MatchCosmics: propagate the seed covariance to the DCA - #15894
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MatchCosmics::process propagates every seed to the DCA to the origin with propagateToDCABxByBz(Point3D, ...). With a Point3D this resolves to the TrackPar_t overload: only the track parameters are propagated, the covariance stays the one at the track's reference X (TPC inner radius). checkPair then compares the two legs at the DCA with these too small errors, so the y/snp cuts and the chi2 are far too tight and genuine legs are rejected (RejY). Using a VertexBase (origin, zero covariance) selects the TrackParCov overload; the propagation itself is unchanged. Tests, same input with and without the fix, TPC-only legs: - COSMICS run 562658 (0.5 T, no TPC distortion correction), 2000 TFs: cosmics with legs in opposite halves 221 -> 402 (total 253 -> 456). Example of a rejected pair (matcher debug tree): dy = 0.79 cm with sigma2_y = 0.0013 cm2 used (= the value at x = 83 cm), while the covariance propagated to the DCA gives sigma2_y = 0.021 cm2, i.e. a 7 sigma window of 1.6 cm instead of < 0.8 cm. - Cosmic MC (O2DPG, GenCosmics, 0.5 T, no distortions, 5 TFs, MC labels): practically unchanged, 159 -> 165 cosmics; efficiency for muons with a TPC leg in each half 79.5 % -> 82.1 %; no wrong leg pairs (legs from different muons) in either case. The gain in data comes from the uncorrected static distortions shifting the legs beyond the too narrow window; without distortions (MC) the legs agree well enough to pass also with the unpropagated covariance. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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MatchCosmics::process propagates every seed to the DCA to the origin with propagateToDCABxByBz(Point3D, ...). With a Point3D this resolves to the TrackPar_t overload: only the track parameters are propagated, the covariance stays the one at the track's reference X (TPC inner radius). checkPair then compares the two legs at the DCA with these too small errors, so the y/snp cuts and the chi2 are far too tight and genuine legs are rejected (RejY). Using a VertexBase (origin, zero covariance) selects the TrackParCov overload; the propagation itself is unchanged.
Tests, same input with and without the fix, TPC-only legs:
COSMICS run 562658 (0.5 T, no TPC distortion correction), 2000 TFs: cosmics with legs in opposite halves 221 -> 402 (total 253 -> 456). Example of a rejected pair (matcher debug tree): dy = 0.79 cm with sigma2_y = 0.0013 cm2 used (= the value at x = 83 cm), while the covariance propagated to the DCA gives sigma2_y = 0.021 cm2, i.e. a 7 sigma window of 1.6 cm instead of < 0.8 cm.
Cosmic MC (O2DPG, GenCosmics, 0.5 T, no distortions, 5 TFs, MC labels): practically unchanged, 159 -> 165 cosmics; efficiency for muons with a TPC leg in each half 79.5 % -> 82.1 %; no wrong leg pairs (legs from different muons) in either case.
The gain in data comes from the uncorrected static distortions shifting the legs beyond the too narrow window; without distortions (MC) the legs agree well enough to pass also with the unpropagated covariance.