Merge pull request #36122 from sbein/from-CMSSW_12_2_X_2021-11-14-0000

Fix for FastSim decays of exotic-descendent SM particles decaying outside pipe
cms-sw · Dec 1, 2021 · f0fde9d · f0fde9d
2 parents 535625c + 2fe14d6
commit f0fde9d
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Showing 2 changed files with 14 additions and 5 deletions.
diff --git a/FastSimulation/SimplifiedGeometryPropagator/interface/ParticleManager.h b/FastSimulation/SimplifiedGeometryPropagator/interface/ParticleManager.h
@@ -146,7 +146,8 @@ inline bool isExotic(int pdgid_) {
   return ((pdgid >= 1000000 && pdgid < 4000000 && pdgid != 3000022) ||  // SUSY, R-hadron, and technicolor particles
           pdgid == 17 ||                                                // 4th generation lepton
           pdgid == 34 ||                                                // W-prime
-          pdgid == 37);                                                 // charged Higgs
+          pdgid == 37 ||                                                // charged Higgs
+          pdgid == 39);                                                 // bulk graviton
 }
 
 #endif
diff --git a/FastSimulation/SimplifiedGeometryPropagator/src/ParticleManager.cc b/FastSimulation/SimplifiedGeometryPropagator/src/ParticleManager.cc
@@ -216,19 +216,27 @@ std::unique_ptr<fastsim::Particle> fastsim::ParticleManager::nextGenParticle() {
     }
     // particles which do not descend from exotics must be produced within the beampipe
     int exoticRelativeId = 0;
-    if (productionVertex->position().perp2() * lengthUnitConversionFactor2_ > beamPipeRadius2_)  //
-    {
+    const bool producedWithinBeamPipe =
+        productionVertex->position().perp2() * lengthUnitConversionFactor2_ < beamPipeRadius2_;
+    if (producedWithinBeamPipe) {
       exoticRelativesChecker(productionVertex, exoticRelativeId, 0);
       if (!isExotic(exoticRelativeId)) {
         continue;
       }
     }
 
-    // particle must not decay before it reaches the beam pipe
-    if (endVertex && endVertex->position().perp2() * lengthUnitConversionFactor2_ < beamPipeRadius2_) {
+    // FastSim will not make hits out of particles that decay before reaching the beam pipe
+    const bool decayedWithinBeamPipe =
+        endVertex && endVertex->position().perp2() * lengthUnitConversionFactor2_ < beamPipeRadius2_;
+    if (decayedWithinBeamPipe) {
       continue;
     }
 
+    // SM particles that descend from exotics and cross the beam pipe radius should make hits but not be decayed
+    if (producedWithinBeamPipe && !decayedWithinBeamPipe) {
+      exoticRelativesChecker(productionVertex, exoticRelativeId, 0);
+    }
+
     // make the particle
     std::unique_ptr<Particle> newParticle(
         new Particle(particle.pdg_id(),