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MamboDecayer.cc
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// -*- C++ -*-
//
// MamboDecayer.cc is a part of Herwig++ - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2011 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 MamboDecayer class.
//
#include "MamboDecayer.h"
#include <ThePEG/Interface/ClassDocumentation.h>
#include "ThePEG/Persistency/PersistentOStream.h"
#include "ThePEG/Persistency/PersistentIStream.h"
#include "ThePEG/Utilities/UtilityBase.h"
#include "ThePEG/Repository/EventGenerator.h"
#include "ThePEG/PDT/EnumParticles.h"
#include "Herwig++/Utilities/Kinematics.h"
#include "ThePEG/Interface/Parameter.h"
#include "ThePEG/Interface/Reference.h"
using namespace Herwig;
using namespace ThePEG;
bool MamboDecayer::accept(tcPDPtr, const tPDVector & ) const {
return true;
}
void MamboDecayer::persistentOutput(PersistentOStream & os) const {
os << _maxweight;
}
void MamboDecayer::persistentInput(PersistentIStream & is, int) {
is >> _maxweight;
}
ClassDescription<MamboDecayer> MamboDecayer::initMamboDecayer;
void MamboDecayer::Init() {
static ClassDocumentation<MamboDecayer> documentation
("Decayer class that implements MAMBO algorithm of Kleiss-"
"Stirling.",
"The MAMBO algorithm of \\cite{Kleiss:1991rn} was used for high"
" multiplicity decays",
"\\bibitem{Kleiss:1991rn} R.~Kleiss and W.~J.~Stirling,\n"
"Nucl.\\ Phys.\\ B {\\bf 385} (1992) 413.\n"
"%%CITATION = NUPHA,B385,413;%%\n");
static Parameter<MamboDecayer,double> interfaceMaximumWeight
("MaxWeight",
"Maximum phase-space weight",
&MamboDecayer::_maxweight, 10.0, 1.0, 50.,
false, false, true);
}
ParticleVector MamboDecayer::decay(const Particle & parent,
const tPDVector & children) const {
useMe();
const int N = children.size();
ParticleVector out(N);
if(N == 1) {
out[0] = children[0]->produceParticle(parent.momentum());
return out;
}
Energy totalMass(ZERO);
for(int i = 0; i < N; ++i) {
totalMass += children[i]->mass();
}
if(totalMass > parent.mass()) {
generator()->log() << "MamboDecayer::decay - The Decay mode "
<< parent.PDGName() << "->";
for(int i = 0; i < N; ++i)
generator()->log() << children[i]->PDGName() << " ";
generator()->log() << " cannot proceed as there is not "
<< "enough phase space.\n";
out.clear();
return out;
}
double wgt(0.);
vector<Lorentz5Momentum> productMomentum(N);
do {
for(int i = 0; i < N; ++i)
productMomentum[i].setMass(children[i]->mass());
wgt = calculateMomentum(productMomentum,parent.mass());
}
while(wgt < _maxweight*UseRandom::rnd());
//set output momenta
int iter = 0;
for(tPDVector::const_iterator it=children.begin();iter<N;
++iter,++it) {
out[iter] = (*it)->produceParticle(productMomentum[iter]);
}
colourConnections(parent, out);
finalBoost(parent, out);
setScales(parent, out);
return out;
}
double MamboDecayer::calculateMomentum(vector<Lorentz5Momentum> & mom,
Energy comEn) const {
const int N = mom.size();
Energy rmtot(ZERO);
Energy2 rm2tot(ZERO);
for(int i = 0;i < N;++i) {
rmtot += mom[i].mass();
rm2tot += mom[i].mass2();
}
Energy wb = sqrt( (N*sqr(comEn) - sqr(rmtot))/N/N/(N - 1.) ) - rmtot/N;
Energy wmax = (2.0/3.0)*wb;
const Energy tol(1e-12*MeV);
long double r(0.), sf1(0.);
Energy2 sm2f2(ZERO);
Energy sf(ZERO), sff1(ZERO), w(ZERO),
wold(wmax), err(ZERO);
