Proton Polarimetry

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Proton Polarimetry

• Proton polarimeter reactions
• RHIC polarimeters

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Proton polarimeters for circulating beams

• p C ? p X Good FOM at low energy (lt 3GeV)
  COSY
• p p ? p p (t 0.15 GeV2) Good FOM up to
  20 GeV AGS
• Plastic target intensity beams limited
• p C ? p X (x0.5,pt0.5 GeV) Good FOM at high
  energy
• Requires large spectrometer
• p p ? p p (t 0.001 GeV2) Good FOM at all
  energies RHIC abs. pol.
• Jet target low luminosity
• Pol. H jet absolute polarimeter
• p C ? p C (t 0.001 GeV2) Good FOM at all
  energies RHIC rel. pol.
• Carbon target high luminosity
• Good and fast relative polarimeter

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Polarized proton collisions in RHIC
RHIC pC Polarimeters
Absolute Polarimeter (H jet)
Siberian Snakes
Spin Rotators
2 ? 1011 Pol. Protons / Bunch e 20 p mm mrad
Partial Siberian Snake
LINAC
BOOSTER
Pol. Proton Source 500 mA, 300 ms
AGS
AGS Internal Polarimeter
200 MeV Polarimeter
Rf Dipoles
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Proton polarization at the AGS

• Full spin flip at all imperfectionresonances
  using partial Siberian snake
• Full spin flip at strong intrinsic resonances
  using rf dipole
• Remaining polarization lossfrom coupling and
  weakintrinsic resonances
• New tune working point and smaller horizontal
  emittancewill reduce polarization loss

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Proton-Carbon CNI Polarimeter (AGS E950)

• 2-3 energy independent analyzing power for
  small-angle elastic scattering in the
  Coulomb-Nuclear Interference (CNI) region
• Slow recoil Carbon detected in between bunch
  crossings
• Fiber target allows for polarization profile
  measurement

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Elastic scattering in small t region
(0.002lttlt0.05) (GeV/c)2

• Large cross section
• Simple equipment
• Weak energy dependence of the asymmetry
• Fast measurement
• Small influence on the beam by the target
• Small analyzing power (1-4)
• No precise theoretical predictions

Physical asymmetry (cancels acceptance
and luminosity asymmetries)
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A RIKEN BNL Research Center Workshop
E950 setup
Carbon ribbon target (3.7 mg/cm2, 6 mm)
1 cm
Silicon strip detector (6 ? 4 mm)
Electrostatic mirror

• DAQ
• LeCroy FERA ADC 4300
• LeCroy 2367 as FERA memory
• IBM/PC with Linux
• Readout between spills
• Dead time 15ms per event

Carbon foil (3.7 mg/cm2)

• AGS internal beam
• ?5109 p/bunch
• 1 bunch in the ring 2.7 ms between bunches
• Bunch length ? 25 ns
• 22 GeV
• Polarization ?40

BNL-2001
8
A RIKEN BNL Research Center Workshop A RIKEN BNL
Research Center Workshop A RIKEN BNL Research
Center Workshop
E950 results
A RIKEN BNL Research Center Workshop
A0.00533?0.00027 ?2/Ndf 1
BNL-2001
9
RHIC year-0 detector set-up

• Thin carbon target 5 ?g/sm2 ? 10?m
• Horizontal and vertical targets
• 4 Detectors 12strips ? 2 mm
• Strips in vertical direction
• Trigger as or of all strips
• DAQ with LeCroy FERA 4300 ADC/TDC
• Dead time 10 ?s per event 1.5s per 40000
  events
• 6-bunch mode
• Upto 5?1010 p/bunch
• About 105 carbon events/min

blue ring
1
3
15 cm
4
2
Carbon identification by time of flight/energy
dependence E, keV -t (GeV/c)2 T,
ns 100 0.0022 118 200 0.0045 84 500 0.0112 53 1000
0.0223 37 2000 0.0446 27
1
12
10
A RIKEN BNL Research Center Workshop A RIKEN BNL
Research Center Workshop A RIKEN BNL Research
Center Workshop
Data
A RIKEN BNL Research Center Workshop
Carbon over strips distribution
C
?
BNL-2001
11
A RIKEN BNL Research Center Workshop A RIKEN BNL
Research Center Workshop A RIKEN BNL Research
Center Workshop
Energy calibration
A RIKEN BNL Research Center Workshop

• Energy calibration of the detector by the time
  of flight
• Agreement with the Tandem test at 10??? 10

• ?-peak ??4.
• Elastic cone slope is in a good agreement with
  the theoretical predictions

BNL-2001
12
A RIKEN BNL Research Center Workshop A RIKEN BNL
Research Center Workshop A RIKEN BNL Research
Center Workshop
Results with p?
A RIKEN BNL Research Center Workshop
A0.002030.00021 Beam polarization 20
Sign changed
Zero polarization from the source
The first nonzero measurement

• Statistically significant asymmetry
• Right correlation with beam changes
• Small systematic errors

BNL-2001
13
Commissioning with a single snake in RHIC
Gg 48 or 60.3
Gg 46.5 or 55.7
-12º
polarimeter

• Inject vertically pol. beam with snake off
• Turn on snake ? Horizontally pol. beam
• Accelerate

snake
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RHIC year-1 configuration
blue ring
yellow ring

• 12 Si detectors.
• one event per bunch crossing
• all channels have independent WFD readout.
• zero dead time.

Shaper
WFD
CAMAC
PC
Si
Preamp.
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72
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Polarized proton injection into RHIC
Injection at Gg 46.5 without snake vertical
polarization!
ny 29.11
Sensitive to betatron tune setting
ny 29.23
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Snake operating points
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Acceleration with single snake
Gg48.0
Gg46.5
Gg60.3
Gg55.7
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Measured RHIC asymmetries
P ? 19 P ? 40 at AGS
Asymmetry (? 10-3)
Gg
24.3
25.1
29.1
31.5 GeV
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Test of WFD
t
Carbon
e
Fast particles
MIPs

• 1 WFD module, 4 channels
• Common trigger
• Everything read to PC

• off-line event reconstruction

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Polarized Hydrogen Jet Target

• pC polarimeter is used as fast relative
  polarization monitor and was calibrated in AGS at
  22 GeV to about 15 .
• Polarized hydrogen jet target allows for absolute
  beam polarization measurement
• Jet target thickness of 3?1011 cm-2
  achievable(HERMES, PINTEX, NIKHEF)
• Jet polarization measurable to better than 3
  using Stern-Gerlach method
• Collaboration started with Wisconsin, IUCF, and
  Amsterdam

Pol. H jet target at Bates from NIKHEF
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Summary

• RHIC proton polarimeter successfully tested
• Efficient relative and absolute high energy
  proton polarimetry possible