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

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

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

*Photonuclear cross sections

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

*Baryon Resonance Spectrum

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

*Most models predict more resonance states than observed

Constituent quark model

Lattice QCD

* 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

*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

*Experimental tools

A B CInjector

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

*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

*Polarized pohoton beamCi

izatio

Circular polarization from 100% polarized electron beam

Linearly polarized photons: coherent bremsstrahlung on oriented diamond crystal

Circularly polarized beam produced by longitudinally polarized electrons

*FROST

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

*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*

*Single pion production

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

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

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

DE=10 MeV

*gpp Photon asymmetry S

Michael Dugger, ASU

preliminary

DE=10 MeV

*gp+n Photon asymmetry S

Michael Dugger, ASU

preliminary

*gp+n Helicity asymmetry E

preliminary

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

*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

*gp0p Helicity asymmetry E

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

*gp+n Target asymmetry T

*gp+n asymmetry F

*K+L photoproduction

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

*γpK+Λ Cross Section

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

*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),

*γpK+Λ Photon Asymmetry S

preliminary

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

*K+L OxC. Patterson

preliminary

*K+L OzC. Patterson

preliminary

*K+L Target AsymmetryC. Patterson

preliminary

(PhD L. Casey, CUA)

*K+L helicity asymmetry E

preliminary

(PhD L. Casey, CUA)

*K+L helicity asymmetry E

preliminary

*Summary

*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

*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

*Conclusion*“compete measurement” in pseudoscalar meson

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

complete*Data are being analyzed

*Extras

*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

* SAID * MAID* NH (K. Nakayama

and H. Haberzettl)

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

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

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

*Variants of model

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

P11(1710)P11(2100)

P13(1720)P13(1900)

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

gη´NN = 1.91

S11(2090)

P11(2100)

P13(1900)

D13(1700)

gη´NN = 0.43

S11(2090)

P11(2100)

P13(1900)

D13(1700)D13(2080)

gη´NN = 0.25

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

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

P13(1900)

D13(1700)D13(2080)

gη´NN = 1.33

S11(1535)

S11(2090)

P11(1710)P11(2100)

D13(1700)D13(2080)

gη´NN = 0.002

I II III IV V

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

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

*R Values for the L

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

2 2 2x zR P C C

*Average R values

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

this CLAS result.

1 .01 0 .01R ±

*Polarization observables in pseudoscalar meson production

Meson photoproduction and nucleon resonances

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