Baryon Spectroscopy at ELSA. R. Beck, University Bonn for the CBELSA/TAPS Collaboration SPIN 2010, 27.9-2.10, 2010, Jülich. Motivation. Crystal Barrel experiment. Recent Results:. Summary and Outlook. supported by the DFG within the SFB/TR16. Introduction.
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Baryon Spectroscopy at ELSA
R. Beck, University Bonn
for the CBELSA/TAPS Collaboration
SPIN 2010, 27.9-2.10, 2010, Jülich
Motivation
Crystal Barrel experiment
Recent Results:
Summary and Outlook
supported by the DFG within the SFB/TR16
Introduction
3.2 GeV photon beam at ELSA used to study meson photoproduction
- study the nucleon resonance spectrum
Breit Wigner Resonances
Total Photon Absorption Cross Section
Spectroscopic Notation
Isospin
Spin
Introduction
PDG 2010: Status on nucleon resonances
only 7N*and 5D*
established in the region 1400 MeV < W < 2000 MeV
L. Tiator
Energy pattern for the dominant states
Various nucleon models predict many more states
weak coupling to pN final state
Constituent Quark Models
insufficient data base
Dynamical Models
Lattice QCD
Experimental program for N*
Common effort at ELSA, JLab and MAMI,
Precision data for different final states (pp0, pp0p0, ph, ....)
Polarization experiments (beam, target and recoil)
“complete experiment”
g + p -> p + p- + p+
g +p -> p + p0 + p0
g +p -> p + p0
g +p -> K+ + L
g +p -> p + h
Observables in Meson Photoproduction
data only for:
data needed for:
Differential cross section:
s
Target asymmetry:
T
Beam asymmetry:
S
Recoil polarization:
P
Double polarization:
E
Double polarization:
G
Sensitive to:
Sensitive to:
Crystal Barrel experiment at ELSA: polarized photons, polarized targets and 4p acceptance
(W. Hillert, F. Klein)
Experiments at ELSA
R. Johnstone,
Parallel Session E, Monday 29.9.
Crystal Barrel Set Up at ELSA
Crystal Barrel Set Up at ELSA
Close to 4p coverage
Polarized Photons
Linearly polarized photons:
- coherent bremsstrahlung
- diamond radiator
Circularly polarized photons:
- longitudinally polarized electrons
- helicity transfer to photon
Linearly polarized photons
Circularly polarized photons
high polarization at
low photon energies
high polarization at
high photon energies
(H. Eberhard)
(S. Kammer)
Butanol (C4H9OH)
Polarized Target
„Frozen Spin Target“
First operating horizontal cryostat with
integrated solenoid to freeze up the spin
Target: Butanol (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. Goertz
Bochum: W. Meyer, S. Reichertz
Polarized Target
Running time over 2500 hours in year 2008
over 2200 hors in year 2009
High. polarization P+ = 83.4 %
P- = - 80.9 %
fast build-up05h04min (May/June) 05h39min (August)
Pol.-time06h10min
horizontal cryostat
in experimental area
data taking
Polarization Observables
Linearly polarized photons -> beam asymmetry S
Circularly polarized photons
-> double polarization asymmetry E
Longitud. polarized protons
Linearly polarized photons
-> double polarization asymmetry G
Longitud. polarized protons
Crystal Barrel experiment at ELSA: New preliminary results for G and E
CBELSA/TAPS Results for ph
V. Crede, O. Bartolomy et al.,
PRL 94 (2005) 012004,
EPJ A33 (2007) 133
Meson photoproduction
Photon helicity couplings: A1/2 und A3/2
S11(1535) : A1/2 (S11(1535)) only
Total cross section:
stot ~ |A1/2(S11)|2 + |A1/2(P13)|2 + |A3/2(P13)|2 + …..
D13(1520) : A1/2 (D13(1520)) and A3/2(D13(1520))
P13(1720) : A1/2 (P13(1720)) and A3/2(P13(1720))
Σ
η-MAID
D15(1675)
Eγ=1250 MeV
D13(1520)
Σ
D13(1520)
BoGa PWA
P13(1720)
θηcm
Θcm
CBELSA/TAPS Results for ph
Beam asymmetry: S
Higher sensitivity because of interference
between different resonance contributions
S~ A1/2(S11) * A1/2(P13)+ …..
