V.I.Mokeev NSTAR2007 at Bonn, September 4-8 1 presented by V.I.Mokeev The studies of N* electrocouplings at various Q 2 elucidate relevant degrees of freedom

1V.I.Mokeev NSTAR2007 at Bonn, September 4-8

presented by V.I.Mokeev

The studies of N* electrocouplings at various Q2 elucidate relevant degrees of freedom in their structure and allow us to understand quark interactions, which are responsible for baryon formation from fundamental constituents.

Promising way to study non-Abelian origin of strong interactions in non-perturbative domain, predicted in lattice simulations for quark binding in baryons.

gluon self coupling inpQCD

Lattice QCD calculation of gluon flux distribution in a system of 3 heavy quarks.

Results from the analysis of the CLAS data on double charge pion electroproduction.


How to obtain reliable information on N* electrocouplings.

Non-resonant amplitudes and N* hadronic couplings in various meson electroproduction channels are entirely different, while N* electrocouplings are expected to be the same.

v Np

p

e

e’

γv

N N’

N*,△

A3/2, A1/2, S1/2

Gm, Ge, Gc

Credible evaluation of N* electrocouplings should be achieved in successful description of all available observables in various electroproduction channels combined with common resonance electrocouplings.


CLAS data on meson electroproduction at Q2<4.0 GeV2

Why the data on 1/2 electroproduction mechanisms are vital for N* electrocoupling evaluation in any exclusive channel.

Exclusive channels in N scattering responsible for FSI in meson electroproduction

12 channels are major contributors.12 channels are strongly coupled by FSI.

W (GeV)


New opportunities for phenomenological studies of electroproduction, offered by the CLAS data.

Simplest measurements with unpolarized e- beam and p target, no use of polarization observables in the final state offer 9 independent single differential cross-sections in each (W,Q2) bin.

All these cross-sections are available from CLAS for the first time.

Contributing mechanisms may be established from theirs manifestations in variety of observables JM approach.

.


JLAB-MSU model (JM) for 2- electroproduction.

3-body processes: Quasi-2-body mechanisms included:

•All well established N*’s with decays and 3/2+(1720) candidate/P13(1720) with major decays to , seen in CLAS 2 data.

•Reggetized Born terms & effective FSI&ISI treatment .

•Extra contact term.

•All well established N*’s with p decays and 3/2+(1720) candidate/modified P13(1720).

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


con’d

3-body processes: Quasi-2-body mechanisms included:

• +D013(1520), +F0

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

isobar channels, observed for the first time in CLAS data at W>1.65 GeV

• the amplitudes were described at phenomenological level (see ref. below) .

Direct 2 production in JM05.

F015(1685)

(P++33(1640))

(-)

(+)

)(1

),( 21)(

42

2min

2

/ PPeW

UUQWA PPbppdM

Exchange processes,parameterized as:

V.Mokeev, V.Burkert, et al., Proc. of NSTAR2005 Workshop p. 47


Direct 2 production mechanisms, established from analysis of the CLAS data: M.Ripani, V.Burkert, et.al., Phys.Rev. Lett. 91, 022002 (2003).

W=1.49 GeV

Q2=0.65 GeV2 Q2=0.95 GeV2

CLAS data fit under various assumptions on direct 2 production mechanisms:

3-body phase space

the contributions from direct 2 mechanisms, described on previous slide

exchange processes


Fit of CLAS 2 data on 3 invariant masses and - angular

distributions within the framework of JM05., mcbn

W, GeV

Q2=0.65 Gev2

Q2=0.95 Gev2

Q2=1.30 Gev2

Reasonable description of invariant mass and - angular distributions was achieved in entire kinematics area covered by CLAS data.

CLAS data M.Ripani, V.D.Burkert, et. al.


Fit of single differential cross-sections from recent CLAS 2 data (1.3<W<1.6 GeV, 0.25<Q2<0.6 GeV2) within the framework of JM05 model.

full-++

+0

2 direct

Failure in description of + and p angular distributions is related to the shortcomings in treatment of direct 2 production (dashed magenta lines).

Preliminary

Reasonable description of 4 differential cross-sections, studied previously, was achieved.


Modification of direct 2 production mechanisms. From JM05 to JM06.

JM05 JM06 JM06


Fit of CLAS data at low W and Q2 (G.Fedotov, L.Elouadrhiri, et.al) within the framework of JM06 model.

-++

+0

2 direct

All significant mechanisms, contributing to ep→-+p channel at W<1.6 GeV and Q2<0.6 GeV2 were established from the CLAS data analysis.

Reasonable description ofi-angular distributions with model parameters fitted to 6 other diff. cross-sections offers compelling evidence for reliability of JM06 model.

Preliminary

JM06 full

resonant part

non-resonant part


Evaluation N* electrocouplings & isobar channel contributions from the CLAS 2 data fit.

Q2-interv., GeV2

2 /d.p.

