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LightClusterDecayer.cc
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LightClusterDecayer.cc
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// -*- C++ -*-
//
// This is the implementation of the non-inlined, non-templated member
// functions of the LightClusterDecayer class.
//
#include "LightClusterDecayer.h"
#include "Pythia7/Interface/ClassDocumentation.h"
#include "Pythia7/Interface/Parameter.h"
#include "Pythia7/Interface/Reference.h"
#include "Pythia7/Persistency/PersistentOStream.h"
#include "Pythia7/Persistency/PersistentIStream.h"
#include "Pythia7/PDT/EnumParticles.h"
#include "Pythia7/Repository/EventGenerator.h"
#include "Cluster.h"
#include "HadronsSelector.h"
#include "Herwig++/Utilities/HwDebug.h"
#include "Herwig++/Utilities/Kinematics.h"
#include "Herwig++/Utilities/CheckId.h"
using namespace Herwig;
// using namespace Pythia7;
LightClusterDecayer::~LightClusterDecayer() {}
void LightClusterDecayer::persistentOutput(PersistentOStream & os) const {
os << _hadronsSelector << _B1Lim;
}
void LightClusterDecayer::persistentInput(PersistentIStream & is, int) {
is >> _hadronsSelector >> _B1Lim;
}
ClassDescription<LightClusterDecayer> LightClusterDecayer::initLightClusterDecayer;
// Definition of the static class description member.
void LightClusterDecayer::Init() {
static ClassDocumentation<LightClusterDecayer> documentation
("There is the class responsible for the one-hadron decay of light clusters");
static Reference<LightClusterDecayer,HadronsSelector>
interfaceHadronsSelector("HadronsSelector",
"A reference to the HadronsSelector object",
&Herwig::LightClusterDecayer::_hadronsSelector,
false, false, true, false);
static Parameter<LightClusterDecayer,Energy>
interfaceB1Lim ("B1Lim","one-hadron decay of b-cluster over threshold",
&LightClusterDecayer::_B1Lim, 0, 0.0, 0.0, 100.0);
}
void LightClusterDecayer::decay(const StepPtr &pstep,
ClusterVector & clusters)
throw (Veto, Stop, Exception) {
// Loop over all clusters, and for those that were not heavy enough
// to undergo to fission, check if they are below the threshold
// for normal two-hadron decays. If this is the case, then the cluster
// should be decayed into a single hadron: this can happen only if
// it is possible to reshuffle momenta between the cluster and
// another one; in the rare occasions in which such exchange of momenta
// is not possible (because all of the clusters are too light) then
// the event is skipped.
// Notice that, differently from what happens in Fortran Herwig,
// light (that is below the threshold for the production of the lightest
// pair of hadrons with the proper flavours) fission products, produced
// by the fission of heavy clusters in class ClusterFissioner
// have been already "decayed" into single hadron (the lightest one
// with proper flavour) by the same latter class, without requiring
// any reshuffling. Therefore the light clusters that are treated in
// this LightClusterDecayer class are produced directly
// (originally) by the class ClusterFinder.
// To preserve all of the information, the cluster partner with which
// the light cluster (that decays into a single hadron) exchanges
// momentum in the reshuffling procedure is redefined and inserted
// in the vector vecNewRedefinedCluPtr. Only at the end, when all
// light clusters have been examined, the elements this vector will be
// copied in collecCluPtr (the reason is that it is not allowed to
// modify a STL container while iterating over it. At the same time,
// this ensures that a cluster can be redefined only once, which seems
// sensible although not strictly necessary).
// Notice that the cluster reshuffling partner is normally redefined
// and inserted in the vector vecNewRedefinedCluPtr, but not always:
// in the case it is also light, then it is also decayed immediately
// into a single hadron, without redefining it (the reason being that,
// otherwise, the would-be redefined cluster could have undefined
// components).
vector<tClusterPtr> redefinedClusters;
for (ClusterVector::iterator it = clusters.begin();
it != clusters.end(); ++it) {
// Skip the clusters that are not available or that are
// heavy, intermediate, clusters that have undergone to fission,
if ( ! (*it)->isAvailable() || ! (*it)->isReadyToDecay() ) continue;
// We need to require (at least at the moment, maybe in the future we
// could change it) that the cluster has exactly two components,
// because otherwise we don't know how to deal with the kinematics.
