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Decay_QtildaShowerKinematics1to2.cc
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Decay_QtildaShowerKinematics1to2.cc
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// -*- C++ -*-
//
// Decay_QtildaShowerKinematics1to2.cc 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.
//
//
// This is the implementation of the non-inlined, non-templated member
// functions of the Decay_QtildaShowerKinematics1to2 class.
//
#include "Decay_QtildaShowerKinematics1to2.h"
#include "ThePEG/PDT/EnumParticles.h"
#include "Herwig++/Shower/SplittingFunctions/SplittingFunction.h"
#include "Herwig++/Shower/Base/ShowerParticle.h"
#include <cassert>
using namespace Herwig;
void Decay_QtildaShowerKinematics1to2::
updateChildren(const tShowerParticlePtr theParent,
const ShowerParticleVector theChildren ) const {
if(theChildren.size() != 2)
throw Exception() << "Decay_QtildaShowerKinematics1to2::updateChildren() "
<< "Warning! too many children!" << Exception::eventerror;
// get the interaction type
const ShowerIndex::InteractionType interaction =splittingFn()->interactionType();
// copy scales etc
Energy dqtilde = scale();
double dz = z();
double dphi = phi();
// set the values
if(theParent->showerVariables().empty()) {
theParent->showerVariables().resize(3);
theParent->showerParameters().resize(2);
theParent->showerParameters()[0]=1.;
}
for(unsigned int ix=0;ix<2;++ix) {
theChildren[ix]->showerVariables() .resize(3);
theChildren[ix]->showerParameters().resize(2);
}
theChildren[0]->setEvolutionScale(interaction, dqtilde);
theChildren[1]->setEvolutionScale(interaction, (1.-dz)*dqtilde);
// determine alphas of children according to interpretation of z
theChildren[0]->showerParameters()[0]= dz *theParent->showerParameters()[0];
theChildren[1]->showerParameters()[0]=(1.-dz)*theParent->showerParameters()[0];
theChildren[0]->showerVariables()[0]= pT()*cos(dphi) +
dz *theParent->showerVariables()[0];
theChildren[0]->showerVariables()[1]= pT()*sin(dphi) +
dz *theParent->showerVariables()[1];
theChildren[1]->showerVariables()[0]= - pT()*cos(dphi) +
(1.-dz)*theParent->showerVariables()[0];
theChildren[1]->showerVariables()[1]= - pT()*sin(dphi) +
(1.-dz)*theParent->showerVariables()[1];
for(unsigned int ix=0;ix<2;++ix)
theChildren[ix]->showerVariables()[2]=
sqrt(sqr(theChildren[ix]->showerVariables()[0])+
sqr(theChildren[ix]->showerVariables()[1]));
// set up the colour connections
splittingFn()->colourConnection(theParent,theChildren[0],theChildren[1],false);
// make the products children of the parent
theParent->addChild(theChildren[0]);
theParent->addChild(theChildren[1]);
}
void Decay_QtildaShowerKinematics1to2::
reconstructParent( const tShowerParticlePtr, const ParticleVector ) const {
throw Exception() << "Decay_QtildaShowerKinematics1to2::updateParent not implemented"
<< Exception::abortnow;
}
void Decay_QtildaShowerKinematics1to2::
reconstructLast(const tShowerParticlePtr theLast,
unsigned int iopt,Energy mass) const {
// set beta component and consequently all missing data from that,
// using the nominal (i.e. PDT) mass.
Energy theMass = mass>0.*GeV ? mass : theLast->data().constituentMass();
theLast->showerParameters()[1]=
(sqr(theMass) + sqr(theLast->showerVariables()[2])
- sqr( theLast->showerParameters()[0] )*pVector().m2())
/ ( 2.*theLast->showerParameters()[0]*p_dot_n() );
// set that new momentum
theLast->set5Momentum( sudakov2Momentum( theLast->showerParameters()[0],
theLast->showerParameters()[1],
theLast->showerVariables()[0],
theLast->showerVariables()[1],iopt));
}
void Decay_QtildaShowerKinematics1to2::initialize(ShowerParticle & particle,PPtr) {
Lorentz5Momentum p, n, ppartner, pcm;
assert(particle.perturbative()!=1);
// this is for the initial decaying particle
if(particle.perturbative()==2) {
p = particle.momentum();
ShowerParticlePtr partner=particle.partners()[splittingFn()->interactionType()];
Lorentz5Momentum ppartner(partner->momentum());
if(partner->getThePEGBase()) ppartner=partner->getThePEGBase()->momentum();
pcm=ppartner;
Boost boost(p.findBoostToCM());
pcm.boost(boost);
n = Lorentz5Momentum( 0.0*MeV,0.5*p.mass()*pcm.vect().unit());
n.boost( -boost);
}
else {
tShoKinPtr kin=dynamic_ptr_cast<ShowerParticlePtr>(particle.parents()[0])
->showerKinematics();
p = kin->getBasis()[0];
n = kin->getBasis()[1];
}
setBasis(p,n);
}

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