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// -*- C++ -*-
//
// ME2to2Base.cc is a part of ThePEG - Toolkit for HEP Event Generation
// Copyright (C) 1999-2011 Leif Lonnblad
//
// ThePEG 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 ME2to2Base class.
//
#include "ME2to2Base.h"
#include "ThePEG/Interface/ClassDocumentation.h"
#include "ThePEG/Interface/Switch.h"
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/Utilities/SimplePhaseSpace.h"
#include "ThePEG/Repository/EventGenerator.h"
#include "ThePEG/Handlers/StandardXComb.h"
#include "ThePEG/Cuts/Cuts.h"
using namespace ThePEG;
ME2to2Base::~ME2to2Base() {}
Energy2 ME2to2Base::scale() const {
switch ( scaleChoice() ) {
case 1:
return -tHat()*uHat()/(tHat() + uHat());
default:
return tHat()*uHat()/sHat();
}
}
void ME2to2Base::setKinematics() {
MEBase::setKinematics();
theLastTHat = (meMomenta()[0] - meMomenta()[2]).m2();
theLastUHat = (meMomenta()[1] - meMomenta()[2]).m2();
theLastPhi = meMomenta()[2].phi();
}
bool ME2to2Base::generateKinematics(const double * r) {
// generate the masses of the particles
for ( int i = 2, N = meMomenta().size(); i < N; ++i ) {
meMomenta()[i] = Lorentz5Momentum(mePartonData()[i]->generateMass());
}
double ctmin = -1.0;
double ctmax = 1.0;
Energy q = ZERO;
try {
q = SimplePhaseSpace::
getMagnitude(sHat(), meMomenta()[2].mass(), meMomenta()[3].mass());
} catch ( ImpossibleKinematics ) {
return false;
}
Energy e = sqrt(sHat())/2.0;
Energy2 m22 = meMomenta()[2].mass2();
Energy2 m32 = meMomenta()[3].mass2();
Energy2 e0e2 = 2.0*e*sqrt(sqr(q) + m22);
Energy2 e1e2 = 2.0*e*sqrt(sqr(q) + m22);
Energy2 e0e3 = 2.0*e*sqrt(sqr(q) + m32);
Energy2 e1e3 = 2.0*e*sqrt(sqr(q) + m32);
Energy2 pq = 2.0*e*q;
Energy2 thmin = lastCuts().minTij(mePartonData()[0], mePartonData()[2]);
if ( thmin > ZERO ) ctmax = min(ctmax, (e0e2 - m22 - thmin)/pq);
thmin = lastCuts().minTij(mePartonData()[1], mePartonData()[2]);
if ( thmin > ZERO ) ctmin = max(ctmin, (thmin + m22 - e1e2)/pq);
thmin = lastCuts().minTij(mePartonData()[1], mePartonData()[3]);
if ( thmin > ZERO ) ctmax = min(ctmax, (e1e3 - m32 - thmin)/pq);
thmin = lastCuts().minTij(mePartonData()[0], mePartonData()[3]);
if ( thmin > ZERO ) ctmin = max(ctmin, (thmin + m32 - e0e3)/pq);
Energy ptmin = max(lastCuts().minKT(mePartonData()[2]),
lastCuts().minKT(mePartonData()[3]));
if ( ptmin > ZERO ) {
double ctm = 1.0 - sqr(ptmin/q);
if ( ctm <= 0.0 ) return false;
ctmin = max(ctmin, -sqrt(ctm));
ctmax = min(ctmax, sqrt(ctm));
}
double ymin2 = lastCuts().minYStar(mePartonData()[2]);
double ymax2 = lastCuts().maxYStar(mePartonData()[2]);
double ymin3 = lastCuts().minYStar(mePartonData()[3]);
double ymax3 = lastCuts().maxYStar(mePartonData()[3]);
double ytot = lastCuts().Y() + lastCuts().currentYHat();
if ( ymin2 + ytot > -0.9*Constants::MaxRapidity )
ctmin = max(ctmin, sqrt(sqr(q) + m22)*tanh(ymin2)/q);
if ( ymax2 + ytot < 0.9*Constants::MaxRapidity )
ctmax = min(ctmax, sqrt(sqr(q) + m22)*tanh(ymax2)/q);
if ( ymin3 + ytot > -0.9*Constants::MaxRapidity )
ctmax = min(ctmax, sqrt(sqr(q) + m32)*tanh(-ymin3)/q);
