V.I.Mokeev APS09 Meeting May 2th Denver

Victor I. MokeevJefferson Lab

Nucleon resonance electrocouplings from the CLAS data on charge double pion electroproduction

• Introduction

• JM model for evaluation of N* electrocouplings in analyzing the +-p electroproduction

• New results on N* electrocouplings from our studies on the +-p CLAS data

• Conclusions and outlook

V.I.Mokeev APS09 Meeting May 2th Denver

CLAS data on meson electroproduction at Q2 < 4.0 GeV2

Why p electroproduction channel is important

• N/N channels are the two major contributors in N* excitation region;

• these two channels combined are sensitive to almost all excited proton states;

• they are strongly coupled by N→N final state interaction;

• may substantially affect exclusive channels having smaller cross sections, such as p,K, and K.

Therefore knowledge on electro production mechanisms is key for the entire N* Program

V.I.Mokeev APS09 Meeting May 2th Denver

electroproduction data from CLAS

The measurements with an unpolarized e- beam onto a proton target: offer nine independent differential cross sections in each (W,Q2) bin.

.

Number data points > 82001.3 < W < 2.1 GeV ; 0.25 < Q2< 1.5 GeV2

M. Ripani et al., PRL,91, 022002 (2003);G. Fedotov et al., PRC 79, 015204 (2009).

V.I.Mokeev User Group Meeting June 18 2008 4

JLAB-MSU isobar model (JM) for N electroproduction.

3-body processes:Isobar channels included:

• All well established N*s with decays and 3/2+(1720) candidate, seen in CLAS 2 data.

• Reggeized Born terms with effective FSI & ISI treatment .

• Extra contact term.

•All well established N*s with p decays and 3/2+(1720) candidate.

•Diffractive ansatz for non-resonant part and -line shrinkage in N* region.

-++

p

V.I.Mokeev APS09 Meeting May 2th Denver

continued3-body processes: Isobar channels included:

• +D013(1520), +F0

15(1685), -P++33(1640)

isobar channels; observed for the first time in the CLAS data at W > 1.5 GeV.

Direct 2 production

F015(1685)

(P++33(1640))

(-)

(+)

V. Mokeev, V .Burkert, J. Phys. 69, 012019 (2007); V. Mokeev et al., arXiv:0809:4158[hep-ph]

V.I.Mokeev APS09 Meeting May 2th Denver

Description of the CLAS N differential cross sections within the framework of JM model

full JM calc.

-++

+0

2 direct

p

+D013(1520)

+F015(1685)

V.I.Mokeev APS09 Meeting May 2th Denver

Resonant & non-resonant parts of N cross sections as determined from the CLAS data fit with the framework of JM model

full cross sections resonant part non-resonant part

V.I.Mokeev APS09 Meeting May 2th Denver

P11(1440) electrocouplings from the CLAS data on N/N electroproduction

NN

Light front models:

I. Aznauryan

S. Capstick

hybrid P11(1440)

• Good agreement between the electrocouplings obtained from the N and N channels: Reliable measure of the electrocouplings.

• The electrocouplings for Q2 > 2.0 GeV2 are consistent with P11(1440)

structure as a 3-quark radial excitation.

• Zero crossing for the A1/2 amplitude has been observed for the first time, indicating an importance of light-front dynamics.

V.I.Mokeev APS09 Meeting May 2th Denver

High lying resonance electrocouplings from N CLAS data analysis

NCLASpreliminary

Nworld

Nworld Q2=0

Δ(1700)D33

N(1720)P13

V.I.Mokeev APS09 Meeting May 2th Denver

Conclusions and outlook

• Phenomenological approach JM has been developed by the CLAS Collaboration with the goal of determining N* electrocouplings from combined fits of measured observables in N electroproduction data.

• A good description of the CLAS data on p differential cross sections has

been achieved, affording us to access the resonant parts of amplitudes, which are directly related to N* electrocouplings.

• The P11(1440) and D13(1520) electrocouplings have been determined for the first time N dataset.

• The consistent results extracted from N & N channels strongly indicate a reliable electrocoupling measurement.

