Add variable Jpsi-hadron kstar and histograms for femtoscopy

Author: Yuanjing Ji

PWGDQ/Core/HistogramsLibrary.cxx

@@ -1773,6 +1773,9 @@ void o2::aod::dqhistograms::DefineHistograms(HistogramManager* hm, const char* h
       hm->AddHistogram(histClass, "InvMass_DelEta_DelPhi", "", 4, varsJPsiHadCorr, nJPsiHadCorr); // Without efficiency
       // hm->AddHistogram(histClass, "InvMass_DelEta_DelPhi", "", 4, varsJPsiHadCorr, nJPsiHadCorr, nullptr, VarManager::kJpsiHadronEff);
     }
+    if (subGroupStr.Contains("dilepton-hadron-femto")) {
+      hm->AddHistogram(histClass, "DileptonHadronKstar_DileptonMass", "", false, 150, 0.0, 3.0, VarManager::kDileptonHadronKstar, 100, 1.5,4.5, VarManager::kPairMassDau);
+    }
     if (subGroupStr.Contains("opencharm")) {
       hm->AddHistogram(histClass, "Delta_Mass_DstarD0region", "", false, 50, 0.14, 0.16, VarManager::kDeltaMass);
     }

PWGDQ/Core/VarManager.cxx

@@ -926,6 +926,8 @@ void VarManager::SetDefaultVarNames()
   fgVariableUnits[kPairPhi] = "rad.";
   fgVariableNames[kPairPhiv] = "#varphi_{V}";
   fgVariableUnits[kPairPhiv] = "rad.";
+  fgVariableNames[kDileptonHadronKstar] = "Dilepton-hadron k^{*}";
+  fgVariableUnits[kDileptonHadronKstar] = "GeV/c^{2}";
   fgVariableNames[kDeltaEta] = "#Delta#eta";
   fgVariableUnits[kDeltaEta] = "";
   fgVariableNames[kDeltaPhi] = "#Delta#phi";
@@ -1627,6 +1629,7 @@ void VarManager::SetDefaultVarNames()
   fgVarNamesMap["kPairEta"] = kPairEta;
   fgVarNamesMap["kPairPhi"] = kPairPhi;
   fgVarNamesMap["kPairPhiv"] = kPairPhiv;
+  fgVarNamesMap["kDileptonHadronKstar"] = kDileptonHadronKstar;
   fgVarNamesMap["kDeltaEta"] = kDeltaEta;
   fgVarNamesMap["kDeltaPhi"] = kDeltaPhi;
   fgVarNamesMap["kDeltaPhiSym"] = kDeltaPhiSym;

PWGDQ/Core/VarManager.h

@@ -144,6 +144,7 @@ class VarManager : public TObject
     kElectronMuon,              // e.g. Electron - muon correlations
     kBcToThreeMuons,            // e.g. Bc           -> mu+ mu- mu+
     kBtoJpsiEEK,                // e.g. B+           -> e+ e- K+
+    kJpsiEEProton,              // e.g. Jpsi-proton correlation, Jpsi to e+e-
     kXtoJpsiPiPi,               // e.g. X(3872)      -> J/psi pi+ pi-
     kChictoJpsiEE,              // e.g. Chi_c1      -> J/psi e+ e-
     kDstarToD0KPiPi,            // e.g. D*+ -> D0 pi+ -> K- pi+ pi+
@@ -806,6 +807,7 @@ class VarManager : public TObject
     kDeltaPhi,
     kDeltaPhiSym,
     kNCorrelationVariables,
+    kDileptonHadronKstar,
 
     // Dilepton-track-track variables
     kQuadMass,
@@ -4710,7 +4712,7 @@ void VarManager::FillDileptonHadron(T1 const& dilepton, T2 const& hadron, float*
     values = fgValues;
   }
 
-  if (fgUsedVars[kPairMass] || fgUsedVars[kPairPt] || fgUsedVars[kPairEta] || fgUsedVars[kPairPhi] || fgUsedVars[kPairMassDau] || fgUsedVars[kPairPtDau]) {
+  if (fgUsedVars[kPairMass] || fgUsedVars[kPairPt] || fgUsedVars[kPairEta] || fgUsedVars[kPairPhi] || fgUsedVars[kPairMassDau] || fgUsedVars[kPairPtDau] || fgUsedVars[kDileptonHadronKstar]) {
     ROOT::Math::PtEtaPhiMVector v1(dilepton.pt(), dilepton.eta(), dilepton.phi(), dilepton.mass());
     ROOT::Math::PtEtaPhiMVector v2(hadron.pt(), hadron.eta(), hadron.phi(), hadronMass);
     ROOT::Math::PtEtaPhiMVector v12 = v1 + v2;
@@ -4722,6 +4724,11 @@ void VarManager::FillDileptonHadron(T1 const& dilepton, T2 const& hadron, float*
     values[kPairPtDau] = dilepton.pt();
     values[kMassDau] = hadronMass;
     values[kDeltaMass] = v12.M() - dilepton.mass();
+    // Calculate kstar of Dilepton and hadron pair
+    ROOT::Math::PtEtaPhiMVector v12_Qvect = v1 - v2;
+    double Pinv = v12.M();
+    double Q1 = ( dilepton.mass()*dilepton.mass() - hadronMass*hadronMass )/Pinv;
+    values[kDileptonHadronKstar] = sqrt(Q1*Q1-v12_Qvect.M2())/2.0;
   }
   if (fgUsedVars[kDeltaPhi]) {
     double delta = dilepton.phi() - hadron.phi();