From 0f82a978f1290e21637f92f89a22757510a9a066 Mon Sep 17 00:00:00 2001
From: Daiki Sekihata <daiki.sekihata@cern.ch>
Date: Thu, 27 Feb 2025 18:19:48 +0900
Subject: [PATCH] PWGEM/Dilepton: update sturyMCTruth.cxx

---
 PWGEM/Dilepton/Tasks/studyMCTruth.cxx | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/PWGEM/Dilepton/Tasks/studyMCTruth.cxx b/PWGEM/Dilepton/Tasks/studyMCTruth.cxx
index 4e5fbf44ae3..f3563a0bbd4 100644
--- a/PWGEM/Dilepton/Tasks/studyMCTruth.cxx
+++ b/PWGEM/Dilepton/Tasks/studyMCTruth.cxx
@@ -82,6 +82,8 @@ struct studyMCTruth {
     const AxisSpec axis_mll{ConfMllBins, "m_{ll} (GeV/c^{2})"};
     const AxisSpec axis_ptll{ConfPtllBins, "p_{T,ll} (GeV/c)"};
 
+    fRegistry.add("Event/hReccollsPerMCcoll", "Rec. colls per MC coll;Rec. colls per MC coll;Number of MC collisions", kTH1D, {{21, -0.5, 20.5}}, false);
+    fRegistry.add("Event/hSelReccollsPerMCcoll", "Selected Rec. colls per MC coll;Selected Rec. colls per MC coll;Number of MC collisions", kTH1D, {{21, -0.5, 20.5}}, false);
     fRegistry.add("Event/hDiffBC", "diffrence in BC;BC_{rec. coll.} - BC_{mc coll.}", kTH1D, {{101, -50.5, +50.5}}, false);
     fRegistry.add("Event/allMC/hZvtx", "MC Zvtx;Z_{vtx} (cm)", kTH1D, {{100, -50, +50}}, false);
     fRegistry.add("Event/allMC/hImpactParameter", "impact parameter;impact parameter b (fm)", kTH1D, {{200, 0, 20}}, false);
@@ -238,6 +240,10 @@ struct studyMCTruth {
       const auto& bc_from_mcCollision = mcCollision.template bc_as<TBCs>();
       bool isSelectedMC = isSelectedCollision(mcCollision, bc_from_mcCollision);
 
+      auto rec_colls_per_mccoll = collisions.sliceBy(recColperMcCollision, mcCollision.globalIndex());
+      fRegistry.fill(HIST("Event/hReccollsPerMCcoll"), rec_colls_per_mccoll.size());
+      int nselrec_colls_per_mccoll = 0;
+
       bool isSelectedRec = false;
       bool hasRecCollision = false;
       if (mcCollision.mpemeventId() >= 0) {
@@ -246,7 +252,14 @@ struct studyMCTruth {
         const auto& bc_from_collision = collision.template foundBC_as<TBCs>();
         isSelectedRec = isSelectedCollision(collision, bc_from_collision);
         fRegistry.fill(HIST("Event/hDiffBC"), bc_from_collision.globalBC() - bc_from_mcCollision.globalBC());
+
+        for (const auto& rec_col : rec_colls_per_mccoll) {
+          if (isSelectedCollision(rec_col, bc_from_collision)) {
+            nselrec_colls_per_mccoll++;
+          }
+        } // end of reconstructed collision
       }
+      fRegistry.fill(HIST("Event/hSelReccollsPerMCcoll"), nselrec_colls_per_mccoll);
 
       fRegistry.fill(HIST("Event/allMC/hZvtx"), mcCollision.posZ());
       fRegistry.fill(HIST("Event/allMC/hImpactParameter"), mcCollision.impactParameter());
@@ -312,6 +325,7 @@ struct studyMCTruth {
 
   SliceCache cache;
   Preslice<aod::McParticles> perMcCollision = aod::mcparticle::mcCollisionId;
+  PresliceUnsorted<aod::McCollisionLabels> recColperMcCollision = aod::mccollisionlabel::mcCollisionId;
 
   using MyMcCollisions = soa::Join<aod::McCollisions, aod::MostProbableEMEventIdsInMC>;