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SplittingFunction.h
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// -*- C++ -*-
//
// SplittingFunction.h is a part of Herwig++ - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2007 The Herwig Collaboration
//
// Herwig++ is licenced under version 2 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
#ifndef HERWIG_SplittingFunction_H
#define HERWIG_SplittingFunction_H
//
// This is the declaration of the SplittingFunction class.
//
#include "ThePEG/Interface/Interfaced.h"
#include "Herwig++/Shower/ShowerConfig.h"
#include "ThePEG/EventRecord/ColourLine.h"
#include "Herwig++/Shower/Couplings/ShowerIndex.h"
#include "ThePEG/Helicity/RhoDMatrix.h"
#include "Herwig++/Decay/DecayMatrixElement.h"
#include "SplittingFunction.fh"
namespace Herwig {
using namespace ThePEG;
using Helicity::RhoDMatrix;
/** \ingroup Shower
*
* This is an abstract class which defines the common interface
* for all \f$1\to2\f$ splitting functions, for both initial-state
* and final-state radiation.
*
* The SplittingFunction class contains a number of purely virtual members
* which must be implemented in the inheriting classes. The class also stores
* the interaction type of the spltting function.
*
* The inheriting classes need to specific the splitting function
* \f$P(z,2p_j\cdot p_k)\f$, in terms of the energy fraction \f$z\f$ and
* the evolution scale. In order to allow the splitting functions to be used
* with different choices of evolution functions the scale is given by
* \f[2p_j\cdot p_k=(p_j+p_k)^2-m_{jk}^2=Q^2-(p_j+p_k)^2=z(1-z)\tilde{q}^2=
* \frac{p_T^2}{z(1-z)}-m_{jk}^2+\frac{m_j^2}{z}+\frac{m_k^2}{1-z},\f]
* where \f$Q^2\f$ is the virtuality of the branching particle,
* $p_T$ is the relative transverse momentum of the branching products and
* \f$\tilde{q}^2\f$ is the angular variable described in hep-ph/0310083.
*
* In addition an overestimate of the
* splitting function, \f$P_{\rm over}(z)\f$ which only depends upon \f$z\f$,
* the integral, inverse of the integral for this overestimate and
* ratio of the true splitting function to the overestimate must be provided
* as they are necessary for the veto alogrithm used to implement the evolution.
*
* @see \ref SplittingFunctionInterfaces "The interfaces"
* defined for SplittingFunction.
*/
class SplittingFunction: public Interfaced {
public:
/** @name Standard constructors and destructors. */
//@{
/**
* The default constructor.
* @param a All splitting functions must have an interaction type
* @param b All splitting functions must have an interaction order
*/
inline SplittingFunction(ShowerIndex::InteractionType a, unsigned int b);
//@}
public:
/**
* Methods to return the interaction type and order for the splitting function
*/
//@{
/**
* Return the type of the interaction
*/
inline ShowerIndex::InteractionType interactionType() const;
/**
* Return the order of the splitting function in the interaction
*/
inline unsigned int interactionOrder() const;
//@}
/**
* Purely virtual method which should determine whether this splitting
* function can be used for a given set of particles.
* @param ids The PDG codes for the particles in the splitting.
*/
virtual bool accept(const IdList & ids) const = 0;
/**
* Methods to return the splitting function.
*/
//@{
/**
* Purely virtual method which should return the exact value of the splitting function,
* \f$P\f$ evaluated in terms of the energy fraction, \f$z\f$, and the evolution scale
\f$\tilde{q}^2\f$.
* @param z The energy fraction.
* @param t The scale \f$t=2p_j\cdot p_k\f$.
* @param ids The PDG codes for the particles in the splitting.
* @param mass Whether or not to include the mass dependent terms
*/
virtual double P(const double z, const Energy2 t, const IdList & ids,
const bool mass) const = 0;
/**
* Purely virtual method which should return
* an overestimate of the splitting function,
* \f$P_{\rm over}\f$ such that the result \f$P_{\rm over}\geq P\f$. This function
* should be simple enough that it does not depend on the evolution scale.
* @param z The energy fraction.
* @param ids The PDG codes for the particles in the splitting.
*/
virtual double overestimateP(const double z, const IdList & ids) const = 0;
/**
* Purely virtual method which should return
* the ratio of the splitting function to the overestimate, i.e.
* \f$P(z,\tilde{q}^2)/P_{\rm over}(z)\f$.
* @param z The energy fraction.