if ( ymax3 + ytot < 0.9*Constants::MaxRapidity )
ctmin = max(ctmin, sqrt(sqr(q) + m32)*tanh(-ymax3)/q);
if ( ctmin >= ctmax ) return false;
double cth = getCosTheta(ctmin, ctmax, r);
Energy pt = q*sqrt(1.0-sqr(cth));
theLastPhi = rnd(2.0*Constants::pi);
meMomenta()[2].setVect(Momentum3( pt*sin(phi()), pt*cos(phi()), q*cth));
meMomenta()[3].setVect(Momentum3(-pt*sin(phi()), -pt*cos(phi()), -q*cth));
meMomenta()[2].rescaleEnergy();
meMomenta()[3].rescaleEnergy();
vector<LorentzMomentum> out(2);
out[0] = meMomenta()[2];
out[1] = meMomenta()[3];
tcPDVector tout(2);
tout[0] = mePartonData()[2];
tout[1] = mePartonData()[3];
if ( !lastCuts().passCuts(tout, out, mePartonData()[0], mePartonData()[1]) )
return false;
theLastTHat = pq*cth + m22 - e0e2;
theLastUHat = m22 + m32 - sHat() - theLastTHat;
jacobian((pq/sHat())*Constants::pi*jacobian());
return true;
}
double ME2to2Base::getCosTheta(double ctmin, double ctmax, const double * r) {
double cth = 0.0;
static const double eps = 1.0e-6;
if ( 1.0 + ctmin <= eps && 1.0 - ctmax <= eps ) {
jacobian(ctmax - ctmin);
cth = ctmin + (*r)*jacobian();
} else if ( 1.0 + ctmin <= eps ) {
cth = 1.0 - (1.0 - ctmax)*pow((1.0 - ctmin)/(1.0 - ctmax), *r);
jacobian(log((1.0 - ctmin)/(1.0 - ctmax))*(1.0 - cth));
} else if ( 1.0 - ctmax <= eps ) {
cth = -1.0 + (1.0 + ctmin)*pow((1.0 + ctmax)/(1.0 + ctmin), *r);
jacobian(log((1.0 + ctmax)/(1.0 + ctmin))*(1.0 + cth));
} else {
double zmin = 0.5*(1.0 - ctmax);
double zmax = 0.5*(1.0 - ctmin);
double A1 = -ctmin/(zmax*(1.0-zmax));
double A0 = -ctmax/(zmin*(1.0-zmin));
double A = *r*(A1 - A0) + A0;
double z = A < 2.0? 2.0/(sqrt(sqr(A) + 4.0) + 2 - A):
0.5*(A - 2.0 + sqrt(sqr(A) + 4.0))/A;
cth = 1.0 - 2.0*z;
jacobian(2.0*(A1 - A0)*sqr(z)*sqr(1.0 - z)/(sqr(z) + sqr(1.0 - z)));
}
return cth;
}
CrossSection ME2to2Base::dSigHatDR() const {
return me2()*jacobian()/(16.0*sqr(Constants::pi)*sHat())*sqr(hbarc);
}
void ME2to2Base::persistentOutput(PersistentOStream & os) const {
os << theScaleChoice << ounit(theLastTHat, GeV2) << ounit(theLastUHat, GeV2)
<< theLastPhi;
}
void ME2to2Base::persistentInput(PersistentIStream & is, int) {
is >> theScaleChoice >> iunit(theLastTHat, GeV2) >> iunit(theLastUHat, GeV2)
>> theLastPhi;
}
AbstractClassDescription<ME2to2Base> ME2to2Base::initME2to2Base;
// Definition of the static class description member.
Switch<ME2to2Base,int> & ME2to2Base::interfaceScaleChoice() {
static Switch<ME2to2Base,int> dummy
("ScaleChoice",
"Different options for calculating the scale of the generated "
"hard sub-process.",
&ME2to2Base::theScaleChoice, 0, false, false);
return dummy;
}
void ME2to2Base::Init() {
static ClassDocumentation<ME2to2Base> documentation
("The ThePEG::ME2to2Base class may be used as a base class "
"for all \\f$2\\rightarrow 2\\f$ matrix elements.");
static SwitchOption interfaceScaleChoice0
(interfaceScaleChoice(),
"that.uhat/shat", "\\f$\\hat{t}\\hat{u}/\\hat{s}\\f$", 0);
static SwitchOption interfaceScaleChoice1
(interfaceScaleChoice(),
"that.uhat/(that+uhat)",
"\\f$-\\hat{t}\\hat{u}/(\\hat{t}+\\hat{u})\\f$", 1);
}
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