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New Results in MesonNew Results in Meson--PhotoproductionPhotoproductionppat ELSA at ELSA
R. Beck, University Bonn
MENU 2010, 31.5-4.6, 2010, Williamsburg
Motivation
Crystal Barrel experiment
Recent Results
Summary and Outlook
supported by the DFG within the SFB/TR16
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IntroductionIntroduction3.2 GeV photon beam at ELSA used to study meson photoproduction
- study the nucleon resonance spectrum
Total Photon Absorption Cross SectionBreit Wigner Resonances
JIX 22
Spectroscopic Notation
Isospin
SpinJIX 22
K);1();0( === ππ lPlSX
Spin
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IntroductionIntroduction
only 7only 7 N*N* and 5and 5 ΔΔ**
PDG 2010: Status on nucleon resonances
only 7only 7 NN and 5and 5 ΔΔ
established in the region 1400 MeV < W < 2000 MeVestablished in the region 1400 MeV < W < 2000 MeV
L. Tiator
Energy pattern for the dominant states
Constituent Quark Models
Various nucleon models predict many more states
weak coupling to πN final state Dynamical Models
Lattice QCD
p ginsufficient data base
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Experimental program for N*Experimental program for N*
Precision data for different final states (pπ0, pπ0π0, pη, ....)
Common effort at ELSA, JLab and MAMI,
P l i ti i t (b t t d il)Polarization experiments (beam, target and recoil)“complete experiment”
Xp →+γ pγ
γ + p −> p + π− + π+
γ + p −> p + π0 + π0γ p pγ + p −> p + π0
γ + p −> K+ + Λ γ + p −> p + η
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Complete ExperimentComplete Experimentπγ +→+ NN
rr
8 well chosen observable have to be measured to determine the production amplitudes (F1,F2,F3 and F4)
π- threshold until Δ+(1232)- region
additional constraints:additional constraints:
(a) s- and p- wave approximation
(b) Fermi- Watson theorem(b) Fermi Watson theorem
πγ +→+ NNππ +→+ NN
same I, J in the final statesame scattering phase δIJ
two observable sufficient for “complete experiment”differential cross section : dσ/dΩ
b t Σ
above ππ- threshold
beam asymmetry : Σ
Fermi- Watson theorem not valid any moreMore observable needed to find unique partial wave solution
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Observables in Meson PhotoproductionObservables in Meson PhotoproductionPhoton polarization
Targetpolarization
Recoil nucleonpolarization
Target and recoil polarizations
X Y Z(beam) X’ Y’ Z’ X’ X’ Z’ Z’X Z X Z
unpolarizedlinearcircular
σΣ
- T -H (-P) GF E
- P -Ox (-T) Oz
C C
Tx Lx Tz Lz
(-Lz) (Tz) (Lx) (-Tx)circular - F - E Cx - Cz - - - -
data only for: data needed for:
Differential cross section:
Beam asymmetry:
σΣ
Target asymmetry:
Recoil polarization:
TP
Double polarization:
Sensitive to: )Re( 21 PP ⋅
E Double polarization:
Sensitive to: )Im( 21 PP ⋅
G)e( 21 )( 21
Crystal Barrel experiment at ELSA: polarized photons, polarized targets and 4π acceptance
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Crystal Barrel Set Up at ELSACrystal Barrel Set Up at ELSA
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Crystal Barrel Set Up at ELSACrystal Barrel Set Up at ELSA
03πη
γγη
→
→γγπ →0• Crystal Barrel detector
1230 CsI crystals 3πη →
• Inner-detectorcylinder of 513 scintillating fibers
1230 CsI crystals
cylinder of 513 scintillating fibers
• forward detector (FWPlug)90 CsI crystals with PM’s 120-30090 CsI crystals with PM s, 12 -30
• forward detector (MiniTAPS)216 BaF2 10-120 216 BaF2 , 1 12
Close to 4π coverage
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Polarized PhotonsPolarized PhotonsLinearly polarized photons:
- coherent bremsstrahlung- diamond radiator
