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 // -*- C++ -*-
 //
 // MEqq2gZ2ffPowheg.h is a part of Herwig - A multi-purpose Monte Carlo event generator
 // Copyright (C) 2002-2019 The Herwig Collaboration
 //
 // Herwig is licenced under version 3 of the GPL, see COPYING for details.
 // Please respect the MCnet academic guidelines, see GUIDELINES for details.
 //
 #ifndef HERWIG_MEqq2gZ2ffPowheg_H
 #define HERWIG_MEqq2gZ2ffPowheg_H
 //
 // This is the declaration of the MEqq2gZ2ffPowheg class.
 //
 
 #include "Herwig/MatrixElement/Hadron/MEqq2gZ2ff.h"
 #include "ThePEG/PDF/BeamParticleData.h"
 
 namespace Herwig {
 using namespace ThePEG;
 
 /**
  * The MEqq2gZ2ffPowheg class implements the products of Standard Model
  * fermion antifermion pairs via the \f$Z^0\f$ resonance including
  * photon interference terms.
  *
  * @see \ref MEqq2gZ2ffPowhegInterfaces "The interfaces"
  * defined for MEqq2gZ2ffPowheg.
  */
 class MEqq2gZ2ffPowheg: public MEqq2gZ2ff {
 
 public:
 
   /**
    * The default constructor.
    */
   MEqq2gZ2ffPowheg();
 
   /** @name Virtual functions required by the MEBase class. */
   //@{
   /**
    * Return the scale associated with the last set phase space point.
    */
   virtual Energy2 scale() const;
 
   /**
    * The number of internal degreed of freedom used in the matrix
    * element.
    */
   virtual int nDim() const;
 
   /**
    * Generate internal degrees of freedom given 'nDim()' uniform
    * random numbers in the interval ]0,1[. To help the phase space
    * generator, the 'dSigHatDR()' should be a smooth function of these
    * numbers, although this is not strictly necessary. Return
    * false if the chosen points failed the kinematical cuts.
    */
   virtual bool generateKinematics(const double * r);
 
   /**
    * Return the matrix element for the kinematical configuation
    * previously provided by the last call to setKinematics(). Uses
    * me().
    */
   virtual CrossSection dSigHatDR() const;
   //@}
 
 
 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:
 
   /**
    * Calculate the correction weight with which leading-order
    * configurations are re-weighted.
    */
   double NLOweight() const;
   
   /**
    * Calculate the variable \f$x=M_{B}^2/s\f$ from the integration variables. 
    */
   double x(double xt, double v) const;
   /**
    * Calculate the momentum fraction of the first parton. 
    */
   double x_a(double x, double v) const;
   /**
    * Calculate the momentum fraction of the second parton. 
    */
   double x_b(double x, double v) const;
   /**
    * Calculate the minimum of \f$x\f$. 
    */
   double xbar(double v) const;
   /**
    * Calculate the ratio of the radiative luminosity funcion to the
    * Born luminosity function for the \f$qg\f$ initiated channel. 
    */
   double Ltilde_qg(double x, double v) const;
   /**
    * Calculate the ratio of the radiative luminosity funcion to the
    * Born luminosity function for the \f$g\bar{q}\f$ initiated channel. 
    */
   double Ltilde_gq(double x, double v) const;
   /**
    * Calculate the ratio of the radiative luminosity funcion to the
    * Born luminosity function for the \f$q\bar{q}\f$ initiated channel. 
    */
   double Ltilde_qq(double x, double v) const;
   /**
    * Calculate the soft-virtual contribution to the NLO weight. 
    */
   double Vtilde_qq() const;
   /**
    * Function for calculation of the \f$qg\f$ and \f$g\bar{q}\f$ initiated real
    * contributions.
    */
   double Ccalbar_qg(double x) const;
   /**
    * Function for calculation of the \f$qg\f$  
    * initiated real contribution.
    */
   double Fcal_qg(double x, double v) const;
   /**
    * Function for calculation of the \f$g\bar{q}\f$ initiated real
    * contribution.
    */
   double Fcal_gq(double x, double v) const;
   /**
    * Function for calculation of the \f$q\bar{q}\f$ initiated real
    * contribution.
    */
   double Fcal_qq(double x, double v) const;
   /**
    * Function for calculation of the \f$qg\f$ initiated real
    * contribution.
    */
   double Ftilde_qg(double xt, double v) const;
   /**
    * Function for calculation of the \f$g\bar{q}\f$ initiated real
    * contribution.
    */
   double Ftilde_gq(double xt, double v) const;
   /**
    * Function for calculation of the \f$q\bar{q}\f$ initiated real
    * contribution.
    */
   double Ftilde_qq(double xt, double v) const;
   /**
    * Function for calculation of the \f$qg\f$ initiated real
    * contribution.
    */
   double Ctilde_qg(double x, double v) const;
   /**
    * Function for calculation of the \f$g\bar{q}\f$ initiated real
    * contribution.
    */
   double Ctilde_gq(double x, double v) const;
   /**
    * Function for calculation of the \f$q\bar{q}\f$ initiated real
    * contribution.
    */
   double Ctilde_qq(double x, double v) const;
 
