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PerturbativeDecayer.h
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// -*- C++ -*-
#ifndef Herwig_PerturbativeDecayer_H
#define Herwig_PerturbativeDecayer_H
//
// This is the declaration of the PerturbativeDecayer class.
//
#include "Herwig/Decay/DecayIntegrator.h"
#include "Herwig/Shower/ShowerAlpha.h"
#include "Herwig/Shower/ShowerInteraction.h"
namespace Herwig {
using namespace ThePEG;
/**
* The PerturbativeDecayer class is the base class for perturbative decays in
* Herwig and implements the functuality for the POWHEG corrections
*
* @see \ref PerturbativeDecayerInterfaces "The interfaces"
* defined for PerturbativeDecayer.
*/
class PerturbativeDecayer: public DecayIntegrator {
protected:
/**
* Type of dipole
*/
enum dipoleType {FFa, FFc, IFa, IFc, IFba, IFbc, FFg};
/**
* Phase-space region for an emission (assumes \f$a\to b,c\f$
*/
enum phaseSpaceRegion {emissionFromB,emissionFromC,emissionFromA1,emissionFromA2,deadZone};
/**
* Type of dipole
*/
struct DipoleType {
DipoleType() {}
DipoleType(dipoleType a, ShowerInteraction b)
: type(a), interaction(b)
{}
dipoleType type;
ShowerInteraction interaction;
};
public:
/**
* The default constructor.
*/
PerturbativeDecayer() : inter_(ShowerInteraction::QCD),
pTmin_(GeV), useMEforT2_(true),
C_(5.), ymax_(10.), phaseOpt_(1),
pT_(ZERO),mb_(ZERO), e_(0.),
s_(0.), e2_(0.), s2_(0.), enhance_(1.)
{}
/**
* Has a POWHEG style correction
*/
virtual POWHEGType hasPOWHEGCorrection() {return No;}
/**
* Member to generate the hardest emission in the POWHEG scheme
*/
virtual RealEmissionProcessPtr generateHardest(RealEmissionProcessPtr);
/**
* Apply the hard matrix element correction to a given hard process or decay
*/
virtual RealEmissionProcessPtr applyHardMatrixElementCorrection(RealEmissionProcessPtr);
public:
/** @name Functions used by the persistent I/O system. */
//@{
/**
* Function used to write out object persistently.
* @param os the persistent output stream written to.
*/
void persistentOutput(PersistentOStream & os) const;
/**
* Function used to read in object persistently.
* @param is the persistent input stream read from.
* @param version the version number of the object when written.
*/
void persistentInput(PersistentIStream & is, int version);
//@}
/**
* 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();
protected:
/**
* Calculate matrix element ratio \f$\frac{M^2}{\alpha_S}\frac{|\overline{\rm{ME}}_3|}{|\overline{\rm{ME}}_2|}\f$
*/
virtual double matrixElementRatio(const Particle & inpart, const ParticleVector & decay2,
const ParticleVector & decay3, MEOption meopt,
ShowerInteraction inter);
/**
* Work out the type of process
*/
bool identifyDipoles(vector<DipoleType> & dipoles,
PPtr & aProgenitor,
PPtr & bProgenitor,
PPtr & cProgenitor,
ShowerInteraction inter) const;
/**
* Coupling for the generation of hard QCD radiation
*/
ShowerAlphaPtr alphaS() {return alphaS_;}
/**
* Coupling for the generation of hard QED radiation
*/
ShowerAlphaPtr alphaEM() {return alphaEM_;}
/**
* Return the momenta including the hard emission
*/
vector<Lorentz5Momentum> hardMomenta(PPtr in, PPtr emitter,
PPtr spectator,
const vector<DipoleType> & dipoles,
int i, bool inDeadZone);
/**
* Calculate momenta of all the particles
*/
bool calcMomenta(int j, Energy pT, double y, double phi, double& xg,
double& xs, double& xe, double& xe_z,
vector<Lorentz5Momentum>& particleMomenta);
/**
* Check the calculated momenta are physical
*/
