Status of meson photoproduction experiments with CLAS

Status of meson photoproduction experiments

with CLAS

Eugene PasyukJefferson Lab

for the CLAS Collaboration

NSTAR 2013 Workshop Peñiscola, Valencian Community, SpainMay 27-30, 2013

Resonance status for N* and Δ*

• Nearly half the states have only fair or poor evidence!

• Most states need more work to learn details

• Are there missing states?E. Pasyuk NSTAR 2013 Workshop, Peñiscola, May 27-30,

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

Most models predict more resonance states than observed

E. Pasyuk NSTAR 2013 Workshop, Peñiscola, May 27-30, 2013

Baryon Resonance Spectrum

S. Capstik and W. Roberts

Lattice QCD

Mass(π) = 396 MeV

R.G. Edwards et al. Phys. Rev. D84 074508 (2011)

4E. Pasyuk NSTAR 2013 Workshop, Peñiscola, May 27-30, 2013

From the Experiment to Theory

Experimentcross section,

spin observables

TheoryLQCD,

quark models,QCD sum rules,

Reaction Theorydynamical frameworks

Amplitude analysis→multipole amplitudes

→phase shifts

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

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

CEBAF Large Acceptance Spectrometer 1997-2012

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 beamC

Circular polarization from 100% polarized electron beam

Linearly polarized photons: coherent bremsstrahlung on oriented diamond crystal

Circularly polarized beam produced by longitudinally polarized electrons

H. Olsen and L.C. Maximon, Phys. Rev. 114, 887 (1959)

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 small background

HDIce polarized target

γp→π0p, π+nγp→ηp γp→η’pγp→KY (K+Λ, K+Σ0, K0Σ+)γp→π+π-p ωp, ρp, ϕp….

γn→π-pγn→π+π-nγn→Σ-K+ , ΛK0

What we measure with CLAS

See parallel talks:

B1 – E. PhelpsB1 - B. VernarskyC2 – R. TuckerC2 – T. KageaA4 – N. WalfordA4 - C. TaylorA4 – P. MattioneB4 – P. ColeB4 - K. ParkB5 – I. Senderovich

Single pion production

Σ for γp → nπ+

60 1200 60 1200

DU12CM12MAIDBbGa

M. Dugger et al.

Σ for γ p → p π0

DU12CM12MAIDBbGa M. Dugger et al.

Σ for γ p → p π0

DU12CM12MAIDBbGa M. Dugger et al.

Solution A1/2 A3/2

D(1700)3/2- DU12 132 ± 5 108 ± 5CM12 105 ± 5 92 ± 4BnGa 170 ± 20 170 ± 25MD07 226 210PDG12 104 ± 15 85 ± 22

D(1905)5/2+ DU12 20 ± 2 -49 ± 5CM12 19 ± 2 -38 ± 4BnGa 25 ± 5 -49 ± 4MD07 18 -28PDG12 26 ± 11 -45 ± 20

Changes in couplings

T for γ p → n π+

M. Dugger et al.

F for γ p → n π+

• Agreement with predictions get much worse at higher energies

• SAID13 are predictions based on preliminary fits to CLAS pion Σ measurements

(new) (new)

M. Dugger et al.

E for γ p → p π0

• Early stage results• Predictions agree

better at lower energies

M. Dugger et al.

E for γ p → n π+

S. Strauch

PRELIMINARY PRELIMINARY PRELIMINARY PRELIMINARY PRELIMINARY PRELIMINARY

PRELIMINARYPRELIMINARYPRELIMINARYPRELIMINARYPRELIMINARYPRELIMINARY

PRELIMINARYPRELIMINARYPRELIMINARYPRELIMINARYPRELIMINARY

PRELIMINARY

PRELIMINARY PRELIMINARY PRELIMINARY

Predictions worse at higher energies above 1.7 GeV

SAIDSAID (new fit)MAID

Cos(θπc.m.)

