Expected Modulation Factor of PoGO calculated with Geant4 Simulator with PoGO-fix

1
Expected Modulation Factor of PoGO calculated
with Geant4 Simulator with PoGO-fix

• June 1, 2004
• Tsunefumi Mizuno
• mizuno_at_SLAC.Stanford.EDU

2
Simulated Geometry

• Thickness of fast scint. 2.63cm
• (D 2.23cm)
• W (thickness of slow scint.) 0.2cm
• L1 (slow scint. length) 60cm
• L2 (fast scint. length) 20cm
• Thickness of Sn collimator 0.01cm
• Thickness of btm BGO 2.68cm
• Length of btm BGO 3cm
• (not tapered in simulator for simplicity)
• Gap between BGOs 0.5cm
• (including BaSo4 eflector)
• Thickness of side Anti BGO 3cm
• Length of side Anti BGO 60cm
• of units 217 (geometrical area of fast scint.
  not covered by slow scint. 934.4 cm2)

3
Simulation Condition

• The same Crab spectrum as that used in Hiros
  EGS4 simulation was simulated here. That is,
• E-2.1 spectrum with 100mCrab intensity, 20-200keV
  (300.8 c/s/m2)
• 100 polarized, 6h exposure
• Attenuation by air of 4g/cm2 (atmospheric depth
  in zenith direction is 3g/cm2 and that in
  line-of-sight direction is 4g/cm2)
• Atmospheric downward/upward gamma spectra for
  GLAST BFEM simulation were used as background.
• Use Geant4 ver5.1. Serious bug in polarized
  Compton scattering was fixed by user. We also
  implemented polarized Rayleigh scattering.
• Fluorescence X-ray are not taken into account in
  BG simulation.

4
Detector Resopnses

• The same detector responses as those used in
  Hiros EGS4 simulation
• If there is a hit in slow/anti/btm scintillators,
  event is rejected. (Threshold is 30 keV). Energy
  smearing and poisson fluctuation are not taken
  into account yet for veto scintillators.
• Assumed detector resposes
• 0.5 photo-electron/keV
• fluctuated by poisson distribution
• smeared by gaussian of sigma0.5 keV (PMT energy
  resolution)
• minimum hit threshold after three steps above is
  3 keV

5
Event Analysis

• The same as those of Hiros EGS4 Simulation
• Use events in which two or three fast
  scintillators detected a hit.
• The largest energy deposit is considered to be
  photo absorption
• The second largest energy deposit is considered
  to be Compton scattering.
• Smallest energy deposit (in case of three
  scintillators with hit) is ignored.
• Smear azimuth angle distribution with Hiros
  resolution function.
• No event selection on compton kinematics

6
Predicted Azimuth Angle Distribution(1)

• 100m Crab spectrum (E-2.1 in 20-200keV), 6 hour
  exposure, 100 polarized
• Fit the azimuth angle distribution with
  p0(1p1cos(2phipi))
• Assumed detector response and event selection
  criteria are given in pages 4-5
• Measured energy is 20-100 keV

with atmospheric gamma
No BG
MF26.3-0.8
MF21.9-0.7
azimuth angle (radian)
7
Predicted Azimuth Angle Distribution(2)
No BG
MF23.5-0.9
azimuth angle (radian)
with atmospheric gamma

• L130cm (from top to intermediate)

MF18.1-0.8