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Institut
für Kernphysik
Annual Meeting of the GDR PH-QCD
27. November 2013
Saclay
Andreas Thomas
Review on the last developments
on polarized targets at Mainz
1.- Exp. Boundary Conditions: What do we want to measure? How?
2.- Polarised Solid Target: a) Frozen Spin Target at MAMI
b) Cryogenics
c) New Magnet Technology
d) New Active Target Material
3.- Conclusion and outlook
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Picture of a Proton (Skale fm). Standard Model
QCD Colourless objects:
Baryons (qqq)
Mesons (qq)
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Löhrig, Metsch, Petry, Eur.Phys.J. A10 (2001) 395-446
Introduction: Excitation Spectrum of the Nucleon
H
The light baryon spectrum in a relativistic quark model
He Hg
Atom Nucleon
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E[eV] E[GeV]
S11(1535)
P33(1232)
Hydrogen Atom Nucleon
G ~ 10-6 eV
MeV120G
Lifetime
G
sMeV 2210582.6
s2410 ~ 10-8 s
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Polarisation
Observables
Disentangle broad, overlapping resonances,
Measure meson threshold production, quark mass ratios,
Determine fundamental properties: Spin Polarisibiltities,
GDH sumrule.
Beam Target
s
p p p
g g g g
E G P
P T P
F H P
d
d P
P P P
z
y
x
unpol
circ lin lin
unpol
- -
- -
- -
- -
4 ,
4
2 , 0 Target
Beam
S
W
+
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[C.Bradtke et al., NIM A436, 430 (1999)]
Bonn Frozen Spin Target at A2 / MAMI First measurement of GDH sum rule.
Polarisation observable E with 4 p detector
DAPHNE.
Prototype for CLAS/FROST and MPT.
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Helicity Dependence E of Meson Photoproduction on the Proton and Neutron
GDH sum rule on Proton and Neutron
100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850
-200
-100
0
100
200
300
400
500
600
total
pp
p+n
p+p
p
p+p
n
pp
p
MAID2000 (pN)
Phys. Rev. Lett. 84 (2000) 5950
Phys. Rev. Lett. 87 (2001) 022003
Phys. Rev. Lett. 88 (2002) 232002
Physics Letters B 624 (2005) 173-180
Eur. Phys. J. A 34, 11-21 (2007)
GDHs
-
s
(b)
photon energy (MeV)
Published data: GDH-Experiment at ELSA and MAMI (DAPHNE).
Preliminary results: ’Crystal Barrel ’ and ’CLAS’ for E > 500 MeV.
’LEGS experiment at BNL Brookhaven’ in the P33(1232) region.
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4p photon Spectrometer @ MAMI
TAPS:
366 BaF2 detectors
72 PbWO4 detectors
Max. kin. energy:
p+- : 180 MeV
K+- : 280 MeV
P : 360 MeV
Crystal Ball:
672 NaJ detectors
Max. kin. energy:
+- : 233MeV
p+- : 240 MeV
K+- : 341 MeV
P : 425 MeV
Vertex detector:
2 Cylindr. MWPCs
480 wires, 320stripes
PID detector:
24 thin plastic
detectors gp S ph
ppp
gggggg
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He3/He4 Roots
4000m3/h
Vacuum system
Mikrowaves
70GHz
Dynamic
Nuclear
Polarization
NMR-Apparatus
106MHz
Polarisation meas.
Components of the polarized
target
for the Crystal Ball detector
Horizontal He3/He4
Dilutionrefrigerator
(30mKelvin)
with internal
Holding coil
Superconducting
Polarization magnet
5Tesla
Targetmaterial
H-Butanol D-Butanol
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Polarized Target for Crystal Ball
Tagged CW photon beam 4p- detector
Frozen spin target (26 mKelvin achieved).
Pproton ~ 85%
Pdeuteron~75%
All directions of polarization.
~1000 ….2000 hours
sec105 7 g
New 3He4He-Dilution refrigerator
(in collaboration with JINR Dubna)
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Cryogenics
Evaporation cooling
2 Precooling stages:
Evaporator
(1.5Kelvin)
Separator
(4.2Kelvin pot)
3He4He-Dilution refrigerator
Dilution circuit
(0.03Kelvin)
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Alignment thermal radiation shields
Alignment still and evaporator
Impressions from
the technical realisation
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Cryostat Performance
Temperature stability:
DT ~ +- 0.2mKelvin (one day)
(typical one week measurement period).
T=24mK
T=27mK
T=29mK
Dt=40h
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Transverse
And
Longitudinal
Internal
Holding coil
1.2 Kelvin
1Tesla at 46A
achieved
Magnet Technology
Separator (4.2Kelvin)
Evaporator (1.5Kelvin)
Mixing chamber(25mK)
Still (0.7K)
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Holding Coil
Coil has to be as thin as
possible to allow low
energetic particles
to punch through.
Subcooled Superconductor
F54-1.35(0.20)TV
jcrit
B
T
@4.2Kelvin
@1.3Kelvin
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• Copper/scandium wire with 54 Nb-Ti filaments embedded in it.
• Cu:Sc=1.35:1
• Alloy composition: Nb47wt.%Ti
• Diameter=0.222mm
• It achieves currents up to 50A at 4.2K and 1T.
