[PWGDQ] Add impact parameter variable (d_0) to pair vertexing (#18589)

Author: sigurdnese

PWGDQ/Core/VarManager.cxx

@@ -1365,6 +1365,8 @@ void VarManager::SetDefaultVarNames()
   fgVariableUnits[kMCVertexingTauxyzProjected] = "ns";
   fgVariableNames[kCosPointingAngle] = "cos(#theta_{pointing})";
   fgVariableUnits[kCosPointingAngle] = "";
+  fgVariableNames[kVertexingImpactParameter] = "d_{0}";
+  fgVariableUnits[kVertexingImpactParameter] = "cm";
   fgVariableNames[kMCCosPointingAngle] = "MC cos(#theta_{pointing})";
   fgVariableUnits[kMCCosPointingAngle] = "";
   fgVariableNames[kD0DcaDaughters] = "DCA of D0 daughters";
@@ -2687,6 +2689,7 @@ void VarManager::SetDefaultVarNames()
   fgVarNamesMap["kQuadDCAsigXYZ"] = kQuadDCAsigXYZ;
   fgVarNamesMap["kSignQuadDCAsigXY"] = kSignQuadDCAsigXY;
   fgVarNamesMap["kCosPointingAngle"] = kCosPointingAngle;
+  fgVarNamesMap["kVertexingImpactParameter"] = kVertexingImpactParameter;
   fgVarNamesMap["kMCCosPointingAngle"] = kMCCosPointingAngle;
   fgVarNamesMap["kD0ImpParProduct"] = kD0ImpParProduct;
   fgVarNamesMap["kD0DcaDaughters"] = kD0DcaDaughters;

PWGDQ/Core/VarManager.h

@@ -892,6 +892,7 @@ class VarManager : public TObject
     kQuadDCAsigXYZ,
     kSignQuadDCAsigXY,
     kCosPointingAngle,
+    kVertexingImpactParameter,
     kD0ImpParProduct,
     kD0DcaDaughters,
     kImpParXYJpsi,
@@ -5318,6 +5319,7 @@ void VarManager::FillPairVertexing(C const& collision, T const& t1, T const& t2,
 
       values[kCosPointingAngle] = (dx * v12.Px() + dy * v12.Py() + dz * v12.Pz()) /
                                   (v12.P() * values[VarManager::kVertexingLxyz]);
+      values[kVertexingImpactParameter] = values[VarManager::kVertexingLxyz] * std::sqrt(1 - values[VarManager::kCosPointingAngle] * values[VarManager::kCosPointingAngle]);
       // Decay length defined as in Run 2
       values[kVertexingLzProjected] = (dz * v12.Pz()) / TMath::Sqrt(v12.Pz() * v12.Pz());
       values[kVertexingLxyProjected] = (dx * v12.Px()) + (dy * v12.Py());
@@ -5398,6 +5400,7 @@ void VarManager::FillPairVertexing(C const& collision, T const& t1, T const& t2,
                                      std::sqrt(dyPair2PV * dyPair2PV) * v12.Py() +
                                      std::sqrt(dzPair2PV * dzPair2PV) * v12.Pz()) /
                                     (v12.P() * values[VarManager::kVertexingLxyz]);
+        values[kVertexingImpactParameter] = values[VarManager::kVertexingLxyz] * std::sqrt(1 - values[VarManager::kCosPointingAngle] * values[VarManager::kCosPointingAngle]);
       }
       // As defined in Run 2 (projected onto momentum)
       if (fgUsedVars[kVertexingLxyProjected] || fgUsedVars[kVertexingLxyzProjected] || fgUsedVars[kVertexingLzProjected]) {