unsigned int iter(0), maxiter(50);
do {
sf = ZERO; sf1 = 0.; sff1 = ZERO; sm2f2 = ZERO;
for(int i = 0;i < N;++i) {
r = abs(mom[i].mass()/wold);
Energy f(ZERO);
long double f1(0.);
if (r == 0.0) {
f=2.*wold;
f1=2.;
}
else {
long double fk0(0.), fkp(0.);
BesselFns(r, fk0, fkp);
f = wold*(2.0 + r*fk0);
f1 = 2.- r*r*fkp;
}
sf += f;
sf1 += f1;
sff1 += f*f1;
sm2f2 -= f*f;
}
Energy u1 = 2.*(sf*sf1 - sff1);
Energy2 u0 = sf*sf + sm2f2 + rm2tot - sqr(comEn);
w = wold - u0/u1;
err = abs(w - wold);
wold = w;
++iter;
}
while(err > tol && iter < maxiter);
long double xu,xv;
vector<long double> alpha(N),um(N),vm(N);
for(int i = 0;i < N;++i) {
alpha[i] = 2.*(mom[i].mass()/w);
xu = (1.-alpha[i]+sqrt(1.+alpha[i]*alpha[i]))/2.;
xv = (3.-alpha[i]+sqrt(9.+ 4.*alpha[i]+alpha[i]*alpha[i]))/2.;
um[i] = exp(-xu/2.)*pow((xu*(xu+alpha[i])),0.25l);
vm[i] = xv*exp(-xv/2.)*pow((xv*(xv+alpha[i])),0.25l);
}
//start k-momenta generation
long double u(0.),v(0.),x(0.);
vector<Lorentz5Momentum> qk(N);
Lorentz5Momentum qktot;
do {
qktot=LorentzMomentum();
for(int i=0;i<N;++i) {
long double usq(0.),bound(0.);
do {
u = UseRandom::rnd()*um[i];
v = UseRandom::rnd()*vm[i];
x = v/u;
usq = u*u;
bound = exp(-x)*sqrt(x*(x+alpha[i]));
}
while(usq>bound);
double ck,phi;
Kinematics::generateAngles(ck,phi);
double sk = sqrt(1.0-ck*ck);
Energy qkv = w*sqrt(x*(x+alpha[i]));
qk[i] = Lorentz5Momentum(qkv*sk*sin(phi),qkv*sk*cos(phi),qkv*ck,
mom[i].mass()+w*x);
qktot += qk[i];
}
qktot.rescaleMass();
x = sqrt(comEn*comEn/qktot.mass2());
}
while(x>1.0);
//Perform lorentz boost from k to q
vector<Lorentz5Momentum> q(N);
Energy q0=ZERO, q1=ZERO, q2=ZERO, q3=ZERO;
long double t=0.;
vector<Energy2> qsq(N);
for(int i = 0;i<N;++i){
q3 = (qk[i]*qktot)/qktot.mass();
t = (q3+qk[i].e())/(qktot.e()+qktot.mass());
q2 = qk[i].z()-qktot.z()*t;
q1 = qk[i].y()-qktot.y()*t;
q0 = qk[i].x()-qktot.x()*t;
q[i] = Lorentz5Momentum(x*q0,x*q1,x*q2,x*q3);
qsq[i] = sqr(q[i].e())-x*x*mom[i].mass2();
}
long double xiold(1.),xi(0.);
vector<Energy> en(N);
iter = 0;
do {
Energy f = -comEn;
Energy f1 = ZERO;
for(int i = 0; i < N; ++i) {
en[i] = sqrt((xiold*xiold*qsq[i]) + mom[i].mass2());
f += en[i];
f1 += qsq[i]/en[i];
}
xi = xiold - f/(xiold*f1);
err = abs(xi-xiold)*MeV;
xiold = xi;
++iter;
}
while(err > tol && iter < maxiter);
//Now have desired momenta
for(int i = 0;i < N;++i)
mom[i] = Lorentz5Momentum(xi*q[i].x(),xi*q[i].y(),xi*q[i].z(),en[i]);
//Calculate weight of distribution
double s1(1.);
Energy s2(ZERO),s3(ZERO);
double wxi(0.);
for(int i=0;i<N;++i) {
s1 *= q[i].e()/mom[i].e();
s2 += mom[i].mass2()/q[i].e();
s3 += mom[i].mass2()/mom[i].e();
}
wxi = pow(xi,(3*N-3))*s1*(comEn-x*x*s2)/(comEn-s3);
return wxi;
}
void MamboDecayer::colourConnections(const Particle & parent,
ParticleVector & out) const {
const int N = out.size();
// fix 3-gluon colour lines / general colour lines
if(N == 3 && out[0]->id()==ParticleID::g && out[1]->id()==ParticleID::g
&& out[2]->id()== ParticleID::g ) {
out[0]->antiColourNeighbour(out[2]);
out[0]->colourNeighbour(out[1]);
out[1]->colourNeighbour(out[2]);
}
// incoming colour3/3bar state
else if(parent.data().iColour() == PDT::Colour3 ||
parent.data().iColour() == PDT::Colour3bar) {
PPtr pparent = const_ptr_cast<PPtr>(&parent);
// find outgoing coloured particles