// If this is not the case, then send a warning because it is not suppose
// to happen, and then do nothing with (ignore) such cluster.
if ( (*it)->numComponents() != 2 ) {
generator()->logWarning( Exception("LightClusterDecayer::decay "
"***Still cluster with not exactly 2 components*** ",
Exception::warning) );
if ( HERWIG_DEBUG_LEVEL >= HwDebug::full_Hadronization ) {
generator()->log() << " ===>" << " num components = " << (*it)->numComponents()
<< endl << endl;
}
continue;
}
// Extract the id and particle pointer of the two components of the cluster.
long idQ1 = 0, idQ2 = 0;
tPPtr ptrQ1 = tPPtr(), ptrQ2 = tPPtr();
ptrQ1 = (*it)->particle(0);
idQ1 = ptrQ1->id();
ptrQ2 = (*it)->particle(1);
idQ2 = ptrQ2->id();
// Sanity check (normally skipped) to control that the two components of a
// cluster are consistent, that is they can form a meson or a baryon.
if ( HERWIG_DEBUG_LEVEL >= HwDebug::minimal_Hadronization ) {
if ( ! CheckId::canBeMeson(idQ1,idQ2) && ! CheckId::canBeBaryon(idQ1,idQ2) ) {
generator()->logWarning( Exception("LightClusterDecayer::decay "
"***The two components of the cluster are inconsistent***",
Exception::warning) );
std::cout << "LightClusterDecayer::decay ****the two components are "
<< idQ1 << " and " << idQ2 << " ***\n";
if ( HERWIG_DEBUG_LEVEL >= HwDebug::full_Hadronization ) {
generator()->log() << " ===>"
<< " idQ1=" << idQ1 << " idQ2=" << idQ2 << endl << endl;
}
}
}
// Determine the sum of the nominal masses of the two lightest hadrons
// with the right flavour numbers as the cluster under consideration.
// Notice that we don't need real masses (drawn by a Breit-Wigner
// distribution) because the lightest pair of hadrons does not involve
// any broad resonance.
Energy threshold = _hadronsSelector->massLightestHadronsPair(idQ1,idQ2);
// Special for b-flavour: it allows one-hadron decays also above threshold.
if ( CheckId::hasBeauty(idQ1,idQ2) ) {
threshold *= (1.0 + rnd()*_B1Lim);
}
//***TRICK***: scale artificially threshold if you want to test
// LightClusterDecayer with a huge statistics.
// // // threshold *= (1.0 + rnd()*2.0);
if ( (*it)->mass() < threshold ) {
long idhad = _hadronsSelector->lightestHadron(idQ1,idQ2);
// We assume that the candidate reshuffling cluster partner,
// with whom the light cluster can exchange momenta,
// is chosen as the closest in space-time between the available
// clusters. Notice that an alternative, sensible approach
// could be to consider instead the "closeness" in the colour
// structure...
// Notice that nor a light cluster (which decays into a single hadron)
// neither its cluster reshuffling partner (which either has a
// redefined cluster or also decays into a single hadron) can be
// a reshuffling partner of another light cluster.
// This because we are requiring that the considered candidate cluster
// reshuffling partner has the status "isAvailable && isReadyToDecay" true;
// furthermore, the new redefined clusters are not added to the collection
// of cluster before the end of the entire reshuffling procedure, avoiding
// in this way that the redefined cluster of a cluster reshuffling partner
// is used again later. Needless to say, this is just an assumption,
// although reasonable, but nothing more than that!
// Build a multimap of available reshuffling cluster partners,
// with key given by the module of the invariant space-time distance
// w.r.t. the light cluster, so that this new collection is automatically
// ordered in increasing distance values.
