V.Mokeev NSTAR 2005 Workshop 1 Phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton Outline :

1V.Mokeev NSTAR 2005 Workshop

Phenomenological analysis of recent CLAS data on double charged pion photo- and

electroproduction off proton

Outline:2 exclusive channel in N* physics.Analysis of CLAS 2 electroproduction data within the framework of JLAB-MSU model (2003’-version)Complementary non-resonant mechanisms, established in analysis of recent CLAS data. Comprehensive test of the recent JLAB-MSU model in combined fit of 1 and 2 data from CLAS. N* photocouplings and hadronic parameters extracted from CLAS 2 data fit within the framework of 2005’ JLAB-MSU model Conclusion and outlook

Victor Mokeev


N* in CLAS data.

p(e,e’)X (trigger)

p(e,e’p)

p(e,e’+)n

p(e,e’p+)

p(e,e’p+)X

2 channel is sensitiveto contributions from most N*’s heavier than 1.4 GeV. It provides complementary information on N* with respect to 1 channels, in particular for high mass states (M>1.65 GeV)which mostly decay with

2 emission

Q2<4.0GeV2

Double pion production by photons off protons offers a promising way to search for “missing” baryon states.


JLAB-MSU model for 2- electroproduction(2003’-version).

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•Minimal set of Reggetized gauge invariant Born terms•Effective treatment of couplings with other open channels

•All well established N* with p decays+P11(1710)&P13(1720) 3-star states.•Diffractive ansatz for non-resonant pproduction


JLAB-MSU model (2003’-version).

3-body processes Quasi-2-body mechanisms included

•Minimal set of Born terms similar to what wasused for states, except an additional 5 matrixto account for the opposite parities of and D13(1520)

Residual mechanisms, beyond shown on the plots, were parameterized either as 3-body phase space or through a set of partial waves with J<13/2. Both lead to a similar description.

Details of the 2003’-version of model may be found in:M.Ripani et. al., Nucl. Phys., A672, 220 (2000);V.Mokeev, et. al., Phys. of Atom. Nucl., 64, 1292 (2001);V.D.Burkert, et.al., Phys. of Atom Nucl.,66, 2199 (2003); V.D.Burkert, et. al., Phys. of Atom Nucl., 67, 1018 (2004);


Electroproduction data fit. A candidate 3/2+(1720) baryon state.

CLAS data fit

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

Difference between curves due to signal from candidate 3/2+(1720) state

Fit with candidate 3/2+(1720) state

Contributions from conventional states only

N*photocouplings were varied within 30% around values obtained from world meson photo and electroproduction data analysis in SQTM approach: V.D.Burkert et. al., Phys. Rev. C67, 035204 (2003)


M, MeV MeV /,

%

p/,

%

modified

P13(1720)

1725±20 114±19 60±12 19±9

PDG

P13(1720)

1650-1750 100-200 absent 70-85

candidate

3/2+(1720)

1720±20 88±17 41±13 17±10

Two alternative ways to describe the structure at 1.7 GeV: • Modification of hadronic couplings for P13(1720) PDG state with respect to established values• Implementation of candidate baryon state with J = 3/2+.

Description of 1.7 GeV mass region.


JLAB-MSU model 2003-version, described on p.3-4

2005’ JLAB-MSU model, see p. 7-15

W=1.45 GeV

2 direct production mechanisms at the photon point.

2 direct production

M.Bellis, et. al., (CLAS Collaboration) Proc of NSTAR2004 Workshop, March 24-27,2004, Grenoble, France, World Scientific 2005, ed. by J.-P.Bocquet, V.Kuznetsov, D.Rebreyend, 139

Preliminary real photon data from:


Manifestation of 2- direct production at Q2>0.

W=1.49 GeV

Q2=0.65 GeV2 Q2=0.95 GeV22005’ JLAB-MSU model

2003’-version

2 direct production


2 direct production mechanisms and an additional term for channels needed to fit data.

