V.Mokeev NSTAR 2005 Workshop 1 Phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton Outline :  2  exclusive channel in N* physics.  Analysis of CLAS 2  electroproduction data within the framework of JLAB-MSU model (2003’-version)  Complementary non-resonant mechanisms, established in analysis of recent CLAS data.  Comprehensive test of the recent JLAB-MSU model in combined fit of 1  and 2  data from CLAS.  N* photocouplings and hadronic parameters extracted from CLAS 2  data fit within the framework of 2005’ JLAB-MSU model  Conclusion and outlook Victor Mokeev

V.Mokeev NSTAR 2005 Workshop 2 N* in CLAS data. p(e,e’)X (trigger) p(e,e’p)   p(e,e’  + )n p(e,e’p  + )   p(e,e’p  + )X 2  channel is sensitive to contributions from most N*’s heavier than 1.4 GeV. It provides complementary information on N* with respect to 1  channels, in particular for high mass states (M>1.65 GeV) which mostly decay with 2  emission Q 2 <4.0GeV 2 Double pion production by photons off protons offers a promising way to search for “missing” baryon states.

V.Mokeev NSTAR 2005 Workshop 3 JLAB-MSU model for 2-  electroproduction (2003’-version). 3-body processesQuasi-2-body mechanisms included All well established N* with  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  p decays +P11(1710)&P13(1720) 3-star states. Diffractive ansatz for non-resonant  p production

V.Mokeev NSTAR 2005 Workshop 4 JLAB-MSU model (2003’-version). 3-body processes Quasi-2-body mechanisms included Minimal set of Born terms similar to what was used for  states, except an additional  5 matrix to account for the opposite parities of  and D13(1520) Residual mechanisms, beyond shown on the plots, were parameterized either as 3- body phase space or through a set of partial waves with J<13/2. Both lead to a similar description. 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);

V.Mokeev NSTAR 2005 Workshop 5 Electroproduction data fit. A candidate 3/2 + ( 1720) baryon state. CLAS data fit M.Ripani et. al. Phys. Rev. Lett.91, (2003) Difference between curves due to signal from candidate 3/2 + (1720) state Fit with candidate 3/2 + (1720) state Contributions from conventional states only N*  photocouplings were varied within 30%  around values obtained from world meson photo and electroproduction data analysis in SQTM approach: V.D.Burkert et. al., Phys. Rev. C67, (2003)

V.Mokeev NSTAR 2005 Workshop 6 M, MeV  MeV   / , % p/,%p/,% modified P13(1720) 1725±20114±1960±1219±9 PDG P13(1720) absent70-85 candidate 3/2 + (1720) 1720±2088±1741±1317±10 Two alternative ways to describe the structure at 1.7 GeV: Modification of hadronic couplings for P13(1720) PDG state with respect to established values Implementation of candidate baryon state with J  = 3/2 +. Description of 1.7 GeV mass region.

V.Mokeev NSTAR 2005 Workshop 7 JLAB-MSU model 2003-version, described on p ’ JLAB-MSU model, see p W=1.45 GeV 2  direct production mechanisms at the photon point. 2  direct production M.Bellis, et. al., (CLAS Collaboration) Proc of NSTAR2004 Workshop, March 24-27,2004, Grenoble, France, World Scientific 2005, ed. by J.-P.Bocquet, V.Kuznetsov, D.Rebreyend, 139 Preliminary real photon data from:

V.Mokeev NSTAR 2005 Workshop 8 Manifestation of 2-  direct production at Q 2 >0. W=1.49 GeV Q 2 =0.65 GeV 2 Q 2 =0.95 GeV ’ JLAB-MSU model 2003’-version 2  direct production

V.Mokeev NSTAR 2005 Workshop 9 2  direct production mechanisms and an additional term for  channels needed to fit data.  2 = 1.64 GeV 2

V.Mokeev NSTAR 2005 Workshop 10 Manifestation of  direct production and complementary term for  channels in real photon data. W=1.63 GeV W=1.78 GeV  +  0 with complementary term on p. 9

V.Mokeev NSTAR 2005 Workshop 11 Evidences for  p  + F 0 15 (1685) and  p  - P (1600) channels.  p  - P (1600)  p  + F 0 15 (1685)

V.Mokeev NSTAR 2005 Workshop 12 The amplitudes for  p  + F 0 15 (1685) and  p  - P (1600) channels.

