hooks and configuration for POWHEG

Author: amorsch

Generators/share/egconfig/pythia8_powheg.cfg

@@ -0,0 +1,79 @@
+Beams:eCM 13000. 		# GeV
+### processes
+Next:numberShowLHA = 1
+Next:numberShowInfo = 1
+Next:numberShowProcess = 1
+Next:numberShowEvent = 1
+Main:timesAllowErrors = 10
+! Read LHE file from POWHEG
+Beams:frameType = 4
+Beams:LHEF = powheg.lhe
+
+! Number of outgoing particles of POWHEG Born level process
+! (i.e. not counting additional POWHEG radiation)
+POWHEG:nFinal = 2
+
+! How vetoing is performed:
+!  0 - No vetoing is performed (userhooks are not loaded)
+!  1 - Showers are started at the kinematical limit.
+!      Emissions are vetoed if pTemt > pThard.
+!      See also POWHEG:vetoCount below
+POWHEG:veto = 1
+
+! After 'vetoCount' accepted emissions in a row, no more emissions
+! are checked. 'vetoCount = 0' means that no emissions are checked.
+! Use a very large value, e.g. 10000, to have all emissions checked.
+POWHEG:vetoCount = 3
+
+! Selection of pThard (note, for events where there is no
+! radiation, pThard is always set to be SCALUP):
+!  0 - pThard = SCALUP (of the LHA/LHEF standard)
+!  1 - the pT of the POWHEG emission is tested against all other
+!      incoming and outgoing partons, with the minimal value chosen
+!  2 - the pT of all final-state partons is tested against all other
+!      incoming and outgoing partons, with the minimal value chosen
+POWHEG:pThard = 2
+
+! Selection of pTemt:
+!  0 - pTemt is pT of the emitted parton w.r.t. radiating parton
+!  1 - pT of the emission is checked against all incoming and outgoing
+!      partons. pTemt is set to the minimum of these values
+!  2 - the pT of all final-state partons is tested against all other
+!      incoming and outgoing partons, with the minimal value chosen
+! WARNING: the choice here can give significant variations in the final
+! distributions, notably in the tail to large pT values.
+POWHEG:pTemt = 0
+
+! Selection of emitted parton for FSR
+!  0 - Pythia definition of emitted
+!  1 - Pythia definition of radiator
+!  2 - Random selection of emitted or radiator
+!  3 - Both are emitted and radiator are tried
+POWHEG:emitted = 0
+
+! pT definitions
+!  0 - POWHEG ISR pT definition is used for both ISR and FSR
+!  1 - POWHEG ISR pT and FSR d_ij definitions
+!  2 - Pythia definitions
+POWHEG:pTdef = 1
+
+! MPI vetoing
+!  0 - No MPI vetoing is done
+!  1 - When there is no radiation, MPIs with a scale above pT_1 are vetoed,
+!      else MPIs with a scale above (pT_1 + pT_2 + pT_3) / 2 are vetoed
+POWHEG:MPIveto = 0
+! Note that POWHEG:MPIveto = 1 should be combined with
+! MultipartonInteractions:pTmaxMatch = 2
+! which here is taken care of in main31.cc.
+
+! QED vetoing
+!  0 - No QED vetoing is done for pTemt > 0.
+!  1 - QED vetoing is done for pTemt > 0.
+!  2 - QED vetoing is done for pTemt > 0.   If a photon is found
+!      with pT>pThard from the Born level process, the event is accepted
+!      and no further veto of this event is allowed (for any pTemt).
+POWHEG:QEDveto = 2
+
+### decays
+ParticleDecays:limitTau0 on	
+ParticleDecays:tau0Max 10.	

Generators/src/GeneratorFactory.cxx

@@ -216,6 +216,11 @@ void GeneratorFactory::setPrimaryGenerator(o2::conf::SimConfig const& conf, Fair
     auto py8config = std::string(std::getenv("O2_ROOT")) + "/share/Generators/egconfig/pythia8_hi.cfg";
     auto py8 = makePythia8Gen(py8config);
     primGen->AddGenerator(py8);
+  } else if (genconfig.compare("pythia8powheg") == 0) {
+    // pythia8 with powheg
+    auto py8config = std::string(std::getenv("O2_ROOT")) + "/share/Generators/egconfig/pythia8_powheg.cfg";
+    auto py8 = makePythia8Gen(py8config);
+    primGen->AddGenerator(py8);
 #endif
   } else if (genconfig.compare("external") == 0 || genconfig.compare("extgen") == 0) {
     // external generator via configuration macro

Generators/src/GeneratorPythia8.cxx

@@ -22,6 +22,7 @@
 #include "SimulationDataFormat/MCGenProperties.h"
 #include "SimulationDataFormat/ParticleStatus.h"
 #include "Pythia8/HIUserHooks.h"
+#include "Pythia8Plugins/PowhegHooks.h"
 #include "TSystem.h"
 #include "ZDCBase/FragmentParam.h"
 
@@ -107,7 +108,28 @@ Bool_t GeneratorPythia8::Init()
   /** inhibit hadron decays **/
   mPythia.readString("HadronLevel:Decay off");
 #endif
-
+  if (mPythia.settings.mode("Beams:frameType") == 4) {
+    // Hook for POWHEG
+    // Read in key POWHEG merging settings
+    int vetoMode = mPythia.settings.mode("POWHEG:veto");
+    int MPIvetoMode = mPythia.settings.mode("POWHEG:MPIveto");
+    bool loadHooks = (vetoMode > 0 || MPIvetoMode > 0);
+    // Add in user hooks for shower vetoing
+    std::shared_ptr<Pythia8::PowhegHooks> powhegHooks;
+    if (loadHooks) {
+      // Set ISR and FSR to start at the kinematical limit
+      if (vetoMode > 0) {
+        mPythia.readString("SpaceShower:pTmaxMatch = 2");
+        mPythia.readString("TimeShower:pTmaxMatch = 2");
+      }
+      // Set MPI to start at the kinematical limit
+      if (MPIvetoMode > 0) {
+        mPythia.readString("MultipartonInteractions:pTmaxMatch = 2");
+      }
+      powhegHooks = std::make_shared<Pythia8::PowhegHooks>();
+      mPythia.setUserHooksPtr((Pythia8::UserHooksPtr)powhegHooks);
+    }
+  }
   /** initialise **/
   if (!mPythia.init()) {
     LOG(fatal) << "Failed to init \'Pythia8\': init returned with error";
@@ -123,8 +145,6 @@ Bool_t GeneratorPythia8::Init()
 Bool_t
   GeneratorPythia8::generateEvent()
 {
-  /** generate event **/
-
   /** generate event **/
   if (!mPythia.next()) {
     return false;