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HardBranching.cc
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HardBranching.cc
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// -*- C++ -*-
//
// This is the implementation of the non-inlined, non-templated member
// functions of the HardTree class.
//
#include "HardBranching.h"
#include "ThePEG/PDT/EnumParticles.h"
#include "ThePEG/Repository/CurrentGenerator.h"
using namespace Herwig;
void HardBranching::setMomenta(LorentzRotation R,double aparent,
Lorentz5Momentum ptparent,
bool setMomentum) {
if(setMomentum) _original=R*_particle->momentum();
// compute the shower variables
Energy2 dot = _n*_p;
if(dot==ZERO) return;
double alpha = (_original*_n)/dot;
//set x for incoming partons
if( status() == HardBranching::Incoming ) x_frac( alpha );
_z=alpha/aparent;
double beta = ((_original*_p)-alpha*sqr(_p.mass()))/dot;
_qt = _original - alpha*_p - beta*_n - _z*ptparent;
_pt=sqrt(max(-_qt*_qt,ZERO));
// reconstruct children
for(unsigned int ix=0;ix<_children.size();++ix) {
_children[ix]->_p=_p;
_children[ix]->_n=_n;
_children[ix]->setMomenta( R, alpha, _qt + _z*ptparent, setMomentum);
}
// calculate the evolution scale and phi
if(!_children.empty()) {
IdList ids(3);
ids[0]=_particle->id();
ids[1]=_children[0]->_particle->id();
ids[2]=_children[1]->_particle->id();
double z;
Energy pt;
Lorentz5Momentum vect;
if( _status==Outgoing ||
( (_status==Incoming || _status==Decay ) &&
_children[1]->_status == Outgoing ) ) {
z = _children[0]->_z ;
pt = _children[0]->_pt;
vect=_children[0]->_qt;
}
else {
z = _children[1]->_z ;
pt = _children[1]->_pt;
swap(ids[1],ids[2]);
vect=_children[1]->_qt;
}
_scale=_sudakov->calculateScale(z,pt,ids,_status);
// get the pt vector
if(_status!=Decay) {
Boost beta_bb = -(_p+ _n).boostVector();
Lorentz5Momentum p_bb = _p;
vect.boost(beta_bb);
p_bb.boost( beta_bb );
Axis axis(p_bb.vect().unit());
LorentzRotation rot;
if(axis.perp2()>0.) {
double sinth(sqrt(sqr(axis.x())+sqr(axis.y())));
rot.setRotate(-acos(axis.z()),
Axis(-axis.y()/sinth,axis.x()/sinth,0.));
vect.transform(rot);
}
else if(axis.z()<0.) {
vect.setZ(vect.z());
}
_phi= atan2(vect.y(),vect.x());
if(_phi<0.) _phi+=Constants::twopi;
}
else {
const Boost beta_bb = -pVector().boostVector();
Lorentz5Momentum p_bb = pVector();
Lorentz5Momentum n_bb = nVector();
p_bb.boost( beta_bb );
n_bb.boost( beta_bb );
vect.boost( beta_bb);
Axis axis(n_bb.vect().unit());
LorentzRotation rot;
if(axis.perp2()>0.) {
double sinth(sqrt(sqr(axis.x())+sqr(axis.y())));
rot.setRotate(-acos(axis.z()),
Axis(-axis.y()/sinth,axis.x()/sinth,0.));
vect.transform(rot);
}
else if(axis.z()<0.) {
vect.setZ(vect.z());
}
_phi= atan2(vect.y(),vect.x());
if(_phi<0) _phi+=Constants::twopi;
}
}
}
HardBranching::HardBranching(ShowerParticlePtr particle, SudakovPtr sudakov,
tHardBranchingPtr parent,Status status)
: _particle(particle), _original(), _p(particle->momentum()), _n(), _qt(),
_shower(particle->momentum()), _pt(ZERO), _x_frac(0.),
_status(status), _scale(ZERO), _z(0.),_phi(0.), _parent(parent),
_sudakov(sudakov), type_(ShowerPartnerType::Undefined)
{}

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