diff --git a/Hadronization/ClusterDecayer.cc b/Hadronization/ClusterDecayer.cc
--- a/Hadronization/ClusterDecayer.cc
+++ b/Hadronization/ClusterDecayer.cc
@@ -1,557 +1,620 @@
// -*- C++ -*-
//
// ClusterDecayer.cc is a part of Herwig - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2019 The Herwig Collaboration
//
// Herwig is licenced under version 3 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 ClusterDecayer class.
//
#include "ClusterDecayer.h"
#include <ThePEG/Interface/ClassDocumentation.h>
#include <ThePEG/Interface/Reference.h>
#include <ThePEG/Interface/Parameter.h>
#include <ThePEG/Interface/Switch.h>
#include <ThePEG/Persistency/PersistentOStream.h>
#include <ThePEG/Persistency/PersistentIStream.h>
#include <ThePEG/PDT/EnumParticles.h>
#include <ThePEG/Repository/EventGenerator.h>
#include "Herwig/Utilities/Kinematics.h"
#include "Cluster.h"
#include <ThePEG/Utilities/DescribeClass.h>
#include <ThePEG/Repository/UseRandom.h>
#include "ThePEG/Interface/ParMap.h"
+#include "Herwig/Utilities/Histogram.h"
+
using namespace Herwig;
DescribeClass<ClusterDecayer,Interfaced>
describeClusterDecayer("Herwig::ClusterDecayer","Herwig.so");
ClusterDecayer::ClusterDecayer() :
_clDirLight(1),
_clDirExotic(1),
_clSmrLight(0.0),
_clSmrExotic(0.0),
_onshell(false),
_masstry(20),
_covariantBoost(false),
_kinematics(0)
{}
IBPtr ClusterDecayer::clone() const {
return new_ptr(*this);
}
IBPtr ClusterDecayer::fullclone() const {
return new_ptr(*this);
}
void ClusterDecayer::persistentOutput(PersistentOStream & os) const
{
os << _clDirLight << _clDirHeavy
<< _clDirExotic << _clSmrLight << _clSmrHeavy
<< _clSmrExotic << _onshell << _masstry
<< _covariantBoost
<< _kinematics
<< _hadronSpectrum;
}
void ClusterDecayer::persistentInput(PersistentIStream & is, int) {
is >> _clDirLight >> _clDirHeavy
>> _clDirExotic >> _clSmrLight >> _clSmrHeavy
>> _clSmrExotic >> _onshell >> _masstry
>> _covariantBoost
>> _kinematics
>> _hadronSpectrum;
}
void ClusterDecayer::doinit() {
Interfaced::doinit();
for ( const long& id : spectrum()->heavyHadronizingQuarks() ) {
if ( _clSmrHeavy.find(id) == _clSmrHeavy.end() ||
_clDirHeavy.find(id) == _clDirHeavy.end() )
throw InitException() << "not all parameters have been set for heavy quark cluster decay";
}
}
void ClusterDecayer::Init() {
static ClassDocumentation<ClusterDecayer> documentation
("This class is responsible for the two-body decays of normal clusters");
static Reference<ClusterDecayer,HadronSpectrum> interfaceHadronSpectrum
("HadronSpectrum",
"Set the hadron spectrum for this parton splitter.",
&ClusterDecayer::_hadronSpectrum, false, false, true, false);
//ClDir for light, Bottom, Charm and exotic (e.g Susy) quarks
static Switch<ClusterDecayer,bool> interfaceClDirLight
("ClDirLight",
"Cluster direction for light quarks",
&ClusterDecayer::_clDirLight, true, false, false);
static SwitchOption interfaceClDirLightPreserve
(interfaceClDirLight,
"Preserve",
"Preserve the direction of the quark from the perturbative stage"
" as the direction of the meson produced from it",
true);
static SwitchOption interfaceClDirLightIsotropic
(interfaceClDirLight,
"Isotropic",
"Assign the direction of the meson randomly",
false);