* @param t The scale \f$t=2p_j\cdot p_k\f$.
* @param ids The PDG codes for the particles in the splitting.
* @param mass Whether or not to include the mass dependent terms
*/
virtual double ratioP(const double z, const Energy2 t, const IdList & ids,
const bool mass) const = 0;
/**
* Purely virtual method which should return the indefinite integral of the
* overestimated splitting function, \f$P_{\rm over}\f$.
* @param z The energy fraction.
* @param ids The PDG codes for the particles in the splitting.
* @param PDFfactor Which additional factor to include for the PDF
* 0 is no additional factor,
* 1 is \f$1/z\f$, 2 is \f$1/(1-z)\f$ and 3 is \f$1/z/(1-z)\f$
*
*/
virtual double integOverP(const double z, const IdList & ids,
unsigned int PDFfactor=0) const = 0;
/**
* Purely virtual method which should return the inverse of the
* indefinite integral of the
* overestimated splitting function, \f$P_{\rm over}\f$ which is used to
* generate the value of \f$z\f$.
* @param r Value of the splitting function to be inverted
* @param ids The PDG codes for the particles in the splitting.
* @param PDFfactor Which additional factor to include for the PDF
* 0 is no additional factor,
* 1 is \f$1/z\f$, 2 is \f$1/(1-z)\f$ and 3 is \f$1/z/(1-z)\f$
*/
virtual double invIntegOverP(const double r, const IdList & ids,
unsigned int PDFfactor=0) const = 0;
//@}
/**
* Purely virtual method which should make the proper colour connection
* between the emitting parent and the branching products.
* @param parent The parent for the branching
* @param first The first branching product
* @param second The second branching product
* @param back Whether this is foward or backward evolution.
*/
virtual void colourConnection(tShowerParticlePtr parent,
tShowerParticlePtr first,
tShowerParticlePtr second,
const bool back) const=0;
/**
* Method to calculate the azimuthal angle
* @param particle The particle which is branching
* @param showerkin The ShowerKinematics object
* @param z The energy fraction
* @param qtilde The scale.
* @param ids The PDG codes for the particles in the splitting.
* @param The azimuthal angle, \f$\phi\f$.
* @return The weight
*/
virtual double generatePhi(ShowerParticle & particle,ShoKinPtr showerkin,
const double z, const Energy qtilde, const IdList & ids,
const RhoDMatrix &, const double phi);
/**
* Calculate the matrix element for the splitting
*/
virtual DecayMatrixElement matrixElement(ShowerParticle & particle,ShoKinPtr showerkin,
const double z, const Energy qtilde,
const IdList & ids,
const RhoDMatrix &, const double phi);
public:
/**
* 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();
private:
/**
* The static object used to initialize the description of this class.
* Indicates that this is an abstract class without persistent data.
*/
static AbstractNoPIOClassDescription<SplittingFunction> initSplittingFunction;
/**
* The assignment operator is private and must never be called.
* In fact, it should not even be implemented.
*/
SplittingFunction & operator=(const SplittingFunction &);
private:
/**
* The interaction type for the splitting function.
*/
const ShowerIndex::InteractionType _interactionType;
/**
* The order of the splitting function in the coupling
*/
const unsigned int _interactionorder;
};
}
#include "ThePEG/Utilities/ClassTraits.h"
namespace ThePEG {
/** @cond TRAITSPECIALIZATIONS */
/** This template specialization informs ThePEG about the
* base classes of SplittingFunction. */
template <>
struct BaseClassTrait<Herwig::SplittingFunction,1> {
/** Typedef of the first base class of SplittingFunction. */
typedef Interfaced NthBase;
};
/** This template specialization informs ThePEG about the name of
* the SplittingFunction class and the shared object where it is defined. */
template <>
struct ClassTraits<Herwig::SplittingFunction>
: public ClassTraitsBase<Herwig::SplittingFunction> {
/** Return a platform-independent class name */
static string className() { return "Herwig::SplittingFunction"; }
/**
* The name of a file containing the dynamic library where the class
* SplittingFunction is implemented. It may also include several, space-separated,
* libraries if the class SplittingFunction depends on other classes (base classes
* excepted). In this case the listed libraries will be dynamically
* linked in the order they are specified.
*/
static string library() { return "HwMPI.so HwMPIPDF.so HwRemDecayer.so HwShower.so"; }
};
/** @endcond */
}
#include "SplittingFunction.icc"
#endif /* HERWIG_SplittingFunction_H */

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