Yerevan Physics Institute Electroexcitation of P11(1440), D13(1520), and S11(1535) from CLAS data and quark model predictions. On the definitions of the g*p N* helicity amplitudes I. G. Aznauryan Jefferson Lab Yerevan Physics Institute October 13, 2008, Jlab Electromagnetic N-N* Transition Form Factors Workshop

Q2 dependence of the g* NN* amplitudes extracted in wide region Outline Results on the g * pP11(1440), D13(1520), S11(1535) helicity amplitudes extracted from CLAS p and 2p electroproduction data, comparison with earlier data Correct definition of the amplitudes : very important as Q2 dependence of the g* NN* amplitudes extracted in wide region of Q2 is highly sensitive to different description of N and N* : - 3q picture - additional qq components - hybrid q3G states - resonances dynamically generated in p N interaction - results of lattice QCD Comparison with quark model predicions Summary

CLAS: the eNeNp data Q2 = 0.4, 065 GeV2 s(epeNp+,0 )  14 863 data points: K. Joo et al., PRL 88 (2002) 122001 PR C68 (2003) 032201 PR C70 (2004) 042201 H.Egiyan et al., PR C73(2006) 025204 Analysis: DR, UIM I.Aznauryan et al., PR C71 (2005) 015201 PR C72 (2005) 045201 Q2 = 1.72, 2.05, 2.44, 2.91, 3.48, 4.16 GeV2 s(epeNp+ )  36 300 data points: K. Park et al., PR C77 (2008) 015208 Analysis: DR, UIM I.Aznauryan et al., nucl-exp/0804.0447, will appear in PRC

CLAS: the epepp+p- data Q2 = 0.65 GeV2 Combined analysis of epepp , epepp+p- data: I.Aznauryan, V.Burkert, V.Mokeev et al., PR C72 (2005) 045201 Q2 = 0.275, 0.325, 0.375, 0.425, 0.475, 0.525, 0.575 GeV2 Data: G.Fedotov,V.Mokeev, V.Burkert,… nucl-ex/0809.1562 Analysis: V.Mokeev, V.Burkert, J.Phys. Conf.Ser. 69 (2007) 012019; Proc. of NSTAR2007, p. 76

Helicity amplitudes of the g*p P11 (1440) transition CLAS data : Np Np, Npp, combined Npp (preliminary) gppp0 M.Dugger et al., PR C76 025211,2007 PDG First measurements of A1/2 at Q2 > 0 First measurements of S1/2

Helicity amplitudes of the g*p S11 (1535) transition CLAS data : Np Nh gppp0 M.Dugger PDG First measurements of S1/2 : it is difficult to extract S1/2 in h electroproduction Results for A 1/2 obtained in p and h production agree with each other with bp N = 0.45, b hN = 0.52  PDG: bp N = 0.35-0.55, b hN = 0.45-0.6 Slow falloff of A1/2 observed in h production is confirmed by p data

Helicity amplitudes of the g*p D13(1520) transition CLAS data : Np Np, Npp, combined Npp (preliminary) gppp0 , M. Dugger Old data: Bonn, DESY, NINA PDG First definite results for A 1/2 , A 3/2 in wide range of Q2 First measurements of S1/2

Definitions: common sign of the g*p N* amplitudes In the analyses of g*N N p data, the g*p N* helicity amplitudes are defined through reaction multipole amplitudes. For example, for g*p P11(1440) in g*p p p0 we have: N* N g* p This definition contains information on signs of two vertices g*NN* and N*Np : g(N*Np )  {G (N*Np)}1/2

Common sign of the g*p N* amplitudes (con-d) Definition of A1/2 in theoretical approaches : Depends on the phase of FN* Contains information on the g*N N* vertex only g* p N* N FN* (FN*)*

Common sign of the g*p N* amplitudes (con-d) Commonly used definition of A1/2 in quark model is : A1/2 sign pNN* R.L.Walker, Proc. of IV Int. Symp. on Electron-Photon Inter. at High Energies, Liverpool (1969), p. 21. In QM, traditionally, the sign pNN* was chosen to describe the sign of the experimental A1/2 amplitude for Q2=0; sometimes this can bring to confusing and wrong results Possibly, it will be right to make some changes in conventions to avoid this confusion, for example, to reflect in the amplitude extracted from experiment the final state: A ApN, …?

Common sign of the g*p N* amplitudes (con-d) We need explicit formulas, how to account for the relative sign of the contributions : Res.: Born terms: I.Aznauryan, V.Burkert, H.Lee, nucl-th/0810.0997 Through covariant calculations, we have obtained the relations: For example, for P11 (1440) : , if

Definition of the g*p N* amplitudes (con-d) In this way, we have also checked, which definition of gives the sign consistent with the relative sign of the amplitudes extracted from experiment, i.e. S1/2 relatively to A1/2, A3/2 We have presented different definitions of A1/2, A3/2, S1/2 : Through the g*N N p multipole amplitudes Through the g*N N* electromagnetic current Through the g*N N* form factors In nonrelativistic quark model These definitions are consistent with each other, and may be useful in theoretical calculations

Common sign of the g*p N* amplitudes (con-d) For the resonances of [70,1- ] –plet, common signs of the g*p N* amplitudes in quark model were found (using PCAC for the pN N* vertex) by Aznauryan, Bagdasaryan, Sov.J.Nucl.Phys. 41 (1985) 158 For all resonances, except D13(1700), traditionally used sign is right For P11(1440), sign of the g*p N* amplitudes was found using 3Po model for the pN N* vertex by Capstick, Keister, PR D51 (1995) 3598 using PCAC for the pN N* vertex by Aznauryan, PR C76 (2007) 025212