static ParMap<ClusterDecayer,bool> interfaceClDirHeavy
("ClDirHeavy",
"Preserve the direction of the given heavy quark from the perturbative stage.",
&ClusterDecayer::_clDirHeavy, -1, true, false, true,
false, false, Interface::limited);
static Switch<ClusterDecayer,bool> interfaceClDirExotic
("ClDirExotic",
"Cluster direction for exotic quarks",
&ClusterDecayer::_clDirExotic, true, false, false);
static SwitchOption interfaceClDirExoticPreserve
(interfaceClDirExotic,
"Preserve",
"Preserve the direction of the quark from the perturbative stage"
" as the direction of the meson produced from it",
true);
static SwitchOption interfaceClDirExoticIsotropic
(interfaceClDirExotic,
"Isotropic",
"Assign the direction of the meson randomly",
false);
static Switch<ClusterDecayer,bool> interfaceCovariantBoost
("CovariantBoost",
"Use single Covariant Boost for Cluster Fission",
&ClusterDecayer::_covariantBoost, false, false, false);
static SwitchOption interfaceCovariantBoostYes
(interfaceCovariantBoost,
"Yes",
"Use Covariant boost",
true);
static SwitchOption interfaceCovariantBoostNo
(interfaceCovariantBoost,
"No",
"Do NOT use Covariant boost",
false);
static Switch<ClusterDecayer,int> interfaceKinematics
("Kinematics",
"Choose kinematics of Cluster Decay",
&ClusterDecayer::_kinematics, 0, true, false);
static SwitchOption interfaceKinematicsDefault
(interfaceKinematics,
"Default",
"default kinematics",
0);
static SwitchOption interfaceKinematicsTchannel
(interfaceKinematics,
"Tchannel",
"t channel like kinematics",
1);
// ClSmr for ligth, Bottom, Charm and exotic (e.g. Susy) quarks
static Parameter<ClusterDecayer,double>
interfaceClSmrLight ("ClSmrLight", "cluster direction Gaussian smearing for light quark",
&ClusterDecayer::_clSmrLight, 0, 0.0 , 0.0 , 2.0,false,false,false);
static ParMap<ClusterDecayer,double> interfaceClSmrHeavy
("ClSmrHeavy",
"cluster direction Gaussian smearing for heavy quarks",
&ClusterDecayer::_clSmrHeavy, -1, 0.0, 0.0, 2.0,
false, false, Interface::limited);
static Parameter<ClusterDecayer,double>
interfaceClSmrExotic ("ClSmrExotic", "cluster direction Gaussian smearing for exotic quark",
&ClusterDecayer::_clSmrExotic, 0, 0.0 , 0.0 , 2.0,false,false,false);
static Switch<ClusterDecayer,bool> interfaceOnShell
("OnShell",
"Whether or not the hadrons produced should by on shell or generated using the"
" mass generator.",
&ClusterDecayer::_onshell, false, false, false);
static SwitchOption interfaceOnShellOnShell
(interfaceOnShell,
"Yes",
"Produce the hadrons on shell",
true);
static SwitchOption interfaceOnShellOffShell
(interfaceOnShell,
"No",
"Generate the masses using the mass generator.",
false);
static Parameter<ClusterDecayer,unsigned int> interfaceMassTry
("MassTry",
"The number attempts to generate the masses of the hadrons produced"
" in the cluster decay.",
&ClusterDecayer::_masstry, 20, 1, 50,
false, false, Interface::limited);
}
void ClusterDecayer::decay(const ClusterVector & clusters, tPVector & finalhadrons) {
// Loop over all clusters, and if they are not too heavy (that is
// intermediate clusters that have undergone to fission) or not
// too light (that is final clusters that have been already decayed
// into single hadron) then decay them into two hadrons.
