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Positron Asymmetry and Polarizationfrom the E166 September 2005 run
Gideon Alexander & Erez Reinherz-Aronis
DESY/Hamburg, 1-Nov-06
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DESY/Hamburg, 1-Nov-06
CsI
Analyzing magnet (-60/+60)
W-Target
Lens
SpectrometerSpectrometerSpectrometerSpectrometer
e-
e+
γ
γ
Undulator
Bend magnets
SLC
e-
e-
Analyzing magnet (-60/+60)
γ detectors
E-166 Schematic view
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DESY/Hamburg, 1-Nov-06
• Presently only the central CsI crystal (Crystal #5) was considered. A preliminary look into nearby crystals has been started.
• We chained all the events belonging to the same energy together under the reasonable expectation that local variations will, to a large extend, average out.
• We tried to avoid as much as possible arbitrary, unique cuts and procedures.
• Instead, we preferred to study by how much the results depend on the a priori range of different possible procedures and cuts from which one could choose.{e.g, tried Low sensitivity (12 bit) and High sensitivity (15 bit)}. The spread of some of these results may serve later as one input to the systematic errors.
Some General Guidelines and Comments
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DESY/Hamburg, 1-Nov-06
Selection of Runs and Events• 1st stage:
SuperRuns.Runs with Spectrometer and Lens values
Runs were rejected whenEmpty runs.Beam off.15 Hz runs.
• 2nd stagePairs of events were accepted by ‘Trigger’ word.
Note: Events with ADC above 4000 were filtered out.
Spectrometer [A] 100 120 140 160 180
Lens [A] 220 260 340 360 374
Positron energy [MeV] 3.89 4.77 5.65 6.52 7.42
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DESY/Hamburg, 1-Nov-06
The main use of the toroid 6130
• The toroid currents was used to define the appropriate range of the data, taking ±2σ range from an overall Gaussian fit.
• The analysis was then carried out with and without a toroid normalization.
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Positron Asymmetry• Event Pair : Signal*, Background (Bg).• Gaussian Fit in general is poor so we use it only to define the sample
range (σ cut, we also studied by how much the results depend on this specific choice).
• For each spectrometer value we calculate L and R via the mean:
601601
)(1
)(1
magnets
N
iii
eventsmagnets
N
iii
events
eventsevents
BgSignalN
RBgSignalN
L
*Signal = Signal over Background (Signal + Bg)
RL
RLAsyor
BgSignalBgSignal
BgSignalBgSignalAsy
6060
6060
)()(
)()( 160 A
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DESY/Hamburg, 1-Nov-06
Fraction of L events surviving the cuts(low sensitivity)
306 K 278 K 602 K 265 K 242 K Events
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
80 100 120 140 160 180 200
Spectrometer [A]
Fra
ctio
n a
fter
cu
ts
1 sigma
1.5 sigma
3 sigma
6 sigma
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DESY/Hamburg, 1-Nov-06
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
80 100 120 140 160 180 200
Spectrometer [A]
Fra
ctio
n af
ter
cuts
1 sigma
1.5 sigma
3 sigma
6 sigma
306 K 278 K 602 K 265 K 242 K Events
Fraction of L events surviving the cuts(high sensitivity)
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DESY/Hamburg, 1-Nov-06
Asymmetry Error
R
R
L
L
NRR
R
NLL
L
LRRLRL
LRAsy
RL
RLAsy
11
)()()(
2 222
• For a Gaussian distribution:
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DESY/Hamburg, 1-Nov-06
Asymmetry Error
R
R
L
L
N
ii
NR
s
NL
s
RL
LRAsy
xxN
s
11
)(
2
)(1
1
22
2
1
222
• Note: Gaussian Fit in general is very poor (χ2/d.o.f. >> 1)
• But one can estimate σ2 by
• so that the Asymmetry error can be written as
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DESY/Hamburg, 1-Nov-06
Low sensitivity norm
σ cut Asy Err Asy Err
1 1.2062 0.0595 1.0042 0.0594
1.5 0.9873 0.0662 0.9950 0.0728
3 1.0053 0.0609 1.0534 0.0977
6 0.9780 0.0601 0.9299 0.0956
High sensitivity norm
σ cut Asy Err Asy Err
1 1.0103 0.0595 1.0277 0.0592
1.5 0.9943 0.0692 1.0047 0.0726
3 1.0672 0.0642 1.0831 0.0747
6 1.0310 0.0631 1.0143 0.0735
Error dependence on the σ cut(spec = 160 [A])
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DESY/Hamburg, 1-Nov-06
0
0.2
0.4
0.6
0.8
1
1.2
1.4
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25 6.5 6.75 7
Positron Energy [MeV]
As
ym
me
try
[%
]
1 sigma
1 sigma / tor6130
1.5 sigma
1.5 sigma / tor6130
3 sigma
3 sigma / tor6130
Asymmetry resultsGain 1, Low sensitivity (12 bit)
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DESY/Hamburg, 1-Nov-06
0
0.2
0.4
0.6
0.8
1
1.2
1.4
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25 6.5 6.75 7
Positron Energy [MeV]
As
ym
me
try
[%
]
1 sigma
1 sigma / tor6130
1.5 sigma
1.5 sigma / tor6130
3 sigma
3 sigma / tor6130
Asymmetry resultsGain 1, High sensitivity (15 bit)
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DESY/Hamburg, 1-Nov-06
Comparison between Berlin and TA. positrons asymmetries
0
0.2
0.4
0.6
0.8
1
1.2
1.4
3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25 6.5 6.75 7 7.25 7.5 7.75 8
Positron Energy [MeV]
Asy
mm
etry
[%]
Method A
Method B
e- Method A
e- Method B
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DESY/Hamburg, 1-Nov-06
; ( ) 0.073e e
e e
AsyP P Fe
P A
Positron Polarization
Ae+ Analyzing power
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DESY/Hamburg, 1-Nov-06
Positron PolarizationUsing Ae+ from GEAT4
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
Positron Energy [MeV]
Pola
riza
tion
[%]
Method A
Method B
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DESY/Hamburg, 1-Nov-06
Positron PolarizationUsing Ae+ from GEAT4
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6 7 8 9 10
Positron Energy [MeV]
Polar
izatio
n [%
]
Method A
Method B
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DESY/Hamburg, 1-Nov-06
• It is very assuring that the two analyses yielded essentially the same asymmetry values so that together they enhance the confidence in the undulator-based method to produce longitudinal polarized positrons.
• The errors given are essentially the statistical ones and one should expect that the final errors will be dominated by the systematic ones.
• It is reassuring that the positron polarization values and behavior as a function of energy corresponded to there expectations.
• The electrons asymmetry seems to be significantly higher than that of the positrons. This observation demands some more study.
Some final remarks
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DESY/Hamburg, 1-Nov-06
Positron Asymmetry and Polarizationfrom the E166 September 2005 run
Gideon Alexander & Erez Reinherz-Aronis
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DESY/Hamburg, 1-Nov-06
Values for the Analyzing Power Ae+
Spectrometer [A] Ee+[MeV] Ae+
100 3.65 0.1931
120 4.38 0.1867
140 5.11 0.1688
160 5.84 0.1600
180 6.57 0.1585
Extracted from Table 13, E-166 Proposal, June 2003 (Averages).
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DESY/Hamburg, 1-Nov-06
Backup - Toriod cutsSpectrometer [A] Low
limitHigh
limit
100 490 550
120 500 520
120 520 570
140 480 538
140 538 600
160 530 567
180 525 565
electrons 500 520
electrons 520 550
electrons 560 590
Backup 5