 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();
   //@}
 
 private:
 
   /**
    * The assignment operator is private and must never be called.
    * In fact, it should not even be implemented.
    */
   MEqq2gZ2ffPowheg & operator=(const MEqq2gZ2ffPowheg &) = delete;
 
 private:
  
   /**
    *  The momentum fraction of the first parton in the Born process
    */
   mutable double _xb_a;
 
   /**
    *  The momentum fraction of the second parton in the Born process
    */
   mutable double _xb_b;
 
   /**
    *  The ParticleData object for the first parton in the Born process
    */
   mutable tcPDPtr _parton_a;
 
   /**
    *  The ParticleData object for the second parton in the Born process
    */
   mutable tcPDPtr _parton_b;
 
   /**
    *  The BeamParticleData object for the first  hadron
    */
   mutable Ptr<BeamParticleData>::transient_const_pointer _hadron_A;
 
   /**
    *  The BeamParticleData object for the second hadron
    */
   mutable Ptr<BeamParticleData>::transient_const_pointer _hadron_B;
 
   /**
    *  the ParticleData object for the gluon
    */
   tcPDPtr _gluon;
 
   /**
    * The \f$T_R\f$ colour factor
    */
   const double TR_;
 
   /**
    *  The \f$C_F\f$ colour factor
    */
   const double CF_;
 
   /**
    *  The value of \f$\frac{\alpha_S}{2\pi}\f$ used for the calculation
    */
   mutable double _alphaS2Pi;
 
   /**
    *  The mass squared of the lepton pair
    */
   mutable Energy2 _mll2;
 
   /**  
    * The renormalization/factorization scale
    */
   mutable Energy2 _mu2;
 
   /**
    *  Parameters for the NLO weight
    */
   //@{
   /**
    *  Whether to generate the positive, negative or leading order contribution
    */
   unsigned int _contrib;
 
   /**
    *  Whether to use a fixed or a running QCD coupling for the NLO weight
    */
   unsigned int _nlo_alphaS_opt;
 
   /**
    *  The value of alphaS to use for the nlo weight if _nloalphaSopt=1
    */
   double _fixed_alphaS;
 
   /**
    *  The magnitude of the correction term to reduce the negative contribution
    */
   double _a;
 
   /**
    *  The power of the correction term to reduce the negative contribution
    */
   double _p;
 
   /**
    *  Cut-off for the correction function
    */
   double _eps;
   //@}
 
   /**
    *  Choice of the scale
    */
   //@{
   /**
    *  Type of scale
    */
   unsigned int _scaleopt;
 
   /**
    *  Fixed scale if used
    */
   Energy _fixedScale;
 
   /**
    *  Prefactor if variable scale used
    */
   double _scaleFact;
   //@}
 
   /**
    *  Radiation variables
    */
   //@{
   /**
    *   The \f$\tilde{x}\f$ variable
    */
   double _xt;
 
   /**
    *  The \f$v\f$ angular variable
    */
   double _v;
   //@}
 
   /**
    *  Values of the PDF's before radiation
    */
   //@{
   /**
    *  For the quark
    */
   mutable double _oldq;
 
   /**
    *  For the antiquark
    */
   mutable double _oldqbar;
   //@}
 };
 
 }
 
 #endif /* HERWIG_MEqq2gZ2ffPowheg_H */

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