diff --git a/Trigger/TrigAnalysis/TriggerMatchingTool/Root/R3MatchingTool.cxx b/Trigger/TrigAnalysis/TriggerMatchingTool/Root/R3MatchingTool.cxx
new file mode 100644
index 0000000000000000000000000000000000000000..6ef34c6e8bbbe6f5cb3be83983c4258ed70a6720
--- /dev/null
+++ b/Trigger/TrigAnalysis/TriggerMatchingTool/Root/R3MatchingTool.cxx
@@ -0,0 +1,104 @@
+/*
+ Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+*/
+
+#include "TriggerMatchingTool/R3MatchingTool.h"
+#include "xAODBase/IParticleContainer.h"
+
+// Anonymous namespace for helper functions
+namespace
+{
+ // Helper function to efficiently decide if two objects are within a drThreshold of each other
+ bool fastDR(float eta1, float phi1, float eta2, float phi2, float drThreshold)
+ {
+ float dEta = eta1 - eta2;
+ if (dEta > drThreshold)
+ return false;
+ float dPhi = phi1 - phi2;
+ if (dPhi > drThreshold)
+ return false;
+ return dEta * dEta + dPhi * dPhi < drThreshold * drThreshold;
+ }
+} // namespace
+
+namespace Trig
+{
+
+ R3MatchingTool::R3MatchingTool(const std::string &name) : asg::AsgTool(name)
+ {
+ declareProperty("TrigDecisionTool", m_trigDecTool, "The trigger decision tool");
+ }
+
+ R3MatchingTool::~R3MatchingTool() {}
+
+ StatusCode R3MatchingTool::initialize()
+ {
+ ATH_CHECK(m_trigDecTool.retrieve());
+ return StatusCode::SUCCESS;
+ }
+
+ bool R3MatchingTool::match(
+ const std::vector<const xAOD::IParticle *> &recoObjects,
+ const std::string &chain,
+ double matchThreshold,
+ bool rerun) const
+ {
+ if (recoObjects.size() == 0)
+ // If there are no reco objects, the matching is trivially true
+ return true;
+ // Make the LinkInfo type less verbose
+ using IPartLinkInfo_t = TrigCompositeUtils::LinkInfo<xAOD::IParticleContainer>;
+ // TODO - detect if we're looking at run 3 data.
+ // If we are, then setting rerun to true should give a warning as it no
+ // longer makes sense for run 3
+ if (recoObjects.size() != 1)
+ {
+ ATH_MSG_WARNING("Matching of multiple objects is not yet supported!");
+ return false;
+ }
+ // This has to assume that the last IParticle feature in each chain is the
+ // correct one - I don't *think* this will cause any issues.
+ // Unlike with TEs, each chain should build in nodes that it actually uses.
+ // This means that we don't need anything clever for the etcut triggers any more (for example)
+ std::vector<IPartLinkInfo_t> features = m_trigDecTool->features<xAOD::IParticleContainer>(
+ chain,
+ rerun ? TrigDefs::Physics | TrigDefs::allowResurrectedDecision : TrigDefs::Physics);
+ ATH_MSG_DEBUG("Found " << features.size() << " features for chain group " << chain);
+ // TODO:
+ // Right now we are only looking at single object chains, so we only need
+ // to find a single match for one reco-object.
+ // Longer term we need to deal with combinations so this gets harder
+ const xAOD::IParticle &recoObject = *recoObjects.at(0);
+ for (const IPartLinkInfo_t &info : features)
+ {
+ if (!info.link.isValid())
+ {
+ // This could result in false negatives...
