meson photoproduction and nucleon resonances

Meson photoproduction and nucleon resonancesEugene Pasyuk

Jefferson Labfor the CLAS Collaboration

Moscow, September 20-23, 2012XIII International Seminar onElectromagnetic Interactions of Nuclei

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2E. Pasyuk, EMIN-2012, Moscow, September 20-23 2012

*Outline*Introduction*Experimental tools*Single pion photporoduction*K+L photoproduction*Summary

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*Photonuclear cross sections

E. Pasyuk, EMIN-2012, Moscow, September 20-23 2012

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*Baryon Resonance Spectrum

*Masses, widths, and coupling constants not well known for many resonances

*Most models predict more resonance states than observed

N*

Constituent quark model

Lattice QCD


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* Polarization observables in pseudoscalar meson production

4 Complex amplitudes: 16 real polarization observables.Complete measurement from 8 carefully chosen observables. πN has large cross section but in KY recoil is self-

analysing

I. S. Barker, A. Donnachie, J. K. Storrow, Nucl. Phys. B95 347 (1975).

πN KYrecoil targ

γ γ targ recoil

☻☻☻

☻

linearly polarized photons

☻☻☻☻☻☻

longitudinally polarized target

☻☻☻☻☻☻

circ polarized photons

☻☻☻☻☻☻☻☻☻☻☻☻

transversely polarized target

Complete, andover-determined


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*From the Experiment to Theory

Experimentcross section,

spin observables

TheoryLQCD,

quark models,QCD sum rules,

…

Reaction Theorydynamical frameworks

Amplitude analysis→multipole amplitudes

→phase shifts

σ,dσ/dΩ,Σ,P,T(beam-target) E,F,G,H,(beam-recoil) Cx,Cz,Ox,Oz,(target-recoil) Lx,Lz, Tx,Tz,

Coupled channels: resonance parameter

ExtractionThis session

Hiroyuki Kamano


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*Experimental tools


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A B CInjector

LIN

AC LINAC

Experimental Halls

*CEBAF

* E: 0.75 –6 GeV* Imax: 200μA* Duty Cycle: 100%* δE/E: 2.5x10-5

* Polarization: ≥85%* Simultaneous distribution to

3 experimental Halls


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*CEBAF Large Acceptance Spectrometer1997-2012

Torus magnet6 superconducting coils

Gas Cherenkov counterse/ separation, 256 PMTs

Time-of-flight countersplastic scintillators, 684 photomultipliers

Drift chambers35,000 cells

target + start counter

Electromagnetic calorimetersLead/scintillator, 1296 photomultipliers


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*Polarized pohoton beamCi

rcul

ar p

olar

izatio

n

Circular polarization from 100% polarized electron beam

Linearly polarized photons: coherent bremsstrahlung on oriented diamond crystal

Circularly polarized beam produced by longitudinally polarized electrons


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*FROST


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HDIce Solid Deuterium-Hydride (HD) – a new class of polarized target

*HDIce polarized target

* Polarized at very high magnetic field and very low temperature

* Transferred to in-beam cryostat

* Spin can be moved between H and D with RF transitions

* All material can be polarized with almost no background


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*What we measure with CLAS* γp→π0p, π+n* γp→ηp* γp→ηp* γp→KY (K+Λ, K+Σ0, K0Σ+)* γp→π+π-p, ωp, ρp, ϕp

* γn→π-p* γn→π+π-n* γn→Σ-K+ , ΛK0 …..

Reactions γp→ηp, ηp, K+Λ provide isospin filter, directly coupled only to N*


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*Single pion production

E. Pasyuk, EMIN-2012, Moscow, September 20-23 2012 14

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*gp+n

•CLAS SP07 MAID07 SP08 SN08M. Dugger et al. PRC 79, 065206 (2009) Constrained SAID fit at higher energies. Does not need any new resonances


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16Forum for MAX-IV Ring, Lund, Nov 2011

DE=10 MeV

*gpp Photon asymmetry S

preliminary

Michael Dugger, ASUE. Pasyuk, EMIN-2012, Moscow, September 20-23 2012

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DE=10 MeV

*gpp Photon asymmetry S

Michael Dugger, ASU

preliminary


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DE=10 MeV

*gp+n Photon asymmetry S

Michael Dugger, ASU

preliminary


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*gp+n Helicity asymmetry E

preliminary

S. Strauch, USCE. Pasyuk, EMIN-2012, Moscow, September 20-23 2012

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*gp+n Helicity asymmetry E

For W< 1.75 GeV all of the models represent the data fairly well.For W> 1.75 GeV none of the models represents the data well.

