[PWGCF] add deta differential study (#12781)

Author: jikim1290

PWGCF/Tasks/correlations.cxx

@@ -182,6 +182,7 @@ struct CorrelationTask {
       if (doprocessSame2Prong2Prong || doprocessSame2Prong2ProngML) {
         registry.add("invMassTwoPart", "2D 2-prong invariant mass (GeV/c^2)", {HistType::kTHnSparseF, {axisSpecMass, axisSpecMass, axisPtTrigger, axisPtAssoc, axisMultiplicity}});
         registry.add("invMassTwoPartDPhi", "2D 2-prong invariant mass (GeV/c^2)", {HistType::kTHnSparseF, {axisSpecMass, axisSpecMass, axisPtTrigger, axisPtAssoc, axisDeltaPhi}});
+        registry.add("invMassTwoPartDEta", "2D 2-prong invariant mass (GeV/c^2)", {HistType::kTHnSparseF, {axisSpecMass, axisSpecMass, axisPtTrigger, axisPtAssoc, axisDeltaEta}});
       }
     }
     if (doprocessSameDerivedMultSet) {
@@ -394,6 +395,9 @@ struct CorrelationTask {
                 continue;
               registry.fill(HIST("invMassTwoPart"), track1.invMass(), track2.invMass(), track1.pt(), track2.pt(), multiplicity);
               registry.fill(HIST("invMassTwoPartDPhi"), track1.invMass(), track2.invMass(), track1.pt(), track2.pt(), TVector2::Phi_0_2pi(track1.phi() - track2.phi() + TMath::Pi() / 2.0) - TMath::Pi() / 2.0);
+              if (std::abs(track1.phi() - track2.phi()) < constants::math::PI * 0.5) {
+                registry.fill(HIST("invMassTwoPartDEta"), track1.invMass(), track2.invMass(), track1.pt(), track2.pt(), track1.eta() - track2.eta());
+              }
             }
           }
         }
@@ -637,7 +641,7 @@ struct CorrelationTask {
             continue; // skip particles that do not match the decay mask
           }
           if (cfgV0RapidityMax > 0) {
-            auto [t, y] = getV0Rapidity(track1);
+            auto [t, y] = getV0Rapidity(track2);
             if (t && std::abs(y) > cfgV0RapidityMax)
               continue; // V0s are not allowed to be outside the rapidity range
           }