W = 1.25 GeV W = 1.27 GeV

W = 1.29 GeV W = 1.31 GeV W = 1.33 GeV W = 1.35 GeV

W = 1.47 GeVW = 1.45 GeV

W = 1.43 GeVW = 1.41 GeVW = 1.39 GeVW = 1.37 GeV

W = 1.49 GeV W = 1.51 GeV W = 1.53 GeV W = 1.55 GeV W = 1.57 GeV W = 1.59 GeV

W = 1.71 GeVW = 1.69 GeVW = 1.67 GeVW = 1.65 GeVW = 1.63 GeVW = 1.61 GeV

W = 1.73 GeVW = 1.75 GeV W = 1.77 GeV W = 1.81 GeV W = 1.83 GeV W = 1.9 GeV

W = 2.19 GeVW = 2.13 GeVW = 2.07 GeV

W = 2.02 GeVW = 1.98 GeVW = 1.94 GeV

W=1.25 GeV

W=1.73 GeV

Σ for γ n → p π-

D. Sokhan

preliminary

Curve - SAIDRed GRAALMagenta and Blue - Erevan 9 out of 40 angular bins are shown

Bins 0.04 in cos and 20 MeV in W

E for γn(p) → pπ-(p) C2 - T. Kageya

η photoproduction

Patrick Collins

Σ for η

SAIDMAID

PRELIMINARY PRELIMINARY PRELIMINARY PRELIMINARY PRELIMINARY

PRELIMINARY

PRELIMINARYPRELIMINARY

PRELIMINARYPRELIMINARYPRELIMINARYPRELIMINARY

PRELIMINARY

PRELIMINARY PRELIMINARY

PRELIMINARY

preliminary

See parallel talks:

C2 – R. TuckerB5 – I. Senderovich

KY production

D. G. Ireland, K. Livingston, B. McKinnon, C. A. Paterson

Σ , Ox , Oz for γ p → K+ Λ

Σ , Ox , Oz for γ p → K+ Σ0

T for γ p → K+ Λ and γ p → K+Σ0

Due to the self-analyzing nature of the , determine many observables using only a linearly polarized beam

Direct measurements of TA4 – N. Walford

+- photoproduction

Photoproduction of π+π -p states • Dominates photoproduction cross section for W >1.6 GeV • 64 observables• 28 independent relations related to helicity amplitude magnitudes• 21 independent relations related to helicity amplitude phases• Results in 15 independent numbers

Could be used for search of resonances that decay into other resonances

Preliminary results: integrated cross section at W from 1.6 to 2.8 GeV

SAPHIR(2005)&ABBHHM(1969)

JLAB g11a within CLAS acceptance

JLAB g11aaccept. corr. applied

Systematic errors from accept. corr. procedure ~8-20%

Integrated cross sections for γp → p

E .Golovach

Differential cross sections for γp → p

Blues dots:Measured cross sections within the CLAS acceptance.

Blue line: JM model* prediction within the CLAS acceptance.Black line: JM model results for 100% acceptance.

Black dots: Estimated cross sections when the contribution from inefficient area was obtained employing phase space approximation.

*Mokeev et al. PRC 80 (2009) 045212

E .Golovach

Differential cross sections for γp → p

Blues dots:Measured cross sections within the CLAS acceptance.

Black dots: Estimated cross sections when the contribution from inefficient area was obtained employing phase space approximation.

