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Herwig
7.2.1
MatrixElement
Hadron
MEPP2GammaGamma.h
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// -*- C++ -*-
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//
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// MEPP2GammaGamma.h is a part of Herwig - A multi-purpose Monte Carlo event generator
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// Copyright (C) 2002-2019 The Herwig Collaboration
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//
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// Herwig is licenced under version 3 of the GPL, see COPYING for details.
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// Please respect the MCnet academic guidelines, see GUIDELINES for details.
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//
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#ifndef HERWIG_MEPP2GammaGamma_H
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#define HERWIG_MEPP2GammaGamma_H
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//
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// This is the declaration of the MEPP2GammaGamma class.
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//
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#include "Herwig/MatrixElement/HwMEBase.h"
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#include "ThePEG/Helicity/Vertex/AbstractFFVVertex.h"
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#include "Herwig/MatrixElement/ProductionMatrixElement.h"
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#include "ThePEG/Helicity/WaveFunction/SpinorWaveFunction.h"
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#include "ThePEG/Helicity/WaveFunction/VectorWaveFunction.h"
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#include "ThePEG/Helicity/WaveFunction/SpinorBarWaveFunction.h"
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namespace
Herwig
{
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using namespace
ThePEG
;
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using namespace
ThePEG::Helicity
;
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class
MEPP2GammaGamma
:
public
HwMEBase
{
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public
:
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MEPP2GammaGamma
() : _maxflavour(5),_process(0), scalePreFactor_(1.) {
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massOption(vector<unsigned int>(2,0));
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}
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virtual
unsigned
int
orderInAlphaS()
const
;
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virtual
unsigned
int
orderInAlphaEW()
const
;
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virtual
double
me2()
const
;
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virtual
Energy2 scale()
const
;
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virtual
void
getDiagrams()
const
;
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virtual
Selector<DiagramIndex>
diagrams(
const
DiagramVector
& dv)
const
;
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virtual
Selector<const ColourLines *>
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colourGeometries(tcDiagPtr diag)
const
;
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virtual
void
constructVertex(
tSubProPtr
);
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public
:
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void
persistentOutput(
PersistentOStream
& os)
const
;
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void
persistentInput(
PersistentIStream
& is,
int
version);
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static
void
Init();
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protected
:
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virtual
IBPtr
clone()
const
;
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virtual
IBPtr
fullclone()
const
;
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protected
:
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virtual
void
doinit();
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private
:
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double
qqbarME(vector<SpinorWaveFunction> & fin, vector<SpinorBarWaveFunction> & ain,
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vector<VectorWaveFunction> & p1 , vector<VectorWaveFunction> & p2 ,
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bool
me)
const
;
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double
ggME(vector<VectorWaveFunction> & g1 , vector<VectorWaveFunction> & g2 ,
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vector<VectorWaveFunction> & p1 , vector<VectorWaveFunction> & p2 ,
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bool
me)
const
;
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Complex
ggme
(Energy2 s,Energy2 t,Energy2 u)
const
{
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double
ltu(log(abs(t/u)));
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double
frac1((t-u)/s),frac2((
sqr
(t)+
sqr
(u))/
sqr
(s));
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double
thetatu = (t/u<0) ? 0 : 1;
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double
thetat = (t<
ZERO
) ? 0 : 1;
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double
thetau = (u<
ZERO
) ? 0 : 1;
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using
Constants::pi;
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return
Complex
(1.+frac1*ltu+0.5*frac2*(
sqr
(ltu)+
sqr
(
pi
)*thetatu),
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-
pi
*(thetat-thetau)*(frac1+frac2*ltu));
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}
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private
:
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MEPP2GammaGamma
& operator=(
const
MEPP2GammaGamma
&) =
delete
;
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private
:
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AbstractFFVVertexPtr
_photonvertex
;
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unsigned
int
_maxflavour
;
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unsigned
int
_process
;
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ProductionMatrixElement
_me
;
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mutable
double
_diagwgt[2];
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double
scalePreFactor_
;
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};
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}
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#endif
/* HERWIG_MEPP2GammaGamma_H */
Herwig::MEPP2GammaGamma::_me
ProductionMatrixElement _me
Matrix element for spin correlations.
Definition:
MEPP2GammaGamma.h:236
Herwig::MEPP2GammaGamma::_process
unsigned int _process
Option for which processes to include.
Definition:
MEPP2GammaGamma.h:231
ThePEG::PersistentIStream
Herwig::MEPP2GammaGamma::MEPP2GammaGamma
MEPP2GammaGamma()
The default constructor.
Definition:
MEPP2GammaGamma.h:41
ThePEG::Complex
std::complex< double > Complex
ThePEG::Helicity
ThePEG::PersistentOStream
ThePEG::IBPtr
ThePEG::Ptr< InterfacedBase >::pointer IBPtr
ThePEG::Constants::pi
constexpr double pi
sqr
constexpr auto sqr(const T &x) -> decltype(x *x)
ThePEG
Herwig::MEPP2GammaGamma::ggme
Complex ggme(Energy2 s, Energy2 t, Energy2 u) const
matrix element for the helicity configuration.
Definition:
MEPP2GammaGamma.h:197
Herwig::ProductionMatrixElement
The storage of the helicity amplitude expression for the matrix element of a hard process...
Definition:
ProductionMatrixElement.h:34
Herwig::MEPP2GammaGamma::scalePreFactor_
double scalePreFactor_
Scale prefactor.
Definition:
MEPP2GammaGamma.h:246
ThePEG::tSubProPtr
ThePEG::Ptr< SubProcess >::transient_pointer tSubProPtr
ThePEG::Selector
ThePEG::MEBase::DiagramVector
vector< DiagPtr > DiagramVector
Herwig
-*- C++ -*-
Definition:
BasicConsistency.h:17
Herwig::HwMEBase
The HwMEBase class serves a number of purposes.
Definition:
HwMEBase.h:35
Herwig::MEPP2GammaGamma::_maxflavour
unsigned int _maxflavour
Maximum PDG code of the quarks allowed.
Definition:
MEPP2GammaGamma.h:226
Herwig::MEPP2GammaGamma::_photonvertex
AbstractFFVVertexPtr _photonvertex
Pointer to the quark-antiquark-photon vertex.
Definition:
MEPP2GammaGamma.h:221
ZERO
constexpr ZeroUnit ZERO
Herwig::MEPP2GammaGamma
The MEPP2GammaGamma class implements the production of photon pairs in hadron hadron collisions...
Definition:
MEPP2GammaGamma.h:34
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