)(1

),( 21)(

42

2min

2

/ PPeW

UUQWA PPbppdM

2

1

))2()()((

t

PPUUWBPUUWA pptM

2)( PPt 2 =

1.64 GeV

2


Manifestation of direct production and complementary term for channels in real photon data.

W=1.63 GeV W=1.78 GeV

+0 with complementary term on p. 9


Evidences for p+F015(1685) and

p-P++33(1600) channels.

p-P++33(1600)

p+F015(1685)


Fit of 2 photoproduction data at high W after implementation of new isobar channels.

Full calculations

p-++

p+0

pp

p-P++33(1600)

p+F015(1685)

2 direct


Description of total photoproduction cross-section off protons in 2005’ version of JLAB-MSU model.

Signal from candidate 3/2+(1720) state present, but masked by large background

Background

Resonances

full calculation

3/2+(1720) photocouplings were adjusted to the real photon data. Hadronic couplings and masses were taken from the fit of virtual photon data.

no 3/2+

Q2=0. GeV2

W, GeV

, m

cbn


Description of total +- electroproduction cross-section off protons in 2005’ JLAB-MSU model.

W, GeV

b

Q2=0.65 GeV2

Q2=0.95 GeV2

Q2=1.30 GeV2

Initial values of N* photocouplings were taken from analysis of CLAS 2 data within the framework of 2003’ JLAB-MSU model: V.Burkert et.al., Nucl. Phys. A737, S231 (2004) and further adjusted to the data, using recent version of model.

Signal from candidate 3/2+(1720) state (~ 1.7 GeV) becomes prominent feature at Q2>0.5 GeV2 due to considerable growth of N*/Bckgr. ratio in electroproduction.


Improvements in description of the CLAS 2 electroproduction data after implementation of

complementary non-resonant mechanisms.

Q2, GeV2 0.65 0.95 1.30

2/d.p. 2003’-

version3.91 3.30 2.26

2/d.p. 2005’ JLAB-MSU model

2.83 1.90 2.01

2 was estimated from comparison between calculated and measured1-diff. cross-sections for entire set of data in particular Q2-bin

Quality of CLAS data allows to describe all relevant mechanisms of 2production at W<2.0 GeV and Q2<1.5 GeV2 implementing meson-baryon diagrams needed to reproduce particular features in observables without any necessity for remaining mechanisms of unknown dynamics.

Essentials of recent JLAB-MSU model are highlighted in:V.Mokeev et. al., Proc of NSTAR2004 Workshop, World Scientific 2005 ed.by J.-P.Bocquet, V.Kuznetsov, D.Rebreyend, 317


Combined analysis of the CLAS data on 1 and 2 electroproduction

Data at Q2=0.65 GeV2 were analyzed. It is only Q2 value for which both 1 and 2 CLAS data exist so far. Q2-coverage will be extended soon.

Single pion data: d/ddifferential cross-sections: + at W between 1.1-1.41 GeV, 0 at W between 1.1-1.68 GeV; beam asymmetries: + and 0 at W between 1.1-1.58 GeV

9870 data points Double pion data: +-, +p, -p mass and CM - angular distributions at W between 1.41-1.89 GeV 680 data points The data are available in CLAS Physics DB: http://clasdb3.jlab.org

1 analysis models: I.G. Aznauryan, Phys. Rev. C68, 065204 (2003); I.G. Aznauryan, et. al., Phys. Rev. C71, 015201 (2005).

CLAS 1 data

K.Joo, L.C.Smith, et.al

CLAS 2 dataM.Ripani, V.D.Burkert,et.al.