+ ATH_MSG_WARNING("Invalid link to trigger feature for chain " << chain);
+ continue;
+ }
+ const xAOD::IParticle &trigObject = **info.link;
+ if (fastDR(
+ recoObject.eta(),
+ recoObject.phi(),
+ trigObject.eta(),
+ trigObject.phi(),
+ matchThreshold))
+ // Once we find one match, that is enough
+ return true;
+ }
+ // If we get here then there was no good match
+ return false;
+ }
+
+ bool R3MatchingTool::match(
+ const xAOD::IParticle &recoObject,
+ const std::string &chain,
+ double matchThreshold,
+ bool rerun) const
+ {
+ std::vector<const xAOD::IParticle *> tmpVec{&recoObject};
+ return match(tmpVec, chain, matchThreshold, rerun);
+ }
+
+} // namespace Trig
\ No newline at end of file
diff --git a/Trigger/TrigAnalysis/TriggerMatchingTool/TriggerMatchingTool/R3MatchingTool.h b/Trigger/TrigAnalysis/TriggerMatchingTool/TriggerMatchingTool/R3MatchingTool.h
new file mode 100644
index 0000000000000000000000000000000000000000..00ee2d004b3b948cbaaef29fa508342ee057b4de
--- /dev/null
+++ b/Trigger/TrigAnalysis/TriggerMatchingTool/TriggerMatchingTool/R3MatchingTool.h
@@ -0,0 +1,41 @@
+/*
+ Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+*/
+
+#ifndef TRIGGERMATCHINGTOOL_R3MATCHINGTOOL_H
+#define TRIGGERMATCHINGTOOL_R3MATCHINGTOOL_H
+
+#include "AsgTools/AsgTool.h"
+#include "AsgTools/ToolHandle.h"
+#include "TriggerMatchingTool/IMatchingTool.h"
+#include "TrigDecisionTool/TrigDecisionTool.h"
+
+namespace Trig
+{
+ class R3MatchingTool : public asg::AsgTool, virtual public IMatchingTool
+ {
+ ASG_TOOL_CLASS(R3MatchingTool, IMatchingTool)
+ public:
+ R3MatchingTool(const std::string &name);
+ ~R3MatchingTool();
+
+ virtual StatusCode initialize() override;
+
+ virtual bool match(
+ const std::vector<const xAOD::IParticle *> &recoObjects,
+ const std::string &chain,
+ double matchThreshold,
+ bool rerun) const override;
+
+ virtual bool match(
+ const xAOD::IParticle &recoObject,
+ const std::string &chain,
+ double matchThreshold,
+ bool rerun) const override;
+
+ private:
+ ToolHandle<TrigDecisionTool> m_trigDecTool;
+ }; //> end class R3MatchingTool
+} // namespace Trig
+
+#endif //> !TRIGGERMATCHINGTOOL_R3MATCHINGTOOL_H
\ No newline at end of file
diff --git a/Trigger/TrigAnalysis/TriggerMatchingTool/TriggerMatchingTool/selection.xml b/Trigger/TrigAnalysis/TriggerMatchingTool/TriggerMatchingTool/selection.xml
index 4ceaff3c5b61c7daed88d9f76a51de9f385ba820..6dedd615f8c53e7ecee52b4fa4b60f93cb0fe7b4 100644
--- a/Trigger/TrigAnalysis/TriggerMatchingTool/TriggerMatchingTool/selection.xml
+++ b/Trigger/TrigAnalysis/TriggerMatchingTool/TriggerMatchingTool/selection.xml
@@ -5,4 +5,5 @@
<class name="Trig::IIParticleRetrievalTool" />
<class name="Trig::IParticleRetrievalTool" />
<class name="Trig::MatchFromCompositeTool" />
+ <class name="Trig::R3MatchingTool" />
</lcgdict>
diff --git a/Trigger/TrigAnalysis/TriggerMatchingTool/src/components/TriggerMatchingTool_entries.cxx b/Trigger/TrigAnalysis/TriggerMatchingTool/src/components/TriggerMatchingTool_entries.cxx
index 83133a91681f2f26aebdd260588092cc04f456cf..c69aaf8cdc3910adae2604c43dac3ce4e2577ab5 100644
--- a/Trigger/TrigAnalysis/TriggerMatchingTool/src/components/TriggerMatchingTool_entries.cxx
+++ b/Trigger/TrigAnalysis/TriggerMatchingTool/src/components/TriggerMatchingTool_entries.cxx
@@ -1,14 +1,14 @@
#include "TriggerMatchingTool/MatchingTool.h"
#include "TriggerMatchingTool/IParticleRetrievalTool.h"
#include "TriggerMatchingTool/MatchFromCompositeTool.h"
+#include "TriggerMatchingTool/R3MatchingTool.h"
-DECLARE_COMPONENT( Trig::MatchingTool )
+DECLARE_COMPONENT(Trig::MatchingTool)
-
-DECLARE_COMPONENT( Trig::MatchingTool )
-DECLARE_COMPONENT( Trig::IParticleRetrievalTool )
-DECLARE_COMPONENT( Trig::MatchFromCompositeTool )
+DECLARE_COMPONENT(Trig::MatchingTool)
+DECLARE_COMPONENT(Trig::IParticleRetrievalTool)
+DECLARE_COMPONENT(Trig::MatchFromCompositeTool)
+DECLARE_COMPONENT(Trig::R3MatchingTool)
#include "../TestMatchingToolAlg.h"
-DECLARE_COMPONENT( TestMatchingToolAlg )
-
+DECLARE_COMPONENT(TestMatchingToolAlg)