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 // TimeShower.h is a part of the PYTHIA event generator.
 // Copyright (C) 2025 Torbjorn Sjostrand.
 // PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
 // Please respect the MCnet Guidelines, see GUIDELINES for details.
 
 // Header file for the base class of timelike final-state showers.
 // TimeShower: handles the showering description.
 
 #ifndef Pythia8_TimeShower_H
 #define Pythia8_TimeShower_H
 
 #include "Pythia8/Basics.h"
 #include "Pythia8/BeamParticle.h"
 #include "Pythia8/Event.h"
 #include "Pythia8/Info.h"
 #include "Pythia8/ParticleData.h"
 #include "Pythia8/PartonSystems.h"
 #include "Pythia8/PhysicsBase.h"
 #include "Pythia8/PythiaStdlib.h"
 #include "Pythia8/PartonVertex.h"
 #include "Pythia8/Settings.h"
 #include "Pythia8/StandardModel.h"
 #include "Pythia8/UserHooks.h"
 #include "Pythia8/MergingHooks.h"
 #include "Pythia8/Weights.h"
 
 namespace Pythia8 {
 
 //==========================================================================
 
 // The TimeShower class does timelike showers.
 
 class TimeShower : public PhysicsBase {
 
 public:
 
   // Constructor.
   TimeShower() = default;
 
   // Destructor.
   virtual ~TimeShower() {}
 
   // Initialize various pointers.
   // (Separated from rest of init since not virtual.)
   void initPtrs(MergingHooksPtr mergingHooksPtrIn,
     PartonVertexPtr partonVertexPtrIn,
     WeightContainer* weightContainerPtrIn) {
     coupSMPtr = infoPtr->coupSMPtr;
     mergingHooksPtr = mergingHooksPtrIn;
     partonVertexPtr = partonVertexPtrIn;
     weightContainerPtr = weightContainerPtrIn;
   }
 
   // New beams possible for handling of hard diffraction. (Not virtual.)
   void reassignBeamPtrs( BeamParticle* beamAPtrIn,
     BeamParticle* beamBPtrIn, int beamOffsetIn = 0) {
     beamAPtr = beamAPtrIn; beamBPtr = beamBPtrIn; beamOffset = beamOffsetIn;}
 
   // Initialize alphaStrong and related pTmin parameters.
   // Usage: init( beamAPtr, beamBPtr).
   virtual void init( BeamParticle* = nullptr, BeamParticle* = nullptr) {}
 
   // Find whether to limit maximum scale of emissions, and whether to dampen.
   // Usage: limitPTmax( event, Q2Fac, double Q2Ren).
   virtual bool limitPTmax( Event& , double = 0., double = 0.) {return true;}
 
   // Top-level routine to do a full time-like shower in resonance decay.
   // Usage: shower( iBeg, iEnd, event, pTmax, nBranchMax).
   virtual int shower( int , int , Event& , double , int = 0) {return 0;}
 
   // Top-level routine for QED radiation in hadronic decays.
   // Usage: showerQED( i1, i2, event, pTmax).
   virtual int showerQED( int , int , Event& , double = -1.) {return 0;}
 
   // Optional method to add QED showers after remnants have been added
   // but before hadronisation. (Called from PartonLevel.)
   virtual int showerQEDafterRemnants(Event&) { return 0; }
 
   // Optional method to add QED showers after all hadron decays have been
   // treated, as an alternative to handling QED showers inside each decay.
   virtual int showerQEDafterDecays( int , int , Event&) { return 0; }
 
   // Prepare process-level event for shower + interleaved resonance decays.
   // Usage: prepareProcess( process, event, iPos).
   // iPos provides mapping from process to event entries (before showering).
   virtual void prepareProcess( Event&, Event&, vector<int>&) {};
 
   // Global recoil: reset counters and store locations of outgoing partons.
   // Usage: prepareGlobal( event).
   virtual void prepareGlobal( Event& ) {}
 
   // Prepare system for evolution after each new interaction; identify ME.
   // Usage: prepare( iSys, event, limitPTmax).
   virtual void prepare( int , Event& , bool = true) {}
 
   // Update dipole list after a multiparton interactions rescattering.
   // Usage: rescatterUpdate( iSys, event).
   virtual void rescatterUpdate( int , Event& ) {}
 
   // Update dipole list after each ISR emission.
   // Usage: update( iSys, event, hasWeakRad).
   virtual void update( int , Event& , bool = false) {}
 
   // Select next pT in downwards evolution.
   // Usage: pTnext( event, pTbegAll, pTendAll, isFirstTrial, doTrialIn).
   virtual double pTnext( Event& , double , double , bool = false, bool = false)
     { return 0.;}
 
   // Select next pT for interleaved resonance decays.
   virtual double pTnextResDec() { return 0.; }
 
   // ME corrections and kinematics that may give failure.
   // Usage: branch( event, isInterleaved).
   virtual bool branch( Event& , bool = false) {return true;}
 
