@@ -21,6 +21,7 @@
 
 #include <TRandom.h>
 
+#include <algorithm>
 #include <cmath>
 #include <cstddef>
 #include <cstdint>
@@ -323,7 +324,10 @@ bool TrackSmearer::smearTrack(O2Track& o2track, const lutEntry_t* lutEntry, cons
     for (int j = 0; j < kNumEigenModes; ++j) {
       val += lutEntry->eigvec[j][i] * o2track.getParam(j);
     }
-    params[i] = gRandom->Gaus(val, std::sqrt(lutEntry->eigval[i]));
+    // A LUT covariance close to singular (strongly correlated parameters at low pT) can carry a tiny negative
+    // eigenvalue from numerical precision. std::sqrt of it gives NaN and the track is dropped later on, which
+    // shows up as holes in the tracking efficiency. Such a mode has practically zero width: do not smear along it.
+    params[i] = gRandom->Gaus(val, std::sqrt(std::max(0.f, lutEntry->eigval[i])));
   }
 
   // Transform back params vector
 
@@ -59,6 +59,8 @@ struct RecoDecay {
   static constexpr int PdgBosonMax{37};                          // largest boson (gauge or H) PDG code; o2-linter: disable=pdg/explicit-code (H+ does not have a named constant.)
   static constexpr int PdgDivisorMeson{100};                     // order of magnitude of the meson PDG codes
   static constexpr int PdgDivisorBaryon{1000};                   // order of magnitude of the baryon PDG codes
+  static constexpr int PdgDiquarkSpin0Code{1};                   // last digits of a spin-0 diquark PDG code
+  static constexpr int PdgDiquarkSpin1Code{3};                   // last digits of a spin-1 diquark PDG code
 
   // Auxiliary functions
 
@@ -1179,6 +1181,31 @@ struct RecoDecay {
     return OriginType::None;
   }
 
+  /// Check whether the PDG code corresponds to a diquark state (e.g. 4101, 4201, 5101).
+  /// Diquarks are constituents used by the generators during the hadronisation and are not
+  /// hadrons. A diquark carrying a charm or beauty quark has a PDG code that satisfies the
+  /// pdg / 1000 == 4 or 5 condition used to identify charm and beauty baryons in
+  /// getParticleOrigin, so such a state would be misidentified as a heavy-flavour baryon there.
+  /// This check therefore validates the diquark structure: two quark flavours in
+  /// PDG_t::kDown..kTop (any quark pair, not only a heavy-flavour one), the first flavour not
+  /// smaller than the second, and a spin-0 or spin-1 code.
+  /// \param pdgCode PDG code of the particle
+  /// \return true if the PDG code belongs to a diquark state
+  static bool isDiquark(const int pdgCode)
+  {
+    // a diquark PDG code is composed as pdgQuark1 * PdgDivisorBaryon + pdgQuark2 * PdgDivisorMeson
+    // + spinCode, with pdgQuark1 >= pdgQuark2 the quark flavours and spinCode either
+    // PdgDiquarkSpin0Code or PdgDiquarkSpin1Code
+    const int absPdgCode = std::abs(pdgCode);
+    const int spinCode = absPdgCode % PdgDivisorMeson;
+    if (spinCode != PdgDiquarkSpin0Code && spinCode != PdgDiquarkSpin1Code) {
+      return false;
+    }
+    const int pdgQuark1 = absPdgCode / PdgDivisorBaryon;
+    const int pdgQuark2 = (absPdgCode % PdgDivisorBaryon) / PdgDivisorMeson;
+    return pdgQuark1 >= PDG_t::kDown && pdgQuark1 <= PDG_t::kTop && pdgQuark2 >= PDG_t::kDown && pdgQuark2 <= PDG_t::kTop && pdgQuark1 >= pdgQuark2;
+  }
+
   /// based on getCharmHardronOrigin in order to extend general particle
   /// Finding the origin (from charm hadronisation or beauty-hadron decay) of paritcle (b, c and others)
   /// \param particlesMC  table with MC particles
@@ -1221,6 +1248,17 @@ struct RecoDecay {
             // Check status code
             // auto motherStatusCode = std::abs(mother.getGenStatusCode());
             auto pdgParticleIMother = std::abs(mother.pdgCode()); // PDG code of the mother
+            // in the hadron-level mode, stop the walk when a parton or a diquark is reached: no
+            // heavy-flavour hadron can be found above the partonic level, and a diquark is not a
+            // hadron although its PDG code (e.g. 4101, 4201, 5101) satisfies pdg / 1000 == 4 or 5
+            // and would be misidentified as a charm/beauty baryon below. In the parton-level mode
+            // the walk has to continue through diquarks, since a charm or beauty quark can still be
+            // found above them.
+            if (!searchUpToQuark &&
+                (isDiquark(pdgParticleIMother) || pdgParticleIMother <= PdgQuarkMax ||
+                 (pdgParticleIMother >= PdgBosonMin && pdgParticleIMother <= PdgBosonMax))) {
+              break;
+            }
             // Check mother's PDG code.
             // printf("getMother: ");
             // for (int i = stage; i < 0; i++) // Indent to make the tree look nice.
 
@@ -324,6 +324,9 @@ DECLARE_SOA_DYNAMIC_COLUMN(Eta, eta,
                                                                                                                                                     RecoDecayPtEtaPhi::pVector(pt1, eta1, phi1),
                                                                                                                                                     RecoDecayPtEtaPhi::pVector(pt2, eta2, phi2))); }); //! Eta distribution of charm hadron
 
+DECLARE_SOA_COLUMN(K0sDcaToPv, k0sDcaToPv, float); //! DCA of the K0s candidate to the primary vertex (cm)
+DECLARE_SOA_COLUMN(OriginMcV0, originMcV0, int);   //! MC truth origin of the V0 candidate, see ParticleOriginMCTruth
+
 } // namespace fdhf
 
 namespace fdhf_2prong
@@ -633,7 +636,9 @@ DECLARE_SOA_TABLE(FDHfV0, "AOD", "FDHFV0", //! table to store results for HF fem
                   track::TPCNClsFindable,
                   femtodreamparticle::TPCNClsCrossedRows,
                   femtodreamparticle::TPCNSigmaPr,
-                  femtodreamparticle::TOFNSigmaPr);
+                  femtodreamparticle::TOFNSigmaPr,
+                  fdhf::K0sDcaToPv,
+                  fdhf::OriginMcV0);
 
 DECLARE_SOA_TABLE(FDHfColl, "AOD", "FDHFCOLL", //! table to store results for HF femtoscopy
                   fdhf::GIndexCol,
@@ -745,6 +750,7 @@ enum ParticleOriginMCTruth {
   kElse,                         //! none of the above; (NOTE: used to catch bugs. will be removed once MC usage is properly validated)
   kSecondaryFromHF,              //! Kaon from a charm- or beauty-hadron decay chain
   kSecondaryFromLF,              //! Kaon from a light-flavour decay without a heavy-flavour ancestor
+  kSecondaryFromPhi,             //! Kaon from a phi decay chain (phi -> K0/K0bar -> K0S)
   kNOriginMCTruthTypes
 };
 
@@ -766,7 +772,8 @@ static constexpr std::string_view ParticleOriginMCTruthName[kNOriginMCTruthTypes
   "_SecondaryDaughterXistarMinus",
   "_Else",
   "_SecondaryFromHF",
-  "_SecondaryFromLF"};
+  "_SecondaryFromLF",
+  "_SecondaryFromPhi"};
 
 /// Distinguished between reconstructed and truth
 enum MCType {