diff --git a/Generator/src/GenEvent.cpp b/Generator/src/GenEvent.cpp
index 3e40c65b8476c83a48e98fc4b596e60d15bcab5f..8d8c254253f641fa3a54be063a1a39e210117179 100644
--- a/Generator/src/GenEvent.cpp
+++ b/Generator/src/GenEvent.cpp
@@ -1,7 +1,7 @@
 #include "GenEvent.h" 
 #include "edm4hep/MCParticleCollection.h"//plico
 
-using namespace std;
+// using namespace std;
 
 namespace MyHepMC{
 
@@ -17,7 +17,7 @@ GenEvent::GenEvent(edm4hep::MCParticleCollection& mcCol)
 }
 GenEvent::~GenEvent(){}
 
-void GenEvent::SetEventHeader(long event_id_, long run_id_, float time_, string det_name_){
+void GenEvent::SetEventHeader(long event_id_, long run_id_, float time_, const std::string& det_name_){
     m_event_id = event_id_;
     m_run_id = run_id_;
     m_time = time_;
@@ -28,8 +28,9 @@ void GenEvent::SetMCCollection(edm4hep::MCParticleCollection vec_){
 m_mc_vec = vec_;
 }
 */
-edm4hep::MCParticleCollection GenEvent::getMCVec(){
-return m_mc_vec;
+
+edm4hep::MCParticleCollection& GenEvent::getMCVec(){
+    return m_mc_vec;
 }
 
 long GenEvent::getID(){
diff --git a/Generator/src/GenEvent.h b/Generator/src/GenEvent.h
index 72895413a5d06438fcffe72495ef56b646921c5c..fd1dbe557e0afac14a3397c53c3978b2c66d7a55 100644
--- a/Generator/src/GenEvent.h
+++ b/Generator/src/GenEvent.h
@@ -10,17 +10,18 @@ class GenEvent{
         //GenEvent();
         GenEvent(edm4hep::MCParticleCollection& mcCol);
         ~GenEvent();
-        void SetEventHeader(long event_id_, long run_id_, float time_, std::string det_name_);
+        void SetEventHeader(long event_id_, long run_id_, float time_, const std::string& det_name_);
         //void SetMCCollection(edm4hep::MCParticleCollection vec_);
         long getID();
         long getRun();
         long getTime();
         void ReSet();
         std::string getName();
-        edm4hep::MCParticleCollection getMCVec();
+        edm4hep::MCParticleCollection& getMCVec();
         edm4hep::MCParticleCollection& m_mc_vec;
         //edm4hep::MCParticleCollection m_mc_vec;
     private:
+
         long m_event_id;
         long m_run_id;
         float m_time;