ThePEG/MatrixElement/MEGG2GG.h

0001 // -*- C++ -*-
0002 //
0003 // MEGG2GG.h is a part of ThePEG - Toolkit for HEP Event Generation
0004 // Copyright (C) 1999-2019 Leif Lonnblad
0005 //
0006 // ThePEG is licenced under version 3 of the GPL, see COPYING for details.
0007 // Please respect the MCnet academic guidelines, see GUIDELINES for details.
0008 //
0009 #ifndef ThePEG_MEGG2GG_H
0010 #define ThePEG_MEGG2GG_H
0011 // This is the declaration of the MEGG2GG class.
0012
0013 #include "ThePEG/MatrixElement/ME2to2QCD.h"
0014
0015 namespace ThePEG {
0016
0017 /**
0018  * MEGG2GG inherits from ME2to2QCD and implements the standard
0019  * \f$gg\rightarrow gg\f$ matrix element.
0020  *
0021  * @see \ref MEGG2GGInterfaces "The interfaces"
0022  * defined for MEGG2GG.
0023  * @see ME2to2QCD
0024  */
0025 class MEGG2GG: public ME2to2QCD {
0026
0027 public:
0028
0029   /** @name Virtual functions required by the MEBase class. */
0030   //@{
0031   /**
0032    * The matrix element for the kinematical configuration
0033    * previously provided by the last call to setKinematics(), suitably
0034    * scaled by sHat() to give a dimension-less number.
0035    * @return the matrix element scaled with sHat() to give a
0036    * dimensionless number.
0037    */
0038   virtual double me2() const;
0039
0040   /**
0041    * Add all possible diagrams with the add() function.
0042    */
0043   virtual void getDiagrams() const;
0044
0045   /**
0046    * Return a Selector with possible colour geometries for the selected
0047    * diagram weighted by their relative probabilities.
0048    * @param diag the diagram chosen.
0049    * @return the possible colour geometries weighted by their
0050    * relative probabilities.
0051    */
0052   virtual Selector<const ColourLines *>
0053   colourGeometries(tcDiagPtr diag) const;
0054
0055   /**
0056    * Get diagram selector. With the information previously supplied with the
0057    * setKinematics method, a derived class may optionally
0058    * override this method to weight the given diagrams with their
0059    * (although certainly not physical) relative probabilities.
0060    * @param dv the diagrams to be weighted.
0061    * @return a Selector relating the given diagrams to their weights.
0062    */
0063   virtual Selector<DiagramIndex> diagrams(const DiagramVector & dv) const;
0064   //@}
0065
0066 protected:
0067
0068   /** @name Internal functions returning the matrix element squared
0069    *  for different colour configurations. */
0070   //@{
0071   /**
0072    * Return the matrix element squared (without common pre-factors)
0073    * for the specific colour configuration.
0074    */
0075   double colA1() const { return sqr(1.0 + sHat()/tHat()) + 0.5; }
0076
0077   /**
0078    * Return the matrix element squared (without common pre-factors)
0079    * for the specific colour configuration.
0080    */
0081   double colB1() const { return sqr(1.0 + uHat()/sHat()) + 0.5; }
0082
0083   /**
0084    * Return the matrix element squared (without common pre-factors)
0085    * for the specific colour configuration.
0086    */
0087   double colC1() const { return sqr(1.0 + tHat()/uHat()) + 0.5; }
0088
0089   /**
0090    * Return the matrix element squared (without common pre-factors)
0091    * for the specific colour configuration.
0092    */
0093   double colA2() const { return 0.5 + sqr(1.0 + tHat()/sHat()); }
0094
0095   /**
0096    * Return the matrix element squared (without common pre-factors)
0097    * for the specific colour configuration.
0098    */
0099   double colB2() const { return 0.5 + sqr(1.0 + sHat()/uHat()); }
0100
0101   /**
0102    * Return the matrix element squared (without common pre-factors)
0103    * for the specific colour configuration.
0104    */
0105   double colC2() const { return 0.5 + sqr(1.0 + uHat()/tHat()); }
0106   //@}
0107
0108 public:
0109
0110   /**
0111    * Standard Init function used to initialize the interfaces.
0112    */
0113   static void Init();
0114
0115 protected:
0116
0117   /** @name Clone Methods. */
0118   //@{
0119   /**
0120    * Make a simple clone of this object.
0121    * @return a pointer to the new object.
0122    */
0123   virtual IBPtr clone() const;
0124
0125   /** Make a clone of this object, possibly modifying the cloned object
0126    * to make it sane.
0127    * @return a pointer to the new object.
0128    */
0129   virtual IBPtr fullclone() const;
0130   //@}
0131
0132 private:
0133
0134   /**
0135    * Describe a concrete class without persistent data.
0136    */
0137   static NoPIOClassDescription<MEGG2GG> initMEGG2GG;
0138
0139   /**
0140    *  Private and non-existent assignment operator.
0141    */
0142   MEGG2GG & operator=(const MEGG2GG &) = delete;
0143
0144 };
0145
0146 }
0147
0148
0149 namespace ThePEG {
0150
0151 /** @cond TRAITSPECIALIZATIONS */
0152
0153 /** This template specialization informs ThePEG about the
0154  *  base classes of MEGG2GG. */
0155 template <>
0156 struct BaseClassTrait<MEGG2GG,1>: public ClassTraitsType {
0157   /** Typedef of the first base class of MEGG2GG. */
0158   typedef ME2to2QCD NthBase;
0159 };
0160
0161 /** This template specialization informs ThePEG about the name of
0162  *  the MEGG2GG class and the shared object where it is defined. */
0163 template <>
0164 struct ClassTraits<MEGG2GG>: public ClassTraitsBase<MEGG2GG> {
0165   /** Return a platform-independent class name */
0166   static string className() { return "ThePEG::MEGG2GG"; }
0167   /** Return the name of the shared library be loaded to get
0168    *  access to the MEGG2GG class and every other class it uses
0169    *  (except the base class). */
0170   static string library() { return "MEQCD.so"; }
0171 };
0172
0173 /** @endcond */
0174
0175 }
0176
0177 #endif /* ThePEG_MEGG2GG_H */