From 910ed545a26019883eca255620672338590af3c3 Mon Sep 17 00:00:00 2001
From: Karol Krizka <kkrizka@gmail.com>
Date: Wed, 7 Aug 2024 22:32:21 +0100
Subject: [PATCH] Fix particle hypothesis having to be positive in truth
 tracking.

---
 ACTSTracking/Helpers.hxx         | 11 ++++++++++-
 src/ACTSTruthCKFTrackingProc.cxx |  2 +-
 src/ACTSTruthTrackingProc.cxx    |  2 +-
 src/Helpers.cxx                  | 16 ++--------------
 4 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/ACTSTracking/Helpers.hxx b/ACTSTracking/Helpers.hxx
index 83da45b..1a2a9e3 100644
--- a/ACTSTracking/Helpers.hxx
+++ b/ACTSTracking/Helpers.hxx
@@ -113,7 +113,16 @@ EVENT::TrackState* ACTS2Marlin_trackState(int location,
 EVENT::LCCollection* getCollection(EVENT::LCEvent* evt,
                                    const std::string& name);
 
-Acts::ParticleHypothesis convertParticle(const EVENT::MCParticle* mcParticle);
+//! Get particle hypothesis for a given MCParticle object
+/**
+ * The particle hypothesis is determined by the PDG code of the MCParticle. The
+ * absolute value is taken, as this is a requirement from ACTS.
+ *
+ * \param mcParticle MCParticle object for which to determine a hypothesis
+ *
+ * \return The ACTS particle hypothesis
+ */
+Acts::ParticleHypothesis getParticleHypothesis(const EVENT::MCParticle* mcParticle);
 
 }  // namespace ACTSTracking
 
diff --git a/src/ACTSTruthCKFTrackingProc.cxx b/src/ACTSTruthCKFTrackingProc.cxx
index 05ae0b0..894a98c 100644
--- a/src/ACTSTruthCKFTrackingProc.cxx
+++ b/src/ACTSTruthCKFTrackingProc.cxx
@@ -152,7 +152,7 @@ void ACTSTruthCKFTrackingProc::processEvent(LCEvent* evt) {
         std::pow(_initialTrackError_relP * p / (p * p), 2);
 
     Acts::BoundTrackParameters seed(perigeeSurface, params, cov,
-                                    ACTSTracking::convertParticle(mcParticle));
+                                    ACTSTracking::getParticleHypothesis(mcParticle));
     seeds.push_back(seed);
   }
 
diff --git a/src/ACTSTruthTrackingProc.cxx b/src/ACTSTruthTrackingProc.cxx
index 7dc0dd8..ef9cf54 100644
--- a/src/ACTSTruthTrackingProc.cxx
+++ b/src/ACTSTruthTrackingProc.cxx
@@ -332,7 +332,7 @@ void ACTSTruthTrackingProc::processEvent(LCEvent* evt) {
             Acts::Vector3(mcParticle->getVertex()));
 
     Acts::BoundTrackParameters initialparams(perigeeSurface, params,
-                                             cov, ACTSTracking::convertParticle(mcParticle));
+                                             cov, ACTSTracking::getParticleHypothesis(mcParticle));
     // reference Examples TruthTracking/ParticleSmearing.cpp
     streamlog_out(DEBUG) << "Initial Paramemeters" << std::endl
                          << initialparams << std::endl;
diff --git a/src/Helpers.cxx b/src/Helpers.cxx
index cf67272..c774af9 100644
--- a/src/Helpers.cxx
+++ b/src/Helpers.cxx
@@ -502,37 +502,25 @@ EVENT::LCCollection* getCollection(EVENT::LCEvent* evt,
   }
 }
 
-Acts::ParticleHypothesis convertParticle(const EVENT::MCParticle* mcParticle)
+Acts::ParticleHypothesis getParticleHypothesis(const EVENT::MCParticle* mcParticle)
 {
-  switch (mcParticle->getPDG()) {
+  switch (std::abs(mcParticle->getPDG())) {
   case 11:
     return Acts::ParticleHypothesis {Acts::PdgParticle::eElectron};
-  case -11:
-    return Acts::ParticleHypothesis {Acts::PdgParticle::ePositron};
   case 13:
     return Acts::ParticleHypothesis {Acts::PdgParticle::eMuon};
-  case -13:
-    return Acts::ParticleHypothesis {Acts::PdgParticle::eAntiMuon};
   case 15:
     return Acts::ParticleHypothesis {Acts::PdgParticle::eTau};
-  case -15:
-    return Acts::ParticleHypothesis {Acts::PdgParticle::eAntiTau};
   case 22:
     return Acts::ParticleHypothesis {Acts::PdgParticle::eGamma};
   case 111:
     return Acts::ParticleHypothesis {Acts::PdgParticle::ePionZero};
   case 211:
     return Acts::ParticleHypothesis {Acts::PdgParticle::ePionPlus};
-  case -211:
-    return Acts::ParticleHypothesis {Acts::PdgParticle::ePionMinus};
   case 2112:
     return Acts::ParticleHypothesis {Acts::PdgParticle::eNeutron};
-  case -2112:
-    return Acts::ParticleHypothesis {Acts::PdgParticle::eAntiNeutron};
   case 2212:
     return Acts::ParticleHypothesis {Acts::PdgParticle::eProton};
-  case -2212:
-    return Acts::ParticleHypothesis {Acts::PdgParticle::eAntiProton};
   }
 
   Acts::PdgParticle pdg = Acts::PdgParticle::eInvalid;