Crystal Ball Experiment at MAMIRecent Results
W.J. Briscoe for the A2 Collaboration
(thanks for the sabbatical support)MESONS 2010
SFB443
Overview of MAMI and the Crystal Ball experimental setup Technical capabilities: pion production, strangeness
productionfrom the proton and neutron Selected physics topics:
Coherent pion photoproduction Eta photoproduction
Complete measurements: Transverse spin observables in pion and eta photoproduction Conclusions & Outlook
Overview
MAMI
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.
CB@MAMI Detector System
Crystal Ball
TAPS
PID Detector
MWPCs Target
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: 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)
Technical Capabilities: Kaon Photoproduction
Decay sub-cluster energy
Incident and decay sub-cluster time difference
K+ missing mass
Incident subcluster from K+ ~3ns
Decay sub-cluster from K+→μ+ν
μ decay ~
20ns
Tom JudeEdinburgh University
Coherent π0 photoproduction on 208Pb
Eγ = 160 - 170 MeV Eγ = 190 - 200 MeVEγ = 170 - 180 MeV Eγ = 180 - 190 MeV
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
Prelim
inar
y
Prelim
inar
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Prelim
inar
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Prelim
inar
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Prelim
inar
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Prelim
inar
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Prelim
inar
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Prelim
inar
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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
Excitations of the Nucleon
Δ(1232) Δ(1232)
η photoproduction: γp→ηp
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
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
JLAB ELSA
CB@MAMI preliminary(S. Prakhov)
S11
(1535)JP = 1/2 -
JP = 3/2 -
D13
(1520)
η photoproduction: γp→ηp
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
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
DataG4 totalG4 no nuclear int
Proton scattering angle in graphite
D. P. Watts , Edinburgh D. Glazier, Edinburgh M. Sikora, Edinburgh.D, Howdle, Glasgow
Recoil Polarimetry – π0 Photoproduction
Photon Energy
Deg
ree o
f P
ola
risati
on
Tra
nsfe
r C
x'
p(γ,π0)p polarisation transfer: circ. polarised beam to recoil proton
D. P. Watts, EdinburghD. Glazier, EdinburghM. Sikora, EdinburghD, Howdle, Glasgow
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
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
Polarised Frozen Spin Target
Frozen spin target fully functioning – Polarization > 90%
~1000 hours relaxation time & low He usage – long measurement time!
Running with transverse polarized target!
N. Froemmgen
P=P0exp(t/τ)
First measurement of transverse spin observable F in γp→π0p
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!
N. Froemmgen
EPGPP
PPTP
FPHPP
Pd
d
d
d
circlinz
liny
circlinx
lin
unpol
2sin
2cos
2sin
2cos1
Asymmetry calculated for each bin (above)
Normalized to sin(φ) (target polarization angle corr.)
Weighted average for points with |sin(φ)|>0.3
Background Subtraction on MM(π0)
Eγ = 500 –
600 MeV
Eγ = 400 –
500 MeV
Eγ = 400 – 500 MeV
Eγ = 500 – 600 MeV
Eγ = 300 – 400 MeV
cos(φ
π-9
0)
= s
in (
φπ)
0
First measurement of transverse spin observable F in γp→π0p
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!
PRELIMINARY PRELIMINARY PRELIMINARY
F
First measurement of transverse spin observable F in γp→π0p
SAIDMAID
V. Kashevarov
Conclusions & Outlook
F
PRELIMINARY PRELIMINARY PRELIMINARY
SAIDMAID
F
The CB@MAMI 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...
V. Kashevarov
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
Polarized Target
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
• 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!