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Analysis of GLAST Balloon Experiment Data Annual meeting of the Physical Society of Japan

Analysis of GLAST Balloon Experiment Data Annual meeting of the Physical Society of Japan Tsunefumi Mizuno, Hirofumi Mizushima, Akimitsu Ohto, Yasushi Fukazawa, Takashi Ohsugi (Hiroshima University), Tuneyoshi Kamae, Hiroyasu Tajima (SLAC), Masanobu Ozaki (ISAS)

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Analysis of GLAST Balloon Experiment Data Annual meeting of the Physical Society of Japan

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  1. Analysis of GLAST Balloon Experiment Data • Annual meeting of the Physical Society of Japan • Tsunefumi Mizuno, Hirofumi Mizushima, Akimitsu Ohto, Yasushi Fukazawa, Takashi Ohsugi (Hiroshima University), Tuneyoshi Kamae, Hiroyasu Tajima (SLAC), Masanobu Ozaki (ISAS) • mizuno@hirax6.hepl.hiroshima-u.ac.jp • GLAST LAT/Balloon Experiment(p.2) • Instrument simulator/CR models(p.3) • Data analysis(pp.4-6) • Summary(p.7)

  2. GLAST Large Area Telescope/Balloon Experiment Balloon Flight Engineering Model (BFEM): single tower GLAST LAT(20MeV-300GeV) 4X4=16tower eXternal Gamma-ray Target(XGT) Anti Coincidence Detector (ACD) Si-Strip Tracker (TKR) CsI Calorimeter (CAL) Support Structure • To achieve high sensitivity aimed by GLAST, we need to estimate background in orbit accurately. • During the level flight (@38km), we collectedcosmic-ray events (>=100k) to be used for a background database for LAT.

  3. Instrument simulator and Cosmic-ray models Proton energy spectrum (from zenith) A Geant4-based Monte-Carlo instrument simulator BESS (magnetic north pole) AMS XGT ACD our model (used in Geant4 Simulation) TKR CAL primary with geomagnetic cutoff and solar modulation @ Palestine, 2001 secondary (atmospheric) 0.01 0.1 1 10 100 GeV alpha Support Structure Pressure Vessel electron/positron • particles with underline are expected in orbit atmospheric gamma muon

  4. Count Rate of Each Layer for “Charged Events” Count rate of each layer for “Charged Events” (hit in ACD) • trigger rate (Data) • ~445Hz • simulation total • (our prediction before the flight) • ~350Hz • proton : 145Hz • alpha : 18Hz • e- : 45Hz • e+ : 30Hz • gamma : 50Hz • muon : 62Hz Real Data (level flight) muon gamma e-/e+ alpha proton Count rate observed and simulation prediction agree with each other in ~20% 26 Si layers (13 planes: x-y pair) CAL ACD TKR

  5. Angular distribution of “Charged Events” (preliminary) Zenith angles of the straight/single track Straightness of the reconstructed track Data Data Simulation (total) muon muon gamma e-/e+ proton alpha alpha e-/e+ gamma proton 10-6 10-3 1 103 rms (arbitrary unit) horizontal downward cos (theta) straight track • Data and simulation agree with each other in ~20%. • We may need to increase the proton/alpha/muon flux to explain data.

  6. Count Rate of Each Layer for Neutral Events Count rate of each layer (no hit in ACD) • trigger rate (Data) • ~55Hz • simulation total • (our prediction before the flight) • ~52Hz • proton : 3.1Hz • alpha : ~0Hz • e- : 6.9Hz • e+ : 3.9Hz • gamma : 35.5Hz • muon : 2.4Hz muon thick Lead converters gamma Real Data (level flight) e-/e+ proton • Overall agreement is good between data and prediction. • Count rate in upper layers are smaller than data.

  7. Summary • We performed GLAST Balloon Experiment on August 4th, 2001. • All detector components worked well in high-counting enviroment. • We obtained ~100k Cosmic-ray events to be used as a background database for LAT. • We have developed a Geant4 based instrument simulator and Cosmic-ray flux models. • We have investigated the count rate, straightness of the track and angular dependence of the flux. • Data and simulation prediction agree with each other in ~20%, below uncertainty of CR flux. • Detailed study is underway.

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