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

1. 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

2. 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)

3. Detector pythiaZPolebbbar-0-1000_SLIC_ v1r9p3_sidaug05.slcio, without effects of beamsstrahlung or brehmsstrahlung

4. 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

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

6. 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)

7. 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)

8. 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%)

9. 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%)

10. 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

11. 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

12. 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 (Tyler’s) result: only require that hits are on same side in z. This is not required when using z segmentation.

13. Module Projection (extrapolation) Note: No actual spacing between modules Hit 1 Hit 2 Possible modules for following hits

14. Module Projection (interpolation) Note: No actual spacing between modules Hit 1 Possible modules Hit 2

15. Z Segmentation Results

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

17. 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

18. 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)

19. Tyler’s Results: New vs. Old

20. Z Segmentation Results (Phi-Restricted)

21. ZSeg.java with Phi Restriction 30cm 1cm 5cm 10cm

22. Comparing Z Segmentation with and without Phi Restriction

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

24. 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

25. Shortcomings • Projection in r-zwill 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

26. 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

27. The End