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Phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton. Victor Mokeev. 2 p exclusive channel in N* physics. Analysis of CLAS 2 p electroproduction data within the framework of JLAB-MSU model (2003’-version)

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slide1
Phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton

Victor Mokeev

  • 2p exclusive channel in N* physics.
  • Analysis of CLAS 2p 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 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:

n in clas data
N* in CLAS data.

Q2<4.0GeV2

2p channel is sensitive

to contributions from

most N*’s heavier than

1.4 GeV. It provides

complementary information

on N* with respect to

1p channels, in particular for

high mass states (M>1.65 GeV)

which mostly decay with

2p emission

p(e,e’)X (trigger)

p(e,e’p)p0

p(e,e’p+)n

p(e,e’pp+)p-

Double pion production by

photons off protons offers

a promising way to search for

“missing” baryon states.

p(e,e’pp+)X

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

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
  • All well established N* with rp decays
  • +P11(1710)&P13(1720) 3-star states.
  • Diffractive ansatz for non-resonant rp
  • production
jlab msu model 2003 version
JLAB-MSU model (2003’-version).

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)

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
Electroproduction data fit. A candidate 3/2+(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

slide6

Description of 1.7 GeV mass region.

  • 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 withJp = 3/2+.
2 p direct production mechanisms at the photon point
2p direct production mechanisms at the photon point.

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

W=1.45 GeV

2005’ JLAB-MSU model, see p. 7-15

2pdirect production

Preliminary real photon

data from:

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

manifestation of 2 p direct production at q 2 0
Manifestation of 2-p direct production at Q2>0.

W=1.49 GeV

Q2=0.65 GeV2

Q2=0.95 GeV2

2005’

JLAB-MSU model

2003’-version

2pdirect production

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

2 =1.64 GeV2

manifestation of 2p direct production and complementary term for pd channels in real photon data
Manifestation of 2p directproduction and complementary term for pD channels in real photon data.

W=1.63 GeV

W=1.78 GeV

p+D0 with complementary term on p. 9

evidences for g p p f 0 15 1685 and g p p p 33 1600 channels
Evidences for gpp+F015(1685) and gpp-P++33(1600) channels.

gpp-P++33(1600)

gpp+F015(1685)

slide12

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

Full calculations

gpp-D++

gpp+D0

gprp

gpp-P++33(1600)

gpp+F015(1685)

2p direct

slide13
Description of total p+p- photoproduction cross-section off protons in 2005’ version of JLAB-MSU model.

Q2=0. GeV2

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

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 section off protons in 2005 jlab msu model
Description of total p+p- electroproduction cross-section off protons in 2005’ JLAB-MSU model.
  • 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 mb

Q2=0.65 GeV2

Q2=0.95 GeV2

  • 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.

Q2=1.30 GeV2

W, GeV

slide15
Improvements in description of the CLAS 2p electroproduction data after implementation of complementary non-resonant mechanisms.

c2 was estimated from

comparison between

calculated and measured

1-diff. cross-sections

for entire set of data in

particular Q2-bin

Quality of CLAS data allows to describe all relevant mechanisms of 2p

production 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 p and 2 p electroproduction
Combined analysis of the CLAS data on 1p and 2p electroproduction

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

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).

slide17
N* photocouplings (in 10-3 GeV-1/2) extracted in analyses of 1p/2p exclusive channels at Q2=0.65 GeV2

(…) result from dispersion relations. Roper is only state with

A1/2 dependent from model for 1p analysis

-The states with considerable 1p decays

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

W=1.52 GeV

gvp→p0p

W=1.68 GeV

2 p data description with n photocouplings from combined analysis of 1 p 2 p channels
2p 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

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

con t
Con’t

Integrated 2p cross-section

Q2=0.65 GeV2

Calculations with common sets

of N* photocouplings provided

good description of all available

1p/2p cross-sections and beam

asymmetry data at

Q2=0.65 GeV2..

Strong evidence for reliable

treatment of 1p and 2p production

in both models, developed by

CLAS Collaboration.

The results are presented in:

I.G.Aznauryan et. al., accepted by

Phys. Rev. C., hep-ph/0508057

slide21
N* photocouplings and hadronic parameters from analysis of the CLAS 2p data within the framework of recent 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

slide22
Description of total p+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

slide23
Example of single-differential cross-section description with selected sub-sets of variable parameters.

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

W=1.71 GeV and Q2=0.95 GeV2

Bunches of curves correspond

to selected cross-sections inside

data uncertainties, applying

restriction c2/d.p.<2.04

Similar sets of observables

were fit in all available W and

Q2 bins shown on previous slide

slide24

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

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

P11(1440)

(A1/22+S1/22)1/2 *1000GeV-1

CLAS 2p data

analysis

PDG at Q2=0 GeV2;

1p/2p combined

CLAS data analysis

at Q2=0.65 GeV2

Q2 GeV2

cont d
Cont’d

D13(1520)

CLAS 2p data

analysis

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

A3/2,GeV-1/2

PDG at Q2=0 GeV2;

1p/2p combined

CLAS data analysis

at Q2=0.65 GeV2

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 d1
Cont’d

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)

new candidate state 3 2 1720
New candidate state 3/2+(1720).

CLAS 2p data

analysis in 2005’

JLAB-MSU model

previous analysis

of CLAS data in

2003’ model version

Signal from possible new

baryon state was confirmed

in analysis of electro-

production data and observed

in real photon data.

slide28
N* hadronic parameters derived from analysis of CLAS 2p data (upper rows) in comparison with PDG values (down rows).
conclusions and outlook
Conclusions and outlook.
  • 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. Considerable improvement was achieved in our knowledge on N* 2p 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.