Phenomenological analysis of recent CLAS
data on double charged pion photo- and
electroproduction off proton
Victor Mokeev
2p exclusive channel in N* physics.
Outline: 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
V.Mokeev NSTAR 2005 Workshop
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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
p(e,e’)X
(trigger)
p(e,e’p)p0
p(e,e’p+)n
2p emission
p(e,e’pp+)pDouble pion production by
photons off protons offers
a promising way to search for
“missing” baryon states.
p(e,e’pp+)X
V.Mokeev NSTAR 2005 Workshop
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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 couplings with other
open channels
•All well established N* with rp decays
+P11(1710)&P13(1720) 3-star states.
•Diffractive ansatz for non-resonant rp
production
V.Mokeev NSTAR 2005 Workshop
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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 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 3body 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);
V.Mokeev NSTAR 2005 Workshop
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Electroproduction data fit. A candidate 3/2+(1720)
baryon state.
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)
CLAS data fit
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
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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 with Jp = 3/2+.
M, MeV
G,MeV
GpD/G,
%
Grp/G,
%
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
17±10
88±17
V.Mokeev NSTAR 2005 Workshop
41±13
6
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
2p direct 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
V.Mokeev NSTAR 2005 Workshop
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Manifestation of 2-p direct production at Q2>0.
W=1.49 GeV
2005’
JLAB-MSU model
Q2=0.65 GeV2
Q2=0.95 GeV2
2003’-version
2p direct production
V.Mokeev NSTAR 2005 Workshop
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2p direct production mechanisms and an additional
term for pD channels needed to fit data.
Md
1 b ( P2 - P2min )
 A(W , Q ) U p / g U p 4 e
( P1P2 )
W
g


g

2
g




(
A
(
W
)

U
g
U
P

B
(
W
)

U
g
U
(
2
P
P
 D
p p
 D
p
p
g ))
Mt
1

t - 2
2
2
 = 1.64 GeV
t  ( Pg - Pp )
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Manifestation of 2p direct production 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
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Evidences for gpp+F015(1685) and
gpp-P++33(1600) channels.
gpp-P++33(1600)
gpp+F015(1685)
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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
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Description of total pp- photoproduction cross-section off
protons in 2005’ version of JLAB-MSU model.
 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
Q2=0. GeV2
no 3/2+
full calculation
Background
 Signal from candidate
3/2+(1720) state present,
but masked by large
background
Resonances
W, GeV
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 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 b
Description of total p+p- electroproduction crosssection off protons in 2005’ JLAB-MSU model.
Q2=0.65 GeV2
Q2=0.95 GeV2
 Signal from candidate 3/2+(1720)
Q2=1.30 GeV2
state (~ 1.7 GeV) becomes
prominent feature at Q2>0.5 GeV2
due to considerable growth
of N*/Bckgr. ratio in
electroproduction.
W, GeV
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Improvements in description of the CLAS 2p
electroproduction data after implementation of
complementary non-resonant mechanisms.
Q2, GeV2
0.65
0.95
1.30
c2/d.p. 2003’version
3.91
3.30
2.26
c2/d.p. 2005’
2.83
JLAB-MSU model
1.90
2.01
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
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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,
CLAS 1p data
p0 at W between 1.1-1.68 GeV;
K.Joo, L.C.Smith, et.al beam asymmetries:
p+ and p0 at W between 1.1-1.58 GeV
9870 data points
Double pion data: p+p-, p+p, p-p mass and
CLAS 2p data
CM p- angular distributions at
M.Ripani, V.D.Burkert,
W between 1.41-1.89 GeV
et.al.
680 data points
The data are available in CLAS Physics DB: http://clasdb3.jlab.org
1p analysis models: I.G. Aznauryan, Phys. Rev. C68, 065204 (2003);
I.G. Aznauryan, et. al., Phys. Rev. C71, 015201
(2005).
V.Mokeev NSTAR 2005 Workshop
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N* photocouplings (in 10-3 GeV-1/2) extracted in
analyses of 1p/2p exclusive channels at Q2=0.65 GeV2
N*
1p/2p analysis
A1/2
A3/2
1p analysis
2p analysis
S1/2
A1/2 A3/2
S1/2
A1/2
33± 6
4± 4
(23±4)
40± 4
21± 9
-35± 3
-67± 3
-38± 3
-63± 12
A3/2
S1/2
P11(1440)
21±4
D13(1520)
-65± 4
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)
62± 5
62± 4
(…) result from dispersion relations. Roper is only state with
A1/2 dependent from model for 1p analysis
V.Mokeev NSTAR 2005 Workshop
35± 6
62± 11
-40± 7
-The states with considerable 1p decays
18
1p data description with N* photocouplings from
combined analysis of 1p/2p channels.
W=1.52 GeV
gvp→p0p
V.Mokeev NSTAR 2005 Workshop
W=1.68 GeV
19
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
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Con’t
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..
Integrated 2p cross-section
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
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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 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, pD and rp couplings of N*
were varied and fitted to the data together with parameters of nonresonant mechanisms implemented to the 2005’ JLAB-MSU model.
Hadronic couplings were further constrained, exploiting their Q2independence. 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+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
W-interv., GeV
Q2=0 GeV2
Q2=0 65GeV2
c2/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
Q2=0 95GeV2
Q2=1 30 GeV2
Sub-sets of calculated cross-sections most close to the data
were isolated, applying restriction c2<c2 thresh, listed in the
table
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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. c2/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
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Q2-evolution of N* photocouplings, determined
from analysis of CLAS 2p data (selected
examples, see full list of studied N*’s on p. 22) .
CLAS 2p data
analysis
PDG at Q2=0 GeV2;
1p/2p combined
CLAS data analysis
at Q2=0.65 GeV2
P11(1440)
(A1/22+S1/22)1/2 *1000GeV-1
Photocouplings corresponded
to selected cross-sections
were averaged. Their mean
values were treated as
determined from data fit, while
dispersions were assigned to
uncertainties
Q2 GeV2
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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
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Q2 GeV2
26
Cont’d
D33(1700), P13(1720)
resonances mostly
decay with 2p
emission. 1p data
have 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
2p photo- and electroproduction.
D33(1700)
P13(1720)
V.Mokeev NSTAR 2005 Workshop
D33(1700)
P13(1720)
27
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 electroproduction data and observed
in real photon data.
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N* hadronic parameters derived from analysis of CLAS
2p data (upper rows) in comparison with PDG values
(down rows).
State
Mass, GeV
Total width.
GeV
pD BF,%
rp 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
0.25-0.45
56±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 Npp
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 Npp
89±6
decays
candidate
3/2+(1720)
2003’ model
1.718±0.007
0.084±0.004
50±8
6.5±2
1.720±0.020
0.088±0.017
49±13
17±10
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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 3qconfigurations.
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