// We use a multimap, rather than a map, just for precaution against not properly
// defined cluster positions which could produce all identical (null) distances.
multimap<Length,tClusterPtr> candidates;
for ( ClusterVector::iterator jt = clusters.begin();
jt != clusters.end(); ++jt ) {
if ((*jt)->isAvailable() && (*jt)->isReadyToDecay() && jt != it) {
Length distance = fabs (((*it)->vertex() - (*jt)->vertex()).mag());
candidates.insert(pair<Length,tClusterPtr>(distance,*jt));
}
}
// Loop sequentially the multimap.
multimap<Length,tClusterPtr>::const_iterator mmapIt = candidates.begin();
bool found = false;
while (!found && mmapIt != candidates.end()) {
found = reshuffling(idhad, *it, (*mmapIt).second, pstep, redefinedClusters);
++mmapIt;
}
if (!found) {
if ( HERWIG_DEBUG_LEVEL >= HwDebug::full_Hadronization ) {
int numCluAvailable = 0, numCluAlreadyReshuffled = 0;
for (ClusterVector::const_iterator iter = clusters.begin();
iter != clusters.end(); ++iter ) {
if ( (*iter)->isAvailable() && (*iter)->isReadyToDecay() ) {
numCluAvailable++;
} else if((*iter)->isAvailable() && (*iter)->hasBeenReshuffled()) {
numCluAlreadyReshuffled++;
}
}
generator()->log() << "LightClusterDecayer::decay "
<< " (just before throwing the exception) " << endl
<< " ===> num clusters: all=" << clusters.size()
<< " already reshuffled=" << numCluAlreadyReshuffled
<< " still available=" << numCluAvailable
<< endl << endl;
}
throw Exception("LightClusterDecayer::decay "
"***Skip event: too light clusters (reshuffling problem)***",
Exception::eventerror);
}
// Debugging.
if ( HERWIG_DEBUG_LEVEL == HwDebug::extreme_Hadronization ) {
generator()->log() << "LightClusterDecayer::decay : *** extreme debugging ***" << endl
<< " \t Cluster : mass=" << (*it)->mass()
<< " components ids= " << idQ1 << " " << idQ2
<< " ---> hadron id=" << idhad << endl
<< " before " << ( (*it)->momentum() +
((*mmapIt).second)->momentum() )
<< endl
<< " = " << (*it)->momentum()
<< " + " << ((*mmapIt).second)->momentum() << endl
<< "\t multimap of reshuffling candidates : size = "
<< candidates.size() << endl;
for(multimap<Length,tClusterPtr>::const_iterator
mmapIt = candidates.begin(); mmapIt != candidates.end(); ++mmapIt ) {
generator()->log() << "\t \t distance = " << (*mmapIt).first << " [mm] " << endl;
}
}
} // end if mass < threshold
} // end loop over collecCluPtr
// Add to collecCluPtr all of the redefined new clusters (indeed the
// pointers to them are added) contained in vecNewRedefinedCluPtr.
for (tClusterVector::const_iterator it = redefinedClusters.begin();
it != redefinedClusters.end(); ++it) {
clusters.push_back(*it);
}
}
bool LightClusterDecayer::reshuffling(const long idhad1,
tClusterPtr cluPtr1,
tClusterPtr cluPtr2,
const StepPtr &pstep,
tClusterVector & redefinedClusters )
throw (Veto, Stop, Exception) {
// This method does the reshuffling of momenta between the cluster "1",
// that must decay into a single hadron (with id equal to idhad1), and
// the candidate cluster "2". It returns true if the reshuffling succeed,
// false otherwise.
PPtr ptrhad1 = getParticle( idhad1 );
if ( ! ptrhad1 ) {
generator()->logWarning( Exception("LightClusterDecayer::reshuffling"
"***Cannot create a particle with specified id***",
Exception::warning) );
return false;
}
Energy mhad1 = ptrhad1->mass();
// Let's call "3" and "4" the two constituents of the second cluster
tPPtr part3 = cluPtr2->particle(0);
tPPtr part4 = cluPtr2->particle(1);
// Sanity check (normally skipped) to see if the second cluster
// is consistently defined.
if ( HERWIG_DEBUG_LEVEL >= HwDebug::minimal_Hadronization ) {
if ( cluPtr2->numComponents() != 2 || !part3 || !part4 ) {
generator()->logWarning( Exception("LightClusterDecayer::reshuffling "
"***Inconsistent cluster***",
Exception::warning) );
if ( HERWIG_DEBUG_LEVEL >= HwDebug::full_Hadronization ) {
generator()->log() << " ===>" << " n=" << cluPtr2->numComponents()
<< " compPtr3=" << part3 << " compPtr4=" << part4
<< endl << endl;
}
}
}
// Check if the system of the two clusters can kinematically be replaced by
// an hadron of mass mhad1 (which is the lightest single hadron with the
// same flavour numbers as the first cluster) and the second cluster.
