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MEPP2VVPowheg.h
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MEPP2VVPowheg.h
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// -*- C++ -*-
#ifndef HERWIG_MEPP2VVPowheg_H
#define HERWIG_MEPP2VVPowheg_H
//
// This is the declaration of the MEPP2VVPowheg class.
//
#include "Herwig++/MatrixElement/Hadron/MEPP2VV.h"
#include "Herwig++/MatrixElement/Powheg/VVKinematics.h"
#include "Herwig++/Utilities/Maths.h"
#include "Herwig++/Models/StandardModel/StandardCKM.h"
#include "Herwig++/Shower/Couplings/ShowerAlpha.h"
namespace Herwig {
using namespace ThePEG;
using Math::ReLi2;
using Constants::pi;
/**
* Here is the documentation of the MEPP2VVPowheg class.
*
* @see \ref MEPP2VVPowhegInterfaces "The interfaces"
* defined for MEPP2VVPowheg.
*/
class MEPP2VVPowheg: public MEPP2VV {
public:
/**
* The default constructor.
*/
MEPP2VVPowheg();
/** @name Member functions for the generation of hard QCD radiation */
//@{
/**
* Has a POWHEG style correction
*/
virtual POWHEGType hasPOWHEGCorrection() {return ISR;}
/**
* Apply the POWHEG style correction
*/
virtual HardTreePtr generateHardest(ShowerTreePtr,
vector<ShowerInteraction::Type> inter);
//@}
public:
/**
* Generate internal degrees of freedom given nDim() uniform
* random numbers in the interval \f$ ]0,1[ \f$. To help the phase space
* generator, the dSigHatDR should be a smooth function of these
* numbers, although this is not strictly necessary.
* @param r a pointer to the first of nDim() consecutive random numbers.
* @return true if the generation succeeded, otherwise false.
*/
virtual bool generateKinematics(const double * r);
/**
* The number of internal degrees of freedom used in the matrix
* element.
*/
virtual int nDim() const;
/**
* The matrix element for the kinematical configuration
* previously provided by the last call to setKinematics(), suitably
* scaled by sHat() to give a dimension-less number.
* @return the matrix element scaled with sHat() to give a
* dimensionless number.
*/
virtual double me2() const;
/**
* Return the scale associated with the last set phase space point.
*/
virtual Energy2 scale() const;
/**
* This member check the collinear limits of the
* real emission matrix elements are equal to the
* appropriate combinations of Born ME's multiplied
* by the splitting functions.
*/
bool sanityCheck() const;
/**
* Return the CKM matrix elements.
*/
Complex CKM(int ix,int iy) const { return ckm_[ix][iy]; }
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:
/** @name Standard Interfaced functions. */
//@{
/**
* Initialize this object after the setup phase before saving an
* EventGenerator to disk.
* @throws InitException if object could not be initialized properly.
*/
virtual void doinit();
//@}
public:
/**
* Function to set the born variables.
*/
void getKinematics(double xt, double y, double theta2);
/**
* Calculate the correction weight with which leading-order
* configurations are re-weighted.
*/
double NLOweight() const;
/**
* Calculate the ratio of the NLO luminosity to the LO
* luminosity function for the \f$q\bar{q}\f$ initiated channel.
*/
double Lhat_ab(tcPDPtr a, tcPDPtr b, realVVKinematics Kinematics) const;
/**
* Calculate the universal soft-virtual contribution to the NLO weight.
*/
double Vtilde_universal(realVVKinematics S) const;
/**
* Function for calculation of the \f$q\bar{q}\f$ initiated real
* contribution.
*/
double Ctilde_Ltilde_qq_on_x(tcPDPtr a,tcPDPtr b,realVVKinematics C) const;
/**
* Function for calculation of the \f$gq\f$ initiated real
* contribution.
*/
double Ctilde_Ltilde_gq_on_x(tcPDPtr a,tcPDPtr b,realVVKinematics C) const;
/**
* Function for calculation of the \f$q\bar{q}\f$ initiated real
* contribution.
*/
double Rtilde_Ltilde_qqb_on_x(tcPDPtr a,tcPDPtr b) const;
/**
* Function for calculation of the \f$qg\f$ initiated real
* contribution.
*/
double Rtilde_Ltilde_qg_on_x(tcPDPtr a,tcPDPtr b) const;
/**
* Function for calculation of the \f$gqb\f$ initiated real
* contribution.
