diff --git a/PWGUD/Tasks/upcEventITSROFcounter.cxx b/PWGUD/Tasks/upcEventITSROFcounter.cxx
index 1da6fbfd26c..51241be5d69 100644
--- a/PWGUD/Tasks/upcEventITSROFcounter.cxx
+++ b/PWGUD/Tasks/upcEventITSROFcounter.cxx
@@ -9,12 +9,23 @@
 // granted to it by virtue of its status as an Intergovernmental Organization
 // or submit itself to any jurisdiction.
 
+/// \file upcEventITSROFcounter.cxx
+/// \brief Personal task to analyze tau events from UPC collisions
+///
+/// \author Roman Lavicka <roman.lavicka@cern.ch>, Austrian Academy of Sciences & SMI
+/// \since  09.08.2024
+
+#include <utility>
+#include <vector>
+
 #include "Framework/runDataProcessing.h"
 #include "Framework/AnalysisTask.h"
 #include "Framework/AnalysisDataModel.h"
 #include "ITSMFTBase/DPLAlpideParam.h"
 #include "CCDB/BasicCCDBManager.h"
+#include "ReconstructionDataFormats/Vertex.h"
 
+#include "Common/CCDB/EventSelectionParams.h"
 #include "Common/DataModel/EventSelection.h"
 
 #include "PWGUD/DataModel/UDTables.h"
@@ -25,6 +36,7 @@
 using namespace o2;
 using namespace o2::framework;
 using namespace o2::framework::expressions;
+using namespace o2::dataformats;
 
 using BCsWithRun3Matchings = soa::Join<aod::BCs, aod::Timestamps, aod::Run3MatchedToBCSparse>;
 using CCs = soa::Join<aod::Collisions, aod::EvSels>;
@@ -39,10 +51,10 @@ struct UpcEventITSROFcounter {
   Configurable<int> nTracksForUPCevent{"nTracksForUPCevent", 16, {"Maximum of tracks defining a UPC collision"}};
 
   Configurable<bool> useTrueGap{"useTrueGap", true, {"Calculate gapSide for a given FV0/FT0/ZDC thresholds"}};
-  Configurable<float> cutMyGapSideFV0{"FV0", -1, "FV0A threshold for SG selector"};
-  Configurable<float> cutMyGapSideFT0A{"FT0A", 150., "FT0A threshold for SG selector"};
-  Configurable<float> cutMyGapSideFT0C{"FT0C", 50., "FT0C threshold for SG selector"};
-  Configurable<float> cutMyGapSideZDC{"ZDC", 10., "ZDC threshold for SG selector"};
+  Configurable<float> cutMyGapSideFV0{"cutMyGapSideFV0", -1, "FV0A threshold for SG selector"};
+  Configurable<float> cutMyGapSideFT0A{"cutMyGapSideFT0A", 150., "FT0A threshold for SG selector"};
+  Configurable<float> cutMyGapSideFT0C{"cutMyGapSideFT0C", 50., "FT0C threshold for SG selector"};
+  Configurable<float> cutMyGapSideZDC{"cutMyGapSideZDC", 10., "ZDC threshold for SG selector"};
   ConfigurableAxis axisRunNumbers{"axisRunNumbers", {1400, 544000.5, 545400.5}, "Range of run numbers"};
 
   void init(InitContext&)
@@ -53,6 +65,9 @@ struct UpcEventITSROFcounter {
     histos.add("Events/hCountCollisionsInROFborderMatching", ";;Number of collision (-)", HistType::kTH1D, {{11, -0.5, 10.5}});
     histos.add("Events/hCountUPCcollisionsInROFborderMatching", ";;Number of UPC (mult < 17) collision (-)", HistType::kTH1D, {{11, -0.5, 10.5}});
 
