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MEPP2GammaGamma.h
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MEPP2GammaGamma.h
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// -*- C++ -*-
//
// MEPP2GammaGamma.h is a part of Herwig++ - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2007 The Herwig Collaboration
//
// Herwig++ is licenced under version 2 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
#ifndef HERWIG_MEPP2GammaGamma_H
#define HERWIG_MEPP2GammaGamma_H
//
// This is the declaration of the MEPP2GammaGamma class.
//
#include "Herwig++/MatrixElement/HwME2to2Base.h"
#include "ThePEG/Helicity/Vertex/AbstractFFVVertex.h"
#include "Herwig++/MatrixElement/ProductionMatrixElement.h"
#include "ThePEG/Helicity/WaveFunction/SpinorWaveFunction.h"
#include "ThePEG/Helicity/WaveFunction/VectorWaveFunction.h"
#include "ThePEG/Helicity/WaveFunction/SpinorBarWaveFunction.h"
namespace Herwig {
using namespace ThePEG;
using namespace ThePEG::Helicity;
/**
* The MEPP2GammaGamma class implements the production of photon pairs in
* hadron hadron collisions.
*
* @see \ref MEPP2GammaGammaInterfaces "The interfaces"
* defined for MEPP2GammaGamma.
*/
class MEPP2GammaGamma: public HwME2to2Base {
public:
/**
* The default constructor.
*/
inline MEPP2GammaGamma();
/** @name Virtual functions required by the MEBase class. */
//@{
/**
* Return the order in \f$\alpha_S\f$ in which this matrix
* element is given.
*/
virtual unsigned int orderInAlphaS() const;
/**
* Return the order in \f$\alpha_{EW}\f$ in which this matrix
* element is given.
*/
virtual unsigned int orderInAlphaEW() const;
/**
* The matrix element for the kinematical configuration
* previously provided by the last call to setKinematics(), suitably
* scaled by sHat() to give a dimension-less number.
* @return the matrix element scaled with sHat() to give a
* dimensionless number.
*/
virtual double me2() const;
/**
* Return the scale associated with the last set phase space point.
*/
virtual Energy2 scale() const;
/**
* Add all possible diagrams with the add() function.
*/
virtual void getDiagrams() const;
/**
* Get diagram selector. With the information previously supplied with the
* setKinematics method, a derived class may optionally
* override this method to weight the given diagrams with their
* (although certainly not physical) relative probabilities.
* @param dv the diagrams to be weighted.
* @return a Selector relating the given diagrams to their weights.
*/
virtual Selector<DiagramIndex> diagrams(const DiagramVector & dv) const;
/**
* Return a Selector with possible colour geometries for the selected
* diagram weighted by their relative probabilities.
* @param diag the diagram chosen.
* @return the possible colour geometries weighted by their
* relative probabilities.
*/
virtual Selector<const ColourLines *>
colourGeometries(tcDiagPtr diag) const;
/**
* Construct the vertex of spin correlations.
*/
virtual void constructVertex(tSubProPtr);
//@}
public:
/** @name Functions used by the persistent I/O system. */
//@{
/**
* Function used to write out object persistently.
* @param os the persistent output stream written to.
*/
void persistentOutput(PersistentOStream & os) const;
/**
* Function used to read in object persistently.
* @param is the persistent input stream read from.
* @param version the version number of the object when written.
*/
void persistentInput(PersistentIStream & is, int version);
//@}
/**
* The standard Init function used to initialize the interfaces.
* Called exactly once for each class by the class description system
* before the main function starts or
* when this class is dynamically loaded.
*/
static void Init();
protected:
/** @name Clone Methods. */
//@{
/**
* Make a simple clone of this object.
* @return a pointer to the new object.
*/
inline virtual IBPtr clone() const;
/** Make a clone of this object, possibly modifying the cloned object
* to make it sane.
* @return a pointer to the new object.