*/
double Rtilde_Ltilde_gqb_on_x(tcPDPtr a,tcPDPtr b) const;
/**
* The regular part of the virtual correction matrix element(s).
* For WZ production this is given by Equation B.2 in NPB 383 (1992)
* 3-44 *** modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
double M_V_regular(realVVKinematics S) const;
/**
* Member variable to store the
* regular part of the virtual correction matrix element(s).
* For WZ production this is given by Equation B.2 in NPB 383 (1992)
* 3-44 *** modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
mutable double M_V_regular_;
/**
* The matrix element q + qb -> n + g times tk*uk
*/
Energy2 t_u_M_R_qqb(realVVKinematics R) const;
/**
* Member variable to store the matrix element q + qb -> n + g times tk*uk
*/
mutable Energy2 t_u_M_R_qqb_;
/**
* The matrix element q + g -> n + q times tk*uk
*/
Energy2 t_u_M_R_qg(realVVKinematics R) const;
/**
* Member variable to store the matrix element q + g -> n + q times tk*uk
*/
mutable Energy2 t_u_M_R_qg_;
/**
* The matrix element g + qb -> n + q times tk*uk
*/
Energy2 t_u_M_R_gqb(realVVKinematics R) const;
/**
* Member variable to store the matrix element g + qb -> n + q times tk*uk
*/
mutable Energy2 t_u_M_R_gqb_;
/**
* The matrix element q + qb -> n + g times (tk*uk)^2 - using helicity amplitudes
*/
Energy2 t_u_M_R_qqb_hel_amp(realVVKinematics R) const;
/**
* Member variable to store the
* matrix element q + qb -> n + g times (tk*uk)^2 - using helicity amplitudes
*/
mutable Energy2 t_u_M_R_qqb_hel_amp_;
/**
* The matrix element q + g -> n + q times (tk*uk)^2 - using helicity amplitudes
*/
Energy2 t_u_M_R_qg_hel_amp(realVVKinematics R) const;
/**
* Member variable to store the
* matrix element q + g -> n + q times (tk*uk)^2 - using helicity amplitudes
*/
mutable Energy2 t_u_M_R_qg_hel_amp_;
/**
* The matrix element g + qb -> n + qb times (tk*uk)^2 - using helicity amplitudes
*/
Energy2 t_u_M_R_gqb_hel_amp(realVVKinematics R) const;
/**
* Member variable to store the
* matrix element g + qb -> n + qb times (tk*uk)^2 - using helicity amplitudes
*/
mutable Energy2 t_u_M_R_gqb_hel_amp_;
/**
* The leading order matrix element - using helicity amplitudes
*/
double lo_me() const;
/**
* The Born matrix element as given in Equation 3.1 - 3.3 in NPB 383
* (1992) *** modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
double M_Born_WZ(bornVVKinematics B) const;
/**
* Member variable to store the
* Born matrix element as given in Equation 3.1 - 3.3 in NPB 383
* (1992) *** modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
mutable double M_Born_;
/**
* The Born matrix element as given in Equation 2.18 - 2.19 in NPB 357
* (1991) *** modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
double M_Born_ZZ(bornVVKinematics B) const;
/**
* M_V_regular_ZZ is the regular part of the one-loop ZZ matrix element
* exactly as defined in Eqs. B.1 & B.2 of NPB 357(1991)409-438 ***
* modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
double M_V_regular_ZZ(realVVKinematics S) const;
/**
* t_u_M_R_qqb_ZZ is the q + qb -> n + g times tk*uk real emission
* matrix element as defined in Eq. C.1 of NPB 357(1991)409-438 ***
* modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
Energy2 t_u_M_R_qqb_ZZ(realVVKinematics R) const;
/**
* The Born matrix element as given in Equation 3.2 - 3.8 in NPB 410
* (1993) *** modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
double M_Born_WW(bornVVKinematics B) const;
/**
* M_V_regular_WW is the regular part of the one-loop WW matrix element
* exactly as defined in Eqs. C.1 - C.7 of of NPB 410(1993)280-324 ***
* modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
double M_V_regular_WW(realVVKinematics S) const;
/**
* t_u_M_R_qqb_WW is the q + qb -> n + g times tk*uk real emission
* matrix element as defined in Eq. D.1-D.5 of NPB 410(1993)280-324 ***
* modulo a factor 1/(2s) ***, which is a flux factor that
* those authors absorb in the matrix element.
