ClusterDecayer.cc
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ClusterDecayer.cc
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	// -- 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 "CheckId.h"
	#include "Cluster.h"
	#include <ThePEG/Utilities/DescribeClass.h>
	#include <ThePEG/Repository/UseRandom.h>

	using namespace Herwig;

	DescribeClass<ClusterDecayer,Interfaced>
	describeClusterDecayer("Herwig::ClusterDecayer","Herwig.so");

	ClusterDecayer::ClusterDecayer() :
	_clDirLight(1),
	_clDirBottom(1),
	_clDirCharm(1),
	_clDirExotic(1),
	_clSmrLight(0.0),
	_clSmrBottom(0.0),
	_clSmrCharm(0.0),
	_clSmrExotic(0.0),
	_onshell(false),
	_masstry(20)
	{}

	IBPtr ClusterDecayer::clone() const {
	return new_ptr(*this);
	}

	IBPtr ClusterDecayer::fullclone() const {
	return new_ptr(*this);
	}

	void ClusterDecayer::persistentOutput(PersistentOStream & os) const
	{
	os << _hadronsSelector << _clDirLight << _clDirBottom
	<< _clDirCharm << _clDirExotic << _clSmrLight << _clSmrBottom
	<< _clSmrCharm << _clSmrExotic << _onshell << _masstry;
	}

	void ClusterDecayer::persistentInput(PersistentIStream & is, int) {
	is >> _hadronsSelector >> _clDirLight >> _clDirBottom
	>> _clDirCharm >> _clDirExotic >> _clSmrLight >> _clSmrBottom
	>> _clSmrCharm >> _clSmrExotic >> _onshell >> _masstry;
	}


	void ClusterDecayer::Init() {

	static ClassDocumentation<ClusterDecayer> documentation
	("This class is responsible for the two-body decays of normal clusters");

	static Reference<ClusterDecayer,HadronSelector>
	interfaceHadronSelector("HadronSelector",
	"A reference to the HadronSelector object",
	&Herwig::ClusterDecayer::_hadronsSelector,
	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 Switch<ClusterDecayer,bool> interfaceClDirBottom
	("ClDirBottom",
	"Cluster direction for bottom quarks",
	&ClusterDecayer::_clDirBottom, true, false, false);
	static SwitchOption interfaceClDirBottomPreserve
	(interfaceClDirBottom,
	"Preserve",
	"Preserve the direction of the quark from the perturbative stage"
	" as the direction of the meson produced from it",
	true);
	static SwitchOption interfaceClDirBottomIsotropic
	(interfaceClDirBottom,
	"Isotropic",
	"Assign the direction of the meson randomly",
	false);

	static Switch<ClusterDecayer,bool> interfaceClDirCharm
	("ClDirCharm",
	"Cluster direction for charm quarks",
	&ClusterDecayer::_clDirCharm, true, false, false);
	static SwitchOption interfaceClDirCharmPreserve
	(interfaceClDirCharm,
	"Preserve",
	"Preserve the direction of the quark from the perturbative stage"
	" as the direction of the meson produced from it",
	true);
	static SwitchOption interfaceClDirCharmIsotropic
	(interfaceClDirCharm,
	"Isotropic",
	"Assign the direction of the meson randomly",
	false);

	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);

	// 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 Parameter<ClusterDecayer,double>
	interfaceClSmrBottom ("ClSmrBottom", "cluster direction Gaussian smearing for b quark",
	&ClusterDecayer::_clSmrBottom, 0, 0.0 , 0.0 , 2.0,false,false,false);
	static Parameter<ClusterDecayer,double>
	interfaceClSmrCharm ("ClSmrCharm", "cluster direction Gaussian smearing for c quark",
	&ClusterDecayer::_clSmrCharm, 0, 0.0 , 0.0 , 2.0,false,false,false);
	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
	<< "in ClusterDecayer::decay()"
	<< Exception::eventerror;
	(*it)->addChild(prod.first);
	(*it)->addChild(prod.second);
	finalhadrons.push_back(prod.first);
	finalhadrons.push_back(prod.second);
	}
	}
	}


	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 (CheckId::isExotic(ptr1data)) {
	isHad1FlavSpecial = true;
	cluDirHad1 = _clDirExotic;
	cluSmearHad1 = _clSmrExotic;
	}
	else if (CheckId::hasBottom(ptr1data)) {
	isHad1FlavSpecial = true;
	cluDirHad1 = _clDirBottom;
	cluSmearHad1 = _clSmrBottom;
	}
	else if (CheckId::hasCharm(ptr1data)) {
	isHad1FlavSpecial = true;
	cluDirHad1 = _clDirCharm;
	cluSmearHad1 = _clSmrCharm;
	}

	if (CheckId::isExotic(ptr2data)) {
	isHad2FlavSpecial = true;
	cluDirHad2 = _clDirExotic;
	cluSmearHad2 = _clSmrExotic;
	}
	else if (CheckId::hasBottom(ptr2data)) {
	isHad2FlavSpecial = true;
	cluDirHad2 = _clDirBottom;
	cluSmearHad2 = _clSmrBottom;
	}
	else if (CheckId::hasCharm(ptr2data)) {
	isHad2FlavSpecial = true;
	cluDirHad2 = _clDirCharm;
	cluSmearHad2 = _clSmrCharm;
	}


	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
	= _hadronsSelector->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 {

	Lorentz5Momentum pHad1, pHad2; // 5-momentum vectors that we have to determine
	if ( secondHad ) uSmear_v3 *= -1.0;

	if (pClu.m() < ptrHad1->mass()+ptrHad2->mass() ) {
	throw Exception() << "Impossible Kinematics in ClusterDecayer::decayIntoTwoHadrons()"
	<< Exception::eventerror;
	}
	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;
	}

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