D. Elsner et al., EPJ A33 (2007) 147
P11(1710)
S11 (1535)
P11 (1710)
P13 (1720)
Helicity dependent cross section for ph
reaction:
circularly polarized photons
longitudinally polarized proton
Preliminary results(J. Müller)
N1/2 - N3/2
no acceptance
correction
S11 (1535)
P11 (1710)
P13 (1720)
Helicity dependent cross section for ph
reaction:
circularly polarized photons
longitudinally polarized proton
Helicity dependent cross section for ph
reaction:
Preliminary results(J. Müller)
Angular distribution
N1/2 - N3/2
count rate difference
no acceptance correction
S- and G- Asymmetry for ph
Eg=1050 MeV
reaction:
missing mass cut
fit to the f-distribution
Preliminary results
(A. Thiel, M. Grüner)
Eg=1050 MeV
Eg=1050 MeV
__BoGa
G
S
__ SAID
__ MAID
S- and G- Asymmetry for ph
__BoGa
linearly polarized photons
reaction:
__ SAID
longitudinally polarized proton
Preliminary results
(A. Thiel, M. Grüner)
__ MAID
S
S
S
Eg=850 MeV
Eg=1050 MeV
Eg=950 MeV
G
G
G
Eg=850 MeV
Eg=1050 MeV
Eg=950 MeV
P33 (1232)
F15 (1680)
S11 (1535)
Helicity dependent cross section for pp0
reaction:
circularly polarized photons
longitudinally polarized proton
count rate difference
acceptance correction
Preliminary results(M. Gottschall)
N1/2 - N3/2
with acceptance
correction
+ …
Helicity dependent cross section for pp0
reaction:
Angular distributions sensitive to interference between resonances
Preliminary results(M. Gottschall)
N1/2 - N3/2
N1/2 + N3/2
with acceptance
correction
prediction
partial wave analysis
__MAID
__ SAID
__ BoGa
Polarization Observables
S and G-Asymmetry for pp0
Missing Mass
reaction:
missing mass cut
fit to the f-distribution
Preliminary results CB(A. Thiel)
GRAAL data
Eg=1000 MeV
Eg=1000 MeV
__BoGa
__ SAID
S
G
__ MAID
S and G-Asymmetry for pp0
linearly polarized photons
reaction:
longitudinally polarized proton
Eg=966 MeV
Eg=1000 MeV
Preliminary results
(A. Thiel)
S
S
GRAAL data
prediction
partial wave analysis
G
G
__BoGa
__ SAID
__ MAID
S and G-Asymmetry for pp0
reaction:
Eg=1033 MeV
Eg=1066 MeV
Preliminary results
(A. Thiel)
S
S
GRAAL data
prediction
partial wave analysis
Eg=1033 MeV
Eg=1066 MeV
G
G
__BoGa
__ SAID
__ MAID
S and G-Asymmetry for pp0
reaction:
Eg=1100 MeV
Eg=1133 MeV
Preliminary results
(A. Thiel, M. Grüner)
S
S
GRAAL data
prediction
partial wave analysis
G
G
__BoGa
__ SAID
__ MAID
Energy dependence
Beam-Asymmetry S at q = 110
__without P11 (1440)
__ without D13 (1520)
__ without F15 (1680)
S
Double-Polarization-Asymmetry G at q = 110
Eg in MeV
G
Preliminary results
(A. Thiel, M. Grüner)
Eg in MeV
World Data Base
reaction:
Beam asymmetry S
Differential cross section
First round of double polarization
experiments with CB at ELSA:
Energy range for G: 600- 1300 MeV
Energy range for E: 500- 2100 MeV
Asymmetry E
Asymmetry G
Future plans for CB at ELSA:
Extend energy range to 3 GeV
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Transversally polarized target
Installed and first data taken
Measurements on the neutron
polarized deuteron target
Targetasymmetry in ph
Targetasymmetry in ph
Targetasymmetry in ph
Electromagnetic excitation off the neutron
Electromagnetic excitation off the neutron
ELSA data, I. Jaegle, B. Krusche
Experimental evidence from other Labs
New high statistics measurement at MAMI C
Comparison Narrow Structure
Effect of photo-excitation of D15(1675) ?
Coupled channel effect of S11(1535) and P11(1710) ?
Interference effect of S11(1535) and S11(1650) ?
New narrow state with stronger photo-coupling to the neutron ?
-> polarization observables needed !!
Summary
First round of double polarization experiments
with CBELSA/TAPS at ELSA
Preliminary results for the double polarization
observable G and E
Model independent partial wave analysis
polarization observables are essential
different final states are essential
Will shed new light on the nucleon excitation spectrum
Complete Experiment
8 well chosen observable have to be measured to determine the production amplitudes (F1,F2,F3 and F4)
p- threshold until D+(1232)- region
additional constraints:
(a) s- and p- wave approximation
(b) Fermi- Watson theorem
same I, J in the final state
same scattering phase dIJ
two observable sufficient for “complete experiment”
differential cross section : ds/dW
beam asymmetry : S
above pp- threshold
Fermi- Watson theorem not valid any more
More observable needed to find unique partial wave solution
Double Polarization Experiment for G
reaction:
linearly polarized photons
longitudinally polarized proton
Clear effect from G observed
Helicity dependent cross section
reaction:
circularly polarized photons
longitudinally polarized proton
Preliminary results(D. Piontek)
N1/2 - N3/2
Crystal Barrel/TAPS Results
V. Crede, O. Bartolomy et al.,
PRL 94 (2005) 012004,
EPJ A33 (2007) 133
Meson photoproduction
S11(1535)
GRAAL
S11(1650)
D15(2070)
CB-ELSA
MAMI
CLAS
PWA
Photon helicity couplings: A1/2 und A3/2
Total cross section:
stot ~ |A1/2(S11)|2 + |A1/2(D13)|2 + |A3/2(D13)|2 + …..
S11(1535) : A1/2 (S11(1535)) only
D13(1520) : A1/2 (D13(1520)) and A3/2(D13(1520))
Bonn-Gatchina-Model Analysis
S-wave coupled channel model