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MEee2gZ2ll.h
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// -*- C++ -*-
//
// MEee2gZ2ll.h is a part of Herwig - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2011 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_MEee2gZ2ll_H
#define HERWIG_MEee2gZ2ll_H
//
// This is the declaration of the MEee2gZ2ll class.
//
#include "Herwig/MatrixElement/HwMEBase.h"
#include "Herwig/Models/StandardModel/StandardModel.h"
#include "ThePEG/PDT/EnumParticles.h"
#include "Herwig/MatrixElement/ProductionMatrixElement.h"
#include "ThePEG/Helicity/WaveFunction/SpinorWaveFunction.h"
#include "ThePEG/Helicity/WaveFunction/SpinorBarWaveFunction.h"
#include "Herwig/Shower/QTilde/Couplings/ShowerAlpha.h"
namespace Herwig {
using namespace ThePEG;
/**
* The MEee2gZ2ll class provides the matrix element for
* \f$e^+e^-\to\ell^+\ell^-\f$. N.B. for the production of \f$e^+e^-\f$
* only the \f$s\f$-channel Z and photon diagrams are included.
*
* @see \ref MEee2gZ2llInterfaces "The interfaces"
* defined for MEee2gZ2ll.
*/
class MEee2gZ2ll: public HwMEBase {
public:
/**
* The default constructor.
*/
MEee2gZ2ll() : allowed_(0), pTmin_(GeV),
preFactor_(6.) {
massOption(vector<unsigned int>(2,1));
}
/**
* Members for hard corrections to the emission of QCD radiation
*/
//@{
/**
* Has a POWHEG style correction
*/
virtual POWHEGType hasPOWHEGCorrection() {return FSR;}
/**
* Has an old fashioned ME correction
*/
virtual bool hasMECorrection() {return false;}
/**
* Apply the POWHEG style correction
*/
virtual RealEmissionProcessPtr generateHardest(RealEmissionProcessPtr,
ShowerInteraction::Type);
//@}
public:
/** @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.
*/
virtual IBPtr clone() const {return new_ptr(*this);}
/** Make a clone of this object, possibly modifying the cloned object
* to make it sane.
* @return a pointer to the new object.
*/
virtual IBPtr fullclone() const {return new_ptr(*this);}
//@}
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();
/**
* Rebind pointer to other Interfaced objects. Called in the setup phase
* after all objects used in an EventGenerator has been cloned so that
* the pointers will refer to the cloned objects afterwards.
* @param trans a TranslationMap relating the original objects to
* their respective clones.
* @throws RebindException if no cloned object was found for a given
* pointer.
*/
virtual void rebind(const TranslationMap & trans)
;
/**
* Return a vector of all pointers to Interfaced objects used in this
* object.
* @return a vector of pointers.
*/
virtual IVector getReferences();
//@}
protected:
/**
* Calculate the matrix element for \f$e^+e^-\to \ell^+ \ell^-\f$.
* @param partons The incoming and outgoing particles
* @param momenta The momenta of the incoming and outgoing particles
*/
double loME(const vector<cPDPtr> & partons,
const vector<Lorentz5Momentum> & momenta,
bool first) const;
/**
* Member to calculate the matrix element
* @param fin Spinors for incoming fermion
* @param ain Spinors for incoming antifermion
* @param fout Spinors for outgoing fermion
* @param aout Spinors for outgong antifermion
* @param me Spin summed Matrix element
* @param cont The continuum piece of the matrix element
* @param BW The Z piece of the matrix element
*/
ProductionMatrixElement HelicityME(vector<SpinorWaveFunction> & fin,
vector<SpinorBarWaveFunction> & ain,
vector<SpinorBarWaveFunction> & fout,
vector<SpinorWaveFunction> & aout,
double & me,
double & cont,
double & BW ) const;
/**
* The ratio of the matrix element for one additional jet over the
* leading order result. In practice
* \[\frac{\hat{s}|\overline{\mathcal{M}}|^2_2|D_{\rm emit}|}{4\pi C_F\alpha_S|\overline{\mathcal{M}}|^2_3\left(|D_{\rm emit}|+|D_{\rm spect}\right)}}\]
* is returned where \f$\|\overline{\mathcal{M}}|^2\f$ is
* the spin and colour summed/averaged matrix element.
