diff --git a/include/OverlayTiming.h b/include/OverlayTiming.h
index 24fc31a..5ba89e3 100644
--- a/include/OverlayTiming.h
+++ b/include/OverlayTiming.h
@@ -147,6 +147,8 @@ namespace overlay {
     float _tpcVdrift_mm_ns = 5.0e-2 ;
     bool _randomBX = false, _Poisson = false;
 
+    bool _checkMCC = true;
+
     typedef std::map<unsigned long long, EVENT::SimCalorimeterHit*> DestMap;
     typedef std::map<std::string, DestMap> CollDestMap;
     CollDestMap collDestMap{};
diff --git a/src/OverlayTiming.cc b/src/OverlayTiming.cc
index c85c766..f306e81 100644
--- a/src/OverlayTiming.cc
+++ b/src/OverlayTiming.cc
@@ -263,6 +263,12 @@ namespace overlay {
                                m_startWithBackgroundEvent);
 
 
+    // processo MCContribution
+    registerProcessorParameter("ProcessMCContribution",
+                             "Merging the SimCaloHits check if the MCContributions already exist",
+                             _checkMCC,
+                             bool(true) );
+
   }
 
   //------------------------------------------------------------------------------------------------------------------------------------------
@@ -551,7 +557,7 @@ namespace overlay {
 
     delete permutation;
     ++_nEvt;
-    //we clear the map of calorimeter hits for the next event
+    // we clear the map of calorimeter hits for the next event
     collDestMap.clear();
     const std::vector<std::string> *collection_names_in_evt = evt->getCollectionNames();
 
@@ -560,9 +566,8 @@ namespace overlay {
         streamlog_out(DEBUG) << "Collection " << collection_names_in_evt->at(i) << " has now " << evt->getCollection(collection_names_in_evt->at(i))->getNumberOfElements() << " elements" << std::endl;
       }
 
-    // reset pointer
+    // reset pointer at end
     overlay_Evt = nullptr;
-    
   }
 
   //------------------------------------------------------------------------------------------------------------------------------------------
@@ -794,7 +799,7 @@ namespace overlay {
               {
                 SimCalorimeterHit *CalorimeterHit = static_cast<SimCalorimeterHit*>(source_collection->getElementAt(k));
                 const float _time_of_flight = time_of_flight(CalorimeterHit->getPosition()[0], CalorimeterHit->getPosition()[1], CalorimeterHit->getPosition()[2]);
-
+                float nullStep[3] = { 0.,0.,0. } ;
                 //check whether there is already a hit at this position
                 const unsigned long long lookfor = cellID2long(CalorimeterHit->getCellID0(), CalorimeterHit->getCellID1());
                 DestMap::const_iterator destMapIt = collDestMap[currentDest].find(lookfor);
@@ -809,7 +814,10 @@ namespace overlay {
                         if (((CalorimeterHit->getTimeCont(j) + time_offset) > (this_start + _time_of_flight)) && ((CalorimeterHit->getTimeCont(j) + time_offset) < (this_stop + _time_of_flight)))
                           {
                             add_Hit = true;
-                            newCalorimeterHit->addMCParticleContribution(CalorimeterHit->getParticleCont(j), CalorimeterHit->getEnergyCont(j), CalorimeterHit->getTimeCont(j) + time_offset);
+                            if ( _checkMCC )
+                              newCalorimeterHit->addMCParticleContribution(CalorimeterHit->getParticleCont(j), CalorimeterHit->getEnergyCont(j), CalorimeterHit->getTimeCont(j) + time_offset);
+                            else 
+                              newCalorimeterHit->addMCParticleContribution(CalorimeterHit->getParticleCont(j), CalorimeterHit->getEnergyCont(j), CalorimeterHit->getTimeCont(j) + time_offset, 0, 0, nullStep);
                           }
                       }
                     if (add_Hit)
@@ -862,7 +870,11 @@ namespace overlay {
                       {
                         if (((CalorimeterHit->getTimeCont(j) + time_offset) > (this_start + _time_of_flight)) && ((CalorimeterHit->getTimeCont(j) + time_offset) < (this_stop + _time_of_flight)))
                           {
-                            newCalorimeterHit->addMCParticleContribution(CalorimeterHit->getParticleCont(j), CalorimeterHit->getEnergyCont(j), CalorimeterHit->getTimeCont(j) + time_offset);
+                            if ( _checkMCC )
+                              newCalorimeterHit->addMCParticleContribution(CalorimeterHit->getParticleCont(j), CalorimeterHit->getEnergyCont(j), CalorimeterHit->getTimeCont(j) + time_offset);
+                            else 
+                              newCalorimeterHit->addMCParticleContribution(CalorimeterHit->getParticleCont(j), CalorimeterHit->getEnergyCont(j), CalorimeterHit->getTimeCont(j) + time_offset, 0, 0, nullStep);
+                            
                           }
                       }
                   }
diff --git a/src/OverlayTimingGeneric.cc b/src/OverlayTimingGeneric.cc
index da76093..60e3e89 100644
--- a/src/OverlayTimingGeneric.cc
+++ b/src/OverlayTimingGeneric.cc
@@ -100,6 +100,12 @@ OverlayTimingGeneric::OverlayTimingGeneric(): OverlayTiming("OverlayTimingGeneri
                                "Starting integration time.  Should be shortly before the BX, but may need to be shifted earlier if the vertex is smeared in time.",
                                _DefaultStart_int,
                                float(-0.25));
+    // processo MCContribution
+    registerProcessorParameter("ProcessMCContribution",
+                             "Merging the SimCaloHits check if the MCContributions already exist",
+                             _checkMCC,
+                             bool(true) );
+
 }
 
 void OverlayTimingGeneric::init()