presented by V.I.Mokeev

1V.I.Mokeev N* Analysis Workshop’

presented by V.I.Mokeev

Analysis of 2 Production

p→2N exclusive channels in N* studies.

•modeling of 2 photo- and electroproduction by tree level meson-baryon diagrams.

•phenomenological analysis within the framework of JLAB-MSU model.

•N* studies in combined analysis of major exclusive channels. Argonne-Osaka coupled channel approach.

•Conclusions.


p(e,e’)X (trigger)

p(e,e’p)

p(e,e’+)n

p(e,e’p+)

p(e,e’p+)X

CLAS data on meson electroproduction at Q2<4.0 GeV2

Thep electroproduction amplitudes are needed for credibleevaluation of N* parameters in coupled channel analysis.

Exclusive channels in N scattering responsible for ISI&FSI in meson electro-production


Why the studies of 2 electroproduction are important.

D33(1700) electrocouplings

from world data on 1 electroproduction

from CLAS data on 2 electroproduction

combined analysis of 1 CLAS data


Meson-baryon (MB) models(partial list of references).

1. L. Luke, P. Soding, Springer Tracts in Modern Physics 59 (1971) 39.

2. L.Y. Murphy, J.-M. Laget, DAPNIA-SPHN-96-10.

3. J.A. Gomez Tejedor, E. Oset, Nucl. Phys. A571 (1994) 667.

4. J.A. Gomez Tejedor, E. Oset, Nucl. Phys. A600 (1996) 413.

5. J.C. Nacher, et. al., Nucl. Phys. A695 (2001) 295.

6. S. Ong, J. Van de Wiele, Phys. Rev. C63 (2001) 024614.

7. W. Roberts, A.Rakotovao, hep-ph/9708236

8. W. Roberts, T.Oed, Phys. Rev. C71 (2005) 055201.

9. M. Hirata, K. Ochi, T. Takaki, Phys. Rev. C56 (1997) 1472.

10. M. Hirata, N. Katagiri, T. Takaki, Phys. Rev. C67 (2003) 034601.

11. M. Ripani, V.I. Mokeev, et. al., Nucl. Phys. A672 (2000) 220.

12. V.I. Mokeev, et. al., Phys. of Atom. Nucl. 64 (2001) 1292.

13. V. Bernard, N .Kaiser, U.G. Meissner, Eur. Phys. J. A11 (2001) 209.

14. A. Fix, H. Arenhovel, Eur. Phys. J. A25 (2005) 115.


Valencia group approach.(applicable at W<1.6 GeV)

M=,; B=p,,P11(1440),D13(1520),

D33(1700); relevant for W<1.6 GeV Isobar channels: , p, P11(1440)& N background

non fully relativistic description(resolved in ref. 6 at p.5); c-numbers instead of vertex functions(in part resolved in ref. 6 at p.5) ;

no ISI&FSI effects The contributions:

- Born terms

- to extra terms of JM06

- to direct 2 production of JM06

-s-channel N* excitation


Fully relativistic description. W.Roberts approach.

,V-mesons and all N*,* of 1/2, 3/2 spin are included. A general framework for most comprehensive MB description in N* excitation region.

Open problems:•reliability of effective MB lagrangians→test against data on N* LS partial decay widths;•vertex functions, most of them are still unknown;•ISI&FSI should be implemented

N

N*,*


A.Fix and H.Arenhövel approach.M=B=N,

All N*,D* with masses less then 1.8 GeV are included to s-channel amplitudes.

Effective description of ISI&FSI within the framework of diffractive absorptive ansatz

Open problems:•completeness of mechanisms at high W;•credibility of approximations for ISI&FSI, considering huge absorptive effects


How well MB approaches working?

ABBHHM, TAPS data in comparison with A.Fix, H.Arenhovel model

p→00p

Reasonable description of fully integrated cross-sections in all approaches, BUT huge ad hoc absorptive corrections at W>1.6 GeV.


TAPS data

E.Oset,et.al. model

Discrepancies

p→+0n p→00p

E.Oset,et.al. model

Cont’d

Due to problems with description of 1-diff cross-sections neither of MB approaches was ever used to extract N* parameters from the 2 photo and electroproduction data.


For unpolarized beam/target, the final state, r,v→-+p reaction offers 9 independent 1-differential cross-sections in each (W&Q2) bin. All these cross-sections are available from CLAS for the first time.

New prospects for N* studies in 2 production. Effective lagrangians + phenomenological parametrization hybrid approach.

Contributing mechanisms may be established in phenomenological analysis of all available data combined. It is joint JLAB/MSU effort.

ELSA, MAMI, GRAAL photo- and CLAS electroproduction data extended amount of measured observables considerably.

CLAS electroproduction data.


JLAB-MSU model (JM05) for 2- electroproduction.V.I. Mokeev, V.D.Burkert et.al., Proc. of the Workshop NSTAR2005, World

scientific, p.47

3-body processes Quasi-2-body mechanisms included

•All well established N* with decays +P33(1600)&P11(1710)&P13(1720)&P33(1920) 3-star states and 3/2+(1720) candidate.

