From e170e6e7a05eefd0f97bd1a2036d4c8d3d8fb7b1 Mon Sep 17 00:00:00 2001
From: aferrero2707 <aferrero1975@gmail.com>
Date: Mon, 25 May 2026 01:24:35 +0200
Subject: [PATCH] [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.
---
 PWGDQ/Tasks/qaMatching.cxx | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/PWGDQ/Tasks/qaMatching.cxx b/PWGDQ/Tasks/qaMatching.cxx
index 6f2056d9c24..e2f7e6e955b 100644
--- a/PWGDQ/Tasks/qaMatching.cxx
+++ b/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;
@@ -2480,8 +2480,10 @@ struct QaMatching {
       auto const& muonTrack2 = muonTracks.rawIteratorAt(candidates2[0].globalTrackId);
       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& mchTrack1 = muonTracks.rawIteratorAt(candidates1[0].muonTrackId);
+      auto const& mchTrack2 = muonTracks.rawIteratorAt(candidates2[0].muonTrackId);
+      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 +2509,8 @@ 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);