for (ClusterVector::const_iterator it = clusters.begin();
it != clusters.end(); ++it) {
if ((*it)->isAvailable() && !(*it)->isStatusFinal()
&& (*it)->isReadyToDecay()) {
pair<PPtr,PPtr> prod = decayIntoTwoHadrons(*it);
if(!prod.first)
throw Exception() << "Can't perform decay of cluster ("
<< (*it)->particle(0)->dataPtr()->PDGName() << " "
<< (*it)->particle(1)->dataPtr()->PDGName() << ")\nThreshold = "
<< ounit(spectrum()->massLightestHadronPair((*it)->particle(0)->dataPtr(),
(*it)->particle(1)->dataPtr()),GeV)
<< "\nLightest hadron pair = ( "
<< spectrum()->lightestHadronPair((*it)->particle(0)->dataPtr(),
(*it)->particle(1)->dataPtr()).first->PDGName() << ",\t"
<< spectrum()->lightestHadronPair((*it)->particle(0)->dataPtr(),
(*it)->particle(1)->dataPtr()).second->PDGName() << " )\nCluster =\n"
<< **it
<< "in ClusterDecayer::decay()"
<< Exception::eventerror;
(*it)->addChild(prod.first);
(*it)->addChild(prod.second);
finalhadrons.push_back(prod.first);
finalhadrons.push_back(prod.second);
}
}
}
static double sampleCos(double A, double alpha);
static double sampleCos(double A, double alpha){
if (fabs(A)<=1.0 || fabs(fabs(A)-1.0)<1e-14){
// Force sampling of the pole in the distribution
// TODO do this better by some regulation and actual
// sampling
- return -A;
+ return A;
}
- // sample pole free distribution N/(A+cosTheta)^(2*alpha)
+ // sample pole free distribution N/(A-cosTheta)^(2*alpha)
double r=UseRandom::rnd();
double Ap1=A+1.0;
double Am1=A-1.0;
double cosTheta=A-pow(pow(Ap1,-2*alpha)-pow(Am1,-2*alpha)*r-pow(Ap1,-2*alpha)*r
+A*(pow(Ap1,-2*alpha)+pow(Am1,-2*alpha)*r-pow(Ap1,-2*alpha)*r),1.0/(1.0-2.0*alpha));
if (fabs(cosTheta)>1.0 || std::isnan(cosTheta)){
std::cout << "cosTheta = "<< cosTheta << std::endl;
std::cout << "alpha = "<< alpha << std::endl;
std::cout << "r = "<< r << std::endl;
std::cout << "A = "<< A << std::endl;
std::cout << "Ap1 = "<< Ap1 << std::endl;
std::cout << "Am1 = "<< Am1 << std::endl;
}
assert(fabs(cosTheta)<=1.0);
return cosTheta;
}
+static double sampleCosRegular(double A, double alpha, double R);
+static double sampleCosRegular(double A, double alpha, double R){
+ if (fabs(A)<=1.0 || fabs(fabs(A)-1.0)<1e-14){
+ // Force sampling of the regularised pole with gaussian
+ // TODO do this better by some regulation and actual
+ // sampling better
+ // sample regularised distribution N/((A-cosTheta)^2+R^2)^(alpha)
+ double sigma=sqrt(pow(R,2*(1+alpha))/(2.0*alpha));
+ double cosTheta;
+ do {
+ cosTheta=A+UseRandom::rndGauss(sigma);
+ }
+ while (fabs(cosTheta)>1.0);
+ return cosTheta;
+ }
+ // sample pole free distribution N/(A-cosTheta)^(2*alpha)
+ return sampleCos(A, alpha);
+}
pair<PPtr,PPtr> ClusterDecayer::decayIntoTwoHadrons(tClusterPtr ptr) {
using Constants::pi;
using Constants::twopi;
// To decay the cluster into two hadrons one must distinguish between
// constituent quarks (or diquarks) that originate from perturbative
// processes (hard process or parton shower) from those that are generated
// by the non-perturbative gluon splitting or from fission of heavy clusters.
// In the latter case the two body decay is assumed to be *isotropic*.