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Simulation and Optimisation Transverse Field
cos)(JIdeal case for dipole magnet: 4-layer dipole:
N1=N2=138
N3=N4=78
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Production
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150mm
4-layer dipole:
N1=N2=138
N3=N4=78
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Transverse (Saddle coil)
and
Longitudinal (Solenoid)
Internal
Holding Field (1.2K, 0.6T)
DNP at 200mK and 2.5T with 70GHz microwaves.
Frozen spin target (25mKelvin, 0.6T).
Secondary particles punch through holding coil.
All directions of polarization.
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Cryostat
Polarizing magnet
Crystal Ball
1. External magnet 2.5 T
2. Polarize with microwaves
3. Internal holding coil 0.7 T
4. Remove external magnet
5. Move CB detector in.
6. Data taking.
7. Repolarization
Polarizing magnet
Microwaves Microwaves
Frozen Spin Target Waltz
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Setup in the A2 - Taggerhall
Movable
Crystal Ball
4p-
Photon
Detector
Cryostat
Movable
5Tesla
Polarising
Magnet
First Beam with Transverse Polarisation started 15th December 2009.
In 2010/11 we had more than 5000 hours beam on this target. Longitudinal Target since July 2013.
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Perspectives: Internal Polarising Coil
DNP at 200mK and 2.5T
with 70GHz microwaves.
10Layer coil at 50A.
Secondary particles punch
through holding coil.
Higher momentum threshold.
Problem is the required field homogeniety
of 10-E4. Notched solenoid.
3d finite element calculation, optimisation
and precise production needed.
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2cm
HHHH
HOCCCCH
HHHH
Butanol
X-ray picture with
Beamspot and
NMR coil
Target Material Technology
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Target material D-Butanol Density and species of the radicals
are very important for: •maximum degree of polarization
•polarization build up times •relaxation times
Trityl-Radikal
Highest Deuteron
polarisation due to
new
doping material with
narrow ESR from
Bochum.
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Vacuum
C4H10O – 60% 30mm
3He/4He – 6%
Perspectives: Active Polarised Target
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Data taken in September 2010 & February 2011 Analysis: S. Schumann (MIT)
Eg=320MeV
Carbon Hydrogen Butanol
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Asymmetries T and F in gp pp0 at threshold
Study of the dynamic consequences of md − mu > 0.
Rescattering diagram responsible for the
unitary cusp observed in E0+ (gp pp0 ) gp pp0
Qp74
300hours
mp+=139.6 MeV
mp0 =135 MeV )(2
1 dduu
du
Precission experiment to test the unitary calculations
[Bernstein et al. arXiv:0902.3412 [nucl-th] (Feb. 2009)
and ChPT calculations
[V.Bernard, N.Kaiser, and U.G.Meissner,
Eur. Phys. J. A11, 209 (2001), C. Fernandez-Ramirez et
al., PLB 679 (2009)] of ImE0+ .
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Sim. MM(γ') on Butanol – showing π0 photoproduction and Compton contributions
Pion photoproduction off of a proton is 75-100 times
more likely than Compton (in the 240-280 MeV range)
Kinematic overdetermination used for cuts (missing
mass, proton angle, …).
Test with ‘substraction target’.
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2 Meter
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Vacuum 3He/4He – 6%
Perspectives: Active Polarised Target
Cryogenic
challenge !!!
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Active Polarised Target Material
First tests without
light readout:
10 discs with 20mm
diameter stacked in
teflon container with
teflon spacers.
Spin density 3.0 *1019 cm-3
T=32 mK and B= 0.2 T
Pmax ~ 70%, tau ~ 5.5 h
Spin density 1.5 *1019 cm-3
T=26 mK and B= 0.2 T
Pmax ~ 44%, tau ~ 36 h
Polystyrene
+ ~5%Butanol
Spin density 2.2 *1019 cm
T=25 mK
Pmax ~ 50%
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Optimisation of Pmax and
0
133
2
11 PP
TRd
HT
e
e
n
n
g
[W. de Boer, CERN 1974]
B[T] [h]
0.2 17
0.1 2.6
0.08 0.92
0.05 0.33
#e- (*1019cm-3) 1.5 2.2 (But) 3.0
t[h] @0.2T 36 17 5.5
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Light Readout: Active Polarised Target
Material
&
Detector
challenge !!!
Miskimen (UMass Amherst), Downie (GWU),
Biroth, Thomas (Mainz),
Borisov , Usov (JINR).
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Cryogenic – Insert
Arrived in Mainz last Fri.,
To be mounted.
First warm in beam test
done Yesterday.
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Different methods to stack and glue the active polarized target plates.
(ligth collection efficiency?)
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SiPM in A2 beam. Other candidates are APD‘s. Operation at 2-4Kelvin.
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Frozen Spin Target offers all directions of polarization. ~ 1000 … 4000h.
Data taking for 5000h with CBall TAPS detector system 2010/2011.
Spin observables with focus to P11(1440), S11(1535), and D33(1700)
resonance regions. Meson Production. Complete Experiments.
First Measurement of 4 Vector Spin Polarisabilities in Compton Scattering,
F and T in p-threshold region. Light quark mass difference. Isospin
breaking.
Conclusions
Outlook Technology
Production of an internal polarising coil avoids FST waltz DNP
Target
(+better systematics (position, noise,...), +better statistics (efficiency),
+higher polarisation, +less manpower, -more material, momentum
threshold)
R&D for polarised active szintillator target for threshold production.
(+new kinematic range in combination with 4p detectors)