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Phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton. Victor Mokeev. 2 p exclusive channel in N* physics. Analysis of CLAS 2 p electroproduction data within the framework of JLAB-MSU model (2003’-version)
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Phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton Victor Mokeev • 2p exclusive channel in N* physics. • Analysis of CLAS 2p 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 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:
N* in CLAS data. Q2<4.0GeV2 2p channel is sensitive to contributions from most N*’s heavier than 1.4 GeV. It provides complementary information on N* with respect to 1p channels, in particular for high mass states (M>1.65 GeV) which mostly decay with 2p emission p(e,e’)X (trigger) p(e,e’p)p0 p(e,e’p+)n p(e,e’pp+)p- Double pion production by photons off protons offers a promising way to search for “missing” baryon states. p(e,e’pp+)X
JLAB-MSU model for 2-p electroproduction(2003’-version). 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 • All well established N* with rp decays • +P11(1710)&P13(1720) 3-star states. • Diffractive ansatz for non-resonant rp • production
JLAB-MSU model (2003’-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) 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);
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
Description of 1.7 GeV mass region. • 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 withJp = 3/2+.
2p direct production mechanisms at the photon point. JLAB-MSU model 2003-version, described on p.3-4 W=1.45 GeV 2005’ JLAB-MSU model, see p. 7-15 2pdirect production Preliminary real photon data from: 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
Manifestation of 2-p direct production at Q2>0. W=1.49 GeV Q2=0.65 GeV2 Q2=0.95 GeV2 2005’ JLAB-MSU model 2003’-version 2pdirect production
2p direct production mechanisms and an additional term for pD channels needed to fit data. 2 =1.64 GeV2
Manifestation of 2p directproduction and complementary term for pD channels in real photon data. W=1.63 GeV W=1.78 GeV p+D0 with complementary term on p. 9
Evidences for gpp+F015(1685) and gpp-P++33(1600) channels. gpp-P++33(1600) gpp+F015(1685)
Fit of 2p photoproduction data at high W after implementation of new isobar channels. Full calculations gpp-D++ gpp+D0 gprp gpp-P++33(1600) gpp+F015(1685) 2p direct
Description of total p+p- photoproduction cross-section off protons in 2005’ version of JLAB-MSU model. Q2=0. GeV2 • 3/2+(1720) photocouplings were adjusted to the real photon data. Hadronic couplings and masses were taken from the fit of virtual photon data. s, mcbn no 3/2+ full calculation Background • Signal from candidate 3/2+(1720) state present, but masked by large background Resonances W, GeV
Description of total p+p- electroproduction cross-section off protons in 2005’ JLAB-MSU model. • 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 mb Q2=0.65 GeV2 Q2=0.95 GeV2 • Signal from candidate 3/2+(1720) state (~ 1.7 GeV) becomes prominent feature at Q2>0.5 GeV2 due to considerable growth of N*/Bckgr. ratio in electroproduction. Q2=1.30 GeV2 W, GeV
Improvements in description of the CLAS 2p electroproduction data after implementation of complementary non-resonant mechanisms. 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 allows to describe all relevant mechanisms of 2p production at W<2.0 GeV and Q2<1.5 GeV2 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
Combined analysis of the CLAS data on 1p and 2p electroproduction Data at Q2=0.65 GeV2 were analyzed. It is only Q2 value for which both 1p and 2p CLAS data exist so far. Q2-coverage will be extended soon. 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).
N* photocouplings (in 10-3 GeV-1/2) extracted in analyses of 1p/2p exclusive channels at Q2=0.65 GeV2 (…) result from dispersion relations. Roper is only state with A1/2 dependent from model for 1p analysis -The states with considerable 1p decays
1p data description with N* photocouplings from combined analysis of 1p/2p channels. W=1.52 GeV gvp→p0p W=1.68 GeV
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 1p/2p cross-sections with common sets of N* photocouplings
Con’t Integrated 2p cross-section Q2=0.65 GeV2 Calculations with common sets of N* photocouplings provided good description of all available 1p/2p cross-sections and beam asymmetry data at Q2=0.65 GeV2.. Strong evidence for reliable treatment of 1p and 2p 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/0508057
N* photocouplings and hadronic parameters from analysis of the CLAS 2p data within the framework of recent 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
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
Example of single-differential cross-section description with selected sub-sets of variable parameters. 1-differential cross-sections were calculated for each trial set of parameters. 2/d.p.were determined from comparison with measured values. W=1.71 GeV and Q2=0.95 GeV2 Bunches of curves correspond to selected cross-sections inside data uncertainties, applying restriction c2/d.p.<2.04 Similar sets of observables were fit in all available W and Q2 bins shown on previous slide
Q2-evolution of N* photocouplings, determined from analysis of CLAS 2p data (selected examples, see full list of studied N*’s on p. 22) . Photocouplings corresponded to selected cross-sections were averaged. Their mean values were treated as determined from data fit, while dispersions were assigned to uncertainties P11(1440) (A1/22+S1/22)1/2 *1000GeV-1 CLAS 2p data analysis PDG at Q2=0 GeV2; 1p/2p combined CLAS data analysis at Q2=0.65 GeV2 Q2 GeV2
Cont’d D13(1520) CLAS 2p data analysis (A1/22+S1/22)1/2, GeV-1/2 A3/2,GeV-1/2 PDG at Q2=0 GeV2; 1p/2p combined CLAS data analysis at Q2=0.65 GeV2 World data before CLAS, obtained in analysis of 1p electroproduction: V.D. Burkert, et. al., Phys. Rev. C67, 035204 (2003) Q2 GeV2 Q2 GeV2
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)
New candidate state 3/2+(1720). CLAS 2p 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.
N* hadronic parameters derived from analysis of CLAS 2p data (upper rows) in comparison with PDG values (down rows).
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. Considerable improvement was achieved in our knowledge on N* 2p decays as well as on most hadronic parameters for high lying states. • 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.