   // Handle a resonance decay + resonance shower (including any nested decays).
   // Assumes decay channel and kinematics already selected and present in
   // either the process or event record.
   // May be called recursively for nested decays.
   // Usage: resonanceShower( process, event, iPos, pTmerge), where iPos
   // maps process to event entries, and pTmerge is the scale at which this
   // system should be merged into its parent system.
   virtual bool resonanceShower( Event&, Event&, vector<int>&, double = 0.)
     { return false;}
 
   // Print dipole list; for debug mainly.
   virtual void list() const {}
 
   // Initialize data members for calculation of uncertainty bands.
   virtual bool initUncertainties() {return false;}
 
   // Initialize data members for application of enhancements.
   virtual bool initEnhancements() {return false;}
 
   // Tell whether FSR has done a weak emission.
   virtual bool getHasWeaklyRadiated() {return false;}
 
   // Tell which system was the last processed one.
   virtual int system() const {return 0;}
 
   // Potential enhancement factor of pTmax scale for hardest emission.
   virtual double enhancePTmax() {return 1.;}
 
   // Provide the pT scale of the last branching in the above shower.
   virtual double pTLastInShower() {return 0.;}
 
   // Functions to allow usage of shower kinematics, evolution variables,
   // and splitting probabilities outside of shower.
   // Virtual so that shower plugins can overwrite these functions.
   // This makes it possible for another piece of the code to request
   // these - which is very convenient for merging.
   // Function variable names are not included to avoid compiler warnings.
   // Please see the documentation under "Implement New Showers" for details.
 
   // Return clustering kinematics - as needed for merging.
   virtual Event clustered( const Event& , int , int , int , string )
     { return Event();}
 
   // Return the evolution variable(s).
   // Important note: this map must contain the following entries
   // - a key "t" for the value of the shower evolution variable;
   // - a key "tRS" for the value of the shower evolution variable
   //   from which the shower would be restarted after a branching;
   // - a key "scaleAS" for the argument of alpha_s used for the branching;
   // - a key "scalePDF" for the argument of the PDFs used for the branching.
   // Usage: getStateVariables( event, iRad, iEmt, iRec,  name)
   virtual map<string, double> getStateVariables (const Event& , int , int ,
     int , string ) { return map<string,double>();}
 
   // Check if attempted clustering is handled by timelike shower
   // Usage: isTimelike( event, iRad, iEmt, iRec, name)
   virtual bool isTimelike(const Event& , int , int , int , string )
     { return false; }
 
   // Return a string identifier of a splitting.
   // Usage: getSplittingName( event, iRad, iEmt, iRec)
   virtual vector<string> getSplittingName( const Event& , int, int , int)
     { return vector<string>();}
 
   // Return the splitting probability.
   // Usage: getSplittingProb( event, iRad, iEmt, iRec)
   virtual double getSplittingProb( const Event& , int , int , int , string )
     { return 0.;}
   virtual bool allowedSplitting( const Event& , int , int)
     { return true; }
   virtual vector<int> getRecoilers( const Event&, int, int, string)
     { return vector<int>(); }
 
   virtual double enhanceFactor(const string& name) {
     unordered_map<string, double>::iterator it = enhanceFSR.find(name);
     if ( it == enhanceFSR.end() ) return 1.;
     return it->second;
   }
 
   // Functions to directly extract the probability of no emission between two
   // scales. This functions is not used in the Pythia core code, but can be
   // used by external programs to interface with the shower directly.
   virtual double noEmissionProbability( double, double, double, int, int,
     double, double) { return 1.; }
 
   // Pointer to MergingHooks object for NLO merging.
   MergingHooksPtr  mergingHooksPtr{};
 
   WeightContainer* weightContainerPtr{};
 
 protected:
 
   // Beam location offset in event.
   int              beamOffset{};
 
   // Pointer to assign space-time vertices during parton evolution.
   PartonVertexPtr  partonVertexPtr{};
 
   // Store uncertainty variations relevant to TimeShower.
   bool   doUncertainties{}, uVarMuSoftCorr{}, uVarMPIshowers{},
          noResVariations{}, noProcVariations{};
   int    nUncertaintyVariations{}, nVarQCD{}, uVarNflavQ{};
   double dASmax{}, cNSpTmin{}, uVarpTmin2{}, overFactor{}, overFactorEnhance{};
   map<int,double> varG2GGmuRfac, varQ2QGmuRfac, varG2QQmuRfac, varX2XGmuRfac,
                   varG2GGcNS, varQ2QGcNS, varG2QQcNS, varX2XGcNS;
   map<int,double>* varPDFplus;
   map<int,double>* varPDFminus;
   map<int,double>* varPDFmember;
   unordered_map<string,double> enhanceFSR;
 
 };
 
 //==========================================================================
 
 } // end namespace Pythia8
 
 #endif // Pythia8_TimeShower_H

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