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Cascade vertex fitter - #1186
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bloodyyugo wants to merge 4 commits into
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bloodyyugo wants to merge 4 commits into
bloodyyugo wants to merge 4 commits into
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… with comparison tuples Introduces standalone Kalman gain-matrix vertexers (KalmanV0Vertexer, CascadeVertexer, ThreeTrackVertexer, KalmanNTrackVertexer) alongside the legacy Billoir fitter for displaced 3-prong vertex studies, plus tuple drivers to compare the two on truth-matched V0/cascade/trident MC. Fixes several bugs found along the way in KalmanVertexFitterGainMatrix (arc-length sign, |B| in pT, Joseph-form covariance update, per-iteration prior reset) and BilliorVertex (negative chi2 guard), and adds purity-weighted track-to-MCParticle relations so downstream tuple drivers can pick the best-match track. Also adds a two-track Kalman V0 fit option to HpsReconParticleDriver for production-side comparison, and new steering files for the three-electron skim and N-track vertex studies.
…e hard mode The beam-momentum-constrained vertex fit's covariance modeled only beam divergence, missing the transverse momentum carried by the target nuclear recoil in trident production (true spread ~18.6 MeV vs modeled 0.37 MeV). Add a toggleable sigmaTNuclearRecoil term (soft mode only) that closes most of the real-MC chi2/ndf gap, and adopt it as the default for kalSoft*. Hard/exact mode (fitLagrangeMultiplier) hardcodes a null momentum covariance and can never benefit from this fix, so it is marked @deprecated (kept for regression reference) and its kalHard* tuple columns are no longer computed. Renamed sigmaTRecoil -> sigmaTNuclearRecoil to avoid confusion with a recoil electron from radiative/A' events (unrelated concept).
Renames the gain-matrix vertex fitter class to TrackConstraintVertexFitter to reflect that it shares one per-track constraint linearization across several solve strategies (sequential gain update, Schur-complement, joint Newton-Raphson/KKT) rather than being a single gain-matrix algorithm. Removes the standalone V0 Billoir-vs-Kalman cross-check driver (TwoTrackVertexComparisonTupleDriver) and dead test-only overloads, and adds the new Vertexer/NTrackVertexer abstractions and V0VertexComparisonTupleDriver used by the cascade/N-track all-constraint comparison studies.
mgignac
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Oct 7, 2026
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Looks fine to me and won't change other collections -- so fine to move in and include in our test. Do we really need all those steering files? What the minimum change you'd want to include into a 1% pass?
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closes #1185