E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing Power K. Peter Schüler

e+ Analyzing Power:what we know from old GEANT3 simulations

(an archeological excercise with some useful insights)

2

expected and measured e+ asymmetries

E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing PowerK. Peter Schüler

proposal – the ominous table 13 measurements

actual conditions were different in several ways: beam energy: 50 46.6 GeV

beam current: 1 x 1010 0.5 x 1010

lens/spectrometer CsI-detector geometry

background!!!

to what extent will these differencesaffect the analyzing power and theexpected asymmetries?

3

Conditions assumed for GEANT3 simulations

E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing PowerK. Peter Schüler

Positron Beam at Reconversion Target:• quasi-monochromatic with Gaussian E/E = 20% • zero spatial width and angular divergence• centered on reconversion target

Reconversion Target:• 0.5 r.l. W• 12.5 mm upsteam of active region of iron

Analyzer Iron:• 50 mm dia. x 75 mm long • PE = 0.07

CsI-Detector:• angular photon acceptance: ±8 ° (layout 4b = proposal)• angular photon acceptance: ±14 ° (layout 5a)

GEANT3 processes:• bremsstrahlung (*)• annihilation (*) (*) spin-dependent treatment,• Compton (*) but only through 1st generation• pair production• photo effect• Bhabha, Moller• multiple Coulomb scattering

4

Detector Acceptance

E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing PowerK. Peter Schüler

layout 4b (proposal) vs. layout 5a

4b covers approximately the central crystal,5a covers approximately the full 3x3 crystal array

5

synopsis of geometries

E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing PowerK. Peter Schüler

layout 4b layout 5a

6

e+ Analyzing Power (energy-weighted)

E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing PowerK. Peter Schüler

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12

e+ Energy (MeV)

An

aly

zin

g P

ow

er

(%)Layout 4b Layout 5a

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and by numbers …

E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing PowerK. Peter Schüler

Layout 4b Layout 5a

e+ energy(MeV)

A(%)

ΔA(%)

ΔA/AA

(%)ΔA(%)

ΔA/A

10 13. 93 ±0. 42 0. 030 12. 97 ±0. 25 0. 019

9 13. 98 ±0. 46 0. 033 13. 35 ±0. 28 0. 021

8 15. 16 ±0. 56 0. 037 14. 30 ±0 .33 0. 023

7 15. 75 ±0. 63 0. 040 14. 73 ±0. 38 0. 026

6 15. 84 ±0. 74 0. 047 15. 48 ±0. 45 0. 029

5 17. 07 ±0. 96 0. 056 16. 28 ±0. 54 0. 033

4 19. 63 ±1. 24 0. 063 17. 21 ±0. 72 0. 042

3 18. 57 ±1. 85 0. 100 17. 02 ±0. 92 0. 054

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Positron Beam Polarizations

E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing PowerK. Peter Schüler

spectrometer positron asymmetry (**) no. of analyzing pos. pol. current energy (*) Δ CsI-crystals power Pe Pe+

(A) (MeV) (%) (%) (%) (%) (%) (%)

100 3.7 0.57 0.17 5 19.0 ± 1 7.0 43 ± 13 120 4.5 0.88 0.10 5 18.0 ± 1 7.0 70 ± 9 140 5.2 1.03 0.08 5 16.8 ± 1 7.0 88 ± 9 150 5.6 0.78 (*) 0.10 (*) 5 16.0 ± 1 7.0 70 ± 10 160 6.0 0.83 0.12 5 15.8 ± 1 7.0 75 ± 12 180 6.7 0.89 0.21 5 15.8 ± 1 7.0 80 ± 20 180, ferrofl. 6.7 0.98 0.21 5 15.8 ± 1 7.0 89 ± 20

140 5.2 1.08 0.10 2,4,6,8 ? 7.0 ? 140 5.2 1.06 0.07 2,4,5,6,8 16.0 ± 1 7.0 96 ± 9 140 5.2 0.91 0.07 1-9 16.0 ± 1 7.0 81 ± 10

(*) based on preliminary values shown by Ralph in Vienna (Nov. 2005) (**) based on Zeuthen analysis from 27. Feb. 2006

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Summary

E166 Collaboration MeetingPrinceton, 22-24 May 2006

e+ Analyzing PowerK. Peter Schüler

• original GEANT3 analyzing power generated in 2003 is essentially still valid for the actual experimental conditions in E166• analyzing power decreases only modestly between single central crystal and full 3x3 crystal array• positron beam polarization is indeed large