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Baryon Spectroscopy at ELSA

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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

- Crystal Barrel Set-Up

- BGO-OD Set-Up

R. Johnstone,

Parallel Session E, Monday 29.9.

Crystal Barrel Set Up at ELSA

Crystal Barrel Set Up at ELSA

- Crystal Barrel detector
- 1230 CsI crystals

- Inner-detector
- cylinder of 513 scintillating fibers
- forward detector (FWPlug)
- 90 CsI crystals with PM’s, 120-300

- forward detector (MiniTAPS)
- 216 BaF2 , 10-120

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

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

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