Transcript JasonITPresentation.ppt

GLAST Background Analysis
An examination of events recorded
by the LAT prototype detector
The Experiment
The minitower was exposed to cosmic rays:
•
Muons
•
Electrons / positrons
•
Photons
•
Protons
(Muons are the dominant component of CR
flux at the Earth’s surface)
Raw data is saved to disk for later analysis
Another minitower was delivered a few
weeks ago and we did a preliminary
analysis on that data
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GLAST Background Analysis
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Data Analysis Plan
• Characterize the signature produced by
cosmic ray muons
• Quantify the effects of a threshold change
• Investigate a correlation to angle of
incidence
• Do preliminary studies on the second
minitower ( if time permits)
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Particle Interaction
Strip pitch
0.228 mm
1536 strips / layer
Si
Si thickness
0.400 mm
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Particle Interaction
1 hit
E
Si
h+
e-
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Strip pitch
0.228 mm
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Particle Interaction
2 hits
E
Si
h+
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h+
eGLAST Background Analysis
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Particle Interaction
Electron/hole pairs can drift to a neighboring
strip if the track passes through a “diffusion zone”
E
Si
approx 6 mm
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Strip pitch
0.228 mm
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Particle Interaction
1 - 3 hits
E
Si
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h+e h+
e-
h+e
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Background
•
•
•
•
•
The detector is not 100% efficient
EM showering can occur at any time
Scattering may occur within the detector
Electrical noise can create “hits”
Angular incidence will affect hit clustering
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Background Background
•
•
•
•
The detector is not 100% efficient
EM showering can occur at any time
Scattering may occur within the detector
Electrical noise can create “hits”
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The First Minitower
We expected to see
hits in every SSD…
z
y
x
All coords.
in mm
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The Second Minitower
New prototype gives
much better results!
PRELIMINARY DATA
z
y
x
All coords.
in mm
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Threshold Levels
Data from first minitower
A higher threshold yields more one-hit events in lieu of
events with multiple hits. This is what we expected.
What else is affected by the change? Efficiency!
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Angular correlation
A track with a given
zenith angle can hit
one or multiple
strips depending on
its azimuthal angle
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Angular correlation
A track with a given
zenith angle can hit
one or multiple
strips depending on
its azimuthal angle
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Dq
GLAST Background Analysis
Restricting the
azimuthal angle to a
small “pie slice” we
attain events in an
approximately twodimensional plane
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Angular correlation
Dq
A track with a given
zenith angle can hit
one or multiple
strips depending on
its azimuthal angle
In each event, the bottom
layer will experience low
hit multiplicity…
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Restricting the
azimuthal angle to a
small “pie slice” we
attain events in an
approximately twodimensional plane
the top layer will show
a correlation between
zenith angle and strips hit
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Angular correlation
f
tan f = l / t
t
l
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Data vs Monte Carlo
Data from first minitower
Cuts on experimental data:
• Single track events
~30% difference
• Single cluster per layer
Discrepancy
• Projected track is within 8
degrees from Y axis
• Number of strips hit in
each X layer averaged by
zenith angle
Reconstructed direction (deg)
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Improved Monte Carlo
Data from first minitower
Features added to Monte
Carlo:
• Path length threshold
(128 mm = 0.32 MIPS)
~10% difference
Reconstructed direction (deg)
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Further improvements
Data from first minitower
Features added to Monte
Carlo:
• Path length threshold
(128 mm = 0.32 MIPS)
Most points fit
within error bars!
•Diffusion zones (7 mm)
Reconstructed direction (deg)
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Preliminary Comparisons
Data from second minitower!
Preliminary data from
new tracker yield a much
better fit!
PRELIMINARY DATA
Threshold in Monte
Carlo matches that used
during data taking
(114 mm = 0.29 MIPS)
Reconstructed direction (deg)
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Summary
• Our expectations (threshold, geometry) have been
validated
• A simpler model (no complicated physics!) can be
easier to understand
• A simple model can represent a complicated
process
Thank you Xin Chen,
Tune Kamae and Eduardo do Couto e Silva !!!
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