Efforts to Improve the Reconstruction of Non-Prompt Tracks with the SiD

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Efforts to Improve the Reconstruction of
Non-Prompt Tracks with the SiD
Lori Stevens UCSC ILC Simulation Reconstruction
Meeting May 15, 2007
Includes contributions from Tyler Rice
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Outline

• Tyler Rices efficiency and purity results from
  study of Tim Nelsons AxialBarrelTrackFinder
  algorithm
• Z Segmentation algorithm (ZSeg.java)
• Results after implementing ZSeg.java
• Tylers phi-restriction and results (including
  ZSeg.java implementation)

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Detector

• pythiaZPolebbbar-0-1000_SLIC_ v1r9p3_sidaug05.slci
  o, without effects of beamsstrahlung or
  brehmsstrahlung

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AxialBarrelTrackFinder1.java

• Track pattern recognition using only the 5 outer
  tracking layers
• Works from outside inward (VXDCheater.java has
  already removed hits from prompt tracks
  originating within 20mm of the origin)
• ABTF1 begins by using all sets of isolated hits
  in 3 layers to find circles that pass within 10cm
  of the interaction point (original version had
  1cm)
• When 3 seed track is found, remaining layers are
  checked for nearby hits

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Event and Particle Requirements

• Event (Jet Accept Test)
• 1. Cosine of thrust angle lt 0.5
• 2. Thrust value gt 0.94
• Findable Particles
• 1. Final State or Intermediate State with r
• origin lt 400mm and path length gt 500mm
• 2. Transverse momentum gt 0.75GeV
• 3. Carries a charge
• 4. Cosine theta lt 0.8
• 5. Not backscatter off of the calorimeter

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Particle and Track Definitions

• Found Findable MC Particle associated track
  has purity gt 0.75 (at least 3 of 4 hits from
  same MCP or at least 4 of 5 from same MCP)
• Missed Findable MC Particle all other findable
  MC Particles
• Fake track
• 1. no majority MC Particle associated with track
  
• 2. tracks with bad purity (too few hits from
  same MCP)

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Tylers Results (have already been presented in
Beijing)

• 118/1000 events passed Jet Accept Test
• 304 total MC Particles
• Efficiency
• 131 Found with 5 hits (43)
• 100 Found with 4 hits (33)
• 73 Missed (24)
• Fake rates
• 327 Fake (326/327 are 4 hit tracks this implies
  that 4 hit tracks cannot be used)

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Digression Other Studies by Tyler (why is
reconstruction efficiency not 100?)

• First Tyler tried requiring that particles hit
  each of the 5 outer detector layers once and only
  once
• Fewer candidate particles
• 166 Findable MC Particles (304 before
  requirement)
• Efficiency
• 113 Found with 5 hits (68 vs. 43)
• 25 Found with 4 hits (15 vs. 33)
• 28 Missed (17 vs. 24)

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Tylers Three-Hit Seed Study

• Then Tyler also required all hits from three-hit
  seed tracks to be associated with the same MC
  Particle
• 166 Findable MC Particles (304 before
  requirement)
• Efficiency
• 144 Found with 5 hits (87 vs. 43)
• 15 Found with 4 hits (9 vs. 33)
• 7 Missed (4 vs. 24)

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Motivation for Z Segmentation

• Improve efficiency for finding MC Particles (can
  we clean up the 3 hit seeds?)
• Decrease number of 4 hit fake tracks see if we
  can make 4 hit tracks useable

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Z Segmentation Algorithm (1 of 2)

• ZSeg.java creates segmentation of z-axis into
  separate modules (length set by user)
• Algorithm is capable of offsetting individual
  layers, amount set by user (still testing)
• ZSeg.java contains ZCheckerExt method that takes
  three SimTrackerHit arguments this method is
  called from inside AxialBarrelTrackFinder1.java
• Method calculates minimum and maximum coordinates
  of the z module for each of the 3 hits
• Straight lines in r-z are projected from modules
  in layers containing 1st two hits onto layer
  containing 3rd hit

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Z Segmentation Algorithm (2 of 2)

• Algorithm checks if 3rd hit is in a module
  consistent with the1st two hits
• For now, testing consistency in 3 hit seeds only
  (later to include check for 4th and 5th hits)
• Eventually algorithm will take in a list of hits
  and check all possible 3 hit combinations for
  consistency, including a test for whether to use
  extrapolation or interpolation (currently using
  only extrapolation)
• Original (Tylers) result only require that hits
  are on same side in z. This is not required when
  using z segmentation.

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Module Projection (extrapolation)

• Note No actual spacing between modules

Hit 1
Hit 2
Possible modules for following hits
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Module Projection (interpolation)
Note No actual spacing between modules
Hit 1
Possible modules
Hit 2
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Z Segmentation Results
Tyler 30cm segments 10cm segments 5cm segments 1cm segments
MCPs 304 302 302 302 302
Found with 5 hits 131 122 138 145 148
Found with 4 hits 100 100 104 109 99
Missed 73 80 60 48 55
Fake 327 455 332 267 127
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Implementing ZSeg.java (preliminary results)
30cm
10cm
5cm
1cm
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Another Idea Require Hits to be in Same Sector
in Phi

• Recall Tyler saw that a lot of inefficiency and
  fake tracks due to bad 3 hit seeds
• Clean up seeds by requiring that the phi
  coordinate of all hits must be within p/2 of each
  other
• Also apply criterion to all hits once track is
  found

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Tylers Phi Restriction Results (only require
hits on same side in z)

• 304 total MC Particles
• Efficiency
• 145 Found with 5 hits (48)
• 112 Found with 4 hits (37)
• 47 Missed (15)
• Fake rates
• 158 Fake (all 4 hit)

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Tylers Results New vs. Old
New results of MCPs Old results of MCPs
of MCPs 304 100 304 100
Found with 5 hits 145 48 131 43
Found with 4 hits 112 37 100 33
Missed 47 15 73 24
Fake 158 327
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Z Segmentation Results (Phi-Restricted)
Tyler 30cm segments 10cm segments 5cm segments 1cm segments
MCPs 304 302 302 302 302
Found with 5 hits 145 142 147 152 152
Found with 4 hits 112 113 114 110 101
Missed 47 47 41 40 49
Fake 158 202 142 108 45
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ZSeg.java with Phi Restriction
30cm
1cm
5cm
10cm
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Comparing Z Segmentation with and without Phi
Restriction
30cm phi rest. 30cm 10cm phi rest. 10cm 5cm phi rest. 5cm 1cm phi rest. 1cm
MCPs 302 302 302 302 302 302 302 302
Found with 5 hits 142 122 147 138 152 145 152 148
Found with 4 hits 113 100 114 104 110 109 101 99
Missed 47 80 41 60 40 48 49 55
Fake 202 455 142 332 108 267 45 127
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Graphs of Z Segmentation with and without Phi
Restriction
30cm
10cm
1cm
5cm
30cm
5cm
1cm
10cm
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Comments on Results

• Might expect 30cm segmentation to be worse than
  simply requiring all hits to be on same side of
  the detector
• Assumption that tracks are straight in r-z is
  less valid for low pT

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Shortcomings

• Projection in r-z will actually curve ZSeg.java
  treats track r-z projection as if it were a
  straight line
• Using ZPole qqbar at 500GeV would be even more
  challenging. Would like to study but will need
  500GeV qqbar with no beamsstrahlung or
  brehmsstrahlung

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For the Future

• Check for z consistency in 4th and 5th hits
• Take in list of hits and check all possible hit
  combinations (including interpolation/
• extrapolation check)
• Check validity of straight line approximation as
  a function of pT

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The End