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 // HeavyIons.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.
 
 // This file contains the definition of the HeavyIons class which
 // Provides Pythia with infrastructure to combine several nucleon
 // collisions into a single heavy ion collision event. This file also
 // includes the definition of the Angantyr class which implements the
 // default model for heavy ion collisions in Pythia.
 
 #ifndef Pythia8_HeavyIons_H
 #define Pythia8_HeavyIons_H
 
 #include "Pythia8/HIInfo.h"
 #include "Pythia8/PhysicsBase.h"
 
 namespace Pythia8 {
 
 // Forward declaration of the Pythia class.
 class Pythia;
 
 //==========================================================================
 
 // HeavyIons contains several standard Pythia objects to allow for
 // the combination of different kinds of nucleon-nucleon events into
 // a heavy ion collision event. The actual model for doing this must
 // be implemented in a subclass overriding the the virtual'init()'
 // and 'next()' functions.
 
 class HeavyIons : public PhysicsBase {
 
 public:
 
   // The constructor needs a reference to the main Pythia object to
   // which it will belong. A HeavyIons object cannot belong to more
   // than one main Pythia object.
   HeavyIons(Pythia& mainPythiaIn)
     : mainPythiaPtr(&mainPythiaIn), HIHooksPtr(0),
       pythia(vector<Pythia*>(1, &mainPythiaIn)) {
   }
 
   // Destructor.
   virtual ~HeavyIons() {}
 
   // Virtual function to be implemented in a subclass. This will be
   // called in the beginning of the Pythia::init function if the mode
   // HeavyIon:mode is set non zero. The return value should be true
   // if this object is able to handle the requested collision
   // type. If false Pythia::init will set HeavyIon:mode to zero but
   // will try to cope anyway.
   virtual bool init() = 0;
 
   // Virtual function to be implemented in a subclass. This will be
   // called in the beginning of the Pythia::next function if
   // HeavyIon:mode is set non zero. After the call, Pythia::next will
   // return immediately with the return value of this function.
   virtual bool next() = 0;
 
   // Static function to allow Pythia to duplicate some setting names
   // to be used for secondary Pythia objects.
   static void addSpecialSettings(Settings& settings);
 
   // Return true if the beams in the Primary Pythia object contains
   // heavy ions.
   static bool isHeavyIon(Settings& settings);
 
   // Possibility to pass in pointer for special heavy ion user hooks.
   bool setHIUserHooksPtr(HIUserHooksPtr userHooksPtrIn) {
     HIHooksPtr = userHooksPtrIn; return true;
   }
 
   // Set beam kinematics.
   virtual bool setKinematics(double /*eCMIn*/) {
     loggerPtr->ERROR_MSG("method not implemented for this heavy ion model");
     return false; }
   virtual bool setKinematics(double /*eAIn*/, double /*eBIn*/) {
     loggerPtr->ERROR_MSG("method not implemented for this heavy ion model");
     return false; }
   virtual bool setKinematics(double, double, double, double, double, double) {
     loggerPtr->ERROR_MSG("method not implemented for this heavy ion model");
     return false; }
   virtual bool setKinematics(Vec4, Vec4) {
     loggerPtr->ERROR_MSG("method not implemented for this heavy ion model");
     return false; }
 
   // Set beam particles.
   virtual bool setBeamIDs(int /*idAIn*/, int /*idBIn*/ = 0) {
     loggerPtr->ERROR_MSG("method not implemented for this heavy ion model");
     return false; }
 
   // The HIInfo object contains information about the last generated heavy
   // ion event as well as overall statistics of the generated events.
   HIInfo hiInfo;
 
   // Print out statistics.
   virtual void stat();
 
 protected:
 
   // Update the cross section in the main Pythia Info object using
   // information in the hiInfo object.
   void updateInfo();
 
   // If subclasses has additional Pythia objects for generating
   // minimum bias nucleon collisions and the main Pythia object is
   // set up to generated a hard signal process, this function can be
   // used to clear all selected processes in a clone of the main
   // Pythia object.
   void clearProcessLevel(Pythia& pyt);
 
