feat: cut to the maximum value of delta z between SPs in seedFinder (#…

…1209)

This PR adds a cut to the maximum value of delta z between SPs in seedFinder. By default the cut is not applied since `deltaZMax` is set to `numeric_limits<float>::max()` 

This cut will be used for the strip SPs in the ITk implementation but not for the pixel SPs

Core/include/Acts/Seeding/Seedfinder.ipp

@@ -99,8 +99,9 @@ void Seedfinder<external_spacepoint_t, platform_t>::createSeedsForGroup(
       if (deltaR > m_config.deltaRMaxTopSP) {
         continue;
       }
+      float deltaZ = topSP->z() - zM;
       // ratio Z/R (forward angle) of space point duplet
-      float cotTheta = (topSP->z() - zM) / deltaR;
+      float cotTheta = deltaZ / deltaR;
       if (std::fabs(cotTheta) > m_config.cotThetaMax) {
         continue;
       }
@@ -110,6 +111,9 @@ void Seedfinder<external_spacepoint_t, platform_t>::createSeedsForGroup(
           zOrigin > m_config.collisionRegionMax) {
         continue;
       }
+      if (std::abs(deltaZ) > m_config.deltaZMax) {
+        continue;
+      }
       // cut on the max curvature between top SP and interaction point
       // first transform the space point coordinates into a frame such that the
       // central space point SPm is in the origin of the frame and the x axis
@@ -171,8 +175,9 @@ void Seedfinder<external_spacepoint_t, platform_t>::createSeedsForGroup(
       if (deltaR < m_config.deltaRMinBottomSP) {
         continue;
       }
+      float deltaZ = zM - bottomSP->z();
       // ratio Z/R (forward angle) of space point duplet
-      float cotTheta = (zM - bottomSP->z()) / deltaR;
+      float cotTheta = deltaZ / deltaR;
       if (std::fabs(cotTheta) > m_config.cotThetaMax) {
         continue;
       }
@@ -182,6 +187,9 @@ void Seedfinder<external_spacepoint_t, platform_t>::createSeedsForGroup(
           zOrigin > m_config.collisionRegionMax) {
         continue;
       }
+      if (std::abs(deltaZ) > m_config.deltaZMax) {
+        continue;
+      }
       // cut on the max curvature between bottom SP and interaction point
       // first transform the space point coordinates into a frame such that the
       // central space point SPm is in the origin of the frame and the x axis

Core/include/Acts/Seeding/SeedfinderConfig.hpp

@@ -65,6 +65,10 @@ struct SeedfinderConfig {
   // parameters for forward seed confirmation
   SeedConfirmationRange forwardSeedConfirmationRange;
 
+  // cut to the maximum value of delta z between SPs
+  float deltaZMax =
+      std::numeric_limits<float>::infinity() * Acts::UnitConstants::mm;
+
   // enable cut on the compatibility between interaction point and SPs
   bool interactionPointCut = false;
 
@@ -165,6 +169,7 @@ struct SeedfinderConfig {
     config.rMax /= 1_mm;
     config.rMin /= 1_mm;
     config.bFieldInZ /= 1000. * 1_T;
+    config.deltaZMax /= 1_mm;
 
     config.beamPos[0] /= 1_mm;
     config.beamPos[1] /= 1_mm;

Examples/Python/src/TrackFinding.cpp

@@ -104,6 +104,7 @@ void addTrackFinding(Context& ctx) {
     ACTS_PYTHON_MEMBER(nTrplPerSpBLimit);
     ACTS_PYTHON_MEMBER(nAvgTrplPerSpBLimit);
     ACTS_PYTHON_MEMBER(impactMax);
+    ACTS_PYTHON_MEMBER(deltaZMax);
     ACTS_PYTHON_MEMBER(zBinEdges);
     ACTS_PYTHON_MEMBER(enableCutsForSortedSP);
     ACTS_PYTHON_MEMBER(interactionPointCut);

Examples/Scripts/Python/itk_seeding.py

@@ -69,6 +69,7 @@ def runITkSeeding(field, csvInputDir, outputDir, s=None):
         beamPos=acts.Vector2(0 * u.mm, 0 * u.mm),
         impactMax=gridConfig.impactMax,
         maxPtScattering=float("inf") * u.GeV,
+        deltaZMax=900 * u.mm,
         interactionPointCut=True,
         zBinEdges=gridConfig.zBinEdges,
         enableCutsForSortedSP=True,  # enable cotTheta sorting in SeedFinder