+    histos.add("Events/hPVcontribsVsCollisionsPerITSROFstd", "Collisions reconstructed with standard mode;Number of vertex contributors (-); Number of collisions in one ITSROF (-)", HistType::kTH2D, {{101, -0.5, 100.5}, {11, -0.5, 10.5}});
+    histos.add("Events/hPVcontribsVsCollisionsPerITSROFupc", "Collisions reconstructed with upc mode;Number of vertex contributors (-); Number of collisions in one ITSROF (-)", HistType::kTH2D, {{101, -0.5, 100.5}, {11, -0.5, 10.5}});
+
     histos.add("Runs/hStdModeCollDG", ";Run number;Number of events (-)", HistType::kTH1D, {axisRunNumbers});
     histos.add("Runs/hUpcModeCollDG", ";Run number;Number of events (-)", HistType::kTH1D, {axisRunNumbers});
     histos.add("Runs/hStdModeCollSG1", ";Run number;Number of events (-)", HistType::kTH1D, {axisRunNumbers});
@@ -78,7 +93,7 @@ struct UpcEventITSROFcounter {
     int64_t ts = bcs.iteratorAt(0).timestamp();
     auto alppar = ccdb->getForTimeStamp<o2::itsmft::DPLAlpideParam<0>>("ITS/Config/AlpideParam", ts);
 
-    for (auto bc : bcs) {
+    for (const auto& bc : bcs) {
       uint64_t globalBC = bc.globalBC();
       uint64_t globalIndex = bc.globalIndex();
       if (isFirst) {
@@ -98,7 +113,7 @@ struct UpcEventITSROFcounter {
       previousBCinITSROF = bcInITSROF;
       previousBCglobalIndex = globalIndex;
       // next is based on exact matching of bc and collision
-      for (auto& collision : collisions) {
+      for (const auto& collision : collisions) {
         if (collision.has_foundBC()) {
           if (collision.foundBCId() == bc.globalIndex()) {
             nAllColls++;
@@ -113,16 +128,16 @@ struct UpcEventITSROFcounter {
           }
         }
       } // end loop over collisions
-    }   // end loop over bcs
+    } // end loop over bcs
 
     int arrAllColls[1000] = {0};
     int arrUPCcolls[1000] = {0};
 
     // next is based on matching of collision bc within ITSROF range in bcs
-    for (auto& itsrofBorder : vecITSROFborders) {
+    for (const auto& itsrofBorder : vecITSROFborders) {
       int nAllCollsInROF = 0;
       int nUpcCollsInROF = 0;
-      for (auto& collision : collisions) {
+      for (const auto& collision : collisions) {
         if ((itsrofBorder.first < collision.bcId()) && (collision.bcId() < itsrofBorder.second)) {
           nAllCollsInROF++;
           if (collision.numContrib() < nTracksForUPCevent + 1) {
@@ -138,6 +153,30 @@ struct UpcEventITSROFcounter {
       histos.get<TH1>(HIST("Events/hCountCollisionsInROFborderMatching"))->Fill(ncol, arrAllColls[ncol]);
       histos.get<TH1>(HIST("Events/hCountUPCcollisionsInROFborderMatching"))->Fill(ncol, arrUPCcolls[ncol]);
     }
+
+    // TEST vertex contributors per reconstruction flag (std vs upc)
+    // matching of collision bc within ITSROF range in bcs
+    for (const auto& itsrofBorder : vecITSROFborders) {
+      std::vector<int> vecNumContribsStd;
+      std::vector<int> vecNumContribsUpc;
+      for (const auto& collision : collisions) {
+        if ((itsrofBorder.first < collision.bcId()) && (collision.bcId() < itsrofBorder.second)) {
+          if (collision.flags() & dataformats::Vertex<o2::dataformats::TimeStamp<int>>::Flags::UPCMode) {
+            vecNumContribsUpc.push_back(collision.numContrib());
+          } else {
+            vecNumContribsStd.push_back(collision.numContrib());
+          }
+        }
+      } // end loop over collisions
+
+      for (const auto& numContribs : vecNumContribsStd) {
+        histos.get<TH2>(HIST("Events/hPVcontribsVsCollisionsPerITSROFstd"))->Fill(numContribs, vecNumContribsStd.size());
+      }
+      for (const auto& numContribs : vecNumContribsUpc) {
+        histos.get<TH2>(HIST("Events/hPVcontribsVsCollisionsPerITSROFupc"))->Fill(numContribs, vecNumContribsUpc.size());
+      }
+
+    } // end loop over ITSROFs
   }
 
   void processCounterPerRun(FullSGUDCollision const& coll)
@@ -179,5 +218,5 @@ struct UpcEventITSROFcounter {
 WorkflowSpec defineDataProcessing(ConfigContext const& cfgc)
 {
   return WorkflowSpec{
-    adaptAnalysisTask<UpcEventITSROFcounter>(cfgc, TaskName{"upc-event-itsrof-counter"})};
+    adaptAnalysisTask<UpcEventITSROFcounter>(cfgc)};
 }