*/
Energy2 t_u_M_R_qqb_WW(realVVKinematics R) const;
/**
* Return the factorion scale squared.
*/
Energy2 mu_F2() const;
/**
* Return the renormalisation scale squared.
*/
Energy2 mu_UV2() const;
protected:
/** @name Clone Methods. */
//@{
/**
* Make a simple clone of this object.
* @return a pointer to the new object.
*/
inline virtual IBPtr clone() const { return new_ptr(*this); }
/** Make a clone of this object, possibly modifying the cloned object
* to make it sane.
* @return a pointer to the new object.
*/
inline virtual IBPtr fullclone() const { return new_ptr(*this); }
//@}
private:
/**
* The static object used to initialize the description of this class.
* Indicates that this is a concrete class with persistent data.
*/
static ClassDescription<MEPP2VVPowheg> initMEPP2VVPowheg;
/**
* The assignment operator is private and must never be called.
* In fact, it should not even be implemented.
*/
MEPP2VVPowheg & operator=(const MEPP2VVPowheg &);
private:
/**
* Parameters for the NLO weight
*/
//@{
/**
* Parameter to determine when to use limiting value of real emission
* matrix elements, to avoid rounding error issues.
*/
double tiny;
/**
* The BeamParticleData object for the plus and minus direction hadrons
*/
tcBeamPtr hadron_A_;
tcBeamPtr hadron_B_;
/**
* Born / virtual 2->2 kinematics.
*/
bornVVKinematics B_;
/**
* Soft limit of the 2->3 real emission kinematics.
*/
realVVKinematics S_;
/**
* Soft-collinear limit of the 2->3 kinematics (emission in +z direction).
*/
realVVKinematics SCp_;
/**
* The collinear limit of the 2->3 kinematics (emission in -z direction).
*/
realVVKinematics SCm_;
/**
* The collinear limit of the 2->3 kinematics (emission in +z direction).
*/
realVVKinematics Cp_;
/**
* The collinear limit of the 2->3 kinematics (emission in -z direction).
*/
realVVKinematics Cm_;
/**
* The resolved 2->3 real emission kinematics:
*/
realVVKinematics H_;
/**
* The ParticleData object for the plus and minus lo partons
*/
tcPDPtr ab_, bb_;
/**
* The ParticleData object for the quark and antiquark
* (which can be in a different order to ab_ and bb_).
*/
tcPDPtr quark_, antiquark_;
/**
* Values of the PDF's before radiation
*/
double lo_lumi_;
/**
* The value of the leading order qqbar->VV matrix element
*/
mutable double lo_me2_;
/**
* The CF_ colour factor
*/
double CF_;
/**
* The TR_ colour factor
*/
double TR_;
/**
* The number of colours
*/
double NC_;
/**
* The weak coupling and the sin (squared) of the Weinberg angle
*/
mutable double gW_, sin2ThetaW_;
/**
* The up and down, left handed, quark-boson couplings
*/
mutable double guL_, gdL_;
/**
* The up and down, right handed, quark-boson couplings (for WW & ZZ)
*/
mutable double guR_, gdR_;
/**
* The TGC coupling
*/
mutable double eZ_;
/**
* The TGC coupling squared. This is useful for debugging purposes
* when one wants to turn of t-channel * TGC interference contributions
* but leave the pure TGC contributions intact. It is also needed in
* order to transform WZ matrix elements into WW ones.
*/
mutable double eZ2_;
/**
* The CKM factor (Fij^2)
*/
mutable double Fij2_;
/**
* Whether to generate the positive, negative or leading order contribution
*/
unsigned int contrib_;
/**
* Whether to generate all channels contributions or just qqb or just
* qg+gqb contributions
*/
unsigned int channels_;
/**
* Whether to use a fixed or a running QCD coupling for the NLO weight
*/
unsigned int nlo_alphaS_opt_;
/**
* The value of alphaS to use for the nlo weight if nlo_alphaS_opt_=1
*/
double fixed_alphaS_;
/**
* Flag to remove or multiply in MCFM branching fractions for testing
*/
unsigned int removebr_;
/**
* Selects a dynamic (sHat) or fixed factorization scale
*/
unsigned int scaleopt_;
/**
* The factorization scale
*/
Energy mu_F_;
/**
* The renormalization scale
*/
Energy mu_UV_;
/**
* The pT of V1 in a radiative event in the lab frame (for scale setting only)
*/
Energy2 k1r_perp2_lab_;
/**
* The pT of V2 in a radiative event in the lab frame (for scale setting only)
*/
Energy2 k2r_perp2_lab_;
/**
* The ckm matrix elements (unsquared, to allow interference)
*/
vector< vector<Complex> > ckm_;
/**
* Option to impose helicity conservation on the real NLO ME's (greatly improves evaluation time).