   // Duplicate setting on the form match: to settings on the form HImatch:
   static void setupSpecials(Settings& settings, string match);
 
   // Copy settings on the form HImatch: to the corresponding match:
   // in the given Pythia object.
   static void setupSpecials(Pythia& p, string match);
 
   // Save current beam configuration.
   int idProj, idTarg;
 
   // This is the pointer to the main Pythia object to which this
   // object is assigned.
   Pythia * mainPythiaPtr;
 
   // Object containing information on inclusive pp cross sections to
   // be used in Glauber calculations in subclasses.
   SigmaTotal sigTotNN;
 
   // Optional HIUserHooks object able to modify the behavior of the
   // HeavyIon model.
   HIUserHooksPtr HIHooksPtr;
 
   // The internal Pythia objects. Index zero will always correspond
   // to the mainPythiaPtr.
   vector<Pythia *> pythia;
 
   // The names associated with the secondary pythia objects.
   vector<string> pythiaNames;
 
   // The Info objects associated to the secondary Pythia objects.
   vector<Info*> info;
 
   // Helper class to gain access to the Info object in a Pythia
   // instance.
   struct InfoGrabber : public UserHooks {
 
     // Only one function: return the info object.
     Info* getInfo() {
       return infoPtr;
     }
 
   };
 
 };
 
 //==========================================================================
 
 // The default HeavyIon model in Pythia.
 
 class Angantyr : public HeavyIons {
 
 public:
 
   // Enumerate the different internal Pythia objects.
   enum PythiaObject {
     HADRON = 0,   // For hadronization only.
     MBIAS = 1,    // Minimum Bias processed.
     SASD = 2,     // Single diffractive as one side of non-diffractive.
     SIGPP = 3,    // Optional object for signal processes (pp).
     SIGPN = 4,    // Optional object for signal processes (pn).
     SIGNP = 5,    // Optional object for signal processes (np).
     SIGNN = 6,    // Optional object for signal processes (nn).
     ALL = 7       // Indicates all objects.
   };
 
 public:
 
   // The constructor needs a reference to the main Pythia object to
   // which it will belong. A Angantyr object cannot belong to more
   // than one main Pythia object.
   Angantyr(Pythia& mainPythiaIn);
 
   virtual ~Angantyr();
 
   // Initialize Angantyr.
   virtual bool init() override;
 
   // Produce a collision involving heavy ions.
   virtual bool next() override;
 
   // Set UserHooks for specific (or ALL) internal Pythia objects.
   bool setUserHooksPtr(PythiaObject sel, UserHooksPtr userHooksPtrIn);
 
   // Set beam kinematics.
   bool setKinematicsCM();
   bool setKinematics(double eCMIn) override;
   bool setKinematics(double eAIn, double eBIn) override;
   bool setKinematics(double, double, double, double, double, double) override;
   bool setKinematics(Vec4, Vec4) override;
   bool setKinematics();
 
   // Set beam IDs.
   bool setBeamIDs(int idAIn, int idBIn = 0) override;
 
   // Make sure the correct information is available irrespective of frame type.
   void unifyFrames();
 
   // Print the Angantyr banner.
   void banner() const;
 
   // Subcollisions for the current event.
   const SubCollisionSet& subCollisions() const {
     return subColls; }
 
   // Get the underlying subcollision model.
   const SubCollisionModel& subCollisionModel() const {
     return *collPtr.get(); }
 
   SubCollisionModel* subCollPtr() {
     return collPtr.get();
   }
 
   // Get the underlying impact parameter generator.
   const ImpactParameterGenerator impactParameterGenerator() const {
     return *bGenPtr.get(); }
 
   // Projectile nucleus configuration for the current event.
   const Nucleus& projectile() const {
     return proj; }
 
   // Target nucleus configuration for the current event.
   const Nucleus& target() const {
     return targ; }
 
   // The underlying projectile nucleus model.
   const NucleusModel& projectileModel() const {
     return *projPtr.get(); }
 
