QTilde/SplittingFunctions/OneHalfHalfSplitFn.h

0001 // -*- C++ -*-
0002 //
0003 // OneHalfHalfSplitFn.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_OneHalfHalfSplitFn_H
0010 #define HERWIG_OneHalfHalfSplitFn_H
0011 //
0012 // This is the declaration of the OneHalfHalfSplitFn class.
0013 //
0014
0015 #include "Herwig/Shower/QTilde/SplittingFunctions/SplittingFunction.h"
0016
0017 namespace Herwig {
0018
0019 using namespace ThePEG;
0020
0021 /**\ingroup Shower
0022  *
0023  * This class provides the concrete implementation of the exact leading-order
0024  * splitting function for \f$1\to \frac12\frac12\f$.
0025  *
0026  * In this case the splitting function is given by
0027  * \f[P(z,t) =C\left(1-2z(1-z)+2\frac{m_q^2}{t}\right),\f]
0028  * where \f$C\f$ is the corresponding colour factor
0029  * Our choice for the overestimate is
0030  * \f[P_{\rm over}(z) = C,\f]
0031  * therefore the integral is
0032  * \f[\int P_{\rm over}(z) {\rm d}z =Cz,\f]
0033  * and its inverse is
0034  * \f[\frac{r}{C}\f]
0035  *
0036  * @see \ref OneHalfHalfSplitFnInterfaces "The interfaces"
0037  * defined for OneHalfHalfSplitFn.
0038  */
0039 class OneHalfHalfSplitFn: public SplittingFunction {
0040
0041 public:
0042
0043   /**
0044    *  Concrete implementation of the method to determine whether this splitting
0045    *  function can be used for a given set of particles.
0046    *  @param ids The PDG codes for the particles in the splitting.
0047    */
0048   virtual bool accept(const IdList & ids) const;
0049
0050   /**
0051    *   Methods to return the splitting function.
0052    */
0053   //@{
0054   /**
0055    * The concrete implementation of the splitting function, \f$P\f$.
0056    * @param z   The energy fraction.
0057    * @param t   The scale.
0058    * @param ids The PDG codes for the particles in the splitting.
0059    * @param mass Whether or not to include the mass dependent terms
0060    * @param rho The spin density matrix
0061    */
0062   virtual double P(const double z, const Energy2 t, const IdList & ids,
0063            const bool mass, const RhoDMatrix & rho) const;
0064
0065
0066   /**
0067    * The concrete implementation of the overestimate of the splitting function,
0068    * \f$P_{\rm over}\f$.
0069    * @param z   The energy fraction.
0070    * @param ids The PDG codes for the particles in the splitting.
0071    */
0072   virtual double overestimateP(const double z, const IdList & ids) const;
0073
0074   /**
0075    * The concrete implementation of the
0076    * the ratio of the splitting function to the overestimate, i.e.
0077    * \f$P(z,\tilde{q}^2)/P_{\rm over}(z)\f$.
0078    * @param z   The energy fraction.
0079    * @param t   The scale.
0080    * @param ids The PDG codes for the particles in the splitting.
0081    * @param mass Whether or not to include the mass dependent terms
0082    * @param rho The spin density matrix
0083    */
0084   virtual double ratioP(const double z, const Energy2 t, const IdList & ids,
0085             const bool mass, const RhoDMatrix & rho) const;
0086
0087   /**
0088    * The concrete implementation of the indefinite integral of the
0089    * overestimated splitting function, \f$P_{\rm over}\f$.
0090    * @param z   The energy fraction.
0091    * @param ids The PDG codes for the particles in the splitting.
0092    * @param PDFfactor Which additional factor to include for the PDF
0093    *                  0 is no additional factor,
0094    *                  1 is \f$1/z\f$, 2 is \f$1/(1-z)\f$ and 3 is \f$1/z/(1-z)\f$
0095    */
0096   virtual double integOverP(const double z,  const IdList & ids,
0097                 unsigned int PDFfactor=0) const;
0098
0099   /**
0100    * The concrete implementation of the inverse of the indefinite integral.
0101    * @param r Value of the splitting function to be inverted
0102    * @param ids The PDG codes for the particles in the splitting.
0103    * @param PDFfactor Which additional factor to include for the PDF
0104    *                  0 is no additional factor,
0105    *                  1 is \f$1/z\f$, 2 is \f$1/(1-z)\f$ and 3 is \f$1/z/(1-z)\f$
0106    */
0107   virtual double invIntegOverP(const double r,  const IdList & ids,
0108                    unsigned int PDFfactor=0) const;
0109   //@}
0110
0111   /**
0112    * Method to calculate the azimuthal angle
0113    * @param particle The particle which is branching
0114    * @param showerkin The ShowerKinematics object
0115    * @param z The energy fraction
0116    * @param t The scale \f$t=2p_j\cdot p_k\f$.
0117    * @param ids The PDG codes for the particles in the splitting.
0118    * @param The azimuthal angle, \f$\phi\f$.
0119    * @return The weight
0120    */
0121   virtual vector<pair<int,Complex> >
0122   generatePhiForward(const double z, const Energy2 t, const IdList & ids,
0123           const RhoDMatrix &);
0124
0125   /**
0126    * Method to calculate the azimuthal angle
0127    * @param particle The particle which is branching
0128    * @param showerkin The ShowerKinematics object
0129    * @param z The energy fraction
0130    * @param t The scale \f$t=2p_j\cdot p_k\f$.
0131    * @param ids The PDG codes for the particles in the splitting.
0132    * @param The azimuthal angle, \f$\phi\f$.
0133    * @return The weight
0134    */
0135   virtual vector<pair<int,Complex> >
0136   generatePhiBackward(const double z, const Energy2 t, const IdList & ids,
0137               const RhoDMatrix &);
0138
0139   /**
0140    * Calculate the matrix element for the splitting
0141    * @param z The energy fraction
0142    * @param t The scale \f$t=2p_j\cdot p_k\f$.
0143    * @param ids The PDG codes for the particles in the splitting.
0144    * @param The azimuthal angle, \f$\phi\f$.
0145    */
0146   virtual DecayMEPtr matrixElement(const double z, const Energy2 t,
0147                                    const IdList & ids, const double phi, bool timeLike);
0148
0149 public:
0150
0151   /**
0152    * The standard Init function used to initialize the interfaces.
0153    * Called exactly once for each class by the class description system
0154    * before the main function starts or
0155    * when this class is dynamically loaded.
0156    */
0157   static void Init();
0158
0159 protected:
0160
0161   /** @name Clone Methods. */
0162   //@{
0163   /**
0164    * Make a simple clone of this object.
0165    * @return a pointer to the new object.
0166    */
0167   virtual IBPtr clone() const {return new_ptr(*this);}
0168
0169   /** Make a clone of this object, possibly modifying the cloned object
0170    * to make it sane.
0171    * @return a pointer to the new object.
0172    */
0173   virtual IBPtr fullclone() const {return new_ptr(*this);}
0174   //@}
0175
0176 private:
0177
0178   /**
0179    * The assignment operator is private and must never be called.
0180    * In fact, it should not even be implemented.
0181    */
0182   OneHalfHalfSplitFn & operator=(const OneHalfHalfSplitFn &) = delete;
0183
0184 };
0185
0186 }
0187
0188 #endif /* HERWIG_OneHalfHalfSplitFn_H */