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Kaon Production on the Nucleon
D. G. Ireland
MENU
Rome, September 30 – October 4, 2013
Kaon Photoproduction
very high
momentum
transfer (pQCD)
1
2
Baryon Summary Table (PDG 2008)
3
Baryon Summary Table (PDG 2012)
4
“Missing” Baryon Resonances
5
Resonances in Quark Models
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Baryon Spectrum on the Lattice
Excited state baryon spectroscopy from lattice QCD.
Edwards, Dudek, Richards, Wallace
Phys. Rev. D 84, 074508 (2011)
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Resonance Hunting…
Total Cross-sections
+ differential cross-sections
+ Partial Wave Analysis + ...
Mostly done with pN scattering
Missing resonances may decay through other channels
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Meson Photoproduction Cross Sections
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Jefferson Lab
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CLAS
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g*p →KY Electroproduction
Cross Section:
p
p
… with electron polarization…
Hyperon is
self-analysing
proton
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g*p →KL Separated Structure Functions
D. Carman et al. (CLAS), Phys. Rev. C 87, 025204, 2013
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g*p →KS Separated Structure Functions
D. Carman et al. (CLAS), Phys. Rev. C 87, 025204, 2013
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g*p →KL Q2 Dependence
D. Carman et al. (CLAS), Phys. Rev. C 87, 025204, 2013
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g*p →KS Q2 Dependence
D. Carman et al. (CLAS), Phys. Rev. C 87, 025204, 2013
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gp →KL Photoproduction
g
K+
zˆ 
xˆ
Kc.m.
yˆ 
xˆ
yˆ
L
proton
zˆ
p
xˆ
yˆ
p
zˆ
Hyperon is self-analysing
proton
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CLAS results γp→K+Λ → K+pπBonn-Gatchina Coupled Channel Analysis, A.V. Anisovich et al, EPJ A48, 15 (2012)
(Includes nearly all new photoproduction data)
M. McCracken et al. (CLAS), Phys. Rev. C 81, 025201, 2010
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CLAS results γp→K+Λ → K+pπBonn-Gatchina Coupled Channel Analysis, A.V. Anisovich et al, EPJ A48, 15 (2012)
(Includes nearly all new photoproduction data)
M. McCracken et al. (CLAS), Phys. Rev. C 81, 025201, 2010
R. Bradford et al. (CLAS), Phys.Rev. C75, 035205, 2007
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Fit to K+Λ with PDG2010 states < 2 GeV
EBAC group: Kamano, Nakamura, Lee, Sato (2012)
1965
Includes ***, **** states
1965
PDG states insufficient to fit KΛ data
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Evidence for new N* states and couplings
State
N((mass)JP
PDG 2010
PDG 2012
KΛ
KΣ
Nγ
N(1710)1/2+
***
(not seen in
GW
analysis)
***
***
**
***
N(1880)1/2+
**
**
*
**
N(1895)1/2-
**
**
*
***
***
***
**
***
N(1875)3/2-
***
***
**
***
N(2150)3/2-
**
**
***
**
N(1900)3/2+
N(2000)5/2+
N(2060)5/2-
**
*
***
**
*
**
**
***
Bonn-Gatchina Analysis – A.V. Anisovich et al., EPJ A48, 15 (2012)
(First coupled-channel analysis that includes nearly all new photoproduction data)
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N*  K+L Amplitude Analysis
Ref: Scaling and Resonances in Elementary K+L Photoproduction
[R.A. Schumacher and M.M. Sargsian, Phys. Rev. C 83, 025207 (2011)]
Compute coherent total amplitude:
Fit to observed angular distributions:
Test various resonance sets vs. mass
Free parameters: mass, width, couplings
Structure appears when scaling
utilised.
Spin observables neglected
Sensitive to smaller contributions to reaction
Linearly Polarized Photons
Diamond radiator mounted
on target ladder
Alignment checked by
observing symmetric
“Stonehenge Plot”
Polarization determined by fit to
coherent bremsstrahlung spectrum
Radiator in goniometer
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FROzen Spin Target (FROST)
Target can be longitudinally or transversely polarised
[See talk by Barry Ritchie]
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Transversity Amplitudes
g
p
L
K
g
p
L
K
g
p
L
K
g
p
L
K
}
}
}
}
b1 = <  | M |  >
b2 = <  | M |  >
b3 = <  | M | ‖ >
b4 = <  | M | ‖>
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Observables
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Imaging Multi-dimensional Objects
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Imaging Multi-dimensional Objects
?
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Comparison with other measurements
Experiment
CLAS g11
LEPS
GRAAL
CLAS g8
Final State
W range
(Gev)
S
P
T
Ox
Oz
KL
1.62 – 2.84
N
Y
N
N
N
KS
1.69 – 2.84
N
Y
N
N
N
KL
1.94 – 2.30
Y
N
N
N
N
KS
1.94 – 2.30
Y
N
N
N
N
KL
1.64 – 1.92
Y
Y
Y
Y
Y
KS
1.74 – 1.92
Y
Y
N
N
N
KL
1.71 – 2.19
Y
Y
Y
Y
Y
KS
1.75 – 2.19
Y
Y
Y
Y
Y
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Comparison with other measurements
LEPS
LEPS
CLAS g8
CLAS g8
GRAAL
GRAAL
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Beam Asymmetry Comparison
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Beam-Recoil Comparison
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Beam Asymmetry Comparison
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Summary
• CLAS has measured a large set of data involving Kaon production
• Electroproduction:
•
Separated structure functions
•
Q2 dependence – information on form factors
•
Needs theoretical work
• Photoproduction:
•
Cross sections and recoil polarizations sensitive to N* physics
•
Exact interpretation of N* spectrum still ambiguous
• Outlook:
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More polarization data to come (electro- and photo-production)
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Results from (quasi-free) neutron
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Full set of observables in KL and KS in resonance region
•
Exciting prospect for N* physics (with results from other channels)
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