Circularly polarized photons:- longitudinally polarized electrons - helicity transfer to photond a o d ad a o e c y a s e o p o o
Linearly polarized photons Circularly polarized photons
%70=Linpγ%65=Cirpγhigh polarization at
low photon energies high polarization at high photon energies
(H. Eberhard) (S. Kammer)
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Polarized TargetPolarized Target
internal superconducting 'holding coil’liquid helium from the still„Frozen Spin Target“
m
target
horizontal cryostat with integrated solenoidf h i
60 m
mbeam
Target: Butanol (C4H9OH)
to freeze up the spin
100 mmButanol (C4H9OH)Polarization: DNP at high B-field (2.5 T)
„freeze“ up the spin (0.4 T)relaxation time T~500h
Bonn: H. Dutz, S. GoertzBochum: W. Meyer, S. Reichertz
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Polarized TargetPolarized TargetRunning time over 2500 hours in year 2008
over 2200 hors in year 2009
High. polarization P+ = 83.4 %P- = - 80.9 %
f t b ild 05h04 i (M /J )fast build-up 05h04min (May/June) 05h39min (August)
Pol.-time 06h10min
horizontal cryostatin experimental area
data takingg
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Polarization ObservablesPolarization Observables
Linearly polarized photons −> beam asymmetry Σ
Circularly polarized photonsLongitud. polarized protons
−> double polarization asymmetry E
Linearly polarized photonsLongitud. polarized protons
−> double polarization asymmetry G
Crystal Barrel experiment at ELSA: New preliminary results for G and E
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Crystal Barrel/TAPS ResultsCrystal Barrel/TAPS ResultsBeam asymmetry: Σ Higher sensitivity because of interference
between different resonance contributions Σ ~ A1/2(S11) ∗ A1/2(P13) + …..
ηγ +→+ ppr
η MAID
D. Elsner et al., EPJ A33 (2007) 147
η-MAID
D15(1675)
Σ
D13(1520)
D15(1675)
Σ
Eγ= 1250 MeV
D13(1520)
BoGa PWAP13(1720)
Θcmθηcm
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Helicity dependent total cross sectionHelicity dependent total cross sectionXp →+
rrγreaction:
circularly polarized photonslongitudinally polarized proton
P33 (1232)
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Helicity dependent cross sectionHelicity dependent cross section0πγ +→+ pprr
reaction:circularly polarized photonslongitudinally polarized proton
count rate differencepreliminary acceptance correction
P33 (1232)
Preliminary results (M. Gottschall)
S (1535)
p y p
S11 (1535)
N1/2 - N3/2
F15 (1680) + …
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Helicity dependent cross sectionHelicity dependent cross section
Preliminary results (M. Gottschall)
Angular distributions sensitive to interference between resonances0πγ +→+ pprrreaction:
N NN1/2 - N3/2
count rate differencewith acceptance correctionp
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Helicity dependent cross sectionHelicity dependent cross sectionηγ +→+ pprr
reaction:circularly polarized photonslongitudinally polarized proton
Preliminary results (M. Gottschall)
S11 (1535)
P11 (1710)
P13 (1720)
N1/2 - N3/2
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Helicity dependent cross sectionHelicity dependent cross section
Preliminary results (M. Gottschall)
ηγ +→+ pprrreaction:
N NN1/2 - N3/2
count rate difference
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Polarization ObservablesPolarization Observables
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Double Polarization Experiment for GDouble Polarization Experiment for Gσσ dd
0πγ +→+ pprrti
))2sin()2cos(1()(),( φφθσφθσγγ ⋅−⋅Σ−
Ω=
ΩGppp
dd
dd
zLinLin
πγ +→+ ppreaction:
linearly polarized photonslongitudinally polarized protong y p p
Clear effect from G observed