// In the former case instead, if proper flag are activated, the two body
// decay is assumed to "remember" the direction of the constituents inside
// the cluster, in the cluster frame. The actual smearing of the hadron
// directions around the direction of the constituents, in the cluster
// frame, can be different between non-b hadrons and b-hadrons, but is given
// by the same functional form:
// cosThetaSmearing = 1 + smearFactor * log( rnd() )
// (repeated until cosThetaSmearing > -1)
// where the factor smearFactor is different between b- and non-b hadrons.
//
// We need to require (at least at the moment, maybe in the future we
// could change it) that the cluster has exactly two components.
// If this is not the case, then send a warning because it is not suppose
// to happen, and then return.
if ( ptr->numComponents() != 2 ) {
generator()->logWarning( Exception("ClusterDecayer::decayIntoTwoHadrons "
"***Still cluster with not exactly 2 components*** ",
Exception::warning) );
return pair<PPtr,PPtr>();
}
// Extract the id and particle pointer of the two components of the cluster.
tPPtr ptr1 = ptr->particle(0);
tPPtr ptr2 = ptr->particle(1);
tcPDPtr ptr1data = ptr1->dataPtr();
tcPDPtr ptr2data = ptr2->dataPtr();
bool isHad1FlavSpecial = false;
bool cluDirHad1 = _clDirLight;
double cluSmearHad1 = _clSmrLight;
bool isHad2FlavSpecial = false;
bool cluDirHad2 = _clDirLight;
double cluSmearHad2 = _clSmrLight;
if (spectrum()->isExotic(ptr1data)) {
isHad1FlavSpecial = true;
cluDirHad1 = _clDirExotic;
cluSmearHad1 = _clSmrExotic;
} else {
for ( const long& id : spectrum()->heavyHadronizingQuarks() ) {
if ( spectrum()->hasHeavy(id,ptr1data) ) {
cluDirHad1 = _clDirHeavy[id];
cluSmearHad1 = _clSmrHeavy[id];
}
}
}
if (spectrum()->isExotic(ptr2data)) {
isHad2FlavSpecial = true;
cluDirHad2 = _clDirExotic;
cluSmearHad2 = _clSmrExotic;
} else {
for ( const long& id : spectrum()->heavyHadronizingQuarks() ) {
if ( spectrum()->hasHeavy(id,ptr2data) ) {
cluDirHad2 = _clDirHeavy[id];
cluSmearHad2 = _clSmrHeavy[id];
}
}
}
bool isOrigin1Perturbative = ptr->isPerturbative(0);
bool isOrigin2Perturbative = ptr->isPerturbative(1);
// We have to decide which, if any, of the two hadrons will have
// the momentum, in the cluster parent frame, smeared around the
// direction of its constituent (for Had1 is the one pointed by
// ptr1, and for Had2 is the one pointed by ptr2).
// This happens only if the flag _ClDirX is 1 and the constituent is
// perturbative (that is not coming from nonperturbative gluon splitting
// or cluster fission). In the case that both the hadrons satisfy this
// two requirements (of course only one must be treated, because the other
// one will have the momentum automatically fixed by the momentum
// conservation) then more priority is given in the case of a b-hadron.
// Finally, in the case that the two hadrons have same priority, then
// we choose randomly, with equal probability, one of the two.
