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Kinematics.cc
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Kinematics.cc
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// -*- C++ -*-
//
// This is the implementation of the non-inlined, non-templated member
// functions of the Kinematics class.
//
#include "Kinematics.h"
#include <ThePEG/CLHEPWrap/Lorentz5Vector.h>
#include <ThePEG/CLHEPWrap/LorentzVector.h>
#include <ThePEG/CLHEPWrap/LorentzRotation.h>
#include <math.h>
using namespace Herwig;
using namespace ThePEG;
void MyKinematics::twoBodyDecay(const Lorentz5Momentum & p,
const double m1, const double m2,
const Vector3 & unitDir1,
Lorentz5Momentum & p1, Lorentz5Momentum & p2 )
{
if ( p.m() >= m1 + m2 && m1 >= 0.0 && m2 >= 0.0 ) {
Momentum3 pstarVector = unitDir1;
pstarVector *= CMMomentum(p.mass(),m1,m2);
p1 = Lorentz5Momentum(m1,pstarVector);
p2 = Lorentz5Momentum(m2,-pstarVector);
p1.boost( p.boostVector() ); // boost from CM to LAB
p2.boost( p.boostVector() );
}
}
void MyKinematics::twoBodyDecay(const Lorentz5Momentum & p,
const double m1, const double m2,
const double cosThetaStar1, const double phiStar1,
Lorentz5Momentum & p1, Lorentz5Momentum & p2 )
{ twoBodyDecay(p,m1,m2,unitDirection(cosThetaStar1,phiStar1),p1,p2); }
// Utility to create a rotation matrix to take p to the z axis, rotate it
// by psi about the z axis (cp = cos(psi), sp = sin(psi))
LorentzRotation MyKinematics::rotation(const Lorentz5Momentum p,
const double cp,
const double sp)
{
double pt, pp, ct, st, cf, sf;
#define PTCUT 1E-20
#define sq(a) (a)*(a)
pt = sq(p.x())+ sq(p.y());
pp = sq(p.z()) + pt;
if(pt < pp*PTCUT) {
ct = p.z() > 0 ? 1.0 : -1.0;
st = 0.0; cf = 1.0; sf = 0.0;
} else {
pp = sqrt(pp); pt = sqrt(pt);
ct = p.z()/pp; st = pt/pp; cf = p.x()/pt; sf = p.y()/pt;
}
#undef PTCUT
#undef sq
return LorentzRotation(LorentzVector(cp*cf*ct+sp*sf, -cp*sf+sp*cf*ct, cf*st, 0),
LorentzVector(cp*sf*ct-sp*cf, cp*cf+sp*sf*ct, sf*st, 0),
LorentzVector(-cp*st, -sp*st, ct, 0),
LorentzVector(0, 0, 0, 1));
}
void MyKinematics::generateAngles(tEGPtr gen, double &ct, double &az) {
ct = gen->rnd()*2.0 - 1.0;
az = gen->rnd()*2.0*M_PI;
}

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