the CLAS Collaboration with the goal of determining N* electrocouplings from combined fits of measured observables in Npp electroproduction data.
A good description of the CLAS data on p+p-p differential cross sections has been achieved, affording us to access the resonant parts of amplitudes, which are directly related to N* electrocouplings.
The P11(1440) and D13(1520) electrocouplings have been determined for the first time Npp dataset.
The consistent results extracted from Np & Npp channels strongly indicate a reliable electrocoupling measurement.
Analysis of the Npp CLAS data provides first-time information on the electrocouplings for D33(1700) & P13(1720) resonances that decay primarily to the Npp final states .
Comprehensive data on electrocouplings of almost all well established excited proton states with masses less than 1.8 GeV at photon virtualities from 0.5 to 1.5 GeV2 will be obtained from analysis of p+p-p electroproduction by the first half of 09’. Eventually analysis will be extended for photon virtualitulities 1.5<Q2<5.0 GeV2. The CLAS p+p-p data at W<2.0 GeV and 1.5<Q2<5.0 GeV2 are close to completion

11. Back-up

12. very preliminary Resonance signals in 2p electroproduction at high Q2.
Fully integrated 2p cross section at
Q2 from 4.5 to 5.2 GeV2
After 12 GeV Upgrade CLAS12 will be only facility foreseen worldwide, capable to study electrocouplings for full spectrum of N*’s at Q2 from 5.0 to 10 GeV2.
very preliminary
D33(1700),P13(1720)
3/2+(1720),F15(1685)
D13(1520)
S11(1535)
Access to constituent quark structure and interactions through quark core excitation in N*’s for the first time.
Evidence for substantial N* contributions

13. Data from exclusive π0 production
Meson-baryon dressing vs Quark core contribution in NΔ Transition Form Factor – GM. EBAC analysis.
One third of G*M at low Q2 is due to contributions from meson–baryon (MB) dressing:
GD = 1
(1+Q2/0.71)2
Data from exclusive π0 production
bare quark core
Within the framework of relativistic QM [B.Julia-Diaz et al., PRC 69, (2004)], the bare-core contribution is very well described by the three-quark component of the wf.
Q2=5GeV2

14. Meson-baryon dressing / Quark core contributions in the A1/2 electrocouplings of the P11(1440) & D13(1520) states.
Estimates from EBAC for the MB dressing: B.Julia-Diaz et al., PRC 76, 5201 (2007).
hypercentric -quark model
by M.Giannini
Light Front quark model
by I.Aznauryan
P11(1440)
D13(1520)
MB dressing effects have substantial contribution to low lying N* electrouplings at Q2<1.0 GeV2 and gradually decrease with Q2;
Contribution from dressed quarks increases with Q2 and are expected to be dominant at Q2>5.0 GeV2.

15. D13(1520) electrocouplings from the CLAS data on Np/Npp electroproduction
electrocouplings as determined from the Np & Npp channels are in good agreement overall
but the apparent discrepancies for the A3/2 amplitude at Q2 < 0.4 GeV2 will be further investigated in a combined Np/Npp analysis
hypercentric Consituent Quark Model calculations reasonably describe electrocouplings at Q2>2.5 GeV2, suggesting that the 3-quark component is the primary contribution to the structure of this state at high Q2.
error bars include systematic uncertainties
M.Giannini/
E.Santopinto
hyper-centric
CQM

16. Projections for N* Transitions
CLAS12
Projections for N* Transitions
For the foreseeable future, CLAS12 will be the only facility worldwide, which will be able to access the N* electrocouplings in the Q2 regime of 5 GeV2 to 10 GeV2, where the quark degrees of freedom are expected to dominate. Our experimental proposal “Nucleon Resonance Studies with CLAS12” was approved by PAC34 for the full 60-day beamtime request
CLAS published
CLAS published
CLAS preliminay
CLAS12 projected
CLAS PRL subm.
CLAS12projected

17. Physics objectives in the N* studies with CLAS12
explore the interactions between the dressed quarks, which are responsible for the formation for both ground and excited nucleon states.
probe the mechanisms of light current quark dressing, which is responsible for >97% of nucleon mass.
Q2=10GeV2
Approaches for theoretical analysis of N* electrocouplings: LQCD, DSE, relativistic quark models. See details in the White Paper of EmNN* JLAB Workshop, October 13-15, 2008:
DSE: lines and LQCD: triangles
Q2 = 12 GeV2 = (p times number of quarks)2= 12 GeV2→ p = 1.15 GeV