Fixes stuck particles in far backward hadron beampipe

.github/workflows/linux-eic-shell.yml

@@ -294,7 +294,7 @@ jobs:
     strategy:
       matrix:
         option: ['m'] #, 's'] # FIXME
-        detector_config: [epic_craterlake] # FIXME
+        detector_config: [epic_craterlake, epic_ip6_extended] # FIXME
       fail-fast: false
     steps:
     - uses: actions/checkout@v5
@@ -347,7 +347,11 @@ jobs:
       - build
     strategy:
       matrix:
-        detector_config: [epic_craterlake]
+        include:
+          - detector_config: epic_craterlake
+            tolerance_mm: 0.1
+          - detector_config: epic_ip6_extended
+            tolerance_mm: 0.01
       fail-fast: false
     steps:
     - uses: actions/checkout@v5
@@ -363,7 +367,7 @@ jobs:
         setup: install/bin/thisepic.sh
         run: |
           mkdir -p doc
-          python scripts/checkOverlaps.py -c ${DETECTOR_PATH}/${{ matrix.detector_config }}.xml | tee doc/overlap_check_geant4.out
+          python scripts/checkOverlaps.py -t ${{ matrix.tolerance_mm }} -c ${DETECTOR_PATH}/${{ matrix.detector_config }}.xml | tee doc/overlap_check_geant4.out
           noverlaps="$(grep -c GeomVol1002 doc/overlap_check_geant4.out || true)"
           if [[ "${noverlaps}" -gt "0" ]] ; then echo "${noverlaps} overlaps found!" && false ; fi
 

compact/far_backward/beamline_extension_hadron.xml

@@ -49,8 +49,8 @@
     type="BeamPipeChain"
     wall_thickness="2*mm">
       <pipe id="0" name="Pipe_to_Q1APR"
-        xcenter="(Hadron_Beampipe_End*sin(CrossingAngle)+Q1APR_StartX)/2." zcenter="(Hadron_Beampipe_End+Q1APR_StartZ)/2."
-        length="(Hadron_Beampipe_End-Q1APR_StartZ)/cos(CrossingAngle)" theta="CrossingAngle"
+        xcenter="(Hadron_Beampipe_End*sin(CrossingAngle)+Q1APR_StartX)/2." zcenter="(Hadron_Beampipe_End*cos(CrossingAngle)+Q1APR_StartZ)/2."
+        length="sqrt((Hadron_Beampipe_End*sin(CrossingAngle)-Q1APR_StartX)^2+(Hadron_Beampipe_End*cos(CrossingAngle)-Q1APR_StartZ)^2)" theta="CrossingAngle"
         rout1="Hadron_Beampipe_Rad" rout2="Hadron_Beampipe_Rad">
       </pipe>
       <pipe id="1" name="Pipe_in_Q1APR"

src/BeamPipeChain_geo.cpp

@@ -28,7 +28,7 @@ static Ref_t create_detector(Detector& description, xml_h e, SensitiveDetector /
   Material m_Vacuum = description.material("Vacuum");
   string vis_name   = dd4hep::getAttrOrDefault<std::string>(x_det, _Unicode(vis), "BeamPipeVis");
   double thickness  = getAttrOrDefault<double>(x_det, _Unicode(wall_thickness), 0);
-  double bendRadius = 0.00001; //Small bend radius to allow the construction of toruses
+  double bendRadius = 0.00001 * mm; //Small bend radius to allow the construction of toruses
 
   vector<string> names;
   vector<int> ids;
@@ -94,12 +94,13 @@ static Ref_t create_detector(Detector& description, xml_h e, SensitiveDetector /
 
   // If there is an bend in the pipe, calculate the length reduction of the pipe and joint length
   for (uint i = 1; i < thetas.size(); i++) {
+
     // Start at the join between the first two pipes ending at the join between the last two pipes N-1
-    if (thetas[i - 1] == thetas[i]) {
+    double bendAngle = thetas[i] - thetas[i - 1];
+    if (std::abs(bendAngle) < 0.01 * mrad) {
       bendLengths.push_back(0);
     } else // Correct for tubes, not yet cones so imperfect
     {
-      double bendAngle  = thetas[i] - thetas[i - 1];
       double bendLength = abs(rOuters1[i] * tan(bendAngle / 2));
       bendLengths.push_back(bendLength + bendRadius);
     }