E .Golovach

Cross section for γp →pπ+π-

IS for pπ+π-

E=1900-1950 MeV W=2120 MeVOne of 20 energy bins Charles Hanretty

Linearly polarized photons, unpolarized target

I for pπ+π-

S. Strauch et al., PRL. 95, 162003 (2005) W. Roberts and T. Oed, PRC 71, 055201 (2005)A. Fix and H. Arenhovel, EPJA 25, 115 (2005) S. Park

Pz for pπ+π-

W. Roberts and T. Oed, PRC 71, 055201 (2005)A. Fix and H. Arenhovel, EPJA 25, 115 (2005) S. Park

Pz for pπ+π-

W. Roberts and T. Oed, PRC 71, 055201 (2005)A. Fix and H. Arenhovel, EPJA 25, 115 (2005) S. Park

Comparison with model: Pcz

preliminary

A. Fix and H. Arenhovel, EPJA 25, 115 (2005)

Y. Mao

Comparison with model: Psz

preliminary

Y. Mao

A. Fix and H. Arenhovel, EPJA 25, 115 (2005)

Summary 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’ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

K+Λ ✔ ✓ ✓ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

K+Σ0 ✔ ✓ ✓ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

K0*Σ+

✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

“Neutron” targetpπ- ✔ ✓ ✓ ✓ ✓ ✓ ✓

K+Σ- ✓ ✓ ✓ ✓ ✓ ✓ ✓

K0Λ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

K0Σ0 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

✔ - published ✔ - acquired

Data collection with proton and deuteron targets is complete “compete measurement” in pseudoscalar meson

photoproduction is reality In many cases these are the first measurements. In most cases model predictions do not agree with the data

at higher energies Phenomenological and theoretical analyses will have to deal

with tenths of thousands of data points for various observables in different final states.

Summary

NSTAR Workshop

Extras

Polarization observables in pseudoscalar meson production

g14 – E06-101: polarized gamma beams on polarized HD

• Circular and Linear polarized photons• flux up to 108 s-1 tagged (low bkg)• Longitudinally polarized solid HD• P(D) ~ 22%; lifetimes ~ 2 yr• Nov/11 – May/12: 14 billion triggers

R Values for the

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

2 2 2x zR P C C + +

Energy and angle averages are consistent with unity.

No model predicted this CLAS result.

Average R values

1 .0 1 0 .0 1R = ±

Model of effective Lagrangian approach

About the model:•Calculates diff-cross section by using transition amplitudes

•Amplitudes are determined by all the double-pion diagrams

• The diagrams above show the decay from N* resonances.

• Include resonances:

Diagrams of N* for the reaction γN → ππN

Other decays:• N-Born terms• Δ-Born terms

Examples of 2-fold differential g p → p + - cross sections2-fold cross sections within the CLAS acceptance.

Nine one-fold and 18 two-fold differential cross sections have become available for the first time in W-bins of 25 MeV width.

One-fold differential g p → p + - cross sections Blue dots: experimental data within the CLAS acceptanceBlack dots: accounting for the contributions from inefficient areas employing phase space approximationRed dots: extrapolating cross sections into inefficient areas within the framework of the JM model

Two approaches for cross section extrapolation provided close results

recoil polarization P

excitation function

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

M.E. McCracken et al., PRC 81, 025201 (2010)E. Pasyuk NSTAR 2013 Workshop, Peñiscola, May 27-30,

γp→K+Λ: cross section and P

γp→K+Λ: Cx/Cz

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

Comparison with other measurements

Experiment

Final State

W range (Gev)

S P T Ox Oz

CLAS g11K 1.62 – 2.84 N Y N N N

KS 1.69 – 2.84 N Y N N N

LEPSK 1.94 – 2.30 Y N N N N

KS 1.94 – 2.30 Y N N N N

GRAALK 1.64 – 1.92 Y Y Y Y Y

KS 1.74 – 1.92 Y Y N N N

CLAS g8K 1.71 – 2.19 Y Y Y Y Y

KS 1.75 – 2.19 Y Y Y Y Y

Comparison with other measurements

LEPS LEPS

CLAS g8 CLAS g8

Beam Asymmetry Comparison

Beam-Recoil Comparison

Beam Asymmetry

Target Asymmetry

Beam-Recoil, Ox

Beam-Recoil, Oz

Beam Asymmetry

Target Asymmetry

Beam-Recoil, Ox

Beam-Recoil, Oz

Status of meson photoproduction experiments with CLAS

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