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GG--Asymmetry for pAsymmetry for pππ00
Eγ=1050 MeV 0πγ +→+ pprrreaction:
missing mass cut
fit to the φ-distribution
Preliminary results CB (A Thiel)
))2sin()2cos(1()(),( φφθσφθσγγ ⋅−⋅Σ−
Ω=
ΩGppp
dd
dd
zLinLin
E =1050 MeV E =1050 MeV
Preliminary results CB (A. Thiel)GRAAL data
Eγ=1050 MeV Eγ=1050 MeV
GΣ__ SAID
__ MAID
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Asymmetries for pAsymmetries for pππ00
0 linearly polarized photons
Eγ=966 MeV Eγ=1000 MeVP li i lt
0πγ +→+ pprrreaction:
linearly polarized photonslongitudinally polarized proton
Σ Σ
Preliminary results(A. Thiel)
GRAAL dataGRAAL data
predictionpartial wave analysis
__ BoGa
__ SAID
G G
__ MAID
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Asymmetries for pAsymmetries for pππ00
0
Eγ=1033 MeV Eγ=1066 MeV
0πγ +→+ pprrreaction:
P li i lt
Σ Σ
Preliminary results(A. Thiel)
GRAAL dataGRAAL data
predictionpartial wave analysis
Eγ=1033 MeV Eγ=1066 MeV
__ BoGa
__ SAID
GG
__ MAID
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Asymmetries for pAsymmetries for pππ00
0
E =1100 MeV E =1133 MeV
0πγ +→+ pprrreaction:
P li i ltEγ=1100 MeV Eγ=1133 MeV
Σ Σ
Preliminary results(A. Thiel)
GRAAL dataΣ Σ GRAAL data
predictionpartial wave analysis
__ BoGa
__ SAID
G G
__ MAID
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Energy dependenceEnergy dependenceBeam-Asymmetry Σ at θ = 90
__ without P11 (1440)
__ without D13 (1520)
__ without F15 (1680)
Double Polarization Asymmetry G at θ = 90Double-Polarization-Asymmetry G at θ = 90
Preliminary results(A. Thiel)
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Asymmetries for pAsymmetries for pηη
Eγ=1050 MeV ηγ +→+ pprrreaction:
missing mass cut
fit to the φ-distribution
))2sin()2cos(1()(),( φφθσφθσγγ ⋅−⋅Σ−
Ω=
ΩGppp
dd
dd
zLinLin
E =1050 MeVE =1050 MeV Eγ=1050 MeVEγ=1050 MeV
GΣ__ SAID
__ MAID
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Asymmetries for pAsymmetries for pηη
ηγ +→+ pprrreaction: linearly polarized photons
longitudinally polarized proton
Eγ=850 MeV Eγ=950 MeV Eγ=1050 MeVPreliminary results (A. Thiel HK69.6)
ΣCB (D. Elsner)
__ BoGa
Eγ=850 MeV Eγ=950 MeV Eγ=1050 MeVprediction
partial wave analysis
G __ SAID
MAID
G G
__ MAID
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World Data BaseWorld Data Base0πγ +→+ pprr
reaction:
BffFirst round of double polarizationexperiments with CB at ELSA:
Energy range for G: 600 1300 MeV
Beam asymmetry ΣDifferential cross section
Energy range for G: 600- 1300 MeV
Energy range for E: 500- 2100 MeV
Future plans for CB at ELSA:Asymmetry E Asymmetry G
p
Extend energy range to 3 GeV ∗∗∗∗∗
∗∗∗∗∗∗
∗∗∗∗
Transversally polarized target Installed and tested
∗∗
∗∗
∗∗∗
Installed and tested
Measurements on the neutron polarized deuteron target
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TargetasymmetryTargetasymmetry in in η η ProductionProduction
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Electromagnetic excitation off the neutronElectromagnetic excitation off the neutron
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Electromagnetic excitation off the neutronElectromagnetic excitation off the neutron
ELSA data, I. Jaegle, B. Krusche
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Comparison Narrow Structure Comparison Narrow Structure
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SSummary
First round of double polarization experimentswith Crystal Barrel at ELSA
Preliminary results for the double polarization observable G and E
Aim: reach “complete” experiment
Model independent partial wave analysis
Will shed new light on the nucleon excitation spectrum
Model independent partial wave analysis