Eduardo do Couto e Silva

1
Data Analysis Results from the GLAST LAT
Engineering Model tests at SLAC

• Eduardo do Couto e Silva
• SLAC/Stanford University
• May 3rd, 2004
• APS Meeting, Session 10, 10.006
• Representing the Engineering Model Team

2
LAT Engineering Model
EM 10000 readout channels
For the description of the GLAST LAT see Julie
McEnerys talk S10.009 Monitoring the High
Energy Gamma-Ray Sky with GLAST
Scaled down version a LAT tower
6 active layers of silicon microstrip detectors
TKR
8 active layers of CsI crystals
CAL
Electronics Module And Power Supply
3
Experimental Set-up
g BEAM
TKR
EGSE
CAL
MGSE
4
Experimental Signatures
Charged Particle
Photon
W converter
Y3 X3 X2 Y2 Y1 X1
Y3 X3 X2 Y2 Y1 X1
TKR
TKR
Trigger condition At least 1 hit in 6
consecutive TKR layers
CAL
CAL
5
Signal versus Background
Van de Graaff (VDG) Energy Spectrum Narrow line
17.6 MeV (G 100 keV) 67 events Broad
line 14.6 MeV (G 1.5 MeV) 33 events
Cosmic Rays (from all directions)
Photon Source (4psr)
Li Target
Beam pipe
g
proton beam
CAL
TKR
Engineering Model
Fe shield
Signal photon conversions in the
EM Background 1 photon conversions in the Fe
shield Background 2 surface cosmic rays
6
Energy Measurement

• ETOTAL ETKR ECAL
• ETKR
• Use number of hits in the TKR as an estimator
• corrected energy deposited by the event direction
• ECAL
• Sum all calibrated energies recorded in each
  crystal
• correct for threshold effects since each crystal
  only records a hit if the deposited energy is gt
  2 MeV.

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Energy Spectrum DATA
For CAL Calibrations see the Calorimeter Team
talk in this session S10.007 The Calibration
and Environmental Testing of the Engineering
Module of GLAST LAT Calorimeter
Expected g Spectrum Delta function (17.6
MeV) Breit-Wigner (mean 14.5, width1.5MeV)
Disclaimer These results should not be used to
determine the LAT performance due to differences
in the amount of material and algorithms used for
the EM and for the fully instrumented LAT tower
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Monte Carlo Energy Spectrum
only VDG g are simulated
Photons that converted in the TKR
Photons that converted in the shield at the end
of the beam pipe
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Measurement of Energy Deposited in TKR
The time-over-Threshold (TOT) is used to
estimate the energy deposited in a given silicon
layer (TOT is the logical OR of all strips in
the layer)
Charge
TOT Energy strip
threshold
More charge leads to a larger TOT value
TOT
TOT
Time
10
TOT for g and charged particles
W
Multiple scattering
0.10 mm
0.35 mm
Silicon strip
Silicon strip
0.228mm
0.40 mm
Accept events with only one strip hit below W
converter (special topology)
Drawing NOT to scale
11
TOTCharged Particles MC vs DATA
For TKR Calibrations see the Tracker Team talk
in this session S10.010 The GLAST Silicon
Tracker
Cosmic ray DATA
MC simulations (m only)
Landau Fit
12
TOT g Candidates DATA
Data indicates the presence of two peaks . The
second peak is most likely due to two particles
depositing energy on the same strip
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Summary

• We have used cosmic rays and low energy photons
  from a van de Graaff accelerator
• To measure the Energy Spectrum in the Engineering
  Model
• To study how the Time-over-Threshold in the
  Tracker can be used as a tool to resolve between
  1 and 2 minimum ionizing particles
• We have exercised the full analysis chain
• Lots of data ahead of us !
• Flight hardware starts arriving late summer 2004

Special thanks to all LAT Collaborators who
contributed to the successful EM integration and
its corresponding data analysis
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Backup slides
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TOT Calibrations
Calibrations are performed with charge injection
and cosmic rays
Charge injection
Cosmic rays
Calibrated using charge injection results
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TOT g candidates MC vs DATA
Preliminary
MC simulations (g only) Conversion upstream in
the beam pipe
DATA
MC simulations (g only) All events
MC simulations (g only) Conversion within Si