Rich: implementation of matching rings to mcTracks for multiple MC input files

This MR allows to match rings to MCTracks if multiple MC input files are provided, e.g. urqmd and beam background.
Related redmine issue #2731
Might be of interest for @f.kornas @v.friese .

In draft mode, since there are some todo's:
Some required changes:

• In 6 places the 'vector<pair<Int_t, Int_t>>GetMcTrackMotherIdsForRichHit' implementation is used, which will not work after this MR anymore.

- [ ] Remove the 'vector<Int_t>' and 'vector<pair<Int_t, Int_t>>GetMcTrackMotherIdsForRichHit' functions

The CbmRichRingFinderIdeal is disabled (just reconstructing no rings) with this MR and will be properly implemented in a future MR,
supporting time-based mode and multiple MC inputs.
Also hits from the same mother particle in different RICH cameras will then be properly taken into account for the CBM RICH.

core/base/CbmMatchRecoToMC.cxx

@@ -849,51 +849,39 @@ void CbmMatchRecoToMC::MatchStsTracks(const TClonesArray* mvdHitMatches, const T
 
 
 void CbmMatchRecoToMC::MatchRichRings(const TClonesArray* richRings, const TClonesArray* richHits,
-                                      // const TClonesArray* richDigis,
-                                      // const TClonesArray* richDigiMatches,
                                       CbmMCDataArray* richMcPoints, CbmMCDataArray* mcTracks, TClonesArray* ringMatches)
 {
   // Loop over RichRings
   Int_t nRings = richRings->GetEntriesFast();
   for (Int_t iRing = 0; iRing < nRings; iRing++) {
     const CbmRichRing* ring = static_cast<const CbmRichRing*>(richRings->At(iRing));
-    if (nullptr == ring) continue;
-
+    if (!ring) continue;
     CbmTrackMatchNew* ringMatch = new ((*ringMatches)[iRing]) CbmTrackMatchNew();
-
-    Int_t nofHits = ring->GetNofHits();
-    for (Int_t iHit = 0; iHit < nofHits; iHit++) {
-      const CbmRichHit* hit = static_cast<const CbmRichHit*>(richHits->At(ring->GetHit(iHit)));
-      if (nullptr == hit) continue;
-
-      vector<pair<Int_t, Int_t>> motherIds =
-        GetMcTrackMotherIdsForRichHit(fDigiManager, hit, richMcPoints, mcTracks, fEventNumber);
-      for (UInt_t i = 0; i < motherIds.size(); i++) {
-        ringMatch->AddLink(1., motherIds[i].second, motherIds[i].first);
+    Int_t nHits                 = ring->GetNofHits();
+    for (Int_t iHit = 0; iHit < nHits; iHit++) {
+      const CbmRichHit* hit = static_cast<const CbmRichHit*>(richHits->At(static_cast<Int_t>(ring->GetHit(iHit))));
+      if (!hit) continue;
+      vector<CbmLink> motherIds = GetMcTrackMotherIdsForRichHit(fDigiManager, hit, richMcPoints, mcTracks);
+      for (const auto& motherId : motherIds) {
+        ringMatch->AddLink(motherId);
       }
     }
 
     if (ringMatch->GetNofLinks() != 0) {
-
-      Int_t bestTrackId      = ringMatch->GetMatchedLink().GetIndex();
-      Int_t bestTrackEventId = ringMatch->GetMatchedLink().GetEntry();
-
-      Int_t trueCounter  = 0;
-      Int_t wrongCounter = 0;
-      for (Int_t iHit = 0; iHit < nofHits; iHit++) {
-        const CbmRichHit* hit = static_cast<const CbmRichHit*>(richHits->At(ring->GetHit(iHit)));
-        if (nullptr == hit) continue;
-        vector<pair<Int_t, Int_t>> motherIds =
-          GetMcTrackMotherIdsForRichHit(fDigiManager, hit, richMcPoints, mcTracks, fEventNumber);
-        if (std::find(motherIds.begin(), motherIds.end(), std::make_pair(bestTrackEventId, bestTrackId))
-            != motherIds.end()) {
+      CbmLink bestTrackLink = ringMatch->GetMatchedLink();
+      Int_t trueCounter     = 0;
+      Int_t wrongCounter    = 0;
+      for (Int_t iHit = 0; iHit < nHits; iHit++) {
+        const CbmRichHit* hit = static_cast<const CbmRichHit*>(richHits->At(static_cast<Int_t>(ring->GetHit(iHit))));
+        if (!hit) continue;
+        vector<CbmLink> motherIds = GetMcTrackMotherIdsForRichHit(fDigiManager, hit, richMcPoints, mcTracks);
+        if (std::find(motherIds.begin(), motherIds.end(), bestTrackLink) != motherIds.end()) {
           trueCounter++;
         }
         else {
           wrongCounter++;
         }
       }
-
       ringMatch->SetNofTrueHits(trueCounter);
       ringMatch->SetNofWrongHits(wrongCounter);
     }
@@ -901,10 +889,42 @@ void CbmMatchRecoToMC::MatchRichRings(const TClonesArray* richRings, const TClon
       ringMatch->SetNofTrueHits(0);
       ringMatch->SetNofWrongHits(0);
     }
-
   }  // Ring loop
 }
 
+vector<CbmLink> CbmMatchRecoToMC::GetMcTrackMotherIdsForRichHit(CbmDigiManager* digiMan, const CbmRichHit* hit,
+                                                                CbmMCDataArray* richPoints, CbmMCDataArray* mcTracks)
+{
+  vector<CbmLink> result;
+  if (!hit) return result;
+  Int_t digiIndex = hit->GetRefId();
+  if (digiIndex < 0) return result;
+  const CbmRichDigi* digi = digiMan->Get<CbmRichDigi>(digiIndex);
+  if (!digi) return result;
+  const CbmMatch* digiMatch = digiMan->GetMatch(ECbmModuleId::kRich, digiIndex);
+  if (!digiMatch) return result;
+
+  vector<CbmLink> links = digiMatch->GetLinks();
+  for (const auto& link : links) {
+    Int_t pointId = link.GetIndex();
+    if (pointId < 0) continue;  // noise signal from digitizer
+    const CbmRichPoint* point = static_cast<const CbmRichPoint*>(richPoints->Get(link));
+    if (!point) continue;
+    Int_t mcTrackId = point->GetTrackID();
+    if (mcTrackId < 0) continue;
+    const CbmMCTrack* mcTrack =
+      static_cast<const CbmMCTrack*>(mcTracks->Get(link.GetFile(), link.GetEntry(), mcTrackId));
+    if (!mcTrack) continue;
+    if (mcTrack->GetPdgCode() != 50000050) continue;  // select only Cherenkov photons
+    Int_t motherId = mcTrack->GetMotherId();
+    // several photons can have same mother track
+    // count only unique motherIds
+    CbmLink val(1., motherId, link.GetEntry(), link.GetFile());
+    if (std::find(result.begin(), result.end(), val) == result.end()) result.push_back(val);
+  }
+
+  return result;
+}
 
 vector<pair<Int_t, Int_t>> CbmMatchRecoToMC::GetMcTrackMotherIdsForRichHit(CbmDigiManager* digiMan,
                                                                            const CbmRichHit* hit,