bool psCheck(const double xg, const double xs);
/**
* Return dipole corresponding to the DipoleType dipoleId
*/
pair<double,double> calculateDipole(const DipoleType & dipoleId,
const Particle & inpart,
const ParticleVector & decay3);
/**
* Return contribution to dipole that depends on the spin of the emitter
*/
double dipoleSpinFactor(tcPDPtr emitter, double z);
/**
* Return the colour coefficient of the dipole
*/
double colourCoeff(tcPDPtr emitter, tcPDPtr spectator,
tcPDPtr other, DipoleType dipole);
/**
* Set up the colour lines
*/
void getColourLines(RealEmissionProcessPtr real);
/**
* Generate a hard emission
*/
RealEmissionProcessPtr getHardEvent(RealEmissionProcessPtr born,
bool inDeadZone,
ShowerInteraction inter);
/**
* Is the \f$x_g,x_s\f$ point in the dead-zone for all the dipoles
*/
bool inTotalDeadZone(double xg, double xs,
const vector<DipoleType> & dipoles,
int i);
/**
* Is the \f$x_g,x_a\f$ point in the dead-zone for an initial-final colour connection
*/
phaseSpaceRegion inInitialFinalDeadZone(double xg, double xa, double a, double c) const;
/**
* Is the \f$x_b,x_c\f$ point in the dead-zone for a final-final colour connection
*/
phaseSpaceRegion inFinalFinalDeadZone(double xb, double xc, double b, double c) const;
/**
* For me corrections use the shower or me for the T2 region
*/
bool useMEforT2() const {return useMEforT2_;}
protected:
/**
* Access to the kinematics for inheriting classes
*/
//@{
/**
* Transverse momentum of the emission
*/
const Energy & pT() const { return pT_;}
/**
* Mass of decaying particle
*/
const Energy & mb() const {return mb_;}
/**
* Reduced mass of emitter child particle
*/
const double & e() const {return e_;}
/**
* Reduced mass of spectator child particle
*/
const double & s() const {return s_;}
/**
* Reduced mass of emitter child particle squared
*/
const double & e2() const {return e2_;}
/**
* Reduced mass of spectator child particle squared
*/
const double & s2() const {return s2_;}
//@}
private:
/**
* The assignment operator is private and must never be called.
* In fact, it should not even be implemented.
*/
PerturbativeDecayer & operator=(const PerturbativeDecayer &) = delete;
private:
/**
* Members for the generation of the hard radiation
*/
//@{
/**
* Which types of radiation to generate
*/
ShowerInteraction inter_;
/**
* Coupling for the generation of hard QCD radiation
*/
ShowerAlphaPtr alphaS_;
/**
* Coupling for the generation of hard QED radiation
*/
ShowerAlphaPtr alphaEM_;
/**
* Minimum \f$p_T\f$
*/
Energy pTmin_;
/**
* This flag determines whether the T2 region in the decay shower
* (JHEP12(2003)_045) is populated by the ME correction (true) or
* the shower from the decaying particle.
*/
bool useMEforT2_;
/**
* Prefactor for the sampling
*/
double C_;
/**
* Maximum value for y
*/
double ymax_;
/**
* Option for phase-space sampling
*/
unsigned int phaseOpt_;
//@}
private:
/**
* Mmeber variables for the kinematics of the hard emission
*/
//@{
/**
* Transverse momentum of the emission
*/
Energy pT_;
/**
* Mass of decaying particle
*/
Energy mb_;
/**
* Reduced mass of emitter child particle
*/
double e_;
/**
* Reduced mass of spectator child particle
*/
double s_;
/**
* Reduced mass of emitter child particle squared
*/
double e2_;
/**
* Reduced mass of spectator child particle squared
*/
double s2_;
/**
* Enhancement prefactor for special cases
*/
mutable double enhance_;
//@}
};
}
#endif /* Herwig_PerturbativeDecayer_H */

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