MatrixElement/Lepton/MEee2VectorMeson.h

0001 // -*- C++ -*-
0002 //
0003 // MEee2VectorMeson.h is a part of Herwig - A multi-purpose Monte Carlo event generator
0004 // Copyright (C) 2002-2019 The Herwig Collaboration
0005 //
0006 // Herwig 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 HERWIG_MEee2VectorMeson_H
0010 #define HERWIG_MEee2VectorMeson_H
0011 //
0012 // This is the declaration of the MEee2VectorMeson class.
0013 //
0014
0015 #include "ThePEG/MatrixElement/MEBase.h"
0016 #include "Herwig/PDT/GenericMassGenerator.fh"
0017 #include "Herwig/MatrixElement/ProductionMatrixElement.h"
0018 #include "ThePEG/Helicity/WaveFunction/SpinorWaveFunction.h"
0019 #include "ThePEG/Helicity/WaveFunction/SpinorBarWaveFunction.h"
0020 #include "ThePEG/Helicity/WaveFunction/VectorWaveFunction.h"
0021
0022 namespace Herwig {
0023
0024 using namespace ThePEG;
0025
0026 using Helicity::SpinorWaveFunction;
0027 using Helicity::SpinorBarWaveFunction;
0028 using Helicity::VectorWaveFunction;
0029
0030 /**
0031  * The MEee2VectorMeson class is designed to produce neutral vector mesons
0032  * in \f$e^+e^-\f$ collisions and is primarily intended to test the hadronic
0033  * decay package.
0034  *
0035  * @see \ref MEee2VectorMesonInterfaces "The interfaces"
0036  * defined for MEee2VectorMeson.
0037  */
0038 class MEee2VectorMeson: public MEBase {
0039
0040 public:
0041
0042   /**
0043    * The default constructor.
0044    */
0045   MEee2VectorMeson() : coupling_(0.0012), lineShape_(false)
0046   {}
0047
0048   /** @name Virtual functions required by the MEBase class. */
0049   //@{
0050   /**
0051    * Return the order in \f$\alpha_S\f$ in which this matrix
0052    * element is given.
0053    */
0054   virtual unsigned int orderInAlphaS() const;
0055
0056   /**
0057    * Return the order in \f$\alpha_{EW}\f$ in which this matrix
0058    * element is given.
0059    */
0060   virtual unsigned int orderInAlphaEW() const;
0061
0062   /**
0063    * The matrix element for the kinematical configuration
0064    * previously provided by the last call to setKinematics(), suitably
0065    * scaled by sHat() to give a dimension-less number.
0066    * @return the matrix element scaled with sHat() to give a
0067    * dimensionless number.
0068    */
0069   virtual double me2() const;
0070
0071   /**
0072    * Return the scale associated with the last set phase space point.
0073    */
0074   virtual Energy2 scale() const;
0075
0076   /**
0077    * Set the typed and momenta of the incoming and outgoing partons to
0078    * be used in subsequent calls to me() and colourGeometries()
0079    * according to the associated XComb object. If the function is
0080    * overridden in a sub class the new function must call the base
0081    * class one first.
0082    */
0083   virtual void setKinematics();
0084
0085   /**
0086    * The number of internal degrees of freedom used in the matrix
0087    * element.
0088    */
0089   virtual int nDim() const;
0090
0091   /**
0092    * Generate internal degrees of freedom given nDim() uniform
0093    * random numbers in the interval \f$ ]0,1[ \f$. To help the phase space
0094    * generator, the dSigHatDR should be a smooth function of these
0095    * numbers, although this is not strictly necessary.
0096    * @param r a pointer to the first of nDim() consecutive random numbers.
0097    * @return true if the generation succeeded, otherwise false.
0098    */
0099   virtual bool generateKinematics(const double * r);
0100
0101   /**
0102    * Return the matrix element squared differential in the variables
0103    * given by the last call to generateKinematics().