V.Mokeev NSTAR 2005 Workshop 13 Fit of 2  photoproduction data at high W after implementation of new isobar channels. Full calculations  p  -  ++ p+0p+0 pppp  p  - P (1600)  p  + F 0 15 (1685) 2  direct

V.Mokeev NSTAR 2005 Workshop 14 Description of total     photoproduction cross-section off protons in 2005’ version of JLAB-MSU model.  Signal from candidate 3/2 + (1720) state present, but masked by large background Background Resonances full calculation  3/2 + (1720) photocouplings were adjusted to the real photon data. Hadronic couplings and masses were taken from the fit of virtual photon data. no 3/2 + Q 2 =0. GeV 2 W, GeV , mcbn

V.Mokeev NSTAR 2005 Workshop 15 Description of total  +  - electroproduction cross- section off protons in 2005’ JLAB-MSU model. W, GeV  b Q 2 =0.65 GeV 2 Q 2 =0.95 GeV 2 Q 2 =1.30 GeV 2  Initial values of N* photocouplings were taken from analysis of CLAS 2  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.  Signal from candidate 3/2 + (1720) state (~ 1.7 GeV) becomes prominent feature at Q 2 >0.5 GeV 2 due to considerable growth of N*/Bckgr. ratio in electroproduction.

V.Mokeev NSTAR 2005 Workshop 16 Improvements in description of the CLAS 2  electroproduction data after implementation of complementary non-resonant mechanisms. Q 2, GeV  2 /d.p. 2003’- version  2 /d.p. 2005’ JLAB-MSU model  2 was estimated from comparison between calculated and measured 1-diff. cross-sections for entire set of data in particular Q 2 -bin Quality of CLAS data allows to describe all relevant mechanisms of 2  production at W<2.0 GeV and Q 2 <1.5 GeV 2 implementing meson-baryon diagrams needed to reproduce particular features in observables without any necessity for remaining mechanisms of unknown dynamics. Essentials of recent JLAB-MSU model are highlighted in: V.Mokeev et. al., Proc of NSTAR2004 Workshop, World Scientific 2005 ed. by J.-P.Bocquet, V.Kuznetsov, D.Rebreyend, 317

V.Mokeev NSTAR 2005 Workshop 17 Combined analysis of the CLAS data on 1  and 2  electroproduction Data at Q 2 =0.65 GeV 2 were analyzed. It is only Q 2 value for which both 1  and 2  CLAS data exist so far. Q 2 -coverage will be extended soon. Single pion data: d  /d  differential cross-sections:  + at W between GeV,  0 at W between GeV; beam asymmetries:  + and  0 at W between GeV 9870 data points Double pion data:  +  -,  + p,  - p mass and CM  - angular distributions at W between GeV 680 data points The data are available in CLAS Physics DB: 1  analysis models: I.G. Aznauryan, Phys. Rev. C68, (2003); I.G. Aznauryan, et. al., Phys. Rev. C71, (2005). CLAS 1  data K.Joo, L.C.Smith, et.al CLAS 2  data M.Ripani, V.D.Burkert, et.al.

V.Mokeev NSTAR 2005 Workshop 18 N* photocouplings (in GeV -1/2 ) extracted in analyses of 1  /2  exclusive channels at Q 2 =0.65 GeV 2 N* 1  /2  analysis 1  analysis 2  analysis A 1/2 A 3/2 S 1/2 A 1/2 A 3/2 S 1/2 A 1/2 A 3/2 S 1/2 P 11 (1440)21±433± 64± 4 (23±4) 40± 421± 935± 6 D 13 (1520)-65± 462± 5-35± 3-67± 362± 4-38± 3-63± 12  ±  -40± 7 S 31 (1620)16± 4-28± 331± 3-35± 313± 3-25± 4 S 11 (1650)43± 7-6± 343± 2-15± 244± 16-8± 2 F 15 (1680)-32± 551± 4-15± 3-38± 456± 2-18± 2-31± 852± 10-14± 3 D 33 (1700)44± 436± 4-7± 458± 529± 3-15± 549± 836± 8-11± 4 D 13 (1700)-21± 210± 10(input)-6± 8-55± 70±8-19± 311± 20(input) P 13 (1720)55± 3-68±40(input)45± 6-48± 70±756± 6-62± 90(input) - The states with considerable 1  decays (…) result from dispersion relations. Roper is only state with A 1/2 dependent from model for 1  analysis

V.Mokeev NSTAR 2005 Workshop 19 1  data description with N* photocouplings from combined analysis of 1  /2  channels. vp→0pvp→0p W=1.52 GeVW=1.68 GeV

V.Mokeev NSTAR 2005 Workshop 20 2  data description with N* photocouplings from combined analysis of 1  /2  channels. W=1.54 GeV Q 2 =0.65 GeV 2 W=1.66 GeV Q 2 =0.65 GeV 2 Bunches of curves correspond to calculated 1  /2  cross-sections with common sets of N* photocouplings

V.Mokeev NSTAR 2005 Workshop 21 Con’t Integrated 2  cross-section Q 2 =0.65 GeV 2 Calculations with common sets of N* photocouplings provided good description of all available 1  /2  cross-sections and beam asymmetry data at Q 2 =0.65 GeV 2.. Strong evidence for reliable treatment of 1  and 2  production in both models, developed by CLAS Collaboration. The results are presented in: I.G.Aznauryan et. al., accepted by Phys. Rev. C., hep-ph/

