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Nucleon resonance studies in phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton. Victor Mokeev. Analysis objectives. JLAB-MSU model and candidate 3/2 + (1720) state. Model extension from analysis of recent CLAS data.

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Nucleon resonance studies in phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton.

Victor Mokeev

  • Analysis objectives.

  • JLAB-MSU model and candidate 3/2+(1720) state.

  • Model extension from analysis of recent CLAS data.

  • Comprehensive test of 2005’ JLAB-MSU model in

    combined fit of 1p and 2p data from CLAS.

  • N* photocouplings and hadronic parameters extracted

    from CLAS 2p data fit within the framework of 2005’

    JLAB-MSU model.

  • Conclusion and outlook.

Outline:


Jlab msu model for 2 p photo electro production from 2003 to 2005 versions
JLAB-MSU model for 2- recent CLAS data on double charged pion photo- and electroproduction off proton.p photo- electro-production from 2003’ to 2005’-versions.

3-body processes

Quasi-2-body mechanisms included

  • All well established N* with pD decays +P33(1600)&P11(1710)&P13(1720)&P33(1920) 3-star states

  • Minimal set of Reggetized gauge invariant Born terms

  • Effective treatment of couplingswith other open channels

P33(1600)

  • All well established N* with rp decays

  • +P11(1710)&P13(1720) 3-star states.

  • Diffractive ansatz for non-resonant rp

  • production

mechanisms added to

2005’ model version


Jlab msu model from 2003 to 2005 version
JLAB-MSU model from 2003’ to 2005’ version. recent CLAS data on double charged pion photo- and electroproduction off proton.

3-body processes

Quasi-2-body mechanisms included

  • Minimal set of Born terms similar to what was

  • used for pD states, except an additional g5 matrix

  • to account for the opposite parities of D and

  • D13(1520)

mechanisms added to

2005’ model version

F15(1685)

First step in data analysis needed to establish all relevant mechanisms of

2p production from their manifestations in measured cross-sections. Valuable

input for further model development within the framework of rigorous coupled

channel approach.

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
Electroproduction data fit. A candidate 3/2 recent CLAS data on double charged pion photo- and electroproduction off proton.+(1720) baryon state.

CLAS data fit

N*photocouplings were varied within 30% s around values obtained from world meson photo and

electroproduction data analysis in SQTM approach: V.D.Burkert et. al., Phys. Rev. C67, 035204 (2003)

Contributions from conventional

states only

Fit with candidate 3/2+(1720)

state

M.Ripani et. al.

Phys. Rev. Lett.91, 022002 (2003)

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


Manifestation of direct 2 p production mechanisms
Manifestation of direct 2 recent CLAS data on double charged pion photo- and electroproduction off proton.p production mechanisms.

W=1.49 GeV

JLAB-MSU model:

Q2=0. GeV2

Q2=0.65

GeV2

Q2=0.95

GeV2

2003’

2005’

2p direct production

mechanisms


2 p direct production mechanisms and an additional term for pd channels needed to fit data
2 recent CLAS data on double charged pion photo- and electroproduction off proton.p direct production mechanisms and an additional term for pD channels needed to fit data.

2 =1.64 GeV2


Description of total recent CLAS data on double charged pion photo- and electroproduction off proton.p+p- photoproduction cross-section off protons in 2005’ version of JLAB-MSU model.

Q2=0. GeV2

  • Initial values of N* photocouplings were taken from analysis of CLAS 2p 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.

s, mcbn

no 3/2+

full calculation

Background

  • Signal from candidate

    3/2+(1720) state present,

    but masked by large

    background

Resonances

W, GeV


Description of total p p electroproduction cross sections off protons in 2005 jlab msu model
Description of total recent CLAS data on double charged pion photo- and electroproduction off proton.p+p- electroproduction cross-sections off protons in 2005’ JLAB-MSU model.