   // The underlying target nucleus model.
   const NucleusModel& targetModel() const {
     return *targPtr.get(); }
 
   // Hadronic cross sections used by the subcollision model.
   const SigmaTotal sigmaNN() const {
     return sigTotNN; }
 
 protected:
 
   virtual void onInitInfoPtr() override {
     registerSubObject(sigTotNN); }
 
   // Figure out what beams the user want.
   void setBeamKinematics(int idA, int idB);
 
   // Initiaize a specific Pythia object and optionally run a number
   // of events to get a handle of the cross section.
   bool init(PythiaObject sel, string name, int n = 0);
 
   // Setup an EventInfo object from a Pythia instance.
   EventInfo mkEventInfo(Pythia &, Info &, const SubCollision * coll = 0);
 
   // Generate events from the internal Pythia oblects;
   EventInfo getSignal(const SubCollision& coll);
   EventInfo getND() { return getMBIAS(0, 101); }
   EventInfo getND(const SubCollision& coll) { return getMBIAS(&coll, 101); }
   EventInfo getEl(const SubCollision& coll) { return getMBIAS(&coll, 102); }
   EventInfo getSDP(const SubCollision& coll) { return getMBIAS(&coll, 103); }
   EventInfo getSDT(const SubCollision& coll) { return getMBIAS(&coll, 104); }
   EventInfo getDD(const SubCollision& coll) { return getMBIAS(&coll, 105); }
   EventInfo getCD(const SubCollision& coll) { return getMBIAS(&coll, 106); }
   EventInfo getSDabsP(const SubCollision& coll)
     { return getSASD(&coll, 103); }
   EventInfo getSDabsT(const SubCollision& coll)
     { return getSASD(&coll, 104); }
   EventInfo getMBIAS(const SubCollision * coll, int procid);
   EventInfo getSASD(const SubCollision * coll, int procid);
 
   bool genAbs(SubCollisionSet& subCollsIn, list<EventInfo>& subEventsIn);
   void addSASD(const SubCollisionSet& subCollsIn);
   bool addDD(const SubCollisionSet& subCollsIn, list<EventInfo>& subEventsIn);
   bool addSD(const SubCollisionSet& subCollsIn, list<EventInfo>& subEventsIn);
   void addSDsecond(const SubCollisionSet& subCollsIn);
   bool addCD(const SubCollisionSet& subCollsIn, list<EventInfo>& subEventsIn);
   void addCDsecond(const SubCollisionSet& subCollsIn);
   bool addEL(const SubCollisionSet& subCollsIn, list<EventInfo>& subEventsIn);
   void addELsecond(const SubCollisionSet& subCollsIn);
 
   void resetEvent();
   bool buildEvent(list<EventInfo>& subEventsIn);
 
   bool setupFullCollision(EventInfo& ei, const SubCollision& coll,
     Nucleon::Status projStatus, Nucleon::Status targStatus);
   bool isRemnant(const EventInfo& ei, int i, int past = 1 ) const {
     int statNow = ei.event[i].status()*past;
     if ( statNow == 63 ) return true;
     if ( statNow > 70 && statNow < 80 )
       return isRemnant(ei, ei.event[i].mother1(), -1);
     return false;
   }
   bool fixIsoSpin(EventInfo& ei);
   EventInfo& shiftEvent(EventInfo& ei);
   static int getBeam(Event& ev, int i);
 
   // Generate a single diffractive
   bool nextSASD(int proc);
 
   // Add a diffractive event to an exsisting one. Optionally connect
   // the colours of the added event to the original.
   bool addNucleonExcitation(EventInfo& orig, EventInfo& add,
                             bool colConnect = false);
 
   // Find the recoilers in the current event to conserve energy and
   // momentum in addNucleonExcitation.
   vector<int> findRecoilers(const Event& e, bool tside, int beam, int end,
                             const Vec4& pdiff, const Vec4& pbeam);
 
   // Add a sub-event to the final event record.
   void addSubEvent(Event& evnt, Event& sub);
   static void addJunctions(Event& evnt, Event& sub, int coloff);
 
