ThePEG/MatrixElement/ME2to2Base.h

0001 // -*- C++ -*-
0002 //
0003 // ME2to2Base.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_ME2to2Base_H
0010 #define ThePEG_ME2to2Base_H
0011 // This is the declaration of the ME2to2Base class.
0012
0013 #include "ThePEG/MatrixElement/MEBase.h"
0014 #include "ThePEG/MatrixElement/Tree2toNDiagram.h"
0015 #include "ThePEG/Interface/Switch.fh"
0016
0017 namespace ThePEG {
0018
0019 /**
0020  * ME2to2Base can be used as a base class for any matrix element class
0021  * implementing 2\f$\rightarrow\f$ 2 processes. It extends the MEBase
0022  * base class by implementing the virtual scale() method to return the
0023  * assumed scale of a given process according to several options. It
0024  * also caches some useful characteristics of the chosen phase space
0025  * point, such as tHat(), uHat() and the masses of the external
0026  * partons.
0027  *
0028  * @see \ref ME2to2BaseInterfaces "The interfaces"
0029  * defined for ME2to2Base.
0030  * @see MEBase
0031  */
0032 class ME2to2Base: public MEBase {
0033
0034 public:
0035
0036   /** @name Standard constructors and destructors. */
0037   //@{
0038   /**
0039    * Default constructor.
0040    */
0041   ME2to2Base()
0042     : theScaleChoice(0), theLastTHat(ZERO), theLastUHat(ZERO),
0043       theLastPhi(0.0) {}
0044
0045   /**
0046    * Destructor.
0047    */
0048   virtual ~ME2to2Base();
0049   //@}
0050
0051 public:
0052
0053   /** @name Virtual functions required by the MEBase class. */
0054   //@{
0055   /**
0056    * The number of internal degreed of freedom used in the matrix
0057    * element.
0058    */
0059   virtual int nDim() const { return 1; }
0060
0061   /**
0062    * Generate internal degrees of freedom given 'nDim()' uniform
0063    * random numbers in the interval ]0,1[. To help the phase space
0064    * generator, the 'dSigHatDR()' should be a smooth function of these
0065    * numbers, although this is not strictly necessary. Return
0066    * false if the chosen points failed the kinematical cuts.
0067    */
0068   virtual bool generateKinematics(const double * r);
0069
0070   /**
0071    * Return the matrix element for the kinematical configuation
0072    * previously provided by the last call to setKinematics(). Uses
0073    * me().
0074    */
0075   virtual CrossSection dSigHatDR() const;
0076
0077   /**
0078    * Return the scale associated with the last set phase space point.
0079    */
0080   virtual Energy2 scale() const;
0081
0082   /**
0083    * Set the typed and momenta of the incoming and outgoing partons to
0084    * be used in subsequent calls to me() and colourGeometries()
0085    * according to the associated XComb object.
0086    */
0087   virtual void setKinematics();
0088   //@}
0089
0090   /**
0091    * Used internally by generateKinematics, after calculating the
0092    * limits on cos(theta).
0093    */
0094   virtual double getCosTheta(double cthmin, double cthmax, const double * r);
0095
0096   /**
0097    * Give the option corresponding to the way the scale of an
0098    * interaction is calculated.
0099    */
0100   int scaleChoice() const { return theScaleChoice; }
0101
0102 public:
0103
0104   /** @name Access cached values in of the last set phase space point. */
0105   //@{
0106   /**
0107    * Return the \f$\hat{t}\f$ of the last set phase space point.
0108    */
0109   Energy2 tHat() const { return theLastTHat; }
0110
0111   /**
0112    * Return the \f$\hat{u}\f$ of the last set phase space point.
0113    */
0114   Energy2 uHat() const { return theLastUHat; }
0115
0116   /**
0117    * Return the azimuth angle of the last set phase space point.
0118    */
0119   double phi() const { return theLastPhi; }
0120   //@}
0121
0122 public:
0123
0124   /** @name Functions used by the persistent I/O system. */
0125   //@{
0126   /**
0127    * Function used to write out object persistently.
0128    * @param os the persistent output stream written to.
0129    */
0130   void persistentOutput(PersistentOStream & os) const;
0131
0132   /**
0133    * Function used to read in object persistently.
0134    * @param is the persistent input stream read from.
0135    * @param version the version number of the object when written.
0136    */
0137   void persistentInput(PersistentIStream & is, int version);
0138   //@}
0139
0140   /**
0141    * Standard Init function used to initialize the interfaces.
0142    */
0143   static void Init();
0144
0145 protected:
0146
0147   /** @name Set the cached values in of the last set phase space point. */
0148   //@{
0149   /**
0150    * Set the \f$\hat{t}\f$ of the last set phase space point.
0151    */
0152   void tHat(Energy2 e2) { theLastTHat = e2; }
0153
0154   /**
0155    * Set the \f$\hat{u}\f$ of the last set phase space point.
0156    */
0157   void uHat(Energy2 e2) { theLastUHat = e2; }
0158
0159   /**
0160    * Set the azimuth angle of the last set phase space point.
0161    */
0162   void phi(double phi) { theLastPhi = phi; }
0163   //@}
0164
0165 protected:
0166
0167   /**
0168    * Access to the acutal Switch object used to determine the choice
0169    * of scale.
0170    */
0171   static Switch<ME2to2Base,int> & interfaceScaleChoice();
0172
0173 private:
0174
0175   /**
0176    * The option indicating how to calculate the scale of an interaction.
0177    */
0178   int theScaleChoice;
0179
0180   /**
0181    * The \f$\hat{t}\f$ of the last set phase space point.
0182    */
0183   Energy2 theLastTHat;
0184
0185   /**
0186    * The \f$\hat{u}\f$ of the last set phase space point.
0187    */
0188   Energy2 theLastUHat;
0189
0190   /**
0191    * The azimuth angle of the last set phase space point.
0192    */
0193   double theLastPhi;
0194
0195
0196 private:
0197
0198   /**
0199    * Describe an abstract base class with persistent data.
0200    */
0201   static AbstractClassDescription<ME2to2Base> initME2to2Base;
0202
0203   /**
0204    *  Private and non-existent assignment operator.
0205    */
0206   ME2to2Base & operator=(const ME2to2Base &) = delete;
0207
0208 };
0209
0210 }
0211
0212
0213 namespace ThePEG {
0214
0215 /** @cond TRAITSPECIALIZATIONS */
0216
0217 /**
0218  * This template specialization informs ThePEG about the
0219  * base class of ME2to2Base.
0220  */
0221 template <>
0222 struct BaseClassTrait<ME2to2Base,1>: public ClassTraitsType {
0223   /** Typedef of the base class of ME2to2Base. */
0224   typedef MEBase NthBase;
0225 };
0226
0227 /**
0228  * This template specialization informs ThePEG about the name of the
0229  * ME2to2Base class.
0230  */
0231 template <>
0232 struct ClassTraits<ME2to2Base>: public ClassTraitsBase<ME2to2Base> {
0233   /** Return the class name. */
0234   static string className() { return "ThePEG::ME2to2Base"; }
0235 };
0236
0237 /** @endcond */
0238
0239 }
0240
0241 #endif /* ThePEG_ME2to2Base_H */