Generalities of the approaches for extraction of N* electrocouplings at high Q2

• Modeling of resonant / non resonant contributions is needed and should be focused on extraction of gvNN* electrocouplings from measured observables in Np and Npp electroproduction .

•Breit Wigner ansatz represents a reasonable parameterization for resonant amplitudes. It should account as much as possible for constraints imposed by unitarity and analyticity, employing inputs from coupled channel approaches.

•Non-resonant processes should be a mixture of driving terms, that incorporates both MB and quark degrees of freedom, while the remainingpart can be described at the level of phenomenological parameterization and fit to the data.

How to define N* electrocouplings and check their values

γv

N N’

N*,△

A3/2, A1/2, S1/2

GM, GE, GC

, , p hpp,..

N

, , ,..p h pp

N’

+*

• gvNN* electrocouplings can be defined in various ways, BUT should be related to: a) observables , b) transition amplitudes gvp→N* at real energies equal to N* physical masses.

• Consistent results on N* electrocouplings from the analyses of major meson electroproduction channels should show their reaction and model independence.

Resonant amplitudes Non-resonant amplitudes

gvNN* electrocouplings from the CLAS data on Np/Npp electroproduction

N pp CLAS preliminary.

N p CLAS

Good agreement between the electrocouplings obtained from the Np and Npp channels.

I. Aznauryan,V. Burkert, et al., PRC 80,055203 (2009).

A1/2S1/2

A3/2

F15(1685)

A3/2

P11(1440) P11(1440)

D13(1520)

N p world

V. Burkert, et al., PRC 67,035204 (2003).

N p Q2=0, PDG.

N p Q2=0, CLAS

M. Dugger, et al., PRC 79,065206 (2009).

Partial wave (LSJ) amplitude of a b reaction:

Reaction channels:

Transition potentials:

coupled-channels effect

Dynamical coupled-channels model of EBACFor details see Matsuyama, Sato, Lee, Phys. Rep. 439,193 (2007)

)(

)()( *

E

EE ijijNm

After dressing •N* are poles at E complex•N* production and decay amplitudesare complex

BW ansatz projects s-channel N* ‘s

Unitarized Breit-Wigner Anstaz of JM model

The unitarization procedure proposed in I.J.R.Aitchison NP A189 (1972), 417 and modified to be consistent with N* propagators emplyed in JM mpdel:

fSfT pMBMBp

where fagp, fbMBare the a-th N* electroproduction and b-th N* hadronic decay amplitude to the meson-baryon (MB) final state; Sab is the operator for resonance propagation, taking into account all transitions between a and b N* states, allowed by conservation laws in the strong interactions.

N*a N*a

diagonalregular BW

N*a N*b

off-diagonal

Off-diagonal transitions incorporated into JM:

S11(1535) ↔ S11(1650)D13(1520) ↔ D13(1700)3/2+(1720) ↔ P13(1700)

Energy dependencies, phases of N* production and decay amplitudes should be taken from coupled channel approaches together with MB dressing esrimates

WMMMS NNi

N i 2

**

2

*

1 )( Inverse of the JM unitarized N* propagator:

Quark degrees of freedom in non-resonant mechanisms

• Hand-bag diagrams for N , p pD and rp channels. others….

• How to combine quark and MB mechanisms to avoid double counting

• Driving MB mechanisms at Q2>5.0 GeV2

• Use of restrictions from unitarity and analyticity….

• Content of the White Paper chapter, contributors….

Future N* studies in π+π-p electroproduction with CLASgvNN*electrocouplings will become available for most excited proton states with masses less then 2.0 GeV and at photon virtualities up to 5.0 GeV2 Needs to incorporate/check quark degrees of freedom in background

0.65

0.95

1.30

2.30

2.70

3.30

3.90

4.60

Q2 (GeV2)

Resonance structures become more prominent with increasing Q2.

D33, P13 ,F15

3/2+(1720) D13

Extension of JM model toward high Q2

Coupling with Regge trajectory was increasedby a factor 1.8!

How to extend thus description toward W from 1.1 to 2.0 GeV?•GPD parameterization•Extension for pD and rp final states

9

Photon-nucleon current• Composite nucleon must

interact with photon via nontrivial current constrained by Ward-Takahashi identities

• DSE, BSE, Faddeev equation, current → nucleon form factors

Vertex contains dressed-quark anomalous magnetic moment

Oettel, Pichowsky, SmekalEur.Phys.J. A8 (2000) 251-281

Prospects to describe backgroundwithin DSE fraework, attachingpion legs for N , p andreplacing the final N by D for pDfinal states?