[PWGEM/Dilepton] fix DCA calculation (#10912)

Co-authored-by: ALICE Action Bot <alibuild@cern.ch>

Author: dsekihat

PWGEM/Dilepton/Tasks/matchingMFT.cxx

@@ -273,8 +273,8 @@ struct matchingMFT {
     float dcaXY = std::sqrt(dcaX * dcaX + dcaY * dcaY);
     float dcaZ = -dcaXY * std::sinh(eta);
 
-    float dFdx = 2.f * dcaX / dcaXY;
-    float dFdy = 2.f * dcaY / dcaXY;
+    float dFdx = dcaX / dcaXY;
+    float dFdy = dcaY / dcaXY;
     float sigma_dcaXY = std::sqrt(cXXatDCA * dFdx * dFdx + cYYatDCA * dFdy * dFdy + 2.f * cXYatDCA * dFdx * dFdy);
 
     o2::dataformats::GlobalFwdTrack propmuonAtPV_Matched = propagateMuon(mchtrack, collision, propagationPoint::kToVertex);

PWGEM/Dilepton/Utils/EMTrackUtilities.h

@@ -25,36 +25,29 @@ namespace o2::aod::pwgem::dilepton::utils::emtrackutil
 {
 //_______________________________________________________________________
 template <typename T>
-float sigmaDca3D(T const& track)
+float dca3DinSigma(T const& track)
 {
-  float cYY = track.cYY();                              // in cm^2
-  float cZZ = track.cZZ();                              // in cm^2
-  float cZY = track.cZY();                              // in cm^2
-  float dcaXY = track.dcaXY();                          // in cm
-  float dcaZ = track.dcaZ();                            // in cm
-  float dca3d = std::sqrt(dcaXY * dcaXY + dcaZ * dcaZ); // in cm
-  float dFdxy = 2.f * dcaXY / dca3d;
-  float dFdz = 2.f * dcaZ / dca3d;
-  return std::sqrt(cYY * dFdxy * dFdxy + cZZ * dFdz * dFdz + 2.f * cZY * dFdxy * dFdz);
+  float cYY = track.cYY();
+  float cZZ = track.cZZ();
+  float cZY = track.cZY();
+  float dcaXY = track.dcaXY(); // in cm
+  float dcaZ = track.dcaZ();   // in cm
+
+  float det = cYY * cZZ - cZY * cZY; // determinant
+  if (det < 0) {
+    return 999.f;
+  } else {
+    return std::sqrt(std::fabs((dcaXY * dcaXY * cZZ + dcaZ * dcaZ * cYY - 2. * dcaXY * dcaZ * cZY) / det / 2.)); // dca 3d in sigma
+  }
 }
 //_______________________________________________________________________
 template <typename T>
-float dca3DinSigma(T const& track)
+float sigmaDca3D(T const& track)
 {
-  return std::sqrt(track.dcaXY() * track.dcaXY() + track.dcaZ() * track.dcaZ()) / sigmaDca3D(track);
-
-  // float cYY = track.cYY();
-  // float cZZ = track.cZZ();
-  // float cZY = track.cZY();
-  // float dcaXY = track.dcaXY(); // in cm
-  // float dcaZ = track.dcaZ();   // in cm
-
-  // float det = cYY * cZZ - cZY * cZY; // determinant
-  // if (det < 0) {
-  //   return 999.f;
-  // } else {
-  //   return std::sqrt(std::fabs((dcaXY * dcaXY * cZZ + dcaZ * dcaZ * cYY - 2. * dcaXY * dcaZ * cZY) / det / 2.)); // dca 3d in sigma
-  // }
+  float dcaXY = track.dcaXY();                          // in cm
+  float dcaZ = track.dcaZ();                            // in cm
+  float dca3d = std::sqrt(dcaXY * dcaXY + dcaZ * dcaZ); // in cm
+  return dca3d / dca3DinSigma(track);
 }
 //_______________________________________________________________________
 template <typename T>
@@ -70,30 +63,29 @@ float dcaZinSigma(T const& track)
 }
 //_______________________________________________________________________
 template <typename T>
-float sigmaFwdDcaXY(T const& track)
+float fwdDcaXYinSigma(T const& track)
 {
   float cXX = track.cXXatDCA();                       // in cm^2
   float cYY = track.cYYatDCA();                       // in cm^2
   float cXY = track.cXYatDCA();                       // in cm^2
   float dcaX = track.fwdDcaX();                       // in cm
   float dcaY = track.fwdDcaY();                       // in cm
-  float dcaXY = std::sqrt(dcaX * dcaX + dcaY * dcaY); // in cm
-  float dFdx = 2.f * dcaX / dcaXY;
-  float dFdy = 2.f * dcaY / dcaXY;
-  return std::sqrt(cXX * dFdx * dFdx + cYY * dFdy * dFdy + 2.f * cXY * dFdx * dFdy);
+  float det = cXX * cYY - cXY * cXY;                  // determinant
+
+  if (det < 0) {
+    return 999.f;
+  } else {
+    return std::sqrt(std::fabs((dcaX * dcaX * cYY + dcaY * dcaY * cXX - 2. * dcaX * dcaY * cXY) / det / 2.)); // dca xy in sigma
+  }
 }
 //_______________________________________________________________________
 template <typename T>
-float fwdDcaXYinSigma(T const& track)
+float sigmaFwdDcaXY(T const& track)
 {
-  return std::sqrt(track.fwdDcaX() * track.fwdDcaX() + track.fwdDcaY() * track.fwdDcaY()) / sigmaFwdDcaXY(track);
-
-  // float det = cXX * cYY - cXY * cXY; // determinant
-  // if (det < 0) {
-  //   return 999.f;
-  // } else {
-  //   return std::sqrt(std::fabs((dcaX * dcaX * cYY + dcaY * dcaY * cXX - 2. * dcaX * dcaY * cXY) / det / 2.)); // dca xy in sigma
-  // }
+  float dcaX = track.fwdDcaX();                       // in cm
+  float dcaY = track.fwdDcaY();                       // in cm
+  float dcaXY = std::sqrt(dcaX * dcaX + dcaY * dcaY); // in cm
+  return dcaXY / fwdDcaXYinSigma(track);
 }
 //_______________________________________________________________________
 template <bool is_wo_acc = false, typename TTrack, typename TCut, typename TTracks>