Polarimetry of Polarized Positrons K. Peter Schuler

1
e Analyzing Power what we know from old GEANT3
simulations
(an archeological excercise with some useful
insights)
E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler
2
expected and measured e asymmetries
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 differences affect the
analyzing power and the expected asymmetries?
E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler
3
Conditions assumed for GEANT3 simulations

• 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

E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler
4
Detector Acceptance
layout 4b (proposal) vs. layout 5a
4b covers approximately the central crystal, 5a
covers approximately the full 3x3 crystal array
E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler
5
synopsis of geometries
layout 4b
layout 5a
E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler
6
e Analyzing Power (energy-weighted)
E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler
7
and by numbers
E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler
8
Positron Beam Polarizations
spectrometer positron asymmetry
() no. of analyzing
pos. pol. current energy ()
? ?? 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
E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler
9
Summary

• 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

E166 Collaboration Meeting Princeton, 22-24 May
2006
e Analyzing Power K. Peter Schüler