*/
inline virtual IBPtr fullclone() const;
//@}
protected:
/** @name Standard Interfaced functions. */
//@{
/**
* Initialize this object after the setup phase before saving an
* EventGenerator to disk.
* @throws InitException if object could not be initialized properly.
*/
virtual void doinit();
//@}
private:
/**
* Members to return the matrix elements for the different subprocesses
*/
//@{
/**
* Matrix element for \f$q\bar{q}\to \gamma\gamma\f$.
* @param fin Spinors for incoming quark
* @param ain Spinors for incoming antiquark
* @param p1 Polarization vectors for the first outgoing photon
* @param p2 Polarization vectors for the second outgoing photon
* @param me Whether or not to calculate the matrix element for spin correlations
*/
double qqbarME(vector<SpinorWaveFunction> & fin, vector<SpinorBarWaveFunction> & ain,
vector<VectorWaveFunction> & p1 , vector<VectorWaveFunction> & p2 ,
bool me) const;
/**
* Matrix element for \f$gg \to \gamma\gamma\f$.
* @param g1 Polarization vectors for the first incoming gluon
* @param g2 Polarization vectors for the second incoming gluon
* @param p1 Polarization vectors for the first outgoing photon
* @param p2 Polarization vectors for the second outgoing photon
* @param me Whether or not to calculate the matrix element for spin correlations
*/
double ggME(vector<VectorWaveFunction> & g1 , vector<VectorWaveFunction> & g2 ,
vector<VectorWaveFunction> & p1 , vector<VectorWaveFunction> & p2 ,
bool me) const;
//@}
/**
* \f$gg\to\gamma\gamma\f$ matrix element for the \f$++++\f$ helicity configuration.
* @param s The \f$s\f$ invariant
* @param t The \f$t\f$ invariant
* @param u The \f$u\f$ invariant
*/
inline Complex ggme(Energy2 s,Energy2 t,Energy2 u) const;
private:
/**
* The static object used to initialize the description of this class.
* Indicates that this is a concrete class with persistent data.
*/
static ClassDescription<MEPP2GammaGamma> initMEPP2GammaGamma;
/**
* The assignment operator is private and must never be called.
* In fact, it should not even be implemented.
*/
MEPP2GammaGamma & operator=(const MEPP2GammaGamma &);
private:
/**
* Pointer to the quark-antiquark-photon vertex
*/
AbstractFFVVertexPtr _photonvertex;
/**
* Maximum PDG code of the quarks allowed
*/
unsigned int _maxflavour;
/**
* Option for which processes to include
*/
unsigned int _process;
/**
* Matrix element for spin correlations
*/
ProductionMatrixElement _me;
/**
* weights for the different quark annhilation diagrams
*/
mutable double _diagwgt[2];
};
}
#include "ThePEG/Utilities/ClassTraits.h"
namespace ThePEG {
/** @cond TRAITSPECIALIZATIONS */
/** This template specialization informs ThePEG about the
* base classes of MEPP2GammaGamma. */
template <>
struct BaseClassTrait<Herwig::MEPP2GammaGamma,1> {
/** Typedef of the first base class of MEPP2GammaGamma. */
typedef Herwig::HwME2to2Base NthBase;
};
/** This template specialization informs ThePEG about the name of
* the MEPP2GammaGamma class and the shared object where it is defined. */
template <>
struct ClassTraits<Herwig::MEPP2GammaGamma>
: public ClassTraitsBase<Herwig::MEPP2GammaGamma> {
/** Return a platform-independent class name */
static string className() { return "Herwig::MEPP2GammaGamma"; }
/**
* The name of a file containing the dynamic library where the class
* MEPP2GammaGamma is implemented. It may also include several, space-separated,
* libraries if the class MEPP2GammaGamma depends on other classes (base classes
* excepted). In this case the listed libraries will be dynamically
* linked in the order they are specified.
*/
static string library() { return "HwMEHadron.so"; }
};
/** @endcond */
}
#include "MEPP2GammaGamma.icc"
#endif /* HERWIG_MEPP2GammaGamma_H */

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