*/
bool helicityConservation_;
/**
* The q + qb -> v1 + v2 + g helicity amplitudes
*/
mutable ProductionMatrixElement qqb_hel_amps_;
/**
* The q + g -> v1 + v2 + q helicity amplitudes
*/
mutable ProductionMatrixElement qg_hel_amps_;
/**
* The g + qb -> v1 + v2 + qb helicity amplitudes
*/
mutable ProductionMatrixElement gqb_hel_amps_;
//@}
/**
* The vertices
*/
//@{
/**
* The photon fermion-antifermion vertex
*/
AbstractFFVVertexPtr FFPvertex_;
/**
* The W fermion-antifermion vertex
*/
AbstractFFVVertexPtr FFWvertex_;
/**
* The Z fermion-antifermionvertex
*/
AbstractFFVVertexPtr FFZvertex_;
/**
* The triple electroweak gauge boson vertex
*/
AbstractVVVVertexPtr WWWvertex_;
/**
* The quark-antiquark gluon vertex
*/
AbstractFFVVertexPtr FFGvertex_;
//@}
/**
* The value of \f$\alpha_S\f$ used for the calculation
*/
mutable double alphaS_;
protected:
/**
* Returns the matrix element for a given type of process,
* rapidity of the jet \f$y_j\f$ and transverse momentum \f$p_T\f$
* @param emis_type the type of emission,
* (0 is \f$q\bar{q}\to Vg\f$, 1 is \f$qg\to Vq\f$ and 2 is \f$g\bar{q}\to V\bar{q}\f$)
* @param pT The transverse momentum of the jet
* @param R The object containing the kinematics
*/
double getResult(int emis_type, realVVKinematics R, Energy pT);
/**
* generates the hardest emission (yj,p)
* @param pnew The momenta of the new particles
* @param emissiontype The type of emission, as for getResult
* @return Whether not an emission was generated
*/
bool getEvent(vector<Lorentz5Momentum> & pnew,unsigned int & emissiontype);
/**
* sets the QCD, EW and PDF scales
* @param pT The pT of the current step in the veto algorithm
*/
void setTheScales(Energy pT);
/**
* The matrix element q + qb -> n + g times tk*uk
*/
Energy2 t_u_M_R_qqb_hel_amp(realVVKinematics R, bool getMatrix) const;
/**
* The matrix element q + g -> n + q times tk*uk
*/
Energy2 t_u_M_R_qg_hel_amp(realVVKinematics R, bool getMatrix) const;
/**
* The matrix element g + qb -> n + q times tk*uk
*/
Energy2 t_u_M_R_gqb_hel_amp(realVVKinematics R, bool getMatrix) const;
/**
* The matrix element for the kinematical configuration
* previously provided by the last call to setKinematics(), suitably
* scaled by sHat() to give a dimension-less number.
* @return the matrix element scaled with sHat() to give a
* dimensionless number.
*/
double lo_me(bool getMatrix) const;
/**
* Recalculate hard vertex to include spin correlations for radiative events.
*/
void recalculateVertex();
/**
* Member which selects a two body decay mode for each vector
* boson and distributes decay products isotropically
*/
bool isotropicDecayer();
/**
* The triangle function lambda(x,y,z)=sqrt(x^2+y^2+z^2-2*x*y-2*y*z-2*x*z)
*/
Energy2 triangleFn(Energy2,Energy2,Energy2);
private:
/**
* If this boolean is true the n+1 body helicity amplitudes will be
* used to calculate a hard vertex based on those kinematics for spin
* correlations in the decays.
*/
bool realMESpinCorrelations_;
/**
* The colour & spin averaged n-body (leading order) matrix element squared.
*/
double lo_me_;
/**
* The resolved 2->3 real emission kinematics.
*/
realVVKinematics R_;
/**
* This specifies the emitting configuration:
* 1: q + qbar -> V1 + V2 + g
* 2: q + g -> V1 + V2 + q
* 3: g + qbar -> V1 + V2 + qbar.
