[PWGDQ] use correct momentum scaling when computing invariant mass

The mu+mu- invariant mass from global forward tracks in now computed
by extrapolating the MFT tracks with the momentum rescaled to the MCH
one (momentum scaling method), while previously it was computed by
directly extrapolating the global refitted tracks.

Author: aferrero2707

PWGDQ/Tasks/qaMatching.cxx

@@ -1599,30 +1599,30 @@ struct QaMatching {
   }
 
   template <typename TMCH, typename TMFT, class C>
-  o2::dataformats::GlobalFwdTrack propagateToVertexMft(const TMFT& muon,
+  o2::dataformats::GlobalFwdTrack propagateToVertexMft(const TMFT& mftTrack,
                                                        const TMCH& mchTrack,
                                                        const C& collision)
   {
     // extrapolation with MCH tools
     auto mchTrackAtMFT = mExtrap.FwdtoMCH(fwdToTrackPar(mchTrack));
-    o2::mch::TrackExtrap::extrapToVertexWithoutBranson(mchTrackAtMFT, muon.z());
+    o2::mch::TrackExtrap::extrapToVertexWithoutBranson(mchTrackAtMFT, mftTrack.z());
 
-    auto muonTrackProp = mExtrap.FwdtoMCH(fwdToTrackPar(muon));
+    auto mftTrackProp = mExtrap.FwdtoMCH(fwdToTrackPar(mftTrack));
 
     // update global track momentum from the MCH track
-    double pRatio = muonTrackProp.p() / mchTrackAtMFT.p();
-    double newInvBendMom = muonTrackProp.getInverseBendingMomentum() * pRatio;
-    muonTrackProp.setInverseBendingMomentum(newInvBendMom);
-    muonTrackProp.setCharge(mchTrackAtMFT.getCharge());
+    double pRatio = mftTrackProp.p() / mchTrackAtMFT.p();
+    double newInvBendMom = mftTrackProp.getInverseBendingMomentum() * pRatio;
+    mftTrackProp.setInverseBendingMomentum(newInvBendMom);
+    mftTrackProp.setCharge(mchTrackAtMFT.getCharge());
 
-    o2::mch::TrackExtrap::extrapToVertex(muonTrackProp,
+    o2::mch::TrackExtrap::extrapToVertex(mftTrackProp,
                                          collision.posX(),
                                          collision.posY(),
                                          collision.posZ(),
                                          collision.covXX(),
                                          collision.covYY());
 
-    return mExtrap.MCHtoFwd(muonTrackProp);
+    return mExtrap.MCHtoFwd(mftTrackProp);
   }
 
   template <class MCP>
@@ -2440,7 +2440,7 @@ struct QaMatching {
   void fillDimuonPlotsMc(const CollisionInfo& collisionInfo,
                          C const& collisions,
                          TMUON const& muonTracks,
-                         TMFT const& /*mftTracks*/)
+                         TMFT const& mftTracks)
   {
     std::vector<MuonPair> muonPairs;
     std::vector<GlobalMuonPair> globalMuonPairs;
@@ -2476,12 +2476,12 @@ struct QaMatching {
 
       auto const& collision = collisions.rawIteratorAt(muon1.first);
 
-      auto const& muonTrack1 = muonTracks.rawIteratorAt(candidates1[0].globalTrackId);
-      auto const& muonTrack2 = muonTracks.rawIteratorAt(candidates2[0].globalTrackId);
+      auto const& mchTrack1 = muonTracks.rawIteratorAt(candidates1[0].muonTrackId);
+      auto const& mchTrack2 = muonTracks.rawIteratorAt(candidates2[0].muonTrackId);
       auto matchScore1 = candidates1[0].matchScore;
       auto matchScore2 = candidates2[0].matchScore;
-      auto const& mchTrack1 = muonTrack1.template matchMCHTrack_as<TMUON>();
-      auto const& mchTrack2 = muonTrack2.template matchMCHTrack_as<TMUON>();
+      auto const& mftTrack1 = mftTracks.rawIteratorAt(candidates1[0].mftTrackId);
+      auto const& mftTrack2 = mftTracks.rawIteratorAt(candidates2[0].mftTrackId);
       int sign1 = mchTrack1.sign();
       int sign2 = mchTrack2.sign();
 
@@ -2507,8 +2507,8 @@ struct QaMatching {
 
       double massMCH = getMuMuInvariantMass(propagateToVertexMch(mchTrack1, collision),
                                             propagateToVertexMch(mchTrack2, collision));
-      double mass = getMuMuInvariantMass(propagateToVertexMch(muonTrack1, collision),
-                                         propagateToVertexMch(muonTrack2, collision));
+      double mass = getMuMuInvariantMass(propagateToVertexMft(mftTrack1, mchTrack1, collision),
+                                         propagateToVertexMft(mftTrack2, mchTrack2, collision));
       registryDimuon.get<TH1>(HIST("dimuon/invariantMass_MuonKine_GlobalMuonCuts"))->Fill(massMCH);
       registryDimuon.get<TH1>(HIST("dimuon/invariantMass_ScaledMftKine_GlobalMuonCuts"))->Fill(mass);
       registryDimuon.get<TH2>(HIST("dimuon/MC/invariantMass_MuonKine_GlobalMuonCuts_vs_match_type"))->Fill(massMCH, matchType);