Change trackster simToReco association score to handle overlapping simulated particles

When two CaloParticles were overlapping, the previous version of the simToReco score approached one (for ex. in the extreme case of two overlapping photons with same energy). The new score stays close to zero.

Author: tcuisset

SimCalorimetry/HGCalAssociatorProducers/plugins/AllTracksterToSimTracksterAssociatorsByHitsProducer.cc

@@ -342,18 +342,24 @@ void AllTracksterToSimTracksterAssociatorsByHitsProducer::produce(edm::StreamID,
           float simFraction = simFractions[i];
           const auto& recHit = rechitManager[hitIndex];
           float rechitEnergy = recHit.energy();
-          float squaredSimFraction = simFraction * simFraction;
           float squaredRecHitEnergy = rechitEnergy * rechitEnergy;
           float simSharedEnergy = rechitEnergy * simFraction;
           const auto& hitToRecoTracksterVec = hitToAssociatedRecoTracksterMap[i];
           for (const auto& recoTracksterElement : hitToRecoTracksterVec) {
             auto recoTracksterIndex = recoTracksterElement.index();
-            float recoFraction = recoTracksterElement.fraction();
+            float recoFraction =
+                recoTracksterElement.fraction();  // Either zero or one when no sharing of rechits between tracksters
             edm::Ref<std::vector<ticl::Trackster>> recoTracksterRef(recoTrackstersHandle, recoTracksterIndex);
             float sharedEnergy = std::min(recoFraction * rechitEnergy, simSharedEnergy);
-            float squaredFraction =
-                std::min(squaredSimFraction, (recoFraction - simFraction) * (recoFraction - simFraction));
-            float score = invDenominator * squaredFraction * squaredRecHitEnergy;
+            /* SimToReco score logic:
+             - simFraction = 0 && recoFraction >= 0 : trackster contains non-sim associated elements : ignore in simToReco
+             - simFraction > 0 && recoFraction == 0 : simhits not present in reco trackster : penalty in score by simFraction*E
+             - simFraction == 1 && recoFraction == 1 : good association
+             - 1 > simFraction > recoFraction > 0 :  we are missing some sim energy, penalty in score by the missing part : (simFraction-recoFraction)*E
+             - 1 > recoFraction > simFraction > 0 : consider as good association, as there is enough reco to cover the sim
+            */
+            float simMinusRecoFraction = std::max(0.f, simFraction - recoFraction);
+            float score = invDenominator * simMinusRecoFraction * simMinusRecoFraction * squaredRecHitEnergy;
             simTracksterToTracksterMap->insert(simTracksterRef, recoTracksterRef, sharedEnergy, score);
           }
         }

SimCalorimetry/HGCalAssociatorProducers/plugins/AllTracksterToSimTracksterAssociatorsByLCsProducer.cc

@@ -251,7 +251,6 @@ void AllTracksterToSimTracksterAssociatorsByLCsProducer::produce(edm::StreamID,
           unsigned int layerClusterId = layerClustersIds[i];
           const auto& layerCluster = layerClusters[layerClusterId];
           float simFraction = 1.f / simTrackster.vertex_multiplicity(i);
-          float squaredSimFraction = simFraction * simFraction;
           float squaredLayerClusterEnergy = layerCluster.energy() * layerCluster.energy();
           float simSharedEnergy = layerCluster.energy() * simFraction;
           float invLayerClusterEnergy = 1.f / layerCluster.energy();
@@ -261,10 +260,18 @@ void AllTracksterToSimTracksterAssociatorsByLCsProducer::produce(edm::StreamID,
             float recoSharedEnergy = recoTracksterElement.sharedEnergy();
             edm::Ref<std::vector<ticl::Trackster>> recoTracksterRef(recoTrackstersHandle, recoTracksterIndex);
             float sharedEnergy = std::min(recoSharedEnergy, simSharedEnergy);
-            float recoFraction = recoSharedEnergy * invLayerClusterEnergy;
-            float score = invDenominator *
-                          std::min(squaredSimFraction, (simFraction - recoFraction) * (simFraction - recoFraction)) *
-                          squaredLayerClusterEnergy;
+            float recoFraction =
+                recoSharedEnergy *
+                invLayerClusterEnergy;  // Either zero or one when no sharing of rechits between tracksters
+            /* SimToReco score logic:
+             - simFraction = 0 && recoFraction >= 0 : trackster contains non-sim associated elements : ignore in simToReco
+             - simFraction > 0 && recoFraction == 0 : simhits not present in reco trackster : penalty in score by simFraction*E
+             - simFraction == 1 && recoFraction == 1 : good association
+             - 1 > simFraction > recoFraction > 0 :  we are missing some sim energy, penalty in score by the missing part : (simFraction-recoFraction)*E
+             - 1 > recoFraction > simFraction > 0 : consider as good association, as there is enough reco to cover the sim
+            */
+            float simMinusRecoFraction = std::max(0.f, simFraction - recoFraction);
+            float score = invDenominator * simMinusRecoFraction * simMinusRecoFraction * squaredLayerClusterEnergy;
             simTracksterToTracksterMap->insert(tracksterIndex, recoTracksterIndex, sharedEnergy, score);
           }
         }