fix: improved charge sign determination

[osbornjd]

This PR changes the charge sign determination in the track seed track parameter determination by taking the first and last cluster in the seed instead of the first and second cluster. That maximizes the lever arm and decreases the wrong charge sign assignment.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work for users)
• Requiring change in macros repository (Please provide links to the macros pull request in the last section)
• I am a member of GitHub organization of sPHENIX Collaboration, EIC, or ECCE (contact Chris Pinkenburg to join)

What kind of change does this PR introduce? (Bug fix, feature, ...)

TODOs (if applicable)

Links to other PRs in macros and calibration repositories (if applicable)

Pull Request Summary: Improved Charge Sign Determination

Motivation / Context

This PR addresses a bug in the charge sign determination logic for track seed parameter estimation. The original implementation used the first and second clusters in a seed to determine the charge sign. However, this approach has a limited lever arm and can lead to incorrect charge sign assignments, particularly for seeds with limited spatial resolution or close cluster separations. By using the first and last clusters instead, the implementation maximizes the lever arm and improves the robustness of charge sign determination.

Key Changes

• Modified charge sign calculation: In TrackSeedHelper::circleFitByTaubin(), replaced the selection of the first two clusters with the first and last clusters from the seed trajectory
  • Changed from: second position = *(positions_2d.begin() + 1)
  • Changed to: second position = *(positions_2d.rbegin())
• This modification affects the computed azimuthal angles (firstphi and secondphi) based on the radial position vectors from the circle center
• The delta phi (dphi) computation between first and last cluster angles now has maximum separation, improving charge sign determination accuracy
• All other circle fitting logic and algorithms remain unchanged

Lines changed: +2/-2

Potential Risk Areas

• Reconstruction behavior: This change directly affects track charge sign assignment, which is fundamental to track reconstruction. Seeds with incorrect charge assignments from using close clusters may now receive correct assignments, but edge cases with very few clusters (<3) will not be affected due to the existing size check
• Kinematic properties: Tracks with incorrect charge signs will now be corrected, affecting downstream analyses that depend on charge-sensitive parameters (e.g., momentum measurements, curvature interpretation)
• Performance: Minimal expected impact; the change only affects array access patterns (using reverse iterator instead of index-based access)
• Data format/IO: No changes to data storage formats or serialization; only affects runtime charge sign computation

Possible Future Improvements

• Add comprehensive validation studies comparing charge sign accuracy before and after this change, particularly for low-momentum tracks or seeds with limited cluster coverage
• Consider alternative charge sign determination strategies that use all available clusters with spatial-separation-weighted contributions
• Add physics QA histograms to monitor charge sign assignment efficiency and misidentification rates in reconstructed track samples
• Investigate potential correlations between charge sign determination robustness and cluster multiplicity

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Note: AI summary analysis is provided as reference. Please review the actual code changes and conduct appropriate physics validation given the critical nature of charge sign determination in track reconstruction.

[coderabbitai]

📝 Walkthrough

Walkthrough

The circleFitByTaubin function in TrackSeedHelper now selects the first and last 2D positions from the input array to define reference angles, replacing the previous logic that used the first two elements. This modification cascades through subsequent phi and dphi calculations, ultimately affecting the sign determination of the charge-to-momentum ratio.

Changes

Cohort / File(s)	Summary
Circle Fit Geometry offline/packages/trackbase_historic/TrackSeedHelper.cc	Modified position selection strategy in circleFitByTaubin: now uses endpoints (first and last) instead of adjacent initial elements to compute reference angles firstphi and secondphi, impacting downstream dphi and qOverR sign logic

✨ Finishing touches

• 📝 Generate docstrings

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_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[sphenix-jenkins-ci]

Build & test report

Report for commit 7c3201954d3f506ad240cb3af4004d9e3e31be08:

• builds and tests overall are SUCCESS.
• Build with configuration of alma9.2-gcc-14.2.0 / clang is SUCCESS, 📊clang report (full)/(new), build log
• Build with configuration of alma9.2-gcc-14.2.0 / new is SUCCESS, 📊Compiler report (full)/(new), build log
  • Generating DST and readback: build is SUCCESS
  • Calorimeter QA: build is SUCCESS, 📊 trends
    • 📊 QA-calorimeter for e- at p_T=4GeV : combined Chi2/nDoF = 27.45 / 72, and combined p-Value = 1
    • 📊 QA-calorimeter for pi+ at p_T=30GeV : combined Chi2/nDoF = 41.6183 / 72, and combined p-Value = 0.998442
    • 📊 QA-calorimetric-jet for e- at p_T=4GeV : combined Chi2/nDoF = 0.4559 / 42, and combined p-Value = 1
    • 📊 QA-calorimetric-jet for pi+ at p_T=30GeV : combined Chi2/nDoF = 14.2531 / 42, and combined p-Value = 0.999981
  • Tracking QA with Distortions: build is SUCCESS, 📊 trends
    • 📊 QA-distortions
  • Tracking QA at low occupancy: build is SUCCESS, 📊 trends
    • 📊 QA-Intt : combined Chi2/nDoF = -0 / 72, and combined p-Value = 1
    • 📊 QA-Micromegas : combined Chi2/nDoF = -0 / 20, and combined p-Value = 1
    • 📊 QA-Mvtx : combined Chi2/nDoF = -0 / 54, and combined p-Value = 1
    • 📊 QA-Tpc : combined Chi2/nDoF = -0 / 56, and combined p-Value = 1
    • 📊 QA-tracking : combined Chi2/nDoF = 237.099 / 56, and combined p-Value = 3.83593e-24
    • 📊 QA-vertexing : combined Chi2/nDoF = 30.0131 / 112, and combined p-Value = 1
  • Tracking QA for Pythia D0-jet: build is SUCCESS, 📊 trends
    • 📊 QA-Intt : combined Chi2/nDoF = -0 / 72, and combined p-Value = 1
    • 📊 QA-Micromegas : combined Chi2/nDoF = -0 / 20, and combined p-Value = 1
    • 📊 QA-Mvtx : combined Chi2/nDoF = -0 / 54, and combined p-Value = 1
    • 📊 QA-Tpc : combined Chi2/nDoF = -0 / 56, and combined p-Value = 1
    • 📊 QA-tracking : combined Chi2/nDoF = 3.17405e-06 / 50, and combined p-Value = 1
    • 📊 QA-vertexing : combined Chi2/nDoF = 30 / 112, and combined p-Value = 1
  • Tracking QA from run2pp 53877: build is SUCCESS, 📊 trends
    • 📊 QA-intt : combined Chi2/nDoF = -0 / 18, and combined p-Value = 1
    • 📊 QA-micromegas : combined Chi2/nDoF = -0 / 6, and combined p-Value = 1
    • 📊 QA-mvtx : combined Chi2/nDoF = -0 / 18, and combined p-Value = 1
    • 📊 QA-siliconseeds : combined Chi2/nDoF = 0.00727412 / 20, and combined p-Value = 1
    • 📊 QA-tpc : combined Chi2/nDoF = -0 / 48, and combined p-Value = 1
    • 📊 QA-tpcseeds : combined Chi2/nDoF = 0.00169328 / 28, and combined p-Value = 1
    • 📊 QA-trackfit : combined Chi2/nDoF = 5.51613 / 32, and combined p-Value = 1
  • system alma9.2-gcc-14.2.0, build new: run the default sPHENIX macro: build is SUCCESS, output, trends 📊
  • system alma9.2-gcc-14.2.0, build new: run the default CaloProduction/Fun4All_Year2.C macro: build is SUCCESS, output, trends 📊
  • system alma9.2-gcc-14.2.0, build new: run the default StreamingProduction/Fun4All_Stream_Combiner.C macro: build is SUCCESS, output, trends 📊
  • system alma9.2-gcc-14.2.0, build new: Valgrind test of CaloProduction/Fun4All_Year2.C: build is SUCCESS, 📊valgrind report, trends 📊
  • system alma9.2-gcc-14.2.0, build new: Valgrind test of StreamingProduction/Fun4All_Stream_Combiner.C: build is SUCCESS, 📊valgrind report, trends 📊
  • system alma9.2-gcc-14.2.0, build new: run the overlap check for sPHENIX macro: build is SUCCESS, output
  • system alma9.2-gcc-14.2.0, build new: Valgrind test: build is SUCCESS, 📊valgrind report, trends 📊
• Build with configuration of alma9.2-gcc-14.2.0 / scan is SUCCESS, 📊scan-build report (full)/(new), build log
• clang-tidy is SUCCESS, 📊clang-tidy report (full)/(new)
• cpp-check is SUCCESS, 📊cppcheck report (full)/(new)

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