Phenomenological analysis of recent CLAS electroproduction off proton

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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
V.Mokeev NSTAR 2005 Workshop
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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 )
V.Mokeev NSTAR 2005 Workshop
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9
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)
V.Mokeev NSTAR 2005 Workshop
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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
V.Mokeev NSTAR 2005 Workshop
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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
V.Mokeev NSTAR 2005 Workshop
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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).
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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
V.Mokeev NSTAR 2005 Workshop
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.
V.Mokeev NSTAR 2005 Workshop
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