  • All CLAS 2p photo and electro production data were described implementing meson-baryon mechanisms seen in observables without need for an additional mechanisms of unknown dynamics.

s mb

Q2=0.65 GeV2

Q2=0.95 GeV2

  • Quality of CLAS data allowed

    to establish all relevant mechanisms

    for 2p production in N* excitation

    region at Q2<1.5 GeV2

Q2=1.30 GeV2

Would adopted parameterization of

background provide credible

N*/background separation?

W, GeV


Combined analysis of the clas data on 1 p and 2 p electroproduction at q 2 0 65 gev 2
Combined analysis of the CLAS data on 1 recent CLAS data on double charged pion photo- and electroproduction off proton.p and 2p electroproduction at Q2=0.65 GeV2

Successful fit of all 1p/2p observables with common set of N* photocouplings would provide evidence for reliable background description and N*/background separation.

Single pion data: ds/dW differential cross-sections:

p+ at W between 1.1-1.41 GeV,

p0 at W between 1.1-1.68 GeV;

beam asymmetries:

p+ and p0 at W between 1.1-1.58 GeV

9870 data points

CLAS1p data

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

Double pion data:p+p-, p+p, p-p mass and

CM p- 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

CLAS 2p data

M.Ripani, V.D.Burkert,

et.al.

1p analysis models:I.G. Aznauryan, Phys. Rev. C68, 065204 (2003);

I.G. Aznauryan, et. al., Phys. Rev. C71, 015201

(2005).


1 recent CLAS data on double charged pion photo- and electroproduction off proton.p data description with N* photocouplings from combined analysis of 1p/2p channels at Q2=0.65 GeV2.

W=1.52 GeV

gvp→p0p

W=1.68 GeV

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


2 p data description with n photocouplings from combined analysis of 1 p 2 p channels
2 recent CLAS data on double charged pion photo- and electroproduction off proton.p data description with N* photocouplings from combined analysis of 1p/2p channels.

W=1.54 GeV Q2=0.65 GeV2

W=1.66 GeV Q2=0.65 GeV2

accepted by PRC


N* photocouplings and hadronic parameters from analysis of the CLAS 2p data within the framework of 2005’ JLAB-MSU model.

  • Fitted data: p+p-, p+p, p-p mass and CM p- 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 foundin 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, pD and rp 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 the CLAS 2p+p-p cross-sections with N* photocouplings, hadronic and non-resonant mechanism parameters fitted to the data.

Parameter variations

N* photocouplings: within 30% s around values obtained in previous fit (2003’ JLAB-MSU model)

pD, rp decays: wide range, which led to the total width variation between 40-600 MeV

N* masses: inside PDG uncertainties

Q2=0 GeV2

Q2=0 65GeV2

Q2=0 95GeV2

Q2=1 30 GeV2

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


N photocouplings from analysis of clas 2 p data within the framework of 2005 jlab msu model
N* photocouplings from analysis of CLAS 2 the CLAS 2p data within the framework of 2005’ JLAB-MSU model.

D13(1520)

CLAS 2p data

analysis

(A1/22+S1/22)1/2, GeV-1/2

A3/2,GeV-1/2

PDG

1p/2p combined

CLAS data analysis

World data

before CLAS,

obtained in

analysis of 1p

electroproduction:

V.D. Burkert, et. al.,

Phys. Rev. C67,

035204 (2003)

Q2 GeV2

Q2 GeV2


Cont d
Cont’d the CLAS 2

D33(1700), P13(1720)

resonances mostly

decay with 2p

emission. 1p data

have not enough

sensitivity to these

states.

D33(1700)

D33(1700)

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

2p photo- and electro-

production.

P13(1720)

P13(1720)


Conclusions and outlook
Conclusions and outlook. the CLAS 2

  • Phenomenological approach was developed for description of 2p 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+p-p final state.

  • Quality of CLAS data allowed to establish all relevant 2p 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 1p and 2p electroproduction data.

  • The photocouplings in Q2-area between 0 and 1.5 GeV2 were extracted from CLAS 2p 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.

  • 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.


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