int priorityHad1 = 0;
if ( cluDirHad1 && isOrigin1Perturbative ) {
priorityHad1 = isHad1FlavSpecial ? 2 : 1;
}
int priorityHad2 = 0;
if ( cluDirHad2 && isOrigin2Perturbative ) {
priorityHad2 = isHad2FlavSpecial ? 2 : 1;
}
if ( priorityHad2 && priorityHad1 == priorityHad2 && UseRandom::rndbool() ) {
priorityHad2 = 0;
}
Lorentz5Momentum pClu = ptr->momentum();
bool secondHad = false;
Axis uSmear_v3;
if ( priorityHad1 || priorityHad2 ) {
double cluSmear;
Lorentz5Momentum pQ;
if ( priorityHad1 > priorityHad2 ) {
pQ = ptr1->momentum();
cluSmear = cluSmearHad1;
} else {
pQ = ptr2->momentum();
cluSmear = cluSmearHad2;
secondHad = true;
}
// To find the momenta of the two hadrons in the parent cluster frame
// we proceed as follows. First, we determine the unit vector parallel
// to the direction of the constituent in the cluster frame. Then we
// have to smear such direction using the following prescription:
// --- in theta angle w.r.t. such direction (not the z-axis),
// the drawing of the cosine of such angle is done via:
// 1.0 + cluSmear*log( rnd() )
// (repeated until it gives a value above -1.0)
// --- in phi angle w.r.t. such direction, the drawing is simply flat.
// Then, given the direction in the parent cluster frame of one of the
// two hadrons, it is straighforward to get the momenta of both hadrons
// (always in the same parent cluster frame).
pQ.boost( -pClu.boostVector() ); // boost from Lab to Cluster frame
uSmear_v3 = pQ.vect().unit();
// skip if cluSmear is too small
if ( cluSmear > 0.001 ) {
// generate the smearing angle
double cosSmear;
do cosSmear = 1.0 + cluSmear*log( UseRandom::rnd() );
while ( cosSmear < -1.0 );
double sinSmear = sqrt( 1.0 - sqr(cosSmear) );
// calculate rotation to z axis
LorentzRotation rot;
double sinth(sqrt(1.-sqr(uSmear_v3.z())));
if(abs(uSmear_v3.perp2()/uSmear_v3.z())>1e-10)
rot.setRotate(-acos(uSmear_v3.z()),
Axis(-uSmear_v3.y()/sinth,uSmear_v3.x()/sinth,0.));
// + random azimuthal rotation
rot.rotateZ(UseRandom::rnd()*twopi);
// set direction in rotated frame
Lorentz5Vector<double> ltemp(0.,sinSmear,cosSmear,0.);
// rotate back
rot.invert();
ltemp *= rot;
uSmear_v3 = ltemp.vect();
}
}
else {
// Isotropic decay: flat in cosTheta and phi.
uSmear_v3 = Axis(1.0, 0.0, 0.0); // just to set the rho to 1
uSmear_v3.setTheta( acos( UseRandom::rnd( -1.0 , 1.0 ) ) );
uSmear_v3.setPhi( UseRandom::rnd( -pi , pi ) );
}
pair<tcPDPtr,tcPDPtr> dataPair
= _hadronSpectrum->chooseHadronPair(ptr->mass(),
ptr1data,
ptr2data);
if(dataPair.first == tcPDPtr() ||
dataPair.second == tcPDPtr()) return pair<PPtr,PPtr>();
// Create the two hadron particle objects with the specified id.
PPtr ptrHad1,ptrHad2;
// produce the hadrons on mass shell
if(_onshell) {
ptrHad1 = dataPair.first ->produceParticle(dataPair.first ->mass());
ptrHad2 = dataPair.second->produceParticle(dataPair.second->mass());
}
// produce the hadrons with mass given by the mass generator
else {
unsigned int ntry(0);
do {
ptrHad1 = dataPair.first ->produceParticle();
ptrHad2 = dataPair.second->produceParticle();
++ntry;
}
while(ntry<_masstry&&ptrHad1->mass()+ptrHad2->mass()>ptr->mass());
// if fails produce on shell and issue warning (should never happen??)
