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Deuteron polarimetry from 1.0 to 1.5 GeV/c. Ed Stephenson, IUCF EDM discussion April 14, 2006. Based on work from:. France: POMME B. Bonin et al. Nucl. Inst. Methods A288 ,389 (1990) V.P. Ladygin et al., Nucl. Inst. Methods A404 , 129 (1998). Japan: DPOL - PowerPoint PPT Presentation
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Deuteron polarimetry from 1.0 to 1.5 GeV/c
Ed Stephenson, IUCFEDM discussionApril 14, 2006
Based on work from:
France: POMMEB. Bonin et al. Nucl. Inst. Methods A288,389 (1990)V.P. Ladygin et al., Nucl. Inst. Methods A404, 129 (1998)
Japan: DPOLY. Satou, private communication
Emphasizes elastic scatteringCarbon target
Want highest efficiency and vector spin dependence
A typical experimental layout contains:
beamdirection
scatteringplane
y
x
z
leftdetector
β
rightdetector
target
(φ=0)
A polarization of the beam (p) causes a difference in the ratesfor scattering to the left according to:
]2cossin)(2
3
sincossin)(3)1cos3()(8
1
cossin)(31[)()(
222
212
20
11
Tp
TpTp
iTp
T
TT
Vunp
analyzing power(determined by nuclear
effects in scattering)governs spin sensitivity
unpolarized cross section(determined by nuclear
effects in scattering)governs efficiency
φ
θ
left and right detectorsuseful for vector polarization
0
31
101
0
11
fff
fp
ffp
T
V
POMME layout
tracks frommagnetic spectrometer
triggerscintillators
finalscintillator
wire chambersCarbontarget
Ironabsorber
Changes for EDM application:eliminate wire chambers (high rates) and segment final scintillator
adjust carbon thickness to maximize efficiency (FOM)
adjust iron thickness to favor elastic over breakup events
Up
Down
Right
Left
Carbontarget
Ironabsorber
Segmentedscintillator
Functionalpolarimeterelements(must runcontinuously)
RL
RLLR
Left-right asymmetry
carries EDM information.
UD
UDDU
Down-up asymmetrycarries information ong-2 precession.
Carbon target is small.
Detailed design awaits decisionon bringing beam to polarimeter: slow extraction into second beam extract using jet in ring onto annular target tune beam onto annular target
Angle range:4° - 15°
Rate considerations for feedback on phase (g-2 vs. sync.)
Compare two inputs: BPM in dispersed regiondown-up asymmetry
Bin asymmetry data into about 10 bins through one oscillation.
Maximum asymmetry: 3.03.06.07.13 11 iTpV
Events needed:2)(
1
N for δφ = 1%, N = 105
Then: load ring with 1011 deuteronlose half to polarimeter in 1000 s, target rate = 5 x 107 /swith polarimeter efficiency at 6%, detector sees 3 x 106 /s or 3 x 105 /s/bin
Can measure phase to 1% about 3 times per second.
Example:
Sample data:
Bonin Satou
Note differences in peak analyzing power !!!
Bonin did not eliminate breakup as well.Satou did at the expense of efficiency.
270-MeV deuteron elasticscattering – RIKEN[data example](errors not shown)
NEW DEFINITION OFFIGURE OF MERIT
1
)()( 11 iTFOM
Optimize here:favor larger analyzing power,leverage against systematics
Optimize here:favor statistical precision
FIRST TRADE-OFF
At smaller anglesCoulomb andmultiple scatteringdominate, makingcross section largeand analyzing power zero.
The trade-off at high and low energies:
700 MeV
At the higher energies, FOM andanalyzing power peak together.There is no trade-off.
200 MeV
FOM has two comparablepeaks, so two options areequally good statistically.Thus higher analyzing power is favored.
Before optimizing the FOM as a function of energy, consider two other energy dependencies:
The cross section is falling.
More energy allows thicker targets.Dots = French dataLine = curve used here
The SOLID dots and lines follow theFORWARD peak in the FOM curve.
The open/dashed dots and lines followthe analyzing power peak (where thereis enough data to use).
The AVERAGES shown here integrateover some angle range that covers therelevant feature in FOM or iT11.
Satou gets even larger analyzingpowers by cutting out more protonsand losing “efficiency”. The FOMis down about 30% from the opendots.
SECOND TRADE-OFF:
Polarimeter Systematic ErrorsWhat other sources arisefor a left/right asymmetry?
1 Displacement / angle errorsdetectors
θ
angle shift
θ
x
position shift
Usual remedy: measure on both sides (L/R) flip initial spin use cross ratio formula
RL
RL
CC
CCr
r
rpA
1
1
spin
detector
left/right efficiencydifferences cancel
+/ luminositydifferences cancel
Errors that are second-order in θ and u=p++p
22
22223
2
')1(
"'2
1
1
A
A
A
Au
A
Aumeas
logarithmic derivatives of the analyzing poweras a function of scattering angle
We are helped by the small size of the asymmetry and the expected time dependence.
Sizes of logarithmic derivatives need to be evaluated for some polarimeter acceptance geometry.