tParticleVector trip,anti,oct;
for(int i=0;i < N;++i) {
if(out[i]->data().iColour() == PDT::Colour3)
trip.push_back(out[i]);
else if(out[i]->data().iColour() == PDT::Colour3bar)
anti.push_back(out[i]);
else if(out[i]->data().iColour() == PDT::Colour8)
oct .push_back(out[i]);
}
// 3 -> 3 + neutral
if(parent.data().iColour() == PDT::Colour3&&trip.size()==1&&
oct.size()==0&&anti.size()==0) {
trip[0]->incomingColour(pparent);
}
// 3bar -> 3bar + neutral
else if(parent.data().iColour() == PDT::Colour3bar&&trip.size()==0&&
oct.size()==0&&anti.size()==1) {
anti[0]->incomingColour(pparent,true);
}
// sink
else if(parent.data().iColour() == PDT::Colour3 &&
anti.size()==2 && oct.size()==0 && trip.size()==0) {
tColinePtr col[2] = {ColourLine::create(anti[0],true),
ColourLine::create(anti[1],true)};
parent.colourLine()->setSinkNeighbours(col[0],col[1]);
}
// source
else if(parent.data().iColour() == PDT::Colour3bar &&
trip.size()==2 && oct.size()==0 && anti.size()==0) {
tColinePtr col[2] = {ColourLine::create(trip[0]),
ColourLine::create(trip[1])};
parent.antiColourLine()->setSourceNeighbours(col[0],col[1]);
}
// 3 -> 3 + 8 + neutral
else if(parent.data().iColour() == PDT::Colour3&&trip.size()==1&&
oct.size()==1&&anti.size()==0) {
oct [0]->incomingColour(pparent);
oct [0]-> colourNeighbour(trip[0]);
trip[0]->antiColourNeighbour(oct[0]);
}
// 3bar -> 3bar + 8 + neutral
else if(parent.data().iColour() == PDT::Colour3bar&&trip.size()==0&&
oct.size()==1&&anti.size()==1) {
oct [0]->incomingColour(pparent,true);
oct [0]->antiColourNeighbour(anti[0]);
anti[0]-> colourNeighbour(oct[0]);
}
// 3 -> 3 + 3 + 3bar
else if(parent.data().iColour() == PDT::Colour3&&trip.size()==2&&
oct.size()==0&&anti.size()==1) {
int id1 = abs(pparent->id())%10;
int ip(0),io(1);
for(unsigned int ix=0;ix<trip.size();++ix) {
int id2 = abs(trip[ix]->id())%10;
if(id1==id2 || (id1%2==0&&id1==id2+1) ||
(id1%2==1&&id2==id1+1)) {
ip = ix;
io = 1-int(ix);
break;
}
}
trip[io]->antiColourNeighbour(anti[ 0]);
anti[0 ]->colourNeighbour(trip[io]);
trip[ip]->incomingColour(pparent);
}
// 3bar -> 3bar + 3 + 3bar
else if(parent.data().iColour() == PDT::Colour3bar&&trip.size()==1&&
oct.size()==0&&anti.size()==2) {
int id1 = abs(pparent->id())%10;
int ip(0),io(1);
for(unsigned int ix=0;ix<anti.size();++ix) {
int id2 = abs(anti[ix]->id())%10;
if(id1==id2 || (id1%2==0&&id1==id2+1) ||
(id1%2==1&&id2==id1+1)) {
ip = ix;
io = 1-int(ix);
break;
}
}
anti[io]-> colourNeighbour(trip[ 0]);
trip[0 ]->antiColourNeighbour(anti[io]);
anti[ip]->incomingColour(pparent,true);
}
else {
ostringstream dec;
for(unsigned int ix=0;ix<out.size();++ix) dec << out[ix]->PDGName() << " ";
throw Exception() << "Unknown colour for 3/3bar decay in MamboDecayer"
<< pparent->PDGName() << " -> " << dec.str()
<< Exception::runerror;
}
}
//incoming octet
else if(parent.data().iColour() == PDT::Colour8) {
PPtr pparent = const_ptr_cast<PPtr>(&parent);
tParticleVector trip,anti,oct;
for(int i=0;i < N;++i) {
if(out[i]->data().iColour() == PDT::Colour3)
trip.push_back(out[i]);
else if(out[i]->data().iColour() == PDT::Colour3bar)
anti.push_back(out[i]);
else if(out[i]->data().iColour() == PDT::Colour8)
oct .push_back(out[i]);
}
// decay to one octet
if(oct.size()==1&&trip.empty()&&anti.empty()) {
oct[0]->incomingColour(pparent);