N* photocouplings (in 10-3 GeV-1/2) extracted in analyses of 1/2 exclusive channels at Q2=0.65 GeV2

N* 1/2 analysis 1 analysis

2 analysis

A1/2 A3/2 S1/2 A1/2 A3/2 S1/2 A1/2 A3/2 S1/2

P11(1440) 21±4 33± 6 4± 4

(23±4)

40± 4 21± 9 35± 6

D13(1520) -65± 4 62± 5 -35± 3 -67± 3 62± 4 -38± 3 -63± 12 ± -40± 7

S31(1620) 16± 4 -28± 3 31± 3 -35± 3 13± 3 -25± 4

S11(1650) 43± 7 -6± 3 43± 2 -15± 2 44± 16 -8± 2

F15(1680) -32± 5 51± 4 -15± 3 -38± 4 56± 2 -18± 2 -31± 8 52± 10 -14± 3

D33(1700) 44± 4 36± 4 -7± 4 58± 5 29± 3 -15± 5 49± 8 36± 8 -11± 4

D13(1700) -21± 2 10± 1 0(input) -6± 8 -55± 7 0±8 -19± 3 11± 2 0(input)

P13(1720) 55± 3 -68±4 0(input) 45± 6 -48± 7 0±7 56± 6 -62± 9 0(input)

-The states with considerable 1 decays(…) result from dispersion relations. Roper is only state with A1/2 dependent from model for 1analysis


1 data description with N* photocouplings from combined analysis of 1/2channels.

vp→0pW=1.52 GeV W=1.68 GeV


2 data description with N* photocouplings from combined analysis of 1/2channels.

W=1.54 GeV Q2=0.65 GeV2 W=1.66 GeV Q2=0.65 GeV2

Bunches of curves correspond to calculated 1/2 cross-sections with common sets of N* photocouplings


Con’tIntegrated 2 cross-section

Q2=0.65 GeV2Calculations with common sets of N* photocouplings provided good description of all available 1/2 cross-sections and beam asymmetry data at Q2=0.65 GeV2..

Strong evidence for reliable treatment of 1 and 2 productionin both models, developed byCLAS Collaboration.

The results are presented in:I.G.Aznauryan et. al., accepted by Phys. Rev. C., hep-ph/0508057


N* photocouplings and hadronic parameters from analysis of the CLAS 2 data within the framework of recent JLAB-MSU model.

• Fitted data: , p, -p mass and CM - angular distributions at 20 W-bins between 1.41-1.89 GeV and photon virtualities Q2: 0., 0.65, 0.95, 1.30 GeV2. The data may be found in CLAS Physics DB: http://clasdb3.jlab.org.

• Combined fit of 4 Q2 bins was carried out within a framework of 2005’ JLAB-MSU model. W-intervals between 1.41-1.51 GeV, 1.54-1.64 GeV, 1.66-1.76 GeV, 1.79-1.89 GeV were fitted independently.

• Photocouplings and poorly known masses, and p couplings of N* were varied and fitted to the data together with parameters of non-resonant mechanisms implemented to the 2005’ JLAB-MSU model. Hadronic couplings were further constrained, exploiting their Q2-independence. The photocouplings at 4 mentioned above Q2’s were derived from data fit for the states: P11(1440), D13(1520), S31(1620), S11(1650), P33(1600)*), F15(1685), D13(1700), D33(1700), P13(1720), candidate 3/2+(1720), F35(1905), P33(1920), F37(1950).

*)1.65 GeV mass from our analysis


Description of total +-p cross-sections with N* photocouplings, hadronic and non-resonant mechanism parameters fitted to the data.

Parameter variationsN* photocouplings: within 30% around values obtained in previous fit (2003’ JLAB-MSU model) , p decays: wide range, which led to the total width variation between 40-600 MeVN* masses: inside PDG uncertainties

W-interv., GeV 2/d.p 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

Sub-sets of calculated cross-sections most close to the data were isolated, applying restriction 2<2 thresh, listed in the table

Q2=0 GeV2

Q2=0 95GeV2

Q2=0 65GeV2

Q2=1 30 GeV2


Example of single-differential cross-section description with selected sub-sets of variable parameters.

W=1.71 GeV and Q2=0.95 GeV2

Similar sets of observableswere fit in all available W and Q2 bins shown on previous slide

Bunches of curves correspondto selected cross-sections inside data uncertainties, applying restriction 2/d.p.<2.04

1-differential cross-sections were calculated for each trial set of parameters. 2/d.p.were determined from comparison with measured values.