* @param partons The incoming and outgoing particles
* @param momenta The momenta of the incoming and outgoing particles
* @param iemitter Whether the quark or antiquark is regardede as the emitter
* @param inter The type of interaction
*/
double meRatio(vector<cPDPtr> partons,
vector<Lorentz5Momentum> momenta,
unsigned int iemittor,
bool subtract=false) const;
/**
* Calculate the matrix element for \f$e^-e^-\to q \bar q g$.
* @param partons The incoming and outgoing particles
* @param momenta The momenta of the incoming and outgoing particles
* @param inter The type of interaction
*/
InvEnergy2 realME(const vector<cPDPtr> & partons,
const vector<Lorentz5Momentum> & momenta) const;
/**
* Generate the momenta for a hard configuration
*/
Energy generateHard(RealEmissionProcessPtr tree,
vector<Lorentz5Momentum> & emission,
unsigned int & iemit, unsigned int & ispect,
bool applyVeto);
protected:
/**
* Pointer to the fermion-antifermion Z vertex
*/
AbstractFFVVertexPtr FFZVertex() const {return FFZVertex_;}
/**
* Pointer to the fermion-antifermion photon vertex
*/
AbstractFFVVertexPtr FFPVertex() const {return FFPVertex_;}
/**
* Pointer to the particle data object for the Z
*/
PDPtr Z0() const {return Z0_;}
/**
* Pointer to the particle data object for the photon
*/
PDPtr gamma() const {return gamma_;}
private:
/**
* The assignment operator is private and must never be called.
* In fact, it should not even be implemented.
*/
MEee2gZ2ll & operator=(const MEee2gZ2ll &);
private:
/**
* Pointers to the vertices
*/
//@{
/**
* Pointer to the fermion-antifermion Z vertex
*/
AbstractFFVVertexPtr FFZVertex_;
/**
* Pointer to the fermion-antifermion photon vertex
*/
AbstractFFVVertexPtr FFPVertex_;
//@}
/**
* Pointer to the particle data object for the Z
*/
PDPtr Z0_;
/**
* Pointer to the particle data object for the photon
*/
PDPtr gamma_;
/**
* The allowed outgoing
*/
int allowed_;
/**
* The initial kappa-tilde values for radiation from the quark
*/
double d_kt1_;
/**
* Pointer to the EM coupling
*/
ShowerAlphaPtr alphaQED_;
/**
* Variables for the POWHEG style corrections
*/
//@{
/**
* The cut off on pt, assuming massless quarks.
*/
Energy pTmin_;
/**
* Overestimate for the prefactor
*/
double preFactor_;
/**
* ParticleData objects for the partons
*/
vector<cPDPtr> partons_;
/**
* Momenta of the leading-order partons
*/
vector<Lorentz5Momentum> loMomenta_;
//@}
};
}
#include "ThePEG/Utilities/ClassTraits.h"
namespace ThePEG {
/** @cond TRAITSPECIALIZATIONS */
/** This template specialization informs ThePEG about the
* base classes of MEee2gZ2ll. */
template <>
struct BaseClassTrait<Herwig::MEee2gZ2ll,1> {
/** Typedef of the first base class of MEee2gZ2ll. */
typedef Herwig::HwMEBase NthBase;
};
/** This template specialization informs ThePEG about the name of
* the MEee2gZ2ll class and the shared object where it is defined. */
template <>
struct ClassTraits<Herwig::MEee2gZ2ll>
: public ClassTraitsBase<Herwig::MEee2gZ2ll> {
/** Return a platform-independent class name */
static string className() { return "Herwig::MEee2gZ2ll"; }
/**
* The name of a file containing the dynamic library where the class
* MEee2gZ2ll is implemented. It may also include several, space-separated,
* libraries if the class MEee2gZ2ll 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 "HwMELepton.so"; }
};
/** @endcond */
}
#endif /* HERWIG_MEee2gZ2ll_H */

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