oct[0]->incomingAntiColour(pparent);
}
// decay ot triplet/antitriplet
else if(trip.size()==1&&anti.size()==1&&oct.empty()) {
trip[0]->incomingColour(pparent,false);
anti[0]->incomingColour(pparent,true );
}
// baryon number violating decay to quarks
else if(trip.size()==3&&anti.empty()&&oct.empty()) {
unsigned int iloc = UseRandom::irnd(3);
tColinePtr col[2];
for(unsigned int ix=0;ix<trip.size();++ix) {
if(ix==iloc) {
trip[ix]->incomingColour(pparent);
}
else {
if(col[0]) col[1] = ColourLine::create(trip[ix]);
else col[0] = ColourLine::create(trip[ix]);
}
}
parent.antiColourLine()->setSourceNeighbours(col[0],col[1]);
}
// baryon number violating decay to antiquarks
else if(anti.size()==3&&trip.empty()&&oct.empty()) {
unsigned int iloc = UseRandom::irnd(3);
tColinePtr col[2];
for(unsigned int ix=0;ix<anti.size();++ix) {
if(ix==iloc) {
anti[ix]->incomingColour(pparent,true);
}
else {
if(col[0]) col[1] = ColourLine::create(anti[ix],true);
else col[0] = ColourLine::create(anti[ix],true);
}
}
parent.colourLine()->setSinkNeighbours(col[0],col[1]);
}
else {
ostringstream dec;
for(unsigned int ix=0;ix<out.size();++ix) dec << out[ix]->PDGName() << " ";
throw Exception() << "Unknown colour for octet decay in MamboDecayer"
<< pparent->PDGName() << " -> " << dec.str()
<< Exception::runerror;
}
}
else if(N==3 && parent.data().iColour() == PDT::Colour0&&
out[0]->data().iColour() == PDT::Colour3 &&
out[1]->data().iColour() == PDT::Colour3 &&
out[2]->data().iColour() == PDT::Colour3) {
tColinePtr col[3] = {ColourLine::create(out[0]),
ColourLine::create(out[1]),
ColourLine::create(out[2])};
col[0]->setSourceNeighbours(col[1],col[2]);
}
else if(N==3 && parent.data().iColour() == PDT::Colour0&&
out[0]->data().iColour() == PDT::Colour3bar &&
out[1]->data().iColour() == PDT::Colour3bar &&
out[2]->data().iColour() == PDT::Colour3bar) {
tColinePtr col[3] = {ColourLine::create(out[0],true),
ColourLine::create(out[1],true),
ColourLine::create(out[2],true)};
col[0]->setSinkNeighbours(col[1],col[2]);
}
//everything else
else {
for ( int i = 0; i < N; ++i ) {
if ( !out[i]->coloured() )
continue;
else if(i + 1 >= N) {
throw Exception()
<< "MamboDecayer::colourConnections() - "
<< "Cannot find appropriate configuration."
<< Exception::warning;
}
if ( out[i]->hasColour() )
out[i]->antiColourNeighbour(out[i + 1]);
if ( out[i]->hasAntiColour() )
out[i]->colourNeighbour(out[i + 1]);
++i; // skip the one that's linked up already
}
}
}
void MamboDecayer::dataBaseOutput(ofstream & output, bool header) const {
if(header) output << "update decayers set parameters=\"";
// parameters for the PartonicDecayerBase base class
output << "newdef " << name() << ":MaxWeight " << _maxweight << " \n";
if(header) output << "\n\" where BINARY ThePEGName=\""
<< fullName() << "\";" << endl;
}
void MamboDecayer::doinitrun() {
HwDecayerBase::doinitrun();
_a0[0] = 0.5;
_a0[1] = 0.375;
_a0[2] = 0.375;
_a0[3] = 0.4921875;
_a0[4] = 0.84375;
_a0[5] = 1.854492188,
_a0[6] = 5.0625;
_a0[7] = 16.58578491;
_a0[8] = 63.33398438;
_a0[9] = 275.6161079;
_a1[0] = 0.5;
_a1[1] = 0.75;
_a1[2] = 1.125;
_a1[3] = 1.96875;
_a1[4] = 4.21875;
_a1[5] = 11.12695313;
_a1[6] = 35.4375;
_a1[7] = 132.6862793;
_a1[8] = 570.0058594;
_a1[9] = 2756.161079;
}

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