Resolve "pi0 resolution for ECal barrel"

Closes #19 (closed)

benchmarks/barrel_ecal/scripts/emcal_barrel_pions_analysis.cxx

@@ -127,7 +127,7 @@ void emcal_barrel_pions_analysis(const char* input_fname = "sim_output/sim_emcal
               ;
   // Set sampling Fraction, ideally this will be taken from a json file 
   auto svec = d1.Mean<double>("fsam");
-  for (auto ele : svec){cout << ele << endl;}
+  for (auto &ele : svec){cout << ele << endl;}
 
   auto d2 = d1.Define("dE",     eResol,     {"Esim","Ethr"})
               .Define("dE_rel", eResol_rel, {"Esim","Ethr"})