•Reggetiezed Born terms & effective FSI&ISI treatment (Ref. 11 p.5).

•extra contact term

•All well established N* with p decays+P11(1710)&P13(1720) 3-star states and 3/2+(1720) candidate.

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


con’d

3-body processes Quasi-2-body mechanisms included

•for +D013(1520) set of Born terms similar

to what was used for isobar channels.

•for +F015(1685), -P++

33(1640) 3-body contact term with exponential propagators of isobars in 2 body intermediate states.

)(1

),( 21)(

42

2min

2

/ PPeW

UUQWA PPbppdM

Direct 2 production.

Exchange processes,parameterized as:

F015(1685)

(P++33(1640))

(-)

(+)


Evidences for processes beyond isobar channel superposition in 2 production.

The contributions from all isobar channels combined still underestimate 2 cross-sections. 2 direct mechanisms are needed to reproduce CLAS/world data.

2 direct mechanisms

Q2=0.95 GeV2

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


Evidences for exchange mechanisms in direct 2 production from the CLAS data.

W=1.49 GeV

Q2=0.65 GeV2 Q2=0.95 GeV2

E93-006 CLAS data fit with remaining mechanisms:

3-body phase space

remaining mechanismsshown on slide 6

exchange processes


p cross-sections off protons from the fit of mass 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 were achieved without any need for an additional mechanisms beyond implemented to JM05.

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


Global fit of complete set of unpolarized 1-differential cross-sections within the framework of JM06 model (1.3<W<1.6 GeV & 0.25<Q2<0.60 GeV2) .

JM06 full-++

+0

2 direct

Successful description of all E94-005data was achieved.

Complete data on unpolarized1-differential cross-sections for the first time available from CLAS allowed us to establish all significant mechanisms contributing to the 2 electroproduction.

i-angular distributions werecalculated with parameters ofJM06 fitted to 6 other 1-diff. cross-sections.

Preliminary


+

Modification of parameterization for direct 2 amplitudes

)()( p

bt

pp PPeUUWA p

2)( ppPPt

tePPeUUWAbt

p

bt

ppp )()(

2)( PPt

pbt

p

bt

pp tePPeUUWA pp

)()(

2)( PPt pp

JM05 JM06 JM06


P11(1440) and D13(1520) electrocouplings.

from analysis of E94-005 CLAS 2data within the framework of JM06

from analysis of E93-006 CLAS 2data within the framework of JM05

from analysis of 1 CLAS data

combined analysis of 1 CLAS data

Preliminary

P11(1440) D13(1520)


Combined analysis of major exclusive electroproduction channels within the framework of the coupled channel (cc) approach, using phenomenological input from JM06

Argonne-Osaka approach (T-S.H.Lee, et.al.) is only available worldwide, capable to account for full complexity of FSI in the N final states.

resulting AO amplitudes

“bare” amplitudes, established within the framework of JM06

N unitarity cut

“bare’ amplitudes from other electroproduction channels


Current efforts in combined 1/2 analysis. Hall B group & EBAC collaboration.

• The amplitudes of all significant mechanisms in the 1/2 exclusive channels were determined in phenomenological analysis of the CLAS data

(I. Aznauryan for 1, JM06 for 2). Modification of these amplitudes by FSI, is under evaluation, using AO approach at 0.25< Q2<1.5 GeV2 and W<1.5 GeV, where only 1/2 channels contribute

• 1/2 CLAS electroproduction data will be re-fitted, using non-resonant amplitudes accounting for FSI. Clobal fit of observables from major exclusive channels, accounting for unitarity, will be gradually extended up to 2.0 GeV W, allowing us to extract most reliable data on electrocouplings for an entire excited nucleon spectrum.

• Studies of underlying MB/partonic mechanisms for remaining JM06 phenomenological terms will be carried out.

Expected outcome:

a) MB vertex off-shell behavior → input for lattice simulation(?);b) Understanding of the transition from MB mechanisms to p GPD’s,/other

partonic processes needed for N* studies at high Q2.


What mechanisms behind JM06 phenomenological terms?

S.Capstick, T.-S.H.Lee, A. Kiswandhi model

JM06 phenomenological terms will be replaced by MB amplitudes, derived from modern effective Lagrangians of the outlined approach

+residual phenomenological contributions, if any.

For particular mechanisms isolated in JM06 the sum is rather limited


Conclusions.

• Considerable extension of the data on 2 photo- and electroproduction from recent experiments, carried out worldwide on continues beams with 4 detectors, open up new opportunities for N* studies. Global analysis of full set of unpolarized observables for the first time available from CLAS, allowed us to develop the JM06 model with most complete accounting for all significant mechanisms. These studies demonstrated capability to map-out all sizeable mechanisms from the fit of various observables combined. The amplitudes, determined for all contributing mechanisms, provide necessary input for extraction of N* parameters in the cc analyses.

