Michael Dugger

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S 0 pseudoscalar meson photoproduction from the
proton
? p ? p0 p, ? p ? p n? p ? ? p, ? p ? ?' p

• Michael Dugger
• Arizona State University

Work at ASU is supported by the U.S. National
Science Foundation
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Outline

• Motivations Theoretical Practical
• Experimental Facilities
• New and Existing Data
• Brief Look At Models
• Conclusions/Whats Next

Work at ASU is supported by the U.S. National
Science Foundation
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Motivations

• Theoretical
• Practical

Work at ASU is supported by the U.S. National
Science Foundation
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Motivations (Theoretical)

• Pions are the lightest mesons and are copiously
  produced in the strong interaction.

• The ? and ?' mesons have isospin ½ and limit one
  step excited states of the proton to also be
  isospin ½. The ? and ? act as isospin filters to
  the resonance spectrum. This might be useful for
  find missing resonances

• The ? and ?' have strange content but no net
  strangeness May be useful in determining
  differing strange quark content of the proton

• The ?' is the only isosinglet. This can be used
  to indirectly probe gluonic coupling to the proton

Work at ASU is supported by the U.S. National
Science Foundation
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Motivations (Practical)
Photoproduction

• Electromagnetic interactions are well understood
• Real photons are particularly simple Only 2
  polarization states.

Non-strangeness reactions

• The outgoing proton is easy to identify and has
  relatively little contamination

Work at ASU is supported by the U.S. National
Science Foundation
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• Experimental Facilities
• SAPHIR (Spectrometer Arrangement for Photon
  induced Reactions. ELSA)
• CLAS (CEBAF Large Acceptance Spectrometer. JLab)
• CB-ELSA (Crystal Barrel at ELSA)
• GRAAL (at the ESRF in Grenoble)

Work at ASU is supported by the U.S. National
Science Foundation
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SAPHIR at Bonn Electron Stretcher

• Photon energies up to 3.0 GeV
• Good for charged particles
• Small acceptance

Drift chamber
Electrocalorimeter
Time of flight
Magnet
Work at ASU is supported by the U.S. National
Science Foundation
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CLAS

• Photon energies up to 5.7 GeV
• Good for charged particles
• Large acceptance

Work at ASU is supported by the U.S. National
Science Foundation
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CB-ELSA

• Photon energies up to 3.2 GeV
• Good for neutral particles
• Large acceptance

TAPS
Crystal Barrel
Work at ASU is supported by the U.S. National
Science Foundation
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GRAAL

• Photon energies up to 1.1 GeV
• Good for neutral particles
• Large acceptance

Variable collimator
Fixed collimator
Plastic scintillator barrel
Cleaning magnet
Target
Cylindrical wire chambers
BGO calorimeter
Vacuum system
Shielding wall
Scintillator and lead sandwich
Work at ASU is supported by the U.S. National
Science Foundation
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New ? p ? p0 p Results

• New results from GRAAL ds/dO and S
• New results from CLAS ds/dO

Work at ASU is supported by the U.S. National
Science Foundation
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New GRAAL ? p ?p0 p Results

• SAID

• BONN-PNPI
• (Anisivich, Klempt)

• ds/dO from 555 to 1021 MeV

• MAID

Work at ASU is supported by the U.S. National
Science Foundation
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New GRAAL ? p ?p0 p Results

• SAID

• BONN-PNPI
• (Anisivich, Klempt)

• ds/dO from 1036 to 1496 MeV

• MAID

Work at ASU is supported by the U.S. National
Science Foundation
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New GRAAL ? p ?p0 p Results

• SAID

• BONN-PNPI
• (Anisivich, Klempt)

• S from 1036 to 1496 MeV

• MAID

Work at ASU is supported by the U.S. National
Science Foundation
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Preliminary CLAS ? p ?p0 p Results

• ds/dO from 0.675 to 1.425 GeV
• SAID (Blue line)

• Mainz (Blue points)
• CB-ELSA (Red points)

• CLAS (Black points)

Work at ASU is supported by the U.S. National
Science Foundation
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Preliminary CLAS ? p ?p0 p Results

• ds/dO from 1.475 to 2.125 GeV
• SAID (Blue lines)

• CLAS (Black points)
• CB-ELSA (Red points)

Work at ASU is supported by the U.S. National
Science Foundation
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? p ?p0 p Polarization Observables
Beam polarization
Target asymmetry
Recoil polarization
Double polarization
Work at ASU is supported by the U.S. National
Science Foundation
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Status ? p ?p0 p Database