preliminary


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*gp0p Helicity asymmetry E


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PRELIMINARY

PRELIMINARY

PRELIMINARY

PRELIMINARY

PRELIMINARY

cos(q)=-1 to -0.6 cos(q)=-0.6 to -0.2 cos(q)=-0.2 to 0.2

cos(q)=0.2 to 0.6 cos(q)=0.6 to 1.0

*gp+n Helicity asymmetry G

Jo McAndrew )2sin()2cos(10 GPPP

dd

dd

zTT S


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*gp+n Target asymmetry T


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F F F

F F F

F

F

FF

F F

*gp+n asymmetry F


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*K+L photoproduction

E. Pasyuk, EMIN-2012, Moscow, September 20-23 2012 25

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*γpK+Λ Cross Section


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recoil polarization P

excitation function

g11: W=1.7 – 2.8 GeV(unpolarized beam & target)

M.E. McCracken et al., PRC 81, 025201 (2010)

*γp→K+Λ: cross section and P


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*γp→K+Λ: Cx/Cz

Nikonov et al’.’s refit of Bonn-Gachina multi-coupled-channel isobar modelmix includes: S11 wave, P13(1720), P13(1900), P11(1840)

Bradford et al. PRC 75, 035205 (2007),


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*γpK+Λ Photon Asymmetry S

preliminary

C. PattersonE. Pasyuk, EMIN-2012, Moscow, September 20-23 2012

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*K+L OxC. Patterson

preliminary


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*K+L OzC. Patterson

preliminary


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*K+L Target AsymmetryC. Patterson

preliminary


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(PhD L. Casey, CUA)

*K+L helicity asymmetry E

preliminary


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(PhD L. Casey, CUA)

*K+L helicity asymmetry E

preliminary


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*Summary


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*Status of meson photoproduction σ Σ T P E F G H Tx Tz Lx Lz Ox Oz Cx Cz

Proton target

pπ0 ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

nπ+ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

pη ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

pη’ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

pω ✔ ✓ ✓ ✓ ✓ ✓ ✓

K+Λ ✔ ✓ ✓ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

K+Σ0 ✔ ✓ ✓ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

K0*Σ+

✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

“Neutron” targetpπ- ✔ ✓ ✓ ✓ ✓ ✓ ✓

pρ- ✓ ✓ ✓ ✓ ✓ ✓ ✓

K+Σ- ✓ ✓ ✓ ✓ ✓ ✓ ✓

K0Λ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

K0Σ0 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

K0*Σ0

✓ ✓✔ - published ✔ - acquired


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*What was not shown* γp→ηp* γp→η’p* γp→π+π-p ωp, ρp, ϕp

* γn→π-p* γn→π+π-n* γn→Σ-K+ , ΛK0 …..

We have measured cross sections an polarization observables


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*Conclusion*“compete measurement” in pseudoscalar meson

photoproduction is reality*Data collection with proton and deuteron targets is

complete*Data are being analyzed


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*Extras


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*h’ photoproduction

* 1968: 11 events from the ABBHHM bubble chamber experiment* 1976: 7 events from the AHHM streamer chamber

experiment* 1998: 250 events from the SAPHIR collaboration

(first differential cross sections)* 2006: over 2×105 events from the CLAS

collaboration*2009: another few orders of magnitude from CLAS

g11 data set


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*gphp

* SAID * MAID* NH (K. Nakayama

and H. Haberzettl)

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M. Dagger et al. PRL 96, 062001 (2006)


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*gphp

K. Nakayama and H. Haberzettl, Phys. Rev. C 73, 045211 (2006).

Different versions of the model yield similar results for cross section, but quite different predictions for beam asymmetryPredictions for beam asymmetry are quite different

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M. Dugger et al. PRL 96, 062001 (2006)


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*Variants of model

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S11(1535)S11(1650)S11(2090)

P11(1710)P11(2100)

P13(1720)P13(1900)

D13(1520)D13(1700)D13(2080)

gηŃN = 1.91

S11(2090)

P11(2100)

P13(1900)

D13(1700)

gηŃN = 0.43

S11(2090)

P11(2100)

P13(1900)

D13(1700)D13(2080)

gηŃN = 0.25

S11(1535)S11(1650)S11(2090)

P11(1710)P11(2100)P11(2400)

P13(1900)

D13(1700)D13(2080)

gηŃN = 1.33

S11(1535)

S11(2090)

P11(1710)P11(2100)

D13(1700)D13(2080)

gηŃN = 0.002

I II III IV V


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*gphp

M. Williams et al. PRC 80, 045213 (2009)

44E. Pasyuk, EMIN-2012, Moscow, September 20-23 2012

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*R Values for the L

The L appears 100% polarized when created with a fully polarized beam.

2 2 2x zR P C C


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*Average R values

*Energy and angle averages are consistent with unity.*No model predicted

this CLAS result.

1 .01 0 .01R ±


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*Polarization observables in pseudoscalar meson production


meson photoproduction and nucleon resonances

Documents

polarized targetcomplete

polarized pohoton

polarized electrons10e

polarized electron beam

k0 p p

clas collaboration moscow

p npn

beamrecoil cx