*/
unsigned int channel_;
/**
* Identifies the space-like mother of the branching
* as quark (+1) or antiquark (-1):
*/
int fermionNumberOfMother_;
/**
* Pointer to the object calculating the strong coupling
*/
ShowerAlphaPtr showerAlphaS_;
/**
* Constants for the sampling. The distribution is assumed to have the
* form \f$\frac{c}{{\rm GeV}}\times\left(\frac{{\rm GeV}}{p_T}\right)^n\f$
*/
//@{
/**
* The power, \f$n\f$, for the sampling
*/
double power_;
/**
* The prefactor, \f$c\f$ for the \f$q\bar{q}\f$ channel
*/
double preqqbar_;
/**
* The prefactor, \f$c\f$ for the \f$qg\f$ channel
*/
double preqg_;
/**
* The prefactor, \f$c\f$ for the \f$g\bar{q}\f$ channel
*/
double pregqbar_;
/**
* The QCD beta function divided by 4pi, (11-2/3*nf)/4/pi, with nf = 5.
*/
double b0_;
/**
* The fundamental QCD scale in the one-loop alpha_{S} used for the crude
* (not the very crude) overestimate of the Sudakov exponent. The default
* value is set so such that alphaS(MZ), neglecting all flavour threshold
* effects i.e. MZ*exp(-1/2/b0_/alphaS(MZ)).
*/
Energy LambdaQCD_;
/**
* The prefactors as a vector for easy use
*/
vector<double> prefactor_;
//@}
/**
* Properties of the incoming particles
*/
//@{
/**
* Pointers to the ShowerProgenitor objects for the partons
*/
ShowerProgenitorPtr qProgenitor_;
ShowerProgenitorPtr qbProgenitor_;
/**
* Pointers to the Shower particle objects for the partons
*/
ShowerParticlePtr showerQuark_;
ShowerParticlePtr showerAntiquark_;
/**
* Pointers to the BeamParticleData objects
*/
tcBeamPtr qHadron_;
tcBeamPtr qbHadron_;
//@}
/**
* Properties of the boson and jets
*/
//@{
/**
* Pointers to the Shower particle objects for the partons
*/
PPtr gluon_;
ShowerParticlePtr V1_;
ShowerParticlePtr V2_;
vector<PPtr> children_;
vector<PPtr> photons_;
/**
* Flag indicating if the q & qbar are flipped or not i.e. this
* is true if q enters from the -z direction in the lab frame.
*/
bool flipped_;
/**
* the rapidity of the jet
*/
double Yk_;
/**
* The transverse momentum of the jet
*/
Energy pT_;
//@}
/**
* The transverse momentum of the jet
*/
Energy min_pT_;
// Work out the scales we want to use in the matrix elements and the pdfs:
/**
* Scale for alpha_S: pT^2 of the diboson system.
*/
Energy2 QCDScale_;
/**
* Scale for real emission PDF:
*/
Energy2 PDFScale_;
/**
* Scale of electroweak vertices: mVV^2 the invariant mass of the diboson system.
*/
Energy2 EWScale_;
/**
* A matrix to hold the home-grown production matrix element
*/
mutable Complex productionMatrix_[3][3][3][3];
};
}
#include "ThePEG/Utilities/ClassTraits.h"
namespace ThePEG {
/** @cond TRAITSPECIALIZATIONS */
/** This template specialization informs ThePEG about the
* base classes of MEPP2VVPowheg. */
template <>
struct BaseClassTrait<Herwig::MEPP2VVPowheg,1> {
/** Typedef of the first base class of MEPP2VVPowheg. */
typedef Herwig::MEPP2VV NthBase;
};
/** This template specialization informs ThePEG about the name of
* the MEPP2VVPowheg class and the shared object where it is defined. */
template <>
struct ClassTraits<Herwig::MEPP2VVPowheg>
: public ClassTraitsBase<Herwig::MEPP2VVPowheg> {
/** Return a platform-independent class name */
static string className() { return "Herwig::MEPP2VVPowheg"; }
/**
* The name of a file containing the dynamic library where the class
* MEPP2VVPowheg is implemented. It may also include several, space-separated,
* libraries if the class MEPP2VVPowheg 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 "HwMEHadron.so HwPowhegMEHadron.so"; }
};
/** @endcond */
}
#endif /* HERWIG_MEPP2VVPowheg_H */

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