From 2b7bf713aac3143dd8c5b9fe5c09394fd91fe22f Mon Sep 17 00:00:00 2001
From: Kshitish Kumar Pradhan <kshitish.kumar.pradhan@cern.ch>
Date: Sun, 31 Aug 2025 17:27:57 +0530
Subject: [PATCH] Added a loop in processMCGen to fill generated pair
 histograms taking into account selected collisions

This histogram MCTruthGenPairSel_%s fill at generation level similar to MCTruthGenSel_%s but now for pairs.

This is done to fill correct number in generation level for histograms that stores angualr distribution for polarization.
---
 PWGDQ/Tasks/dqEfficiency_withAssoc.cxx | 34 ++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/PWGDQ/Tasks/dqEfficiency_withAssoc.cxx b/PWGDQ/Tasks/dqEfficiency_withAssoc.cxx
index f0b7965ccc4..0d5c7906f87 100644
--- a/PWGDQ/Tasks/dqEfficiency_withAssoc.cxx
+++ b/PWGDQ/Tasks/dqEfficiency_withAssoc.cxx
@@ -2232,6 +2232,40 @@ struct AnalysisSameEventPairing {
         }
       }
     }
+    // Fill Generated PAIR histograms taking into account selected collisions
+    for (auto& event : events) {
+      if (!event.isEventSelected_bit(0)) {
+        continue;
+      }
+      if (!event.has_reducedMCevent()) {
+        continue;
+      }
+
+      if (fHasTwoProngGenMCsignals) {
+        for (auto& [t1, t2] : combinations(mcTracks, mcTracks)) {
+          if (t1.reducedMCeventId() != event.reducedMCeventId()) {
+            continue;
+          }
+          if (t2.reducedMCeventId() != event.reducedMCeventId()) {
+            continue;
+          }
+          auto t1_raw = mcTracks.rawIteratorAt(t1.globalIndex());
+          auto t2_raw = mcTracks.rawIteratorAt(t2.globalIndex());
+          if (t1_raw.reducedMCeventId() == t2_raw.reducedMCeventId()) {
+            for (auto& sig : fGenMCSignals) {
+              if (sig->GetNProngs() != 2) { // NOTE: 2-prong signals required here
+                continue;
+              }
+              if (sig->CheckSignal(true, t1_raw, t2_raw)) {
+                // mcDecision |= (static_cast<uint32_t>(1) << isig);
+                VarManager::FillPairMC<VarManager::kDecayToMuMu>(t1, t2); // NOTE: This feature will only work for muons
+                fHistMan->FillHistClass(Form("MCTruthGenPairSel_%s", sig->GetName()), VarManager::fgValues);
+              }
+            }
+          }
+        }
+      }
+    } // end loop over reconstructed events
   }
 
   void processDummy(MyEvents&)