• World data set becoming quite thorough

Cross Section

• New beam asymmetry and ds/dO measurements from
  GRAAL
• New ds/dO from CLAS
• CLAS experiment (g8b) just finished with data
  taking for beam asymmetry
• CLAS double polarization (target beam) slated
  for 2007

Work at ASU is supported by the U.S. National
Science Foundation
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New ? p ? p n Results

• New results from CLAS ds/dO

Work at ASU is supported by the U.S. National
Science Foundation
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Preliminary CLAS ? p ?p n Results

• Differential cross sections
• E? from 0.625 to 1.625 GeV

• SAID (Blue lines)
• CLAS (Black points)

Work at ASU is supported by the U.S. National
Science Foundation
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Preliminary CLAS ? p ?p n Results

• Differential Cross sections
• E? from 1.675 to 2.275 GeV

• SAID (Blue lines)
• CLAS (Black points)

Work at ASU is supported by the U.S. National
Science Foundation
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? p ?p n Polarization Observables
Beam polarization
Recoil polarization
Target asymmetry
Target asymmetry
Double polarization
Work at ASU is supported by the U.S. National
Science Foundation
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? p ?p n

• World database has good coverage for beam
  polarization, recoil polarization, and target
  asymmetry between 20 and 120 and up to E?
  2300 MeV

Cross Section

• Double polarization data for G and H between 40
  and 100 and up to E? 1900 MeV

• New CLAS data to cover ds/dO up to E? 2275 MeV

Cross section
Work at ASU is supported by the U.S. National
Science Foundation
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? p ?? p

• Data becoming quite thorough
• More polarization measurements coming
• More ds/dO measurements with absolute photon
  flux determination coming

ds/dO
Target polarization
Beam polarization
Work at ASU is supported by the U.S. National
Science Foundation
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New CLAS ? p ??' p Results

• SAPHIR (Blue points)
• CLAS (Black points)

• SAPHIR used indirect method for photon flux
• SAPHIR used a branch to determine ?' and had
  only 1 acceptance
• CLAS ?' results were obtained in similar manner
  as the CLAS p0 results

Work at ASU is supported by the U.S. National
Science Foundation
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New CLAS ? p ??' p Results

• Solid line Nakayama and Haberzettl
• Dashed line Model inspired by A. Sibertsev

• Solid line ? Nakayama, Haberzettl
• Relativistic meson-exchange model
• s-channel j1/2 and j3/2 resonances
• t-channel ?, ? exchange
• Nucleon exchange in s- and u-channels
• Contact current to make gauge-invariant

• Dashed line ? Sibertsev/Dugger
• Relativistic meson-exchange model
• s-channel j1/2 resonances
• t-channel ?, ? exchange
• Nucleon exchange in s- and u-channels

Work at ASU is supported by the U.S. National
Science Foundation
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Some p and ? Photoproduction Models
?

• MAID
• Isobar resonances
• Born terms
• t-channel ?, ? exchange
• Newly Reggeized for higher energy data

?

• Anisivich, Klempt
• Resonances are Breit-Wigner except for two
  channel K matrix for S11(1535) and S11(1650)
• Reggeized t- and u-channel
• Coupled channels (ds/dO and S p n, p0 p, ? p,
  K ?,K S)

• Li, Saghi
• Chiral constituent quark model
• SU(6) x O(3) symmetry broken by gluon exchange

?
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• Red p n and p0 p
• Blue ? p
• LS Li, Saghi
• AK Anisovich, Klempt

• S11(1650) causing
• difficulty in determining width for the
  S11(1535)?
• Missing resonance D15(2070) found?
• Exotic at 1800 MeV?

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Conclusions/Whats Next p0, p, ?, and ?'
photoproduction off the proton

• World database greatly enhanced during past
  several years
• Evidence that a missing D15(2070) resonance may
  have been found
• Need for more polarization observables and
  coupled channel analyses to constrain the
  theoretical models
• More data coming, including double polarization
  observables from CLAS in 2007

Work at ASU is supported by the U.S. National
Science Foundation
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Acknowledgements

• NSF
• ASU Group Members
• J. Ball
• P. Collins
• E. Pasyuk
• B. Ritchie
• CLAS Collaboration

• Theoretical curves for ?'
• Kanzo Nakayama
• Helmut Haberzettl
• New data from GRAAL
• Annalisa DAngelo
• Dominique Rebreyand
• Carlo Schaerf

Work at ASU is supported by the U.S. National
Science Foundation
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