   // Add a nucleus remnant to the given event. Possibly introducing
   // a new particle type.
   bool addNucleusRemnants();
 
 public:
 
   // Helper function to construct two transformations that would give
   // the vectors p1 and p2 the total four momentum of p1p + p2p.
   static bool
   getTransforms(Vec4 p1, Vec4 p2, const Vec4& p1p,
                 pair<RotBstMatrix,RotBstMatrix>& R12);
   static double mT2(const Vec4& p) { return p.pPos()*p.pNeg(); }
   static double mT(const Vec4& p) { return sqrt(max(mT2(p), 0.0)); }
 
 private:
 
   // Private UserHooks class to select a specific process.
   struct ProcessSelectorHook: public UserHooks {
 
     ProcessSelectorHook(): proc(0), b(-1.0) {}
 
     // Yes we can veto event after process-level selection.
     virtual bool canVetoProcessLevel() {
       return true;
     }
 
     // Veto any unwanted process.
     virtual bool doVetoProcessLevel(Event&) {
       return proc > 0 && infoPtr->code() != proc;
     }
 
     // Can set the overall impact parameter for the MPI treatment.
     virtual bool canSetImpactParameter() const {
       return b >= 0.0;
     }
 
     // Set the overall impact parameter for the MPI treatment.
     virtual double doSetImpactParameter() {
       return b;
     }
 
     // The wanted process;
     int proc;
 
     // The selected b-value.
     double b;
 
   };
 
   // Holder class to temporarily select a specific process
   struct HoldProcess {
 
     // Set the given process for the given hook object.
     HoldProcess(shared_ptr<ProcessSelectorHook> hook, int proc,
       double b = -1.0) : saveHook(hook), saveProc(hook->proc), saveB(hook->b) {
       hook->proc = proc;
       hook->b = b;
     }
 
     // Reset the process of the hook object given in the constructor.
     ~HoldProcess() {
       if ( saveHook ) {
         saveHook->proc = saveProc;
         saveHook->b = saveB;
       }
     }
 
     // The hook object.
     shared_ptr<ProcessSelectorHook> saveHook;
 
     // The previous process of the hook object.
     int saveProc;
 
     // The previous b-value of the hook object.
     double saveB;
 
   };
 
   // The process selector for standard minimum bias processes.
   shared_ptr<ProcessSelectorHook> selectMB;
 
   // The process selector for the SASD object.
   shared_ptr<ProcessSelectorHook> selectSASD;
 
 private:
 
   static const int MAXTRY = 999;
   static const int MAXEVSAVE = 999;
 
   // Flag set if there is a specific signal process specified beyond
   // minimum bias.
   bool hasSignal;
 
   // Whether to do hadronization and hadron level effects.
   bool doHadronLevel;
 
   // Flag to determine whether to do single diffractive test.
   bool doSDTest;
 
   // Flag to determine whether to do only Glauber modelling.
   bool glauberOnly;
 
   // All subcollisions in current collision.
   SubCollisionSet subColls;
 
   // The underlying SubCollisionModel for generating nucleon-nucleon
   // subcollisions.
   shared_ptr<SubCollisionModel> collPtr;
 
   // The impact parameter generator.
   shared_ptr<ImpactParameterGenerator> bGenPtr;
 
   // The projectile and target nuclei in the current collision.
   Nucleus proj;
   Nucleus targ;
 
   // The underlying nucleus model for generating nuclons inside the
   // projectile and target nucleus.
   shared_ptr<NucleusModel> projPtr;
   shared_ptr<NucleusModel> targPtr;
 
   // Flag to indicate whether variable energy is enabled.
   bool doVarECM;
 
   // Different choices in choosing recoilers when adding
   // diffractively excited nucleon.
   int recoilerMode;
 
   // Different choices for handling impact parameters.
   int bMode;
 
   // Critical internal error, abort the event.
   bool doAbort;
 
 };
 
 //==========================================================================
 
 } // end namespace Pythia8
 
 #endif // Pythia8_HeavyIons_H

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