• Global analysis of observables from major photo- / electroproduction channels combined, implementing unitarity within the framework of most advanced Argonne-Osaka approach, offers promising way for credible N*/non-resonant processes separation. Therefore, all necessary tools are available to extract reliable values of N* electrocouplings, at various photo virtualities Q2 and to improve knowledge of N* hadronic parameters.

• 2 exclusive channels offer very reach information both on resonant and non-resonant processes, vital for modern hadronic physics. Wealthy of this information may be accessed only in combined efforts, including phenomenological mapping of contributing mechanisms, comprehensive FSI treatment and the studies of actual mechanisms behind phenomenology within the framework of meson-baryon and partonic degrees of freedom.


BACK-UP


Modeling of 2 production by tree level meson-baryon diagrams.

• Set of tree level meson-baryon diagrams. Particular meson and baryon states were implemented based on:

a) manifestation of unstable particles in invariant mass distributions;

b) established in analysis 1 production and experiments with pion beams;

c) needs to improve description of particular data features.

• Full sets of diagrams were created, applying all possible permutations for meson/baryon legs


Fit of E94-005 CLAS 2 data (L.Elouadrhiri, G.Fedotov, et. al.) collected at low W&Q2 within the framework of JM05 model.

full-++

+0

2 direct

JM05 succeeded to describe +p,

-p mass and - angular distributions,

Failure in description of + and pf angular distributions, revealed necessity to modify direct 2 production mechanisms.

Preliminary


General problems of MB approaches.

• Available MB models are unable to establish all significant mechanisms contributing to the 2 production due to lack of guidance from fundamental theory and insufficient amount of analyzed observables to determine complexity of contribution processes from the data fit.

• Most of MB vertex function are unknown and may be only fitted to the data.

• FSI were either neglected or treated in oversimplified approximations. Comprehensive approach for description of FSI complexity in the 3 body N final state was needed. Such approach has been developed just recently by Argonne-Osaka collaboration (see T-S.H.Lee talk, hep-th/0608051).

Neither of MB approaches was ever used to extract N* parameters from the 2 photo and electroproduction data.


An additional contact terms in channels needed to fit data.

2

1

))2()()((

t

PPUUWBPUUWA pptM

2)( PPt 2 =

1.64 GeV

2


The amplitudes for p+F015(1685) and

p-P++33(1600) channels.

215

215

152

)(exp)(),(

F

FpFpp

MMPPUUQWAM

PP

MM

mtUUQWAM

pP

Pppp

1)(exp

1),(

233

233

2*

2


Fit of single differential cross-sections from E93-006 experiment within the framework of JM05.

Full calculationsp-++

p+0

p+D13(1520)ppp-P33

++(1640)p+F15

0(1685)direct 2 production


W-interv., GeV 2 thresh.

1.41-1.54 2.45

1.56-1.64 2.19

1.66-1.76 2.04

1.79-1.89 2.06

Q2=0 95GeV2

Q2=0 65GeV2

Q2=1 30 GeV2

Selected -+p cross-sections calculated within the framework of

JM05, most closed to the E93-006 CLAS data. + p, - +, -p invar. masses and - angulardistributions were fitted within the frameworkof JM05 (V.Mokeev et.al. , Proc. of NSTAR2005Workshop, p.47)

experimetal data from M.Ripani et. al. ,Phys. Rev. Lett.91, 022002 (2003)


Evidence for complementary contributions to isobar channels.

JM05 full:extra contact term in channels

+0

W=1.76 GeV Q2=0.95 GeV2

W=1.81 GeV Q2=0.95 GeV2

p→+0:

-p mass, GeVp mass, GeV

d/

dM

, m

cb

n/G

eV

on off

on off

extra contact term in channels


Manifestation of p→-P33++(1640) and

p→+F15(1685) isobar channels.

p→+F15(1685)

p→P 33(1640)

W=1.89 GeV Q2=0.95 GeV2

JM05 full

-P33++(1640)

F15 (1685)

Contribution from isobar channels:

-P33++(1640) and

+F15 (1685) isobarchannels off


Resonant/non-resonant mechanism separation.

full JM06 calculations

non-resonant part

resonant part

Combined fit of all unpolarized1-diff. cross-sections allows usto isolate resonant/non-resonantparts, exploiting difference in shapes of their cross-sections.

Preliminary


Total -+p cross-sections calculated within the framework of JM06, most closed to the preliminary CLAS data at 0.25<Q2<0.60 GeV2 and W<1.57 GeV.

Q2-interv., GeV2

2 thresh.

0.250-0.400 2.80

0.400-0.500 1.80

0.500-0.600 1.70

preliminary CLAS data,exper. E94-005,L.Elouadrhiri, G.Fedotov, et.al.

Preliminary


High lying N* electrocouplings.

D33(1700) D33(1700)

P13(1720) P13(1720)

D33(1700), P13(1720)resonances mostly decay with 2 emission. 1 data donot have enough

sensitivity to these states.

First preliminary data on Q2 -evolution of S31(1620), D13(1700),D33(1700), P13(1720)electromagnetic formfactors were obtained from analysis of CLAS E93-006 experiment on 2 electroproduction.

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