if( ptrHad1->mass() + ptrHad2->mass() > ptr->mass() ) {
generator()->log() << "Failed to produce off-shell hadrons in "
<< "ClusterDecayer::decayIntoTwoHadrons producing hadrons "
<< "on-shell" << endl;
ptrHad1 = dataPair.first ->produceParticle(dataPair.first ->mass());
ptrHad2 = dataPair.second->produceParticle(dataPair.second->mass());
}
}
if (!ptrHad1 || !ptrHad2) {
ostringstream s;
s << "ClusterDecayer::decayIntoTwoHadrons ***Cannot create the two hadrons***"
<< dataPair.first ->PDGName() << " and "
<< dataPair.second->PDGName();
cerr << s.str() << endl;
generator()->logWarning( Exception(s.str(), Exception::warning) );
} else {
if ( secondHad ) uSmear_v3 *= -1.0;
if (pClu.m() < ptrHad1->mass()+ptrHad2->mass() ) {
throw Exception() << "Impossible Kinematics in ClusterDecayer::decayIntoTwoHadrons()"
<< Exception::eventerror;
}
Lorentz5Momentum pHad1,pHad2;
Energy Pcom=Kinematics::pstarTwoBodyDecay(pClu.m(),ptrHad1->mass(),ptrHad2->mass());
if (_kinematics==1) {
double alpha=1.0;
Energy mHad1 = ptrHad1->mass();
Energy mConst1 = ptr1data->constituentMass();
Energy mConst2 = ptr2data->constituentMass();
Energy PcomHad = Kinematics::pstarTwoBodyDecay(pClu.m(),ptrHad1->mass(),ptrHad2->mass());
Energy PcomConst = Kinematics::pstarTwoBodyDecay(pClu.m(),mConst1,mConst2);
Energy EcomHad1 = sqrt(mHad1*mHad1+PcomHad*PcomHad);
Energy EcomConst1 = sqrt(mConst1*mConst1+PcomConst*PcomConst);
double A=(2*EcomConst1*EcomHad1-mConst1*mConst1-mHad1*mHad1)/(2.0*PcomConst*PcomHad);
if (std::isnan(A)){
std::cout << "A<=1!!! "<< A << std::endl;
std::cout << "mHad1 = "<< mHad1/GeV << std::endl;
std::cout << "mConst1 = "<< mConst1/GeV << std::endl;
std::cout << "PcomHad = "<< PcomHad/GeV << std::endl;
std::cout << "PcomConst = "<< PcomConst/GeV << std::endl;
std::cout << "EcomHad1 = "<< EcomHad1/GeV << std::endl;
std::cout << "EcomConst1 = "<< EcomConst1/GeV << std::endl;
std::cout << "EcomHad1 - PcomHad = "<< (EcomHad1 - PcomHad)/GeV << std::endl;
std::cout << "EcomConst1 - PcomConst1 = "<< (EcomConst1 - PcomConst)/GeV << std::endl;
}
- double cosTheta=sampleCos(A,alpha);
+ // double cosTheta=sampleCos(A,alpha);
+ double cosTheta=sampleCosRegular(A,alpha,2*PcomConst*PcomHad*0.01/GeV2);
+ /*
+ //sanity checks
+ static int firstAsmall=1;
+ static int firstAlarge=1;
+ if (firstAsmall && fabs(A)<1){
+ // Histogram hcosTheta(-1,1,100);
+ Histogram hcosThetaRegular(-1,1,100);
+ int N=10000;
+ double R=1;
+ std::cout << "\nA = "<<A <<"\n";
+ std::cout << "\nR = "<<R <<"\n";
+ for (int i = 0; i < N; i++)
+ {
+ double c=sampleCosRegular(A,alpha,R);
+ hcosThetaRegular+=c;
+ }
+ ofstream out1("hcosThetaRegular_Asmall.dat", std::ios::out);
+ hcosThetaRegular.topdrawOutput(out1);
+ out1.close();
+ ofstream out2("hcosThetaRegular_Asmall_RIVET.dat", std::ios::out);
+ hcosThetaRegular.rivetOutput(out2);
+ out2.close();
+ firstAsmall=0;
+ }
+ if (firstAlarge && fabs(A)>1){
+ Histogram hcosThetaRegular(-1,1,100);
+ std::cout << "\nA = "<<A <<"\n";
+ int N=10000;
+ for (int i = 0; i < N; i++)
+ {
