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SFB443. Crystal Ball Experiment at MAMI Recent Results W.J. Briscoe for the A2 Collaboration (thanks for the sabbatical support) MESONS 2010. Overview. Overview of MAMI and the Crystal Ball experimental setup Technical capabilities: pion production, strangeness production

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SFB443

Crystal Ball Experiment at MAMI

Recent Results

W.J. Briscoe

for the A2 Collaboration

(thanks for the sabbatical support)

MESONS 2010


Overview

  • Overview of MAMI and the Crystal Ball experimental setup

  • Technical capabilities: pion production, strangeness production

  • from the proton and neutron

  • Selected physics topics:

  • Coherent pion photoproduction

  • Eta photoproduction

  • Complete measurements: Transverse spin observables in pion and eta photoproduction

  • Conclusions & Outlook



MAMI

  • Maximum Energy 1604 MeV, ΔE = 100 KeV

  • 100 % duty cycle

  • Current ≤ 100 μA

  • Electron Polarization ~ 85%

  • ~7000 hours beam / year


Photon Tagging Facility

  • Detection of radiating electrons: Eγ = Ee – Ee'

  • Energy resolution 2-4 MeV

  • Tagger Microscope ~6x better E res.

  • Circularly pol. γ from e- pol, upto 85%

  • Linearly pol. γ from crystalline rad., upto 70%

  • Collimation upgrade will give +5% pol.

  • End Point Tagger awaiting funding

Pe-→Pγcirc.



Technical Capabilities: Incoherent π0 photoproduction on 12C

Decay γ spectrum in coinc. with π0 4.4 MeV 2+ state

γ12C→12 C* π0

12C γ(4.4 MeV)

  • First report of σ(γ,π0) for a specific excited state

  • Simultaneous detection of π0 and 4.4 MeV decay γ in CB

  • Important first step in isolation of coherent process

  • PRL 100, 132301 (2008)


Technical Capabilities: Kaon Photoproduction

Incident and decay sub-cluster time difference

Decay sub-cluster energy

Incident subcluster from K+ ~3ns

Decay sub-cluster from K+→μ+νμ decay ~ 20ns

K+ missing mass

Tom Jude

Edinburgh University

  • No time left to discuss: Recoil polarimetry: γN→πN', γN→ηN', determination of η mass,GDH integral on the neutron, in-medium modification of mesons, threshold hyperon production, double pion production and so much more...


Coherent π0 photoproduction on 208Pb

Preliminary

Preliminary

Preliminary

Preliminary

Eγ = 160 - 170 MeV

Eγ = 170 - 180 MeV

Eγ = 180 - 190 MeV

Eγ = 190 - 200 MeV

Preliminary

Preliminary

Preliminary

Preliminary

  • Do heavy stable nuclei have a neutron skin?

  • Size of skin gives direct information on equation of state of n-rich matter

  • Skin size gives important new insights into neutron star physics!

  • Measurements planned on Sn, Ca isotope chains

  • Accuracy ~0.05 fm

    D. P. Watts and C. Tarbert, Edinburgh


Excitations of the Nucleon

Δ(1232)

Δ(1232)

  • Many resonances: broad and overlapping

  • Accurate separation of final states → good detector resolution

  • Sensitivity to small σ processes→ 4π detector acceptance, large γ flux

  • Access to polarization observables → polarized beam, target, recoil


TAPS at MAMI

CB at ELSA

[email protected] preliminary

η photoproduction: γp→ηp

TAPS/MAMI

GRAAL/ESRF

CLAS/JLAB

CB/ELSA

  • S11(1535) dominant resonance in η production

  • “Dip” in cross section due to interference with less dominant resonances

  • Need polarization observables to extract full resonance composition


η photoproduction: γp→ηp

S11(1535)

JLAB

ELSA

[email protected] preliminary

(S. Prakhov)

JP = 1/2 -

JP = 3/2 -

D13(1520)

  • S11(1535) dominant resonance in η production

  • “Dip” in cross section due to interference with less dominant resonances

  • Need polarization observables to extract full resonance composition


Complete Experiment

  • 16 possible unpolarised, single & double polarization observables in pseudoscalar meson photoproduction

  • Need 8 carefully selected observables to fully constrain partial wave analyses

  • These have to include single & double polarization observables

  • All polarization degrees of freedom now uniquely accessible in Mainz!


Recoil Polarimetry

Data

G4 total

G4 no nuclear int

Proton scattering angle in graphite

  • π0 / η decays & is detected as normal

  • Reconstruct π0 / η

  • Recoiling proton then tagged

  • Preconstructed = γbeam + ptarget – π0

  • Large scattering angle → nucl. interaction

  • Asymmetry gives pol. transfer

D. P. Watts , Edinburgh

D. Glazier, Edinburgh

M. Sikora, Edinburgh.

D, Howdle, Glasgow


Recoil Polarimetry – π0 Photoproduction

Degree of Polarisation Transfer Cx'

Photon Energy

  • p(γ,π0)p polarisation transfer: circ. polarised beam to recoil proton

D. P. Watts, Edinburgh

D. Glazier, Edinburgh

M. Sikora, Edinburgh

D, Howdle, Glasgow

  • No time left to discuss: Recoil polarimetry: γN→πN', γN→ηN', determination of η mass,GDH integral on the neutron, in-medium modification of mesons, threshold hyperon production, double pion production and so much more...