0.25-0.40 <2.8

0.4-0.5 <1.9

0.5-0.6 <1.8

preliminary CLAS dataof E94-005 experiment

Preliminary

2/d.p. for selected in fit cross-sections:

N* electrocouplings and parameters for non-resonant mechanisms were varied. The 2/d.p. were estimated from comparison between measured and calculated differential cross-sections.


Isobar channel contributions from CLAS data fit within the framework of JM06.

CLAS data

the contributions from all isobar channels

CLAS data fit

The data on isobar channel contributions are available for N* studies in the coupled channel analysis, under development at EBAC.


P11(1440) and D13(1520) electrocouplings determined from the CLAS data on 1 and 2 electroproduction.

from analysis of CLAS 2data within the framework of JM06

from analysis of 1 CLAS data

combined analysis of 1 CLAS data

P11(1440) D13(1520)

•CLAS 2 data provided compelling evidence for sign flip of P11(1440) A1/2 electrocoupling. •Electrocouplings obtained in two independent analyses of 1 and 2 channels are in reasonable agreement.


N* electrocouplings from exp. data & expectations from the models, accounting for quark degrees of freedom only.

Ground p state P11(1440)

S.Capsticklight cone (LC)model

B.Metsch Bethe-Salpetermodel

I.AznauryanLC model

M.Giannini/E.Santopintohyper-centricCQM

•data on electromagnetic form factors for ground and excited nucleon states offer complementary information on baryon structure.•various degrees of freedom in the structure of P11(1440), D13(1520) are surfaced at low and high Q2

3q core3q core +meson -baryon cloud +??


cont’d

D13(1520)EBAC is developing coupled channel approach to disentangle meson-baryon dressing and “bare” quark core contributions to N* electrocouplings.

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.

3q core

3q core +meson –baryon cloud +??

The contribution from quark core increases with Q2. Data on N* electrocouplings at high Q2 are needed to study quark interactions in baryons .


N* electrocouplings & mechanisms responsible for baryon formation.

The contributions from quark models of baryon structure are needed. In particular: •contributions from potential quark models, allowing us to relate N* electrocouplings to the binding potential and the interactions, responsible for 3q configuration mixing;

• contributions from the models, based on Bethe-Saltpeter formalism, which allow us, using the data on N* electrocouplings, to constrain/establish quark scattering amplitudes, dressed quark propagators and elucidate their connection to QCD within the framework Dyson-Schwinger equations;

•establish constraints, imposed by the data on N* electrocouplings to light cone wave functions (LCWF) for N*, and relate LCWF to QCD. (S.Brodsky hep-ph/0412101)

•it will be important to have LQCD predictions for understanding of the results from N* phenomenology.


Conclusions and outlook.

• Analysis of the most comprehensive worldwide CLAS data on ep→-+p cross-sections, carried out with the framework of JM approach, allowed us to establish from successful data fit the mechanisms with significant contributions to this exclusive channel in N* excitation region at Q2 from 0.2 to 1.5 GeV2.

• The amplitudes/cross-sections of various isobar channels were determined from the fit of the CLAS 2 data. They will be used by EBAC for evaluation of N* electrocouplings in advanced coupled channel analysis of various exclusive channels combined. The resonant amplitudes in 2 electroproduction were isolated in the data fit.

• P11(1440) and D13(1520) electrocouplings at Q2 from 0.2 to 0.6 GeV2 were obtained for the first time from analysis of 2 electroproduction data. Extension of this analysis is in progress with a goal to obtained electrocuplings for almost all N*’s with M < 3.0 GeV at 0.3<Q2<5.0 GeV2.

• Comparison of the CLAS data on P11(1440), D13(1520) electrocouplings with quark model expectations showed, that various degrees of freedom contribute to the structure of N*’s at low and high Q2. Focused effort of baryon structure theory is needed to relate N* phenomenology to fundamental strong interaction mechanisms, responsible for baryon formation.


• Back-up


Further studies of N* electrocoupling from the CLAS data on 2 electroptoduction.

• Short term objective: evaluation of electrocouplings for all well established N*’s with M<2.0 GeV at 0.25<Q2<1.5 GeV2 from E93-006,E94-005 data within the framework of JM06.

• Intermediate term objective: evaluation of electrocouplings for all well established N*, search for new N* in mass range W<3.0 GeV and 0.<Q2<5.0 GeV2 from analysis of e1-6,e1e,g1c,g11 CLAS data. Update of JM06 is expected, implementing partonic degrees of freedom in combination with meson-baryon content.

• Final goal: comprehensive information on electrocouplings for all established N*’s as well as for possible new baryon states in entire N* excitation region and at photon virtualities from 0. to 5.0 GeV2.


Very preliminary results on 2 electroproduction at high Q2.

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

Evidence for substantial N* contributions

Documents

V.I.Mokeev NSTAR2007 at Bonn, September 4-8 1 presented by V.I.Mokeev The studies of N* electrocouplings at various Q 2 elucidate relevant degrees of freedom