[PWGLF] add evsel at gen level (#13223)

Author: rspijkers

PWGLF/Tasks/Strangeness/cascadecorrelations.cxx

@@ -502,9 +502,14 @@ struct CascadeSelector {
 
   } // processCandidate
 
-  void processGenMC(aod::McCollision const&, soa::SmallGroups<soa::Join<aod::McCollisionLabels, MyCollisions>> const& collisions, aod::McParticles const& mcParticles)
+  void processGenMC(aod::McCollision const& mcCollision, soa::SmallGroups<soa::Join<aod::McCollisionLabels, MyCollisions>> const& collisions, aod::McParticles const& mcParticles)
   {
-    // N gen events without any event selection or matched reco event
+    // evsel
+    if (INEL < 0 || pwglf::isINELgtNmc(mcParticles, INEL, pdgDB))
+      return;
+    if (std::abs(mcCollision.posZ()) > maxVertexZ)
+      return;
+
     registry.fill(HIST("gen/hNevents"), 0);
 
     for (auto const& mcPart : mcParticles) {