Positron Asymmetry and Polarization from the E166 September 2005 run

Positron Asymmetry and Polarizationfrom the E166 September 2005 run

Gideon Alexander & Erez Reinherz-Aronis

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


• 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


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


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.

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


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


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)


Asymmetry Error

R

R

L

L

NRR

R

NLL

L

LRRLRL

LRAsy

RL

RLAsy

11

)()()(

2 222

• For a Gaussian distribution:


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


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])


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)


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


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)


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


Asy

mm

etry

[%]

Method A

Method B

e- Method A

e- Method B


; ( ) 0.073e e

e e

AsyP P Fe

P A

Positron Polarization

Ae+ Analyzing power


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


Pola

riza

tion

[%]

Method A

Method B


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


Polar

izatio

n [%

]

Method A

Method B


• 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


Positron Asymmetry and Polarizationfrom the E166 September 2005 run

Gideon Alexander & Erez Reinherz-Aronis


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).


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

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Positron Asymmetry and Polarization from the E166 September 2005 run

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