[PWGDQ] Calculation of kDeltaPhiPair2 in FillPairME (AliceO2Group#8269)

Author: Shunsuke-Kurita

PWGDQ/Core/VarManager.h

@@ -2896,6 +2896,17 @@ void VarManager::FillPairME(T1 const& t1, T2 const& t2, float* values)
   values[kPhi] = v12.Phi() > 0 ? v12.Phi() : v12.Phi() + 2. * M_PI;
   values[kRap] = -v12.Rapidity();
 
+  if (fgUsedVars[kDeltaPhiPair2]) {
+    double phipair2ME = v1.Phi() - v2.Phi();
+    if (phipair2ME > 3 * TMath::Pi() / 2) {
+      values[kDeltaPhiPair2] = phipair2ME - 2 * TMath::Pi();
+    } else if (phipair2ME < -TMath::Pi() / 2) {
+      values[kDeltaPhiPair2] = phipair2ME + 2 * TMath::Pi();
+    } else {
+      values[kDeltaPhiPair2] = phipair2ME;
+    }
+  }
+
   // TODO: provide different computations for vn
   // Compute the scalar product UQ for two muon from different event using Q-vector from A, for second and third harmonic
   values[kU2Q2Ev1] = values[kQ2X0A1] * std::cos(2 * v1.Phi()) + values[kQ2Y0A1] * std::sin(2 * v1.Phi());