1. June 1, 2004 Tsunefumi Mizuno mizuno@SLAC.Stanford.EDU
Expected Modulation Factor of PoGO calculated with Geant4 Simulator with PoGO-fix
June 1, 2004
Tsunefumi Mizuno
PoGO_G4_ ppt

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. = cm2)
PoGO_G4_ ppt

3. Simulation Condition
The same Crab spectrum as that used in Hiro’s EGS4 simulation was simulated here. That is,
E-2.1 spectrum with 100mCrab intensity, keV (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.
PoGO_G4_ ppt

4. Detector Resopnses
The same detector responses as those used in Hiro’s 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 sigma=0.5 keV (PMT energy resolution)
minimum hit threshold after three steps above is 3 keV
PoGO_G4_ ppt

5. Event Analysis The same as those of Hiro’s 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 Hiro’s resolution function.
No event selection on compton kinematics
PoGO_G4_ ppt

6. Predicted Azimuth Angle Distribution(1)
100m Crab spectrum (E-2.1 in keV), 6 hour exposure, 100% polarized
Fit the azimuth angle distribution with p0(1+p1*cos(2*phi+pi))
Assumed detector response and event selection criteria are given in pages 4-5
Measured energy is keV
No BG
with atmospheric gamma
MF= %
MF= %
azimuth angle (radian)
PoGO_G4_ ppt

7. Predicted Azimuth Angle Distribution(2)
No BG
MF= %
azimuth angle (radian)
with atmospheric gamma
L1=30cm (from top to intermediate)
MF= %
PoGO_G4_ ppt