1 V.Mokeev NSTAR 2005 Workshop Phenomenological analysis of recent CLAS data on double charged pion photo- and electroproduction off proton Outline: 2exclusive channel in N* physics. Analysis of CLAS 2electroproduction 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 1and 2data from CLAS. N* photocouplings and hadronic parameters extracted from CLAS 2data fit within the framework of 2005’ JLAB-MSU model Conclusion and outlook Victor Mokeev
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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
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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.
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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
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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);
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Electroproduction data fit. A candidate 3/2+(1720) baryon state.
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)
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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.
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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:
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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
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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
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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
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Evidences for p+F015(1685) and
p-P++33(1600) channels.
p-P++33(1600)
p+F015(1685)
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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
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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
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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.
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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
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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
-The states with considerable 1 decays(…) result from dispersion relations. Roper is only state with A1/2 dependent from model for 1analysis
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1 data description with N* photocouplings from combined analysis of 1/2channels.
vp→0pW=1.52 GeV W=1.68 GeV
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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
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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
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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
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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
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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.
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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
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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:
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.
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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.
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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
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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.