MiniStringFragmentation.h

// MiniStringFragmentation.h is a part of the PYTHIA event generator.
// Copyright (C) 2020 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 class for "cluster" fragmentation.
// MiniStringFragmentation: handle the fragmentation of low-mass systems.

#ifndef Pythia8_MiniStringFragmentation_H
#define Pythia8_MiniStringFragmentation_H

#include "Pythia8/Basics.h"
#include "Pythia8/Event.h"
#include "Pythia8/FragmentationFlavZpT.h"
#include "Pythia8/FragmentationSystems.h"
#include "Pythia8/Info.h"
#include "Pythia8/ParticleData.h"
#include "Pythia8/PythiaStdlib.h"
#include "Pythia8/PhysicsBase.h"
#include "Pythia8/Settings.h"

namespace Pythia8 {

//==========================================================================

// The MiniStringFragmentation class contains the routines to fragment
// occasional low-mass colour singlet partonic systems, where the string
// approach is not directly applicable (for technical reasons).

class MiniStringFragmentation : public PhysicsBase {

public:

  // Constructor.
  MiniStringFragmentation() : flavSelPtr(), pTSelPtr(), zSelPtr(),
    setVertices(), constantTau(), smearOn(), nTryMass(), hadronVertex(),
    bLund(), xySmear(), kappaVtx(), mc(), mb(), isClosed(), mSum(), m2Sum() {}

  // Initialize and save pointers.
  void init(StringFlav* flavSelPtrIn, StringPT* pTSelPtrIn,
    StringZ* zSelPtrIn);

  // Do the fragmentation: driver routine.
  bool fragment( int iSub, ColConfig& colConfig, Event& event,
    bool isDiff = false, bool systemRecoil = true);

private:

  // Constants: could only be changed in the code itself.
  static const int    NTRYDIFFRACTIVE, NTRYLASTRESORT, NTRYFLAV;

  // Pointers to classes for flavour, pT and z generation.
  StringFlav*   flavSelPtr;
  StringPT*     pTSelPtr;
  StringZ*      zSelPtr;

  // Initialization data, read from Settings.
  bool   setVertices, constantTau, smearOn;
  int    nTryMass, hadronVertex;
  double bLund, xySmear, kappaVtx, mc, mb;

  // Data members.
  bool   isClosed;
  double mSum, m2Sum;
  Vec4   pSum;
  vector<int> iParton;
  FlavContainer flav1, flav2;

  // Information from the fragmentation process.
  vector<StringVertex> ministringVertices;

  // Attempt to produce two particles from a cluster.
  bool ministring2two( int nTry, Event& event, bool findLowMass = false);

  // Attempt to produce one particle from a cluster.
  bool ministring2one( int iSub, ColConfig& colConfig, Event& event,
    bool findLowMass = false, bool systemRecoil = true);

  // Set hadron production points in space-time picture.
  void setHadronVertices(Event& event, StringRegion& region,
    int iFirst, int iLast);

};

//==========================================================================

} // end namespace Pythia8

#endif // Pythia8_MiniStringFragmentation_H