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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 Rice’s efficiency and purity results from study of Tim Nelson’s AxialBarrelTrackFinder algorithm Z Segmentation algorithm (ZSeg.java) Results after implementing ZSeg.java Tyler’s phi-restriction and results (including ZSeg.java implementation)

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Detector pythiaZPolebbbar _SLIC_ v1r9p3_sidaug05.slcio, 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 < Cosine of thrust angle < Thrust value > Thrust value > 0.94 “Findable” Particles: 1. Final State or Intermediate State with r 1. Final State or Intermediate State with r origin 500mm origin 500mm 2. Transverse momentum > 0.75GeV 2. Transverse momentum > 0.75GeV 3. Carries a charge 3. Carries a charge 4. |Cosine theta| < |Cosine theta| < Not backscatter off of the calorimeter 5. Not backscatter off of the calorimeter

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Particle and Track Definitions “Found” Findable MC Particle: associated track has “purity” >= 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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Tyler’s 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: 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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Tyler’s 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 1 st two hits onto layer containing 3 rd hit

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Z Segmentation Algorithm (2 of 2) Algorithm checks if 3 rd hit is in a module consistent with the1st two hits For now, testing consistency in 3 hit seeds only (later to include check for 4 th and 5 th 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 (Tyler’s) 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) Hit 1 Hit 2 Possible modules Note: No actual spacing between modules

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Z Segmentation Results Tyler 30cm segments 10cm segments 5cm segments 1cm segments # MCPs Found with 5 hits Found with 4 hits Missed Fake

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Implementing ZSeg.java (“preliminary” results) 1cm 5cm 10cm 30cm

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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 π/2 of each other Also apply criterion to all hits once track is found

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Tyler’s 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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Tyler’s Results: New vs. Old New results % of MCPs Oldresults # of MCPs %304100% Found with 5 hits 14548%13143% Found with 4 hits 11237%10033% Missed4715%7324% Fake158327

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Z Segmentation Results (Phi-Restricted) Tyler 30cm segments 10cm segments 5cm segments 1cm segments # MCPs Found with 5 hits Found with 4 hits Missed Fake

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ZSeg.java with Phi Restriction 1cm5cm10cm 30cm

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Comparing Z Segmentation with and without Phi Restriction 30cm phi rest. 30cm 10cm 10cm phi rest. phi rest.10cm5cm 5cm1cm 1cm #MCPs Found with 5 hits Found with 4 hits Missed Fake

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Graphs of Z Segmentation with and without Phi Restriction 1cm5cm 10cm 30cm 1cm 5cm 10cm 30cm

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

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The End

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