PWGEM/PhotonMeson: improve MC primary selection in tagging (#5440)

Author: dsekihat

PWGEM/PhotonMeson/Tasks/TaggingPi0MC.cxx

@@ -356,23 +356,27 @@ struct TaggingPi0MC {
           auto ele1mc = ele1.template emmcparticle_as<aod::EMMCParticles>();
 
           int photonid1 = FindCommonMotherFrom2Prongs(pos1mc, ele1mc, -11, 11, 22, mcparticles);
-          // if (photonid1 < 0) { // check swap, true electron is reconstructed as positron and vice versa.
-          //   photonid1 = FindCommonMotherFrom2Prongs(pos1mc, ele1mc, 11, -11, 22, mcparticles);
-          // }
-
-          if (photonid1 > 0) {
-            auto mcphoton1 = mcparticles.iteratorAt(photonid1);
-            int pi0id1 = IsXFromY(mcphoton1, mcparticles, 22, 111);
-            if (pi0id1 > 0) {
-              auto mcpi01 = mcparticles.iteratorAt(pi0id1);
-              if (mcpi01.isPhysicalPrimary() || mcpi01.producedByGenerator()) {
-                reinterpret_cast<TH1F*>(list_pcm->FindObject(Form("%s", cut1.GetName()))->FindObject("hPt_v0photon_Pi0_Primary"))->Fill(g1.pt());
-              } else if (IsFromWD(mcpi01.emmcevent(), mcpi01, mcparticles)) {
-                reinterpret_cast<TH1F*>(list_pcm->FindObject(Form("%s", cut1.GetName()))->FindObject("hPt_v0photon_Pi0_FromWD"))->Fill(g1.pt());
-              } else {
-                reinterpret_cast<TH1F*>(list_pcm->FindObject(Form("%s", cut1.GetName()))->FindObject("hPt_v0photon_Pi0_hs"))->Fill(g1.pt());
-              }
-            }
+          if (photonid1 < 0) {
+            continue;
+          }
+          auto mcphoton1 = mcparticles.iteratorAt(photonid1);
+
+          int pi0id1 = IsXFromY(mcphoton1, mcparticles, 22, 111);
+          if (pi0id1 < 0) { // photon from pi0 decay
+            continue;
+          }
+          auto mcpi01 = mcparticles.iteratorAt(pi0id1);
+
+          // // check if pi0 is physical primary or produced by generator, photon should be physical primary or produced by generator.
+          // LOGF(info, "mcphoton1.isPhysicalPrimary() = %d, mcphoton1.producedByGenerator() = %d, mcpi01.isPhysicalPrimary() = %d, mcpi01.producedByGenerator() = %d",
+          //     mcphoton1.isPhysicalPrimary(), mcphoton1.producedByGenerator(), mcpi01.isPhysicalPrimary(), mcpi01.producedByGenerator());
+
+          if (mcpi01.isPhysicalPrimary() || mcpi01.producedByGenerator()) {
+            reinterpret_cast<TH1F*>(list_pcm->FindObject(cut1.GetName())->FindObject("hPt_v0photon_Pi0_Primary"))->Fill(g1.pt());
+          } else if (IsFromWD(mcpi01.emmcevent(), mcpi01, mcparticles)) {
+            reinterpret_cast<TH1F*>(list_pcm->FindObject(cut1.GetName())->FindObject("hPt_v0photon_Pi0_FromWD"))->Fill(g1.pt());
+          } else {
+            reinterpret_cast<TH1F*>(list_pcm->FindObject(cut1.GetName())->FindObject("hPt_v0photon_Pi0_hs"))->Fill(g1.pt());
           }
 
         } // end of pcm photon loop