in nova fert animus mutatas dicere formas corpora; di, coeptis (nam vos mutastis et illas) adspirate...
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In nova fert animus mutatas dicere formas corpora; di, coeptis (nam vos mutastis et illas) adspirate meis primaque ab origine
mundi ad mea perpetuum deducite tempora carmen! Ante mare et terras et quod tegit omnia caelum unus erat toto naturae vultus in orbe quem dixere chaos: rudis indigestaque moles nec quicquam
nisi pondus iners congestaque eodem non bene iunctarum discordia semina rerum. nullus adhuc mundo praebebat lumina Titan, nec
nova crescendo reparabat cornua Phoebe, nec circumfuso pendebat in aere tellus ponderibus librata suis, nec bracchia longo margine
terrarum porrexerat Amphitrite utque erat et tellus illic et pontus et aer, sic erat instabilis tellus, innabilis unda, lucis egens aer
GLAST Background AnalysisGLAST Background Analysis
An examination of events recorded An examination of events recorded by the LAT prototype detectorby the LAT prototype detector
11 September 2003 GLAST Background Analysis 2
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
11 September 2003 GLAST Background Analysis 3
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)
11 September 2003 GLAST Background Analysis 4
Particle Interaction
Si
Si thickness0.400 mm
Strip pitch0.228 mm 1536 strips / layer
11 September 2003 GLAST Background Analysis 5
Particle Interaction
Si
1 hit
E
h+
e-
Strip pitch0.228 mm
11 September 2003 GLAST Background Analysis 6
Particle Interaction
Si
2 hits
h+
e-h+
e-
E
11 September 2003 GLAST Background Analysis 7
Particle Interaction
Si
E
Electron/hole pairs can drift to a neighboring strip if the track passes through a “diffusion zone”
approx 6 m Strip pitch0.228 mm
11 September 2003 GLAST Background Analysis 8
Particle Interaction
Si
E
1 - 3 hits
h+
e-h+
e-
h+
e-
11 September 2003 GLAST Background Analysis 9
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
11 September 2003 GLAST Background Analysis 10
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”
Background
11 September 2003 GLAST Background Analysis 11
The First Minitower
All coords.in mm
z
xy
We expected to see hits in every SSD…
11 September 2003 GLAST Background Analysis 12
The Second Minitower
New prototype gives much better results!
All coords.in mm
z
xy
PRELIMINARY DATA
11 September 2003 GLAST Background Analysis 13
Threshold Levels
A higher threshold yields more one-hit events in lieu ofevents with multiple hits. This is what we expected.
What else is affected by the change? Efficiency!
Data from first minitower
11 September 2003 GLAST Background Analysis 14
Angular correlation
A track with a given zenith angle can hit one or multiple strips depending on its azimuthal angle
11 September 2003 GLAST Background Analysis 15
Angular correlation
A track with a given zenith angle can hit one or multiple strips depending on its azimuthal angle
Restricting the azimuthal angle to a small “pie slice” we
attain events in an approximately two-
dimensional plane
11 September 2003 GLAST Background Analysis 16
Angular correlation
A track with a given zenith angle can hit one or multiple strips depending on its azimuthal angle
Restricting the azimuthal angle to a small “pie slice” we
attain events in an approximately two-
dimensional plane
In each event, the bottom layer will experience low
hit multiplicity…
the top layer will showa correlation between
zenith angle and strips hit
11 September 2003 GLAST Background Analysis 17
Angular correlation
l
t
tan = l / t
11 September 2003 GLAST Background Analysis 18
Data vs Monte Carlo
Cuts on experimental data:• Single track events
• Single cluster per layer
• Projected track is within 8 degrees from Y axis
• Number of strips hit in each X layer averaged by zenith angle
Discrepancy~30% difference
Data from first minitower
Reconstructed direction (deg)
11 September 2003 GLAST Background Analysis 19
Improved Monte Carlo
Features added to Monte Carlo:
• Path length threshold (128 m = 0.32 MIPS)
~10% difference
Data from first minitower
Reconstructed direction (deg)
11 September 2003 GLAST Background Analysis 20
Further improvements
Features added to Monte Carlo:
• Path length threshold (128 m = 0.32 MIPS)
•Diffusion zones (7 m)
Most points fitwithin error bars!
Data from first minitower
Reconstructed direction (deg)
11 September 2003 GLAST Background Analysis 21
Preliminary Comparisons
Preliminary data from new tracker yield a much better fit!
Threshold in Monte Carlo matches that used during data taking(114 m = 0.29 MIPS)
PRELIMINARY DATA
Data from second minitower!
Reconstructed direction (deg)
11 September 2003 GLAST Background Analysis 22
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 !!!