• Analysis of the NCLAS data provides first-time information on the electrocouplings for D33(1700) & P13(1720) resonances that decay primarily to the N final states .

• Comprehensive data on electrocouplings of almost all well established excited proton states with masses less than 1.8 GeV at photon virtualities from 0.5 to 1.5 GeV2 will be obtained from analysis of p electroproduction by the first half of 09’. Eventually analysis will be extended for photon virtualitulities 1.5<Q2<5.0 GeV2. The CLAS p data at W<2.0 GeV and 1.5<Q2<5.0 GeV2 are close to completion

V.I.Mokeev APS09 Meeting May 2th Denver

Back-up

V.I.Mokeev APS09 Meeting May 2th Denver 12

Resonance signals in 2 electroproduction at high Q2.

Fully integrated 2 cross section at Q2 from 4.5 to 5.2 GeV2

Evidence for substantial N* contributions

After 12 GeV Upgrade CLAS12 will be only facility foreseen worldwide, capable to study electrocouplings for full spectrum of N*’s at Q2 from 5.0 to 10 GeV2.

Access to constituent quark structure and interactions through quark core excitation in N*’s for the first time.

D13(1520)S11(1535)

D33(1700),P13(1720)3/2+(1720),F15(1685)

V.I.Mokeev APS09 Meeting May 2th Denver

Meson-baryon dressing vs Quark core contribution in NΔ Transition Form Factor – GM. EBAC analysis.

Within the framework of relativistic QM [B.Julia-Diaz et al., PRC 69, 035212 (2004)], the bare-core contribution is very well described by the three-quark component of the wf.

One third of G*M at low Q2

is due to contributions from meson–baryon (MB) dressing:

GD = 1(1+Q2/0.71)2

Data from exclusive π0 production

bare quark core

Q2=5GeV2

V.I.Mokeev APS09 Meeting May 2th Denver

Meson-baryon dressing / Quark core contributions in the A1/2 electrocouplings of the P11(1440) & D13(1520) states.

Estimates from EBAC for the MB dressing: B.Julia-Diaz et al., PRC 76, 5201 (2007).

P11(1440) D13(1520)

Light Front quark model by I.Aznauryan

hypercentric -quark model by M.Giannini

V.I.Mokeev APS09 Meeting May 2th Denver

error bars include systematic uncertainties

M.Giannini/E.Santopintohyper-centricCQM

D13(1520) electrocouplings from the CLAS data on N/N electroproduction

• electrocouplings as determined from the N & N channels are in good agreement overall

• but the apparent discrepancies for the A3/2 amplitude at Q2 < 0.4 GeV2 will be further investigated in a combined N/N analysis

• hypercentric Consituent Quark Model calculations reasonably describe electrocouplings at Q2>2.5 GeV2, suggesting that the 3-quark component is the primary contribution to the structure of this state at high Q2.

V.I.Mokeev APS09 Meeting May 2th Denver

Projections for N* Transitions

For the foreseeable future, CLAS12 will be the only facility worldwide, which will be able to access the N* electrocouplings in the Q2 regime of 5 GeV2 to 10 GeV2, where the quark degrees of freedom are expected to dominate. Our experimental proposal “Nucleon Resonance Studies with CLAS12” was approved by PAC34 for the full 60-day beamtime request. http://www.physics.sc.edu/~gothe/research/pub/nstar12-12-08.pdf.

CLAS published

CLAS PRL subm.

CLAS12projected

CLAS published

CLAS preliminay

CLAS12 projected

CLAS12

V.I.Mokeev APS09 Meeting May 2th Denver

Physics objectives in the N* studies with CLAS12

Q2 = 12 GeV2 = (p times number of quarks)2= 12 GeV2→ p = 1.15 GeV

DSE: lines and LQCD: triangles

• explore the interactions between the dressed quarks, which are responsible for the formation for both ground and excited nucleon states.

• probe the mechanisms of light current quark dressing, which is responsible for >97% of nucleon mass.

Approaches for theoretical analysis of N* electrocouplings: LQCD, DSE, relativistic quark models. See details in the White Paper of EmNN* JLAB Workshop, October 13-15, 2008:http://www.jlab.org/~mokeev/white_paper/

Q2=10GeV2