Photo and Hadroproduction of meson

1
Photo- and Hadro-production of ?? meson

• H. Haberzettl (GWU)K. Nakayama (UGA)
• key references PRC69, 065212 (04),
• nucl-th/0507044

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Outline of the talk

• Motivation.
• Description of ?N ? ??N
• ? model for gN?h'N.
• ? analysis of the SAPHIR data
  (PLB444, 98).
• Description of NN ? ??NN (in conjunction with
  gN?h'N)
• ? model for NN?h'NN.
• ? analysis of the SPESIII,
  COSY11 and DISTO data.
• Analysis of the new CLAS data on photoproduction
• (M. Dugger et al., in preparation).

3
Motivation

• Extract information on nucleon resonances in the
  less
• explored higher N mass region
• ? high-mass resonances in low
  partial-wave states.
• ? missing resonances.
• ? excitation mechanism of these
  resonances.
• Constrain the NNh' coupling constant (0 gNNh' lt
  7)
• ? particular interest in connection to
  the nucleon-spin crisis
• (EMC collaboration, PLB206, 88).
  NNh' coupling constant is related
• to the flavor-singlet axial charge GA
  through the U(1)
• Goldberger-Treiman relation

ShoreVeneziano, NPB381, 92.
GA(0) 0.160.10 (SMC collaboration, PRD56,97)
quark contribution to the proton spin
gluon contribution to the proton spin
4
Available data models ( ?p???p )
Theory ? quark models Z. Li, JPG23,
97. Q. Zhao, PRC63, 01. ?
(tree-level) effective Lagrangian J.
Zhang et al., PRC52, 95. B. Borasoy,
EPJA9, 00. W. Chiang et al., PRC68,
03. A. Sibirtsev et al.,
nucl-th/0303044. ? unitary approach B.
Borasoy et al., PRC66, 02. (s-wave
coupled channel relativistic unitary
approach )
Experiment ? total cross sections
ABBHHM, PR175, 68. AHHM, NPB108,
76. SAPHIR, PLB444, 98. ?
angular distributions SAPHIR, PLB444,
98. CLAS, Dugger et al., in
preparation. ? expected data Crystal
Barrrel collaboration at ELSA.
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Aim of this work ( ?p???p )

• Shed light on the contradictory conclusions of
  existing model
• calculations
• ? origin of the shape of the observed
  angular distribution
• ? interference among N (S11
  P13) resonances. Zhao,01
• ? interference between N (S11)
  and t-channel (Regge) currents.
• 
  
  Chiang et al., 03
• ? t-channel current (mec
  exponential form factor). Sibirtsev et
  al., 03
• ? t-channel current
• ? Regge trajectory.
  Chiang et al., 03
• ? meson-exchange
  others
• Are we able to identify N resonances from the
  (differential) cross
• section data ?
• Can we constrain the NN?? coupling constant,
  gNN?? ?
• Provide inputs for NN???NN.

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?N ? ?? N (model)
GNNh' ? (gNNh', lNNh')
Gvh'g ? (Lvh'g) cutoff parameter
GRNg ? (fRNg)
mass (mR) width ( GR)
GRNh' ? (gRNh' , l RNh' )
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gp?h'p (SAPHIR data, PLB444,98 )
mecS11
mecS11nuc
ang. distr. abs. norm. due to an
interference among different currents.
gNNh' lt 3
mecS11P11
mecS11P11 nuc
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Resulting model parameters
?R150 MeV
?R150 MeV
9
gp?h'p ( insensitivity of the cross section to
the resonance mass )
cross section rather insensitive to the N mass.
10
gp?h'p (mec x Regge trajectory)
mec
regge
Gvh'g
Regge trajectory. r,wexchange dip./exp. form
factor at Gvh'g.

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Some conclusions with the SAPHIR data

• On the shape of the angular distribution
• Interference among different currents
  (especially, N t-channel) is
• crucial (corroborates the Chiang et
  al.s findings).
• r,wexchange vrs. Regge trajectory
• provided one introduces a form factor
  (dipole/exponential) at the
• vh'g-vertex (mec), they lead
  essentially to the same conclusion.
• Cross sections alone are unable to pin down
  precisely the resonance mass values.
• gNNh' lt 3. To improve, needs more accurate data
  at high-energy and large backward angles.

