Outline :

1. Nucleon resonance studies in phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton. Victor Mokeev • Analysis objectives. • JLAB-MSU model and candidate 3/2+(1720) state. • Model extension from analysis of recent CLAS data. • Comprehensive test of 2005’ JLAB-MSU model in combined fit of 1p and 2p data from CLAS. • N* photocouplings and hadronic parameters extracted from CLAS 2p data fit within the framework of 2005’ JLAB-MSU model. • Conclusion and outlook. Outline:

2. JLAB-MSU model for 2-p photo- electro-production from 2003’ to 2005’-versions. 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 • Minimal set of Reggetized gauge invariant Born terms • Effective treatment of couplingswith other open channels P33(1600) • All well established N* with rp decays • +P11(1710)&P13(1720) 3-star states. • Diffractive ansatz for non-resonant rp • production mechanisms added to 2005’ model version

3. JLAB-MSU model from 2003’ to 2005’ version. 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) mechanisms added to 2005’ model version F15(1685) First step in data analysis needed to establish all relevant mechanisms of 2p production from their manifestations in measured cross-sections. Valuable input for further model development within the framework of rigorous coupled channel approach. Details of the 2003’-version of model may be found in: M.Ripani et. al., Nucl. Phys., A672, 220 (2000); V.Mokeev, et. al., Phys. of Atom. Nucl., 64, 1292 (2001); V.D.Burkert, et.al., Phys. of Atom Nucl.,66, 2199 (2003); V.D.Burkert, et. al., Phys. of Atom Nucl., 67, 1018 (2004);

4. Electroproduction data fit. A candidate 3/2+(1720) baryon state. CLAS data fit N*photocouplings were varied within 30% s around values obtained from world meson photo and electroproduction data analysis in SQTM approach: V.D.Burkert et. al., Phys. Rev. C67, 035204 (2003) Contributions from conventional states only Fit with candidate 3/2+(1720) state M.Ripani et. al. Phys. Rev. Lett.91, 022002 (2003) Difference between curves due to signal from candidate 3/2+(1720) state

5. Manifestation of direct 2p production mechanisms. W=1.49 GeV JLAB-MSU model: Q2=0. GeV2 Q2=0.65 GeV2 Q2=0.95 GeV2 2003’ 2005’ 2p direct production mechanisms

6. 2p direct production mechanisms and an additional term for pD channels needed to fit data. 2 =1.64 GeV2

7. Description of total p+p- photoproduction cross-section off protons in 2005’ version of JLAB-MSU model. Q2=0. GeV2 • Initial values of N* photocouplings were taken from analysis of CLAS 2p data within the framework of 2003’ JLAB-MSU model: V.Burkert et.al., Nucl. Phys. A737, S231 (2004) and further adjusted to the data, using recent version of model. s, mcbn no 3/2+ full calculation Background • Signal from candidate 3/2+(1720) state present, but masked by large background Resonances W, GeV

8. Description of total p+p- electroproduction cross-sections off protons in 2005’ JLAB-MSU model. • All CLAS 2p photo and electro production data were described implementing meson-baryon mechanisms seen in observables without need for an additional mechanisms of unknown dynamics. s mb Q2=0.65 GeV2 Q2=0.95 GeV2 • Quality of CLAS data allowed to establish all relevant mechanisms for 2p production in N* excitation region at Q2<1.5 GeV2 Q2=1.30 GeV2 Would adopted parameterization of background provide credible N*/background separation? W, GeV

9. Combined analysis of the CLAS data on 1p and 2p electroproduction at Q2=0.65 GeV2 Successful fit of all 1p/2p observables with common set of N* photocouplings would provide evidence for reliable background description and N*/background separation. Single pion data: ds/dW differential cross-sections: p+ at W between 1.1-1.41 GeV, p0 at W between 1.1-1.68 GeV; beam asymmetries: p+ and p0 at W between 1.1-1.58 GeV 9870 data points CLAS1p 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 1.41-1.89 GeV 680 data points The data are available in CLAS Physics DB: http://clasdb3.jlab.org CLAS 2p data M.Ripani, V.D.Burkert, et.al. 1p analysis models:I.G. Aznauryan, Phys. Rev. C68, 065204 (2003); I.G. Aznauryan, et. al., Phys. Rev. C71, 015201 (2005).

10. 1p data description with N* photocouplings from combined analysis of 1p/2p channels at Q2=0.65 GeV2. W=1.52 GeV gvp→p0p W=1.68 GeV Bunches of curves correspond to calculated 1p/2p cross-sections with common sets of N* photocouplings

11. 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 accepted by PRC

12. N* photocouplings and hadronic parameters from analysis of the CLAS 2p data within the framework of 2005’ JLAB-MSU model. • Fitted data: p+p-, p+p, p-p mass and CM p- angular distributions at 20 W-bins between 1.41-1.89 GeV and photon virtualities Q2: 0., 0.65, 0.95, 1.30 GeV2. The data may be foundin CLAS Physics DB: http://clasdb3.jlab.org. • Combined fit of 4 Q2 bins was carried out within a framework of 2005’ JLAB-MSU model. W-intervals between 1.41-1.51 GeV, 1.54-1.64 GeV, 1.66-1.76 GeV, 1.79-1.89 GeV were fitted independently. • Photocouplings 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 2005’ JLAB-MSU model. Hadronic couplings were further constrained, exploiting their Q2-independence. The photocouplings at 4 mentioned above Q2’s were derived from data fit 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

13. Description of total p+p-p cross-sections with N* photocouplings, hadronic and non-resonant mechanism parameters fitted to the data. Parameter variations N* photocouplings: within 30% s around values obtained in previous fit (2003’ JLAB-MSU model) pD, rp decays: wide range, which led to the total width variation between 40-600 MeV N* masses: inside PDG uncertainties Q2=0 GeV2 Q2=0 65GeV2 Q2=0 95GeV2 Q2=1 30 GeV2 Sub-sets of calculated cross-sections most close to the data were isolated, applyingrestriction 2<2 thresh, listed in the table

14. N* photocouplings from analysis of CLAS 2p data within the framework of 2005’ JLAB-MSU model. 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, 035204 (2003) Q2 GeV2 Q2 GeV2

15. 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 data on Q2-evolution of S31(1620), D13(1700), D33(1700), P13(1720). F35(1905),P33(1920), F37(1950) photocouplings were obtained from analysis of CLAS experiments on 2p photo- and electro- production. P13(1720) P13(1720)

16. Conclusions and outlook. • Phenomenological approach was developed for description of 2p production by real and virtual photons in N* excitation region and at Q2<1.5 GeV2. The approach provides most complete treatment of contributed mechanisms and allows most reliable evaluation of N* photocouplings and, in part, hadronic parameters from the fit to all measured observables in p+p-p final state. • Quality of CLAS data allowed to establish all relevant 2p production mechanisms, implementing particular meson-baryon diagrams needed for data fit. Good description of all unpolarised CLAS/world data was achieved without any necessity for remaining mechanisms of unknown dynamics. Reliability of background description and N*/background separation was confirmed in combined analysis of CLAS 1p and 2p electroproduction data. • The photocouplings in Q2-area between 0 and 1.5 GeV2 were extracted from CLAS 2p photo- and electroproduction data for most N*’s with masses less then 2.0 GeV. Q2-evolution of photocouplings for S31(1620), D13(1700), D33(1700), P13(1720), F35(1905), P33(1920), F37(1950) states were determined for the first time. • First comprehensive data on Q2-evolution of photocouplings for many N*’s open up an opportunity to establish driving symmetry for quark binding potential in baryons and to access N* structure in terms of contributing 3q-configurations.