Q2-evolution of N* photocouplings, determined from analysis of CLAS 2 data (selected examples, see full list of studied N*’s on p. 22) .

P11(1440)

CLAS 2 dataanalysis

PDG at Q2=0 GeV2;1/2 combined CLAS data analysis at Q2=0.65 GeV2

(A1/

22 +S

1/22 )

1/2

*100

0GeV

-1

Q2 GeV2

Photocouplings corresponded to selected cross-sections were averaged. Their mean values were treated as determined from data fit, while dispersions were assigned to uncertainties


Cont’d

D13(1520)

(A1/22+S1/2

2)1/2, GeV-1/2 A3/2, GeV-1/2

Q2 GeV2Q2 GeV2

CLAS 2 dataanalysis

PDG at Q2=0 GeV2;1/2 combined CLAS data analysis at Q2=0.65 GeV2

World databefore CLAS,obtained inanalysis of 1electroproduction:

V.D. Burkert, et. al., Phys. Rev. C67,035204 (2003)


Cont’d

D33(1700) D33(1700)

P13(1720) P13(1720)

D33(1700), P13(1720)resonances mostly decay with 2 emission. 1 datahave not enough

sensitivity to these states.

First data on Q2 -evolution of S31(1620), D13(1700),D33(1700), P13(1720).F35(1905),P33(1920),F37(1950) photocouplings were obtained from analysis of CLAS experiments on 2 photo- and electro-production.


New candidate state 3/2+(1720).

CLAS 2 dataanalysis in 2005’JLAB-MSU model

previous analysisof CLAS data in2003’ model version

Signal from possible newbaryon state was confirmedin analysis of electro-production data and observedin real photon data.


N* hadronic parameters derived from analysis of CLAS 2 data (upper rows) in comparison with PDG values (down rows).

State Mass, GeV Total width. GeV

BF,% p BF,%

D13(1520) 1.52 fixed

1.515-1.525

0.127±0.003

0.100-0.125

22±4

15-25

11±4

15-25

P33(1600) 1.647±0.011

1.55-1.70

0.262±0.008

0.25-0.4556±5 40-70

0. fixed

<25

D13(1700) 1.70±0.010

1.65-1.75

0.148±0.010

0.050-0.150

49±6

85-95 for N

50±10

decays

P13(1720) 1.735±0.003

1.70-1.75

0.179±0.007

0.150-0.300

<2.5

>70 for N89±6

decays

candidate

3/2+(1720)

2003’ model

1.718±0.007

1.720±0.020

0.084±0.004

0.088±0.017

50±8

49±13

6.5±2

17±10


Conclusions and outlook.• Phenomenological approach was developed for description of 2 production by

real and virtual photons in N* excitation region and at Q2<1.5 GeV2. The approach provides most complete treatment of contributed mechanisms and allows most reliable evaluation of N* photocouplings and, in part, hadronic parameters from the fit to all measured observables in p final state.

• Quality of CLAS data allowed to establish all relevant 2 production mechanisms, implementing particular meson-baryon diagrams needed for data fit. Good description of all unpolarised CLAS/world data was achieved without any necessity for remaining mechanisms of unknown dynamics. Reliability of background description and N*/background separation was confirmed in combined analysis of CLAS 1 and 2 electroproduction data.

• The photocouplings in Q2-area between 0 and 1.5 GeV2 were extracted from CLAS 2 photo- and electroproduction data for most N*’s with masses less then 2.0 GeV. Q2-evolution of photocouplings for S31(1620), D13(1700), D33(1700), P13(1720), F35(1905), P33(1920), F37(1950) states were determined for the first time. Considerable improvement was achieved in our knowledge on N* 2 decays as well as on most hadronic parameters for high lying states.

• First comprehensive data on Q2-evolution of photocouplings for many N*’s open

up an opportunity to establish driving symmetry for quark binding potential in baryons and to access N* structure in terms of contributing 3q-configurations.

Documents

V.Mokeev NSTAR 2005 Workshop 1 Phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton Outline :