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Available data models ( pp???pp )
Theory ? DWBA (meson-exchange models)
Sibirtsev Cassing, EPJA2, 98. Bernard
et al., EPJA4, 99. Gedalin et al.,
NPA650, 99. Baru et al., EPJA6, 99.
Nakayama et al., PRC61, 99.
Experiment ? total cross sections
SPESIII, PLB438,98. DISTO, PLB491,00.
COSY11, PRL80,98
PLB474,00
PLB482,03
EPJA20,04. ? angular distributions
DISTO, PLB491,00. (Q 144 MeV) COSY11,
EPJA20,04. (Q 47 MeV)
too many unknown parameters (need independent
reactions to fix some of those parameters)
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NN - h'NN (model)
DWBA
FSI
ISI
transition current
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pp?h'pp (SPESIII,98 COSY11,98-04 DISTO,00
data)
mecS11 mecS11nuc
mecS11P11
mecS11P11nuc
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pp?h'pp ang. distr. at Q46.6 MeV (COSY11,04)
excluded from the fit
mecS11 mecS11nuc
mecS11P11
mecS11P11nuc
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S11 resonace excitation mechanism(s) ?
mecS11 mecS11nuc
mecS11P11
3.62 16.34
11.11 -0.49 -2.25
11.25 0.24 7.75
-1.93
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pp-h'pp (some conclusions)

• Dominant reaction mechanism S11 resonance.
• Existing data cannot constrain on the excitation
  mechanism(s) of the S11 resonance
• ? data on pn?h'pn and/or pn?h'd will
  impose more stringent
• constraints (isoscalar vrs
  isovector meson-exchange).
• ? and also spin-observables (e.g., Ay
  in ?-meson production can
• disentangle pseudoscalar- and
  vector-meson exchanges also
• Axx ).
• DISTO vrs. COSY11 data on the angular
  distribution needs data for Q gt 50 MeV.

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gp?h'p (new CLAS data, M. Dugger et al., in
preparation)
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gp?h'p (CLAS data, in preparation)
? resonances required S11, P11, P13, D13
? curves correspond to different set of
parameters with comparable c2.
? data at more forward and backward angles
would constrain more the model parameters.
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gp?h'p (dynamical content)
gNN??0.01
gNN??1.49
?2/N3.72
?2/N3.85
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?2/N3.82
gp?h'p (dynamical content)
gNN??0.00
gNN??1.12
?2/N3.55
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Resulting model parameters
?2/N3.82
?2/N3.72
?2/N3.85
?2/N3.55
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gp?h'p ( can nuc mec be fixed ? )
would require data beyond the resonance region
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gp?h'p ( meson-exchange vrs. Regge trajectory )
High-precision CLAS data ?
Regge trajectory is, at best, comparable to the
meson-exchange
c2/N
meson-exchange
Regge trajectory Set I
3.72 4.19 Set IV
3.55
3.82
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gp?h'p ( prediction for the total cross section )

? sharp rise near threshold due to S11
resonance. ? bump around W2.09 GeV due to
D13 (and possibly P11) resonance. PDG
D13(2080) , P11(2100)
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gp?h'p ( beam and target asymmetries )
much more sensitive to the model parameters than
cross sections
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Some conclusions with the CLAS data

• The CLAS data can be reproduced with the
  inclusion of spin-1/2 and -3/2 resonances, whose
  (resonance) parameters are consistent with those
  quoted in the PDG.
• The existing cross section data, however, do not
  impose enough constraints to pin down the
  resonance parameters.
• ? data at more forward and backward
  angles would help constrain more
• those parameters.
• ? spin-observables (beam and target
  asymmetries) will impose much more
• stringent constraints.
• We predict a bump in the total cross section
  around W2.09 GeV. If this is confirmed (needs
  data), D13(2080) and/or P11(2100) resonance is
  likely to be responsible for this bump.
• gNNh' should not be much larger than 2 (more
  exclusive data is needed and/or needs to go
  beyond the resonance region to pin it down).

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pp?h'pp (based on the CLAS data results)
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The End
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Resonance widths
,
,
,
R?Np
qiR qi (WmR )
R?Npp
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Phenomenological contact current
free of any singularities
free parameters