+ double c=sampleCosRegular(A,alpha,2*PcomConst*PcomHad*0.01/GeV2);
+ hcosThetaRegular+=c;
+ }
+ ofstream out1("hcosThetaRegular_Alarge.dat", std::ios::out);
+ hcosThetaRegular.topdrawOutput(out1);
+ out1.close();
+ ofstream out2("hcosThetaRegular_Alarge_RIVET.dat", std::ios::out);
+ hcosThetaRegular.rivetOutput(out2);
+ out2.close();
+ firstAlarge=0;
+ }
+ */
double theta = acos(cosTheta);
double phi = UseRandom::rnd(-M_PI,M_PI);
uSmear_v3.setX(sin(theta)*cos(phi));
uSmear_v3.setY(sin(theta)*sin(phi));
uSmear_v3.setZ(cos(theta));
}
if (_covariantBoost) {
// Use correct boost for a 2 particle constituent cluster
// if (secondHad) std::cout << "\n second had\n";
pHad1=Lorentz5Momentum(ptrHad1->mass(), Pcom*uSmear_v3);
pHad2=Lorentz5Momentum(ptrHad2->mass(),-Pcom*uSmear_v3);
const Lorentz5Momentum pQ1(ptr1data->constituentMass(),ptr->particle(0)->momentum().vect());
const Lorentz5Momentum pQ2(ptr2data->constituentMass(),ptr->particle(1)->momentum().vect());
Kinematics::BoostIntoTwoParticleFrame(pClu.m(),pQ1, pQ2, pHad1, pHad2);
}
else {
// 5-momentum vectors that we have to determine
Kinematics::twoBodyDecay(pClu,ptrHad1->mass(),ptrHad2->mass(),uSmear_v3,
pHad1,pHad2);
}
ptrHad1->set5Momentum(pHad1);
ptrHad2->set5Momentum(pHad2);
// Determine the positions of the two children clusters.
LorentzPoint positionHad1 = LorentzPoint();
LorentzPoint positionHad2 = LorentzPoint();
calculatePositions(pClu, ptr->vertex(), pHad1, pHad2, positionHad1, positionHad2);
ptrHad1->setVertex(positionHad1);
ptrHad2->setVertex(positionHad2);
}
return pair<PPtr,PPtr>(ptrHad1,ptrHad2);
}
void ClusterDecayer::
calculatePositions(const Lorentz5Momentum &pClu,
const LorentzPoint &positionClu,
const Lorentz5Momentum &,
const Lorentz5Momentum &,
LorentzPoint &positionHad1,
LorentzPoint &positionHad2 ) const {
// First, determine the relative positions of the children hadrons
// with respect to their parent cluster, in the cluster reference frame,
// assuming gaussian smearing with width inversely proportional to the
// parent cluster mass.
Length smearingWidth = hbarc / pClu.m();
LorentzDistance distanceHad[2];
for ( int i = 0; i < 2; i++ ) { // i==0 is the first hadron; i==1 is the second one
Length delta[4]={ZERO,ZERO,ZERO,ZERO};
// smearing of the four components of the LorentzDistance, two at the same time to improve speed
for ( int j = 0; j < 3; j += 2 ) {
delta[j] = UseRandom::rndGauss(smearingWidth, Length(ZERO));
delta[j+1] = UseRandom::rndGauss(smearingWidth, Length(ZERO));
}
// set the distance
delta[0] = abs(delta[0]) +sqrt(sqr(delta[1])+sqr(delta[2])+sqr(delta[3]));
distanceHad[i] = LorentzDistance(delta[1],delta[2],delta[3],delta[0]);
// Boost such relative positions of the children hadrons,
// with respect to their parent cluster,
// from the cluster reference frame to the Lab frame.
distanceHad[i].boost(pClu.boostVector());
}
// Finally, determine the absolute positions of the children hadrons
// in the Lab frame.
positionHad1 = distanceHad[0] + positionClu;
positionHad2 = distanceHad[1] + positionClu;
}