include/Pythia8/BeamRemnants.h

0001 // BeamRemnants.h is a part of the PYTHIA event generator.
0002 // Copyright (C) 2024 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, BeamParticle* beamBPtrIn,
0053     int iDSin) {beamAPtr = beamAPtrIn; beamBPtr = beamBPtrIn; iDS = iDSin;}
0054
0055   // Select the flavours/kinematics/colours of the two beam remnants.
0056   bool add( Event& event, int iFirst = 0, bool doDiffCR = false);
0057
0058 protected:
0059
0060   virtual void onInitInfoPtr() override {
0061     registerSubObject(junctionSplitting); }
0062
0063 private:
0064
0065   // Constants: could only be changed in the code itself.
0066   static const bool   ALLOWCOLOURTWICE, CORRECTMISMATCH;
0067   static const int    NTRYCOLMATCH, NTRYKINMATCH;
0068
0069   // Initialization data, read from Settings.
0070   bool   doPrimordialKT, allowRescatter, doRescatterRestoreY, doReconnect;
0071   double primordialKTsoft, primordialKThard, primordialKTremnant,
0072          halfScaleForKT, halfMassForKT, reducedKTatHighY;
0073   int    remnantMode, reconnectMode;
0074
0075   // Information set for events.
0076   bool   isDIS, doMPI, beamA2gamma, beamB2gamma;
0077   int    nSys, oldSize, iDS;
0078   double eCM, sCM;
0079
0080   // Colour collapses (when one colour is mapped onto another).
0081   vector<int> colFrom, colTo;
0082
0083   // Pointer to the colour reconnection class.
0084   ColRecPtr colourReconnectionPtr;
0085
0086   // StringLength class.
0087   StringLength stringLength;
0088
0089   // Junction splitting class.
0090   JunctionSplitting junctionSplitting;
0091
0092   // Select the flavours/kinematics/colours of the two beam remnants.
0093   bool addOld( Event& event);
0094
0095   // Select the flavours/kinematics/colours of the two beam remnants.
0096   bool addNew( Event& event);
0097
0098   // Pointer to assign space-time information.
0099   PartonVertexPtr partonVertexPtr;
0100   bool doPartonVertex;
0101
0102   // Do the kinematics of the collision subsystems and two beam remnants.
0103   bool setKinematics( Event& event);
0104
0105   // Special beam remnant kinematics when only one remnant system added.
0106   // This is the case e.g for Deeply Inelastic Scattering and photon
0107   // collisions with other side ended up to beam photon by ISR.
0108   bool setOneRemnKinematics( Event& event);
0109
0110   // Update colours of outgoing particles in the event.
0111   void updateColEvent( Event& event, vector<pair <int,int> > colChanges);
0112
0113   // Check that colours are consistent.
0114   bool checkColours( Event& event);
0115
0116   // Find junction chains.
0117   vector <vector<int> > findJunChains(vector<vector <int> > iPartonJun,
0118     vector<vector<int> > iPartonAjun);
0119
0120   // Split junction configuration into smaller parts.
0121   bool splitJunChains(Event& event, vector<vector<int > >& iPartonJun,
0122     vector<vector< int > >& ipartonAntiJun);
0123
0124   // Get junction chains.
0125   vector<vector<int > > getJunChains(Event& event);
0126
0127 };
0128
0129 //==========================================================================
0130
0131 } // end namespace Pythia8
0132
0133 #endif // Pythia8_BeamRemnants_H