ITS3: account for epitaxial layer

Author: f3sch

Detectors/ITSMFT/ITS/base/src/GeometryTGeo.cxx

@@ -420,33 +420,20 @@ TGeoHMatrix* GeometryTGeo::extractMatrixSensor(int index) const
   static int chipInGlo{0};
 
   // account for the difference between physical sensitive layer (where charge collection is simulated) and effective sensor thicknesses
+  // in the ITS3 case this accounted by specialized functions
   double delta = Segmentation::SensorLayerThickness - Segmentation::SensorLayerThicknessEff;
-#ifdef ENABLE_UPGRADES
-  if (mIsLayerITS3[getLayer(index)]) {
-    delta = its3::SegmentationSuperAlpide::mSensorLayerThickness - its3::SegmentationSuperAlpide::mSensorLayerThicknessEff;
-  }
-#endif
-
   static TGeoTranslation tra(0., 0.5 * delta, 0.);
-
+#ifdef ENABLE_UPGRADES // only apply for non ITS3 OB layers
+  if (!mIsLayerITS3[getLayer(index)]) {
+    matTmp *= tra;
+  }
+#else
   matTmp *= tra;
+#endif
 
   return &matTmp;
 }
 
-//__________________________________________________________________________
-const o2::math_utils::Transform3D GeometryTGeo::getT2LMatrixITS3(int isn, float alpha)
-{
-  // create for sensor isn the TGeo matrix for Tracking to Local frame transformations
-  static TGeoHMatrix t2l;
-  t2l.Clear();
-  t2l.RotateZ(alpha * RadToDeg()); // rotate in direction of normal to the tangent to the cylinder
-  const TGeoHMatrix& matL2G = getMatrixL2G(isn);
-  const auto& matL2Gi = matL2G.Inverse();
-  t2l.MultiplyLeft(&matL2Gi);
-  return Mat3D(t2l);
-}
-
 //__________________________________________________________________________
 void GeometryTGeo::Build(int loadTrans)
 {
@@ -926,6 +913,24 @@ TGeoHMatrix& GeometryTGeo::createT2LMatrix(int isn)
   return t2l;
 }
 
+//__________________________________________________________________________
+const o2::math_utils::Transform3D GeometryTGeo::getT2LMatrixITS3(int isn, float alpha)
+{
+  // create for sensor isn the TGeo matrix for Tracking to Local frame transformations with correction for effective thickness
+  static TGeoHMatrix t2l;
+  t2l.Clear();
+  t2l.RotateZ(alpha * RadToDeg()); // rotate in direction of normal to the tangent to the cylinder
+  const TGeoHMatrix& matL2G = getMatrixL2G(isn);
+  const auto& matL2Gi = matL2G.Inverse();
+  t2l.MultiplyLeft(&matL2Gi);
+  // correction for effective sensor thickness
+  static TGeoTranslation tra;
+  tra.SetDx(SuperSegmentation::mSensorLayerThicknessCorr * std::cos(alpha));
+  tra.SetDy(SuperSegmentation::mSensorLayerThicknessCorr * std::sin(alpha));
+  t2l *= tra;
+  return Mat3D(t2l);
+}
+
 //__________________________________________________________________________
 int GeometryTGeo::extractVolumeCopy(const char* name, const char* prefix) const
 {

Detectors/Upgrades/ITS3/base/include/ITS3Base/SegmentationSuperAlpide.h

@@ -69,6 +69,7 @@ class SegmentationSuperAlpide
   static constexpr float mPitchRow{constants::pixelarray::width / static_cast<float>(mNRows)};
   static constexpr float mSensorLayerThickness{constants::thickness};
   static constexpr float mSensorLayerThicknessEff{constants::effThickness};
+  static constexpr float mSensorLayerThicknessCorr{constants::corrThickness};
   static constexpr std::array<float, constants::nLayers> mRadii{constants::radii};
 
   /// Transformation from the curved surface to a flat surface

Detectors/Upgrades/ITS3/base/include/ITS3Base/SpecsV2.h

@@ -118,10 +118,11 @@ constexpr unsigned int nTotLayers{7};
 constexpr unsigned int nSensorsIB{2 * nLayers};
 constexpr float equatorialGap{1 * mm};
 constexpr std::array<unsigned int, nLayers> nSegments{3, 4, 5};
-constexpr float epitaxialThickness{10 * mu};
-constexpr float psubThickness{40 * mu};
+constexpr float epitaxialThickness{10 * mu};                                                                                         // eptixial layer (charge collection)
+constexpr float psubThickness{40 * mu};                                                                                              // silicon substrate
 constexpr float thickness{epitaxialThickness + psubThickness};                                                                       // physical thickness of chip
-constexpr float effThickness{epitaxialThickness + psubThickness / 2.0};                                                              // correction to the epitaxial layer
+constexpr float effThickness{epitaxialThickness / 2.0 + psubThickness};                                                              // effective physical thickness
+constexpr float corrThickness{effThickness - thickness / 2.0};                                                                       // correction to get into the epitxial layer
 constexpr std::array<float, nLayers> radii{19.0006 * mm, 25.228 * mm, 31.4554 * mm};                                                 // middle radius e.g. inner radius+thickness/2.
 constexpr std::array<float, nLayers> radiiInner{radii[0] - thickness / 2.0, radii[1] - thickness / 2.0, radii[2] - thickness / 2.0}; // inner radius
 constexpr std::array<float, nLayers> radiiOuter{radii[0] + thickness / 2.0, radii[1] + thickness / 2.0, radii[2] + thickness / 2.0}; // inner radius