0104    */
0105   virtual CrossSection dSigHatDR() const;
0106
0107   /**
0108    * Add all possible diagrams with the add() function.
0109    */
0110   virtual void getDiagrams() const;
0111
0112   /**
0113    * Get diagram selector. With the information previously supplied with the
0114    * setKinematics method, a derived class may optionally
0115    * override this method to weight the given diagrams with their
0116    * (although certainly not physical) relative probabilities.
0117    * @param dv the diagrams to be weighted.
0118    * @return a Selector relating the given diagrams to their weights.
0119    */
0120   virtual Selector<DiagramIndex> diagrams(const DiagramVector & dv) const;
0121
0122   /**
0123    * Return a Selector with possible colour geometries for the selected
0124    * diagram weighted by their relative probabilities.
0125    * @param diag the diagram chosen.
0126    * @return the possible colour geometries weighted by their
0127    * relative probabilities.
0128    */
0129   virtual Selector<const ColourLines *>
0130   colourGeometries(tcDiagPtr diag) const;
0131
0132   /**
0133    *  Set up the spin correlations
0134    */
0135   virtual void constructVertex(tSubProPtr sub);
0136   //@}
0137
0138
0139 public:
0140
0141   /** @name Functions used by the persistent I/O system. */
0142   //@{
0143   /**
0144    * Function used to write out object persistently.
0145    * @param os the persistent output stream written to.
0146    */
0147   void persistentOutput(PersistentOStream & os) const;
0148
0149   /**
0150    * Function used to read in object persistently.
0151    * @param is the persistent input stream read from.
0152    * @param version the version number of the object when written.
0153    */
0154   void persistentInput(PersistentIStream & is, int version);
0155   //@}
0156
0157   /**
0158    * The standard Init function used to initialize the interfaces.
0159    * Called exactly once for each class by the class description system
0160    * before the main function starts or
0161    * when this class is dynamically loaded.
0162    */
0163   static void Init();
0164
0165 protected:
0166
0167   /** @name Clone Methods. */
0168   //@{
0169   /**
0170    * Make a simple clone of this object.
0171    * @return a pointer to the new object.
0172    */
0173   inline virtual IBPtr clone() const {return new_ptr(*this);}
0174
0175   /** Make a clone of this object, possibly modifying the cloned object
0176    * to make it sane.
0177    * @return a pointer to the new object.
0178    */
0179   inline virtual IBPtr fullclone() const {return new_ptr(*this);}
0180   //@}
0181
0182 protected:
0183
0184   /** @name Standard Interfaced functions. */
0185   //@{
0186   /**
0187    * Initialize this object after the setup phase before saving an
0188    * EventGenerator to disk.
0189    * @throws InitException if object could not be initialized properly.
0190    */
0191   virtual void doinit();
0192   //@}
0193
0194 private:
0195
0196   /**
0197    *  Member to return the helicity amplitudes
0198    */
0199   ProductionMatrixElement HelicityME(vector<SpinorWaveFunction> fin,
0200                      vector<SpinorBarWaveFunction> ain,
0201                      vector<VectorWaveFunction> vout,double& me) const;
0202 private:
0203
0204   /**
0205    * The assignment operator is private and must never be called.
0206    * In fact, it should not even be implemented.
0207    */
0208   MEee2VectorMeson & operator=(const MEee2VectorMeson &) = delete;
0209
0210 private:
0211
0212   /**
0213    *  The vector meson being produced
0214    */
0215   PDPtr vector_;
0216
0217   /**
0218    *  The coupling
0219    */
0220   double coupling_;
0221
0222   /**
0223    *  Use the mass generator for the line shape
0224    */
0225   bool lineShape_;
0226
0227   /**
0228    *  Pointer to the mass generator for the Higgs
0229    */
0230   GenericMassGeneratorPtr massGen_;
0231
0232 };
0233
0234 }
0235
0236 #endif /* HERWIG_MEee2VectorMeson_H */