// If not, then try to replace the second cluster with the lightest hadron
// with the same flavour numbers; if it still fails, then give up!
Lorentz5Momentum pSystem = cluPtr1->momentum() + cluPtr2->momentum();
pSystem.rescaleMass(); // set the mass as the invariant of the quadri-vector
Energy mSystem = pSystem.mass();
Energy mclu2 = cluPtr2->mass();
bool normalSecondCluster = true;
//***TRICK***: uncomment the following line and replace it to the
// if statement below if you want to test LightClusterDecayer
// with a huge statistics.
// // // if ( mSystem < (mhad1 + mclu2)*(1.0 + rnd()*5.0) ) {
if ( mSystem < mhad1 + mclu2 ) {
mclu2 = _hadronsSelector->massLightestHadron(part3->id(), part4->id());
if ( mSystem < mhad1 + mclu2 ) {
return false;
}
normalSecondCluster = false; // second cluster must decay into a single hadron
}
// Let's call from now on "Sys" the system of the two clusters, and
// had1 (of mass mhad1) the lightest hadron in which the first
// cluster decays, and clu2 (of mass mclu2) either the second
// cluster or the lightest hadron in which it decays (depending
// which one is kinematically allowed, see above).
// The idea behind the reshuffling is to replace the system of the
// two clusters by the system of the hadron had1 and (cluster or hadron) clu2,
// but leaving the overall system unchanged. Furthermore, the motion
// of had1 and clu2 in the Sys frame is assumed to be parallel to, respectively,
// those of the original cluster1 and cluster2 in the same Sys frame.
// Calculate the unit three-vector, in the frame "Sys" along which the
// two initial clusters move.
Lorentz5Momentum u( cluPtr1->momentum() );
u.boost( - pSystem.boostVector() ); // boost from LAB to Sys
// Calculate the momenta of had1 and clu2 in the Sys frame first,
// and then boost back in the LAB frame.
Lorentz5Momentum phad1, pclu2;
Kinematics::twoBodyDecay(pSystem, mhad1, mclu2, u.vect().unit(), phad1, pclu2);
// Sanity check (normally skipped) to see if the energy-momentum is conserved.
if ( HERWIG_DEBUG_LEVEL >= HwDebug::minimal_Hadronization ) {
Lorentz5Momentum diff = pSystem - ( phad1 + pclu2 );
Energy ediff = fabs( diff.m() );
if ( ediff > 1e-3*GeV ) {
generator()->logWarning( Exception("LightClusterDecayer::reshuffling "
"***Energy-momentum NOT conserved: system***",
Exception::warning) );
if ( HERWIG_DEBUG_LEVEL >= HwDebug::full_Hadronization ) {
generator()->log() << " ===> " << endl
<< " diff " << diff << endl
<< " before " << pSystem << " ---> " << (phad1+pclu2) << endl
<< " = " << phad1 << " + " << pclu2 << endl << endl;
}
}
}
ptrhad1->set5Momentum( phad1 ); // set momentum of first hadron.
ptrhad1->setLabVertex(cluPtr1->vertex()); // set hadron vertex position to the
// parent cluster position.
//cluPtr1->addChild(ptrhad1);
pstep->addDecayProduct(cluPtr1, ptrhad1);
cluPtr1->reshufflingPartnerCluster( cluPtr2 );
cluPtr2->reshufflingPartnerCluster( cluPtr1 );
if ( ! normalSecondCluster ) {
// In the case that also the cluster reshuffling partner is light
// it is decayed into a single hadron, *without* creating the
// redefined cluster (this choice is justified in order to avoid
// clusters that could have undefined components).
long idhad2 = _hadronsSelector->lightestHadron(part3->id(), part4->id());
PPtr ptrhad2 = getParticle( idhad2 );
ptrhad2->set5Momentum( pclu2 