Crystal Ball Experiment at MAMI Recent Results W.J. Briscoe for the A2 Collaboration (thanks for the sabbatical support) MESONS 2010 SFB443
Jan 14, 2016
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
y
Prelim
inar
y
Prelim
inar
y
Prelim
inar
y
Prelim
inar
y
Prelim
inar
y
Prelim
inar
y
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!