MC/PWGEM: add cfg and ini for VM2ll (#2172)

* MC/PWGEM: add cfg and ini for VM2ll

* Comment out Pythia8 function

Comment out the Pythia8 function to disable it.

* Update pythia8_OO_536_VM2ll.C

Author: dsekihat

MC/config/PWGEM/ini/pythia8_OO_536_VM2ll.ini

@@ -0,0 +1,9 @@
+[Diamond]
+width[2]=6.0
+
+[GeneratorExternal]
+fileName=${O2DPG_MC_CONFIG_ROOT}/MC/config/ALICE3/pythia8/generator_pythia8_ALICE3.C
+funcName=generator_pythia8_ALICE3()
+
+[GeneratorPythia8]
+config=${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGEM/pythia8/generator/pythia8_OO_536_VM2ll.cfg

MC/config/PWGEM/ini/tests/pythia8_OO_536_VM2ll.C

@@ -0,0 +1,56 @@
+int External() {
+  std::string path{"o2sim_Kine.root"};
+  // Check that file exists, can be opened and has the correct tree
+  TFile file(path.c_str(), "READ");
+  if (file.IsZombie())
+  {
+    std::cerr << "Cannot open ROOT file " << path << "\n";
+    return 1;
+  }
+  auto tree = (TTree *)file.Get("o2sim");
+  if (!tree)
+  {
+    std::cerr << "Cannot find tree o2sim in file " << path << "\n";
+    return 1;
+  }
+  std::vector<o2::MCTrack> *tracks{};
+  tree->SetBranchAddress("MCTrack", &tracks);
+
+  // Check if all events are filled
+  auto nEvents = tree->GetEntries();
+  for (Long64_t i = 0; i < nEvents; ++i)
+  {
+    tree->GetEntry(i);
+    if (tracks->empty())
+    {
+      std::cerr << "Empty entry found at event " << i << "\n";
+      return 1;
+    }
+  }
+  // check if each event has at least two oxygen ions
+  for (int i = 0; i < nEvents; i++)
+  {
+    auto check = tree->GetEntry(i);
+    int count = 0;
+    for (int idxMCTrack = 0; idxMCTrack < tracks->size(); ++idxMCTrack)
+    {
+      auto track = tracks->at(idxMCTrack);
+      if (track.GetPdgCode() == 1000080160)
+      {
+        count++;
+      }
+    }
+    if (count < 2)
+    {
+      std::cerr << "Event " << i << " has less than 2 oxygen ions\n";
+      return 1;
+    }
+  }
+
+  return 0;
+}
+
+//int Pythia8()  
+//{  
+//    return External();
+//}

MC/config/PWGEM/pythia8/generator/pythia8_OO_536_VM2ll.cfg

@@ -0,0 +1,21 @@
+### OO beams
+Beams:idA = 1000080160
+Beams:idB = 1000080160           
+Beams:eCM = 5360.0                ### energy
+    
+Beams:frameType = 1
+ParticleDecays:limitTau0 = on
+ParticleDecays:tau0Max = 10.      ### match alice: 1cm/c = 10.0mm/c
+
+### Save some CPU at init of jobs
+### To avoid refitting, add the following lines to your configuration file:
+HeavyIon:SigFitNGen = 0
+HeavyIon:SigFitDefPar = 2.15,18.42,0.33
+    
+Random:setSeed = on
+
+# change omega, phi meson's BR below
+223:oneChannel = 1 0.5 0 -11 11
+223:addChannel = 1 0.5 0 -13 13
+333:oneChannel = 1 0.5 0 -11 11
+333:addChannel = 1 0.5 0 -13 13