include/Pythia8/BeamRemnants.h

0001 // BeamRemnants.h is a part of the PYTHIA event generator.
0002 // Copyright (C) 2025 Torbjorn Sjostrand.
0003 // PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
0004 // Please respect the MCnet Guidelines, see GUIDELINES for details.
0005
0006 // Header file for beam-remnants handling.
0007 // BeamRemnants: matches the remnants between the two beams.
0008
0009 #ifndef Pythia8_BeamRemnants_H
0010 #define Pythia8_BeamRemnants_H
0011
0012 #include "Pythia8/Basics.h"
0013 #include "Pythia8/BeamParticle.h"
0014 #include "Pythia8/ColourReconnection.h"
0015 #include "Pythia8/Event.h"
0016 #include "Pythia8/FragmentationFlavZpT.h"
0017 #include "Pythia8/Info.h"
0018 #include "Pythia8/JunctionSplitting.h"
0019 #include "Pythia8/ParticleData.h"
0020 #include "Pythia8/PartonDistributions.h"
0021 #include "Pythia8/PartonSystems.h"
0022 #include "Pythia8/PartonVertex.h"
0023 #include "Pythia8/PhysicsBase.h"
0024 #include "Pythia8/PythiaStdlib.h"
0025 #include "Pythia8/Settings.h"
0026 #include "Pythia8/StringLength.h"
0027
0028 namespace Pythia8 {
0029
0030 //==========================================================================
0031
0032 // This class matches the kinematics of the hard-scattering subsystems
0033 // (with primordial kT added) to that of the two beam remnants.
0034
0035 class BeamRemnants : public PhysicsBase {
0036
0037 public:
0038
0039   // Constructor.
0040   BeamRemnants() : doPrimordialKT(), allowRescatter(), doRescatterRestoreY(),
0041     doReconnect(), primordialKTsoft(), primordialKThard(),
0042     primordialKTremnant(), halfScaleForKT(), halfMassForKT(),
0043     reducedKTatHighY(), remnantMode(), reconnectMode(), isDIS(), doMPI(),
0044     beamA2gamma(), beamB2gamma(), nSys(), oldSize(), iDS(0), eCM(), sCM(),
0045     colourReconnectionPtr(), partonVertexPtr(), doPartonVertex() { }
0046
0047   // Initialization.
0048   bool init( PartonVertexPtr partonVertexPtrIn,
0049     ColRecPtr colourReconnectionPtrIn);
0050
0051   // New beams possible for handling of hard diffraction.
0052   void reassignBeamPtrs( BeamParticle* beamAPtrIn,
0053     BeamParticle* beamBPtrIn, int iDSin) {
0054     beamAPtr = beamAPtrIn; beamBPtr = beamBPtrIn; iDS = iDSin;}
0055
0056   // Select the flavours/kinematics/colours of the two beam remnants.
0057   bool add( Event& event, int iFirst = 0, bool doDiffCR = false);
0058
0059 protected:
0060
0061   virtual void onInitInfoPtr() override {
0062     registerSubObject(junctionSplitting); }
0063
0064 private:
0065
0066   // Constants: could only be changed in the code itself.
0067   static const bool   ALLOWCOLOURTWICE, CORRECTMISMATCH;
0068   static const int    NTRYCOLMATCH, NTRYKINMATCH;
0069
0070   // Initialization data, read from Settings.
0071   bool   doPrimordialKT, allowRescatter, doRescatterRestoreY, doReconnect;
0072   double primordialKTsoft, primordialKThard, primordialKTremnant,
0073          halfScaleForKT, halfMassForKT, reducedKTatHighY;
0074   int    remnantMode, reconnectMode;
0075
0076   // Information set for events.
0077   bool   isDIS, doMPI, beamA2gamma, beamB2gamma;
0078   int    nSys, oldSize, iDS;
0079   double eCM, sCM;
0080
0081   // Colour collapses (when one colour is mapped onto another).
0082   vector<int> colFrom, colTo;
0083
0084   // Pointer to the colour reconnection class.
0085   ColRecPtr colourReconnectionPtr;
0086
0087   // StringLength class.
0088   StringLength stringLength;
0089
0090   // Junction splitting class.
0091   JunctionSplitting junctionSplitting;
0092
0093   // Select the flavours/kinematics/colours of the two beam remnants.
0094   bool addOld( Event& event);
0095
0096   // Select the flavours/kinematics/colours of the two beam remnants.
0097   bool addNew( Event& event);
0098
0099   // Pointer to assign space-time information.
0100   PartonVertexPtr partonVertexPtr;
0101   bool doPartonVertex;
0102
0103   // Do the kinematics of the collision subsystems and two beam remnants.
0104   bool setKinematics( Event& event);
0105
0106   // Special beam remnant kinematics when only one remnant system added.
0107   // This is the case e.g for Deeply Inelastic Scattering and photon
0108   // collisions with other side ended up to beam photon by ISR.
0109   bool setOneRemnKinematics( Event& event);
0110
0111   // Update colours of outgoing particles in the event.
0112   void updateColEvent( Event& event, vector<pair <int,int> > colChanges);
0113
0114   // Check that colours are consistent.
0115   bool checkColours( Event& event);
0116
0117   // Find junction chains.
0118   vector <vector<int> > findJunChains(vector<vector <int> > iPartonJun,
0119     vector<vector<int> > iPartonAjun);
0120
0121   // Split junction configuration into smaller parts.
0122   bool splitJunChains(Event& event, vector<vector<int > >& iPartonJun,
0123     vector<vector< int > >& ipartonAntiJun);
0124
0125   // Get junction chains.
0126   vector<vector<int > > getJunChains(Event& event);
0127
0128 };
0129
0130 //==========================================================================
0131
0132 } // end namespace Pythia8
0133
0134 #endif // Pythia8_BeamRemnants_H