[PWGHF] Add nPVcontributors in THnSparse of Upc process in D0 task (#15438)

Author: phymanshu

PWGHF/D2H/Tasks/taskD0.cxx

@@ -369,6 +369,7 @@ struct HfTaskD0 {
       axes.push_back(thnAxisFDDC);
       axes.push_back(thnAxisZNA);
       axes.push_back(thnAxisZNC);
+      axes.push_back(thnAxisNumPvContr);
     }
 
     if (applyMl) {
@@ -591,6 +592,7 @@ struct HfTaskD0 {
       // Determine gap type using SGSelector with BC range checking
       const auto gapResult = hf_upc::determineGapType(collision, bcs, upcThresholds);
       const int gap = gapResult.value;
+      const auto numPvContributors = collision.numContrib();
 
       // Use the BC with FIT activity if available from SGSelector
       auto bcForUPC = bc;
@@ -652,7 +654,7 @@ struct HfTaskD0 {
         // Fill THnSparse with structure matching histogram axes: [mass, pt, (mlScores if FillMl), rapidity, d0Type, (cent if storeCentrality), (occ, ir if storeOccupancyAndIR), gapType, FT0A, FT0C, FV0A, FDDA, FDDC, ZNA, ZNC]
         auto fillTHnData = [&](float mass, int d0Type) {
           // Pre-calculate vector size to avoid reallocations
-          constexpr int NAxesBase = 12;                       // mass, pt, rapidity, d0Type, gapType, FT0A, FT0C, FV0A, FDDA, FDDC, ZNA, ZNC
+          constexpr int NAxesBase = 13;                       // mass, pt, rapidity, d0Type, gapType, FT0A, FT0C, FV0A, FDDA, FDDC, ZNA, ZNC, nPVcontr
           constexpr int NAxesMl = FillMl ? 3 : 0;             // 3 ML scores if FillMl
           int const nAxesCent = storeCentrality ? 1 : 0;      // centrality if storeCentrality
           int const nAxesOccIR = storeOccupancyAndIR ? 2 : 0; // occupancy and IR if storeOccupancyAndIR
@@ -686,6 +688,7 @@ struct HfTaskD0 {
           valuesToFill.push_back(static_cast<double>(fitInfo.ampFDDC));
           valuesToFill.push_back(static_cast<double>(zdcEnergyZNA));
           valuesToFill.push_back(static_cast<double>(zdcEnergyZNC));
+          valuesToFill.push_back(static_cast<double>(numPvContributors));
 
           if constexpr (FillMl) {
             registry.get<THnSparse>(HIST("hBdtScoreVsMassVsPtVsPtBVsYVsOriginVsD0Type"))->Fill(valuesToFill.data());