Signs for g*p  P11 (1440) Light-front RQM 1. strong model dependence 2. for some models strong disagreement with experiment Corrected signs 1. less model dependence 2. better agreement with exp. Signs taken in ‘traditional way’ Light-front RQM Capstick, Keister (1995) Weber, PR C41 (1990)2783 Simula… PL B397 (1997)13 NRQM Warns… Z.Phys. C45 (1990)627 Giannini… J.Phys. G24 (1998)753

g*p  P11 (1440): 3q picture with P11 (1440) as [56,0+]r All LF RQM describe sign change of A1/2 the amplitude S1/2 Strong evidence in favor of P11 (1440) as a first radial excitation of 3q ground state LF RQM: Weber, PR C41 (2783) 1990 Capstick, Keister, PR D51 (1995) 3598 Pace, Simula et.al., PR D51 (1995) 3598 Aznauryan, PR C76 (2007) 025212 All LF RQM fail to describe the amplitude A1/2 at Q2 < 1 GeV2

P11 (1440): Additional components and contributions Pion cloud EBAC (preliminary) Julia-Diaz et.al., PR C77(2008)045205 30% admixture of qqqqq components in the Roper resonance G(theory) = G (exp) : Li, Riska, PR C74(2006)015202 Pion cloud contributions and additional qqqqq components in the Roper resonance can improve the description at small Q2

P11 (1440) as a q3G hybrid state P11 (1440) as q3G hybrid state is ruled out !!! Supression of S1/2 has its origin in the form of the vertex g*q  qG; it is practically independent of relativistic effects P11 (1440) as q3G: Li, Burkert,Li, PR D46 (1992) 70

g*p D13 (1520): 3q picture + pion cloud In 3q picture, the signs of all amplitudes are described; however, this picture fails to describe A3/2 at small Q2 Pion cloud: EBAC (preliminary) Significant contribution at small Q2 for A3/2 Nonrelativistic approaches: Warns et al., Z.Phys.C45(1990)627 Aiello et.al., J.Phys.G24 (1998)753 Merten…, Eur.Phys.J.A14 (2002)477

g*p S11 (1535): 3q picture Capstick, Keister, PR D51 (1995) 3598 Opposite sign of S1/2!!! Impossible to change in quark model !!! Combined with the difficulties in the description of large width of S11(1535)  h N and large S11(1535)  fN,LK couplings, this shows that 3q picture for S11(1535) should be complemented LF RQM: Capstick, Keister, PR D51 (1995) 3598 Pace, Simula et.al.,

S11 (1535): Additional components and contributions Pion cloud: EBAC (preliminary), MAINZ qq (mostly ss) : An,Zou , nucl-th/0802.3996 sign should be consistent with the interference of (uu,dd) and ss components in G(S11 (1535)hp) It is possible that agreement of 3q picture with experimental data will be achieved by taking into account pion cloud contribution and additional qqqqq components in S11(1535)

Summary For the first time transverse and longitudinal amplitudes of the g* p P11(1440) transition are extracted from experiment for Q2 > 0 in wide range of Q2 For the first time longitudinal amplitudes of the g* p D13(1520), S11(1535) transitions are extracted from experiment, and in wide range of Q2 For the first time definite results are obtained for the transverse amplitudes of the g* p D13(1520) transition in wide range of Q2 The results for the g* p S11(1535) transverse amplitude extracted from p and h electroproduction data are consistent with each other

Summary: P11(1440) The results for g* p P11(1440) available in wide region of Q2 allow us to make conclusions on the nature of P11(1440): Comparison with quark model predictions provides strong evidence in favor of P11(1440) as a first radial excitation of the 3q ground state Presentation of P11(1440) as a q3G hybrid state is ruled out Quark model predictions underestimate the value of A1/2 at small Q2 Pion cloud contributions and additional qq components in the Roper resonance can improve description of A1/2 at small Q2

Summary: D13(1520), S11(1535) Quark models describe the signs of all amplitudes for the g* p D13(1520) transition There is significant underestimation at small Q2 for A3/2 which apparently is related to the pion cloud contribution Quark models predict opposite sign for the S1/2 amplitude of the g* p S11(1535) transition !!! Combined with the difficulties in the description of couplings to hadronic channels, this shows that 3q picture for S11(1535) should be complemented Apparently, agreement of 3q picture with experimental data can be achieved by taking into account pion cloud contribution, and additional qqqqq components in S11(1535)

Summary: definitions of the g* N N* amplitudes The g* N N* amplitudes extracted from the experimental data on the g* N Np reaction are related to the g* N N* amplitudes calculated in theoretical approaches through the sign of the pNN* vertex Possibly, it makes sense to introduce new conventions in order to avoid confusion caused by this fact

S11 (1535) as a dynamically generated resonance generated S11 (1535): Oset… , nucl-th/0712.0038 sign should be checked via calculation of the vertex S11 (1535)pN in addition to g*p S11 (1535) For both signs, presentation of S11 (1535) as only dynamically generated resonance is ruled out. However, it is interesting to investigate the possibility of the dynamically generated resonance as a component additional to 3q state.