refactor: use time info in Kalman vertex fit

CI/physmon/vertexing_config.yml

@@ -19,7 +19,6 @@ histograms:
     min: -6
     max: 6
 
-
   "trk_pull.*":
     nbins: 50
     min: -10

Core/include/Acts/Vertexing/AdaptiveMultiVertexFinder.hpp

@@ -143,9 +143,13 @@ class AdaptiveMultiVertexFinder {
     // Use seed vertex as a constraint for the fit
     bool useSeedConstraint = true;
 
-    // Diagonal constraint covariance entries in case
-    // no beamspot constraint is provided
-    double looseConstrValue = 1e+8;
+    // Initial variance of the vertex position in case no beamspot constraint is
+    // provided
+    double initialSpatialVariance = 1e+8;
+
+    // Initial variance of the vertex time in case no beamspot constraint is
+    // provided
+    double initialTemporalVariance = 1e+8;
 
     // Default fitQuality for constraint vertex in case no beamspot
     // constraint is provided

Core/include/Acts/Vertexing/AdaptiveMultiVertexFinder.ipp

@@ -185,8 +185,12 @@ auto Acts::AdaptiveMultiVertexFinder<vfitter_t, sfinder_t>::
     }
   } else {
     currentConstraint.setFullPosition(seedVertex.fullPosition());
-    currentConstraint.setFullCovariance(SquareMatrix4::Identity() *
-                                        m_cfg.looseConstrValue);
+    // Default initial variances (i.e., diagonal elements of the covariance
+    // matrix)
+    Vector4 variances(
+        m_cfg.initialSpatialVariance, m_cfg.initialSpatialVariance,
+        m_cfg.initialSpatialVariance, m_cfg.initialTemporalVariance);
+    currentConstraint.setFullCovariance(variances.asDiagonal());
     currentConstraint.setFitQuality(m_cfg.defaultConstrFitQuality);
   }
 }

Core/include/Acts/Vertexing/AdaptiveMultiVertexFitter.ipp

@@ -6,7 +6,6 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-#include "Acts/Vertexing/KalmanVertexTrackUpdater.hpp"
 #include "Acts/Vertexing/KalmanVertexUpdater.hpp"
 #include "Acts/Vertexing/VertexingError.hpp"
 
@@ -369,7 +368,9 @@ void Acts::AdaptiveMultiVertexFitter<
     for (const auto trk : state.vtxInfoMap[vtx].trackLinks) {
       auto& trkAtVtx = state.tracksAtVerticesMap.at(std::make_pair(trk, vtx));
       if (trkAtVtx.trackWeight > m_cfg.minWeight) {
-        KalmanVertexTrackUpdater::update<input_track_t>(trkAtVtx, *vtx);
+        // Update the track parameters using the final estimate of the vertex
+        // position. This also updates their chi2 values using a symmetric test.
+        KalmanVertexUpdater::updateTrack<input_track_t>(trkAtVtx, *vtx);
       }
     }
   }