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)
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
GLAST LAT(20MeV-300GeV)
Balloon Flight Engineering Model
(BFEM): single tower
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 we collected cosmic-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)
XGT
AMS
ACD
our model
(used in Geant4
Simulation)
CAL
TKR
secondary
(atmospheric)
primary with geomagnetic cutoff and solar Palestine, 2001
GeV
Support Structure
Pressure Vessel
alpha
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)
Straightness of the reconstructed track
Zenith angles of the straight/single track
Data
Data
Simulation (total)
muon
muon
gamma
e-/e+
proton
alpha
alpha
e-/e+
gamma
proton
rms (arbitrary unit)
horizontal
cos (theta)
downward
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.