PanTau: set decay mode to Mode_NotSet when not evaluated

Hello,

Currently, when taus have 0 or >5 associated tracks, the tau substructure reconstruction ("PanTau" tool) is not run, and the only substructure variable that is set for the tau is "PanTau_isPanTauCandidate = 0".
None of the other PanTau variables are set, and therefore, they all have a default value of 0.
This is very misleading for the PanTau "DecayMode" variable, for which a value of 0 corresponds to "Mode_1p0n" in the TauDefs enum.
The consequence is that "1p0n" taus currently includes 0p and >5p candidates.

In this MR, when PanTau_isPanTauCandidate=0, we also set the DecayMode to Mode_NotSet, to avoid this confusion.
We can now drop the workaround we added in TauCombinedTES.

The only change to the reconstruction output is TauJetsAux.PanTau_DecayMode: 0 -> 6, for 0p and >5p.

Closes ATLTAU-1775.

Cheers,
Bertrand

Reconstruction/PanTau/PanTauAlgs/Root/Tool_DetailsArranger.cxx

@@ -82,6 +82,7 @@ StatusCode PanTau::Tool_DetailsArranger::execute(PanTau::PanTauSeed* inSeed, xAO
   if(isBadSeed == true) {
     ATH_MSG_DEBUG("This seed is not useable for detail arranging (other than validity flag)");
     tauJet->setPanTauDetail(xAOD::TauJetParameters::PanTau_isPanTauCandidate, 0);
+    tauJet->setPanTauDetail(xAOD::TauJetParameters::PanTau_DecayMode, xAOD::TauJetParameters::Mode_NotSet);
     return StatusCode::SUCCESS;
   }
     

Reconstruction/tauRecTools/Root/TauCombinedTES.cxx

@@ -203,15 +203,9 @@ int TauCombinedTES::getEtaIndex(const float& eta) const {
 
 
 
-xAOD::TauJetParameters::DecayMode TauCombinedTES::getDecayMode(const xAOD::TauJet& tau) const{
+xAOD::TauJetParameters::DecayMode TauCombinedTES::getDecayMode(const xAOD::TauJet& tau) const {
   int decayMode = xAOD::TauJetParameters::DecayMode::Mode_Error;
-
-  // When PanTau fails, the decay mode will be set to 1p0n !
-  int isPanTauCandidate;
-  tau.panTauDetail(xAOD::TauJetParameters::PanTauDetails::PanTau_isPanTauCandidate, isPanTauCandidate);
-  if (isPanTauCandidate) {
-    tau.panTauDetail(xAOD::TauJetParameters::PanTauDetails::PanTau_DecayMode, decayMode);
-  }
+  tau.panTauDetail(xAOD::TauJetParameters::PanTauDetails::PanTau_DecayMode, decayMode);
 
   return static_cast<xAOD::TauJetParameters::DecayMode>(decayMode);
 }