Transcript Slide 1

S = 0 pseudoscalar meson
photoproduction from the proton:
γ p → π0 p, γ p → π+ n
γ p → η p, γ p → η' p
Michael Dugger*
Arizona State University
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*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/What’s Next
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*Work at ASU is supported by the U.S. National Science Foundation
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Motivations
• Theoretical
• Practical
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*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 η and η' mesons have isospin ½ and limit one step
excited states of the proton to also be isospin ½. The η and η‘
act as isospin filters to the resonance spectrum. This might be
useful for find “missing” resonances
• The η and η' have strange content but no net strangeness:
May be useful in determining differing strange quark content
of the proton
• The η' is the only isosinglet. This can be used to indirectly
probe gluonic coupling to the proton
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*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
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*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)
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*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
Time of flight
Magnet
Electrocalorimeter
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*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
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*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
Crystal Barrel
TAPS
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*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
Scintillator and lead
sandwich
Shielding wall
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*Work at ASU is supported by the U.S. National Science Foundation
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New γ p → π0 p Results
• New results from GRAAL: dσ/dΩ and Σ
• New results from CLAS: dσ/dΩ
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*Work at ASU is supported by the U.S. National Science Foundation
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New GRAAL γ p →π0 p Results
• dσ/dΩ from 555 to 1021 MeV
• SAID
• MAID
• BONN-PNPI
(Anisivich, Klempt)
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*Work at ASU is supported by the U.S. National Science Foundation
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New GRAAL γ p →π0 p Results
• dσ/dΩ from 1036 to 1496 MeV •• SAID
MAID
• BONN-PNPI
(Anisivich, Klempt)
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*Work at ASU is supported by the U.S. National Science Foundation
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New GRAAL γ p →π0 p Results
• Σ from 1036 to 1496 MeV
• SAID
• MAID
• BONN-PNPI
(Anisivich, Klempt)
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*Work at ASU is supported by the U.S. National Science Foundation
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Preliminary CLAS γ p →π0 p Results
• dσ/dΩ from 0.675 to 1.425 GeV
• SAID (Blue line)
• CLAS (Black points)
• Mainz (Blue points)
• CB-ELSA (Red points)
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*Work at ASU is supported by the U.S. National Science Foundation
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Preliminary CLAS γ p →π0 p Results
• dσ/dΩ from 1.475 to 2.125 GeV
• SAID (Blue lines)
• CLAS (Black points)
• CB-ELSA (Red points)
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*Work at ASU is supported by the U.S. National Science Foundation
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γ p →π0 p Polarization Observables
Beam polarization
Target asymmetry
Recoil polarization
Double polarization
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*Work at ASU is supported by the U.S. National Science Foundation
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Status: γ p →π0 p Database
• World data set becoming quite thorough
Cross Section
• New beam asymmetry and
dσ/dΩ measurements from
GRAAL
• New dσ/dΩ from CLAS
• CLAS experiment (g8b) just
finished with data taking for
beam asymmetry
• CLAS double polarization
(target & beam) slated for 2007
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*Work at ASU is supported by the U.S. National Science Foundation
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New γ p → π+ n Results
• New results from CLAS: dσ/dΩ
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*Work at ASU is supported by the U.S. National Science Foundation
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Preliminary CLAS γ p →π+ n Results
• Differential cross sections
• Eγ from 0.625 to 1.625 GeV
• SAID (Blue lines)
• CLAS (Black points)
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*Work at ASU is supported by the U.S. National Science Foundation
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Preliminary CLAS γ p →π+ n Results
• Differential Cross sections
• Eγ from 1.675 to 2.275 GeV
• SAID (Blue lines)
• CLAS (Black points)
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*Work at ASU is supported by the U.S. National Science Foundation
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γ p →π+ n Polarization Observables
Recoil polarization
Beam polarization
Target
Targetasymmetry
asymmetry
Double polarization
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*Work at ASU is supported by the U.S. National Science Foundation
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γ p →π+ n
• World database has good coverage for beam
polarization, recoil polarization, and target asymmetry
between 20° and 120° and up to Eγ = 2300 MeV
Cross Section
• Double polarization data
for G and H between 40°
and 100° and up to
Eγ = 1900 MeV
• New CLAS data to cover
dσ/dΩ up to Eγ = 2275 MeV
Cross section
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*Work at ASU is supported by the U.S. National Science Foundation
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γ p →η p
• Data becoming quite thorough
• More polarization measurements coming
• More dσ/dΩ measurements with absolute
photon flux determination coming
dσ/dΩ
Beam polarization
Target polarization
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*Work at ASU is supported by the U.S. National Science Foundation
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New CLAS γ p →η' p Results
• SAPHIR (Blue points)
• CLAS (Black points)
• SAPHIR used indirect
method for photon flux
• SAPHIR used a branch to
determine η' and had only
~1% acceptance
• CLAS η' results were
obtained in similar manner
as the CLAS π0 results
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*Work at ASU is supported by the U.S. National Science Foundation
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New CLAS γ p →η' p Results
• Solid line: Nakayama and Haberzettl
• Dashed line: Model inspired by A. Sibertsev
• Solid line → Nakayama, Haberzettl:
1. Relativistic meson-exchange model
2. s-channel j=1/2 and j=3/2 resonances
3. t-channel ρ, ω exchange
4. Nucleon exchange in s- and u-channels
5. Contact current to make gauge-invariant
• Dashed line → Sibertsev/Dugger:
1. Relativistic meson-exchange model
2. s-channel j=1/2 resonances
3. t-channel ρ, ω exchange
4. Nucleon exchange in s- and u-channels
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*Work at ASU is supported by the U.S. National Science Foundation
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Some π and η Photoproduction Models
γ
• MAID:
1. Isobar resonances
2. Born terms
3. t-channel ρ, ω exchange
4. Newly Reggeized for higher energy data
γ
• Anisivich, Klempt:
1. Resonances are Breit-Wigner except for two channel K
matrix for S11(1535) and S11(1650)
2. Reggeized t- and u-channel
3. Coupled channels (dσ/dΩ and Σ: π+ n, π0 p, η p, K Λ,K Σ)
• Li, Saghi:
1. Chiral constituent quark model
2. SU(6) x O(3) symmetry broken by gluon
exchange
γ
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AK 2005
State
N* P11
N* D13
N* S11
N* S11
N* D15
N* F15
N* D13
N* P11
N* P13
N* P11
N* D13
N* P13
N* F15
N* D15
N* D13
N* P13?
π+ n, π0 p
Mass
ηp
1440
♦
1520
♦
♦
1535
Width =210
1650
♦
♦
1675
♦
♦
1680
♦
♦
1700
♦
♦
1710
1720
♦
♦
1840
1875
1900
2000
♦
♦
2070
♦
♦
2170
2200
♦
Exotic ?
1800
Δ P33
Δ S11
Δ D33
Δ F35
Δ P33
Δ D33
Δ F37
1232
1620
1700
1905
1920
1940
1950
♦
♦
♦
♦
♦
♦
♦
MAID 2002 LS 2002
ηp
ηp
♦
♦
♦
Width=191 Width=162
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
• Red:
• Blue:
π+ n and π0 p
ηp
• 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/What’s Next
π0, π+, η, and η' 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
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*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
•
•
• New data from GRAAL
• Annalisa D’Angelo
• Dominique Rebreyand
• Carlo Schaerf
CLAS Collaboration
Theoretical curves for η'
• Kanzo Nakayama
• Helmut Haberzettl
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*Work at ASU is supported by the U.S. National Science Foundation
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