I. G. Aznauryan

Jefferson Lab Yerevan Physics Institute

October 13, 2008, Jlab Electromagnetic N-N* Transition Form Factors Workshop

Electroexcitation of P11(1440), D13(1520), and S11(1535)

from CLAS data and quark model predictions.On the definitions of the p N* helicity

amplitudes

Results on the pP11(1440), D13(1520), S11(1535) helicity amplitudes extracted from CLAS andelectroproduction data, comparison with earlier data

Correct definition of the amplitudes : very important as Q2 dependence of the NN* 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 N interaction - results of lattice QCD Comparison with quark model predicions Summary

Outline

CLAS: the eNeN data

Q2 = 0.4, 065 GeV2

epeN 14 863 data points:

K. Joo et al., PRL 88 (2002) 122001 PR C68 (2003) 032201 PR C70 (2004) 042201H.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

epeN 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 epep data

Q2 = 0.65 GeV2

Combined analysis of epepepepdata:

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 p P11 (1440) transition

N

CLAS data :

PDG

First measurements of A1/2 at Q2 > 0

NNcombined

Npreliminary

pp M.Dugger et al.,PR C76 025211,2007

First measurements of S1/2

Helicity amplitudes of the p S11 (1535) transition

N

CLAS data :

PDG

pp M.Dugger

First measurements of S1/2 :

Results for A 1/2 obtained in and production agree with each other with PDG:

N

it is difficult to extract S1/2 in electroproduction

Slow falloff of A1/2 observed in production is confirmed by data

Helicity amplitudes of the p D13(1520) transition

N

CLAS data :

NNcombined

Npreliminary

Old data:Bonn, DESY, NINA

PDG

pp M. Dugger

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 p N* amplitudes

In the analyses of N N data, the p N* helicity amplitudes are defined through reaction multipole amplitudes. For example, for p P11(1440) in p p

we have:

This definition contains information on signs of two vertices NN* and N*N :

gN*N)

N*N1/2N* NN

Common sign of the p N* amplitudes (con-d)

Definition of A1/2 in theoretical approaches :

N* NN

N*N*)

*

Depends on the phase of N*

Contains information on the N N* vertex only

Common sign of the p N* amplitudes (con-d)

Commonly used definition of A1/2 in quark model

is :

A1/2 sign NN*

R.L.Walker, Proc. of IV Int. Symp. on Electron-Photon Inter. at High Energies, Liverpool (1969), p. 21.

In QM, traditionally, the sign NN* 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 AN, …?

Common sign of the p N* amplitudes (con-d)

We need explicit formulas, how to account for the relativesign of the contributions :

Res.:

Bornterms:

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 p N* amplitudes (con-d)

In this way, we have also checked, which definition ofgives the sign consistent with the relative sign of the amplitudesextracted 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 N N multipole amplitudes

Through the N N* electromagnetic current

Through the 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 p N* amplitudes (con-d)

For the resonances of [70,1- ] –plet, common signs of the

p N* amplitudes in quark model were found

(using PCAC for the N 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 p N* amplitudes was found

using 3Po model for the N N* vertex by

Capstick, Keister, PR D51 (1995) 3598

using PCAC for the N N* vertex by Aznauryan, PR C76 (2007) 025212

Signs forp P11 (1440)

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

1. strong model dependence 2. for some models strong disagreement with experiment

Corrected signs1. less model dependence 2. better agreement with exp.

Signs taken in ‘traditional way’

p P11 (1440): 3q picture with P11 (1440) as [56,0+]r

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 describe

sign change of A1/2 the amplitude S1/2 Strong evidence

in favor of P11 (1440) as a firstradial excitation of3q ground state

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 (theory) = (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

Supression of S1/2 has its origin in the form of the vertex *q qG; it is practically independent ofrelativistic effects

P11 (1440) as qG:Li, Burkert,Li, PR D46 (1992) 70

P11 (1440) as q3Ghybrid state is ruled out !!!

p D13 (1520): 3q picture + pion cloud

Pion cloud: EBAC (preliminary)

Significant contribution at small Q2 for A3/2

In 3q picture, the signsof all amplitudes are described; however, this picture fails to describe A3/2 at small Q2

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

p S11 (1535): 3q picture

Opposite sign

of S1/2!!!

LF RQM:

Capstick, Keister,

PR D51 (1995) 3598

Pace, Simula et.al.,

PR D51 (1995) 3598

Combined with the difficultiesin the description of large width of S11(1535) N and largeS11(1535) N,K couplings, this shows that 3q picture for S11(1535) should be complemented

Impossible to change in quark

model !!!

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 (S11 (1535)p)

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 p P11(1440) transition are extracted from experiment for Q2 > 0 in wide range of Q2 For the first time longitudinal amplitudes of the 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 p D13(1520) transition in wide range of Q2 The results for the p S11(1535) transverse

amplitude extracted from and electroproduction data are consistent with each other

Summary: P11(1440)

The results for 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 outQuark 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 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 p S11(1535) transition !!! Combined with the difficultiesin 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 N N* amplitudes

The N N* amplitudes extracted from the experimental data on the N Nreaction are related to the N N* amplitudes calculated in theoretical approaches through the sign of the NN* vertexPossibly, it makes sense to introduce new conventions in orderto avoid confusion caused by this fact

S11 (1535) as a dynamically generated resonance

Dynamically generated S11 (1535):Oset… , nucl-th/0712.0038

sign should be checked via calculation of the vertex S11 (1535)N in addition to p S11 (1535)

For both signs, presentation of S11 (1535) as only dynamicallygenerated resonance is ruled out.However, it is interesting to investigate the possibility of the dynamically generated resonance as a component additional to 3q state.