V.Mokeev NSTAR 2005 Workshop 22 N* photocouplings and hadronic parameters from analysis of the CLAS 2  data within the framework of recent JLAB-MSU model. Fitted data:    ,   p,  - p mass and CM  - angular distributions at 20 W-bins between GeV and photon virtualities Q 2 : 0., 0.65, 0.95, 1.30 GeV 2. The data may be found in CLAS Physics DB: Combined fit of 4 Q 2 bins was carried out within a framework of 2005’ JLAB-MSU model. W-intervals between GeV, GeV, GeV, GeV were fitted independently. Photocouplings and poorly known masses,  and  p 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 Q 2 - independence. The photocouplings at 4 mentioned above Q 2 ’s were derived from data fit for the states: P 11 (1440), D 13 (1520), S 31 (1620), S 11 (1650), P 33 (1600) *), F 15 (1685), D 13 (1700), D 33 (1700), P 13 (1720), candidate 3/2 + (1720), F 35 (1905), P 33 (1920), F 37 (1950). * ) 1.65 GeV mass from our analysis

V.Mokeev NSTAR 2005 Workshop 23 Description of total  +  - p cross-sections with N* photocouplings, hadronic and non-resonant mechanism parameters fitted to the data. Parameter variations N* photocouplings: within 30%  around values obtained in previous fit (2003’ JLAB-MSU model) ,  p decays: wide range, which led to the total width variation between MeV N* masses: inside PDG uncertainties W-interv., GeV  2 /d.p thresh Sub-sets of calculated cross-sections most close to the data were isolated, applying restriction  2 <  2 thresh, listed in the table Q 2 =0 GeV 2 Q 2 =0 95GeV 2 Q 2 =0 65GeV 2 Q 2 =1 30 GeV 2

V.Mokeev NSTAR 2005 Workshop 24 Example of single-differential cross-section description with selected sub-sets of variable parameters. W=1.71 GeV and Q 2 =0.95 GeV 2 Similar sets of observables were fit in all available W and Q 2 bins shown on previous slide Bunches of curves correspond to selected cross-sections inside data uncertainties, applying restriction  2 /d.p. < differential cross-sections were calculated for each trial set of parameters.  2 /d.p.were determined from comparison with measured values.

V.Mokeev NSTAR 2005 Workshop 25 Q 2 -evolution of N* photocouplings, determined from analysis of CLAS 2  data (selected examples, see full list of studied N*’s on p. 22). P11(1440) CLAS 2  data analysis PDG at Q 2 =0 GeV 2 ; 1  /2  combined CLAS data analysis at Q 2 =0.65 GeV 2 (A 1/2 2 +S 1/2 2 ) 1/2 *1000GeV -1 Q 2 GeV 2 Photocouplings corresponded to selected cross-sections were averaged. Their mean values were treated as determined from data fit, while dispersions were assigned to uncertainties

V.Mokeev NSTAR 2005 Workshop 26 Cont’d D13(1520) (A 1/2 2 +S 1/2 2 ) 1/2, GeV -1/2 A 3/2, GeV -1/2 Q 2 GeV 2 CLAS 2  data analysis PDG at Q 2 =0 GeV 2 ; 1  /2  combined CLAS data analysis at Q 2 =0.65 GeV 2 World data before CLAS, obtained in analysis of 1  electroproduction: V.D. Burkert, et. al., Phys. Rev. C67, (2003)

V.Mokeev NSTAR 2005 Workshop 27 Cont’d D33(1700) P13(1720) D33(1700), P13(1720) resonances mostly decay with 2  emission. 1  data have not enough sensitivity to these states. First data on Q 2 -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 2  photo- and electro- production.

V.Mokeev NSTAR 2005 Workshop 28 New candidate state 3/2 + (1720). CLAS 2  data analysis in 2005’ JLAB-MSU model previous analysis of CLAS data in 2003’ model version Signal from possible new baryon state was confirmed in analysis of electro- production data and observed in real photon data.

V.Mokeev NSTAR 2005 Workshop 29 N* hadronic parameters derived from analysis of CLAS 2  data (upper rows) in comparison with PDG values (down rows). StateMass, GeVTotal width. GeV  BF,%  p BF,% D13(1520) 1.52 fixed ± ± ± P33(1600) 1.647± ± ± fixed <25 D13(1700) 1.70± ± ± for N  50±10 decays P13(1720) 1.735± ± <2.5 >70 for N  89±6 decays candidate 3/2 + (1720) 2003’ model 1.718± ± ± ± ±8 49±13 6.5±2 17±10

V.Mokeev NSTAR 2005 Workshop 30 Conclusions and outlook. Phenomenological approach was developed for description of 2  production by real and virtual photons in N* excitation region and at Q 2 <1.5 GeV 2. 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 final state. Quality of CLAS data allowed to establish all relevant 2  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 1  and 2  electroproduction data. The photocouplings in Q 2 -area between 0 and 1.5 GeV 2 were extracted from CLAS 2  photo- and electroproduction data for most N*’s with masses less then 2.0 GeV. Q 2 -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. Considerable improvement was achieved in our knowledge on N* 2  decays as well as on most hadronic parameters for high lying states. First comprehensive data on Q 2 -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.