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Study on Key Properties of PoGO by Geant4 Simulator

Study on Key Properties of PoGO by Geant4 Simulator. January 28, 2004 Tsunefumi Mizuno mizuno@SLAC.Stanford.EDU. 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

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Study on Key Properties of PoGO by Geant4 Simulator

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  1. Study on Key Properties of PoGO by Geant4 Simulator January 28, 2004 Tsunefumi Mizuno mizuno@SLAC.Stanford.EDU PoGO_G4_2004-01-28.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 W collimator = 0.0025cm • 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 = 397 (geometrical area of fast scint. not covered by slow scint. = 1709 cm2) or 217 (934.4 cm2) PoGO_G4_2004-01-28.ppt

  3. Simulation Condition • The same Crab spectrum as that used in Hiro’s EGS4 simulation is 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 3g/cm2 • Atmospheric downward/upward gamma spectra for GLAST BFEM simulation are used as background. • Use Geant4 ver5.1. Possible minor bug of polarization vector after scattering was fixed by user (found by Y. Fukazawa @ Hiroshima Univ.). PoGO_G4_2004-01-28.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 3 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_2004-01-28.ppt

  5. Event Analysis • The same as those of Hiro’s EGS4 Simulation • Use events in which two or three fast scintillators are with hit. • The largest energy deposit is considered to be photo absorption • 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_2004-01-28.ppt

  6. Incident/measured gamma-ray energy distributions 100mCrab (20-200keV), 6 hour exposure, 217 units Incident gamma energy, 2 or 3 hits in fast scint. no hits in veto scinti. (Eth=3keV) after attenuated by air of 3g/cm2 measured gamma energy, detector responses are convoluted PoGO_G4_2004-01-28.ppt

  7. Incident energy distribution of atmospheric gammas Reduced Design (217 units) atmospheric downward gamma atmospheric upward gamma gammas that hit 2 or 3 fast scintillators gammas that pass the event selection (background) Downward atmospheric gammas below a few MeV and upward ones between a few hundred keV to a few MeV contribute to background. PoGO_G4_2004-01-28.ppt

  8. Collimator thickness dependence of the background(1) atmospheric downward gamma 397 units 217 units 100mCrab (incident) 100mCrab (detected) Background due to atmospheric gamma 10um thickness 25um thickness 50um thickness • # of units does not affect S/N ratio very much • Collimator (W) of 25um could be optimum (see the next slide). • Signal>background below 100 MeV. PoGO_G4_2004-01-28.ppt

  9. Collimator thickness dependence of the background(2) atmospheric upward gamma 217 units 397 units 100mCrab (incident) 100mCrab (detected) Background due to atmospheric gamma 10um thickness 25um thickness 50um thickness • # of units does not affect the S/N ratio very much • Collimator (W) of 25um could be optimum (see the previous slide). • Signal>background below 100 MeV. PoGO_G4_2004-01-28.ppt

  10. Slow scint. energy threshold dependence of the background Reduced Design (217 units) atmospheric downward gamma atmospheric upward gamma 100mCrab (incident) 100mCrab (detected) Background due to atmospheric gamma Eth=3keV, 5keV, 10keV and 1MeV Veto threshold of slow scintillator does not affect the background so much. PoGO_G4_2004-01-28.ppt

  11. Predicted Azimuth Angle Distribution • 100m Crab spectrum (E-2.1 in 20-200keV), 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 20-100 keV 397 units 217 units MF=24.3% Sensitivity; 24.3/0.73=33sigma MF=25.1% Sensitivity; 25.1/0.51=49sigma PoGO_G4_2004-01-28.ppt

  12. Predicted Effective Area • Apply the same event selection as that for polarization measurement (p11). 217 units 397 units Maximum at 40-50 keV, 230cm2 (217 units)/460cm2 (397 units) PoGO_G4_2004-01-28.ppt

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