Polarized Frozen Spin Target

H. Ortega Spina

  • Uses DNP to achieve ~ 90 % proton, 80 % deuteron

  • Needs: Horiz. Dilution cryostat, polarizing magnet, microwave, NMR

  • Two holding coils: solenoid → longitudinal, saddle coil → transverse


Polarised Frozen Spin Target

  • Uses DNP to achieve ~ 90 % proton, 80 % deuteron

  • Needs: Horiz. Dilution cryostat, polarizing magnet, microwave, NMR

  • Two holding coils: solenoid → longitudinal, saddle coil → transverse


Polarised Frozen Spin Target

N. Froemmgen

P=P0exp(t/τ)

  • Frozen spin target fully functioning – Polarization > 90%

  • ~1000 hours relaxation time & low He usage – long measurement time!

  • Running with transverse polarized target!


First measurement of transverse spin observable F in γp→π0p

N. Froemmgen

  • F asymmetry: circ. polarised photons, transverse pol. Target

  • Need to seperate out contribution from 12C and 16O and 3/4He

  • Requiring proton removes coherent contributions

  • Other kinematic cuts and remaining underground fitted & subtracted

  • Data shown from 39 hours minus, 39 hours plus pol. test data, no TAPS

  • Test beamtime ended 07:00 08.03.10, results first shown 10:00 10.03.10

  • VERY PRELIMINARY!


First measurement of transverse spin observable F

in γp→π0p

Background Subtraction on MM(π0)

Eγ = 300 – 400 MeV

Eγ = 400 – 500 MeV

cos(φπ-90) = sin (φπ)

Eγ = 400 –

500 MeV

0

Eγ = 500 – 600 MeV

  • Asymmetry calculated for each bin (above)

  • Normalized to sin(φ) (target polarization angle corr.)

  • Weighted average for points with |sin(φ)|>0.3

Eγ = 500 –

600 MeV


First measurement of transverse spin observable F

in γp→π0p

SAID

MAID

F

PRELIMINARY

PRELIMINARY

PRELIMINARY

V. Kashevarov

  • World first measurement of F – VERY PRELIMINARY!

  • Need more work on Pγ (currently standard conditions assumed)

  • Need to extend to full solid angle coverage (measure with TAPS)

  • Ptarg from average over time – need event-by-event normalisation

  • However – everything works!


Conclusions & Outlook

SAID

MAID

PRELIMINARY

PRELIMINARY

PRELIMINARY

F

F

V. Kashevarov

  • The [email protected] experimental setup is a highly flexible 4π detector system

  • Complete measurements of π and η production within next five years

  • Allow full investigation of: P33(1232), P11(1440), S11(1535)

  • Double meson production (ππ, πη)→ other resonance studies e.g. D33(1700)

  • Compton scattering: access to nucleon vector polarisabilities

  • Strangeness photoproduction, coherent π0 studies of isotope chains

  • η/η' decays & more...

  • The [email protected] experimental setup is a highly flexible 4π detector system

  • Complete measurements of π and η production within next five years

  • Allow full investigation of:P33(1232), P11(1440), S11(1535),

  • Double meson production ( π→ broad range of new resonance studies P33(1232), S11(1535), D33(1700)!


Polarized Target

2 cm

  • Uses DNP to achieve ~ 90 % proton, 80 % deuteron

  • Needs: Horiz. Dilution cryostat, polarising magnet, microwave, NMR

  • Two holding coils: solenoid → longitudinal, saddle coil → transverse

  • Detectors have to move


Polarized Target

  • Uses DNP to achieve ~ 90 % proton, 80 % deuteron

  • Needs: Horiz. Dilution cryostat, polarising magnet, microwave, NMR

  • Two holding coils: solenoid → longitudinal, saddle coil → transverse

  • Detectors have to move



Polarised Target

  • Uses DNP to achieve ~ 90 % proton, 80 % deuteron

  • Needs: Horiz. Dilution cryostat, polarising magnet, microwave, NMR

  • Two holding coils: solenoid → longitudinal, saddle coil → transverse

  • Detectors have to move


Conclusions
Conclusions

  • We are running a full program of Transverse proton and neutron (deuteron) polarized target measurements. (Longitudinal will follow.)

  • Circularly and linearly polarized tagged photons.

  • Have preliminary results for F.

  • MAMI B and MAMI C experiments are being analyzed and prepared for publication by a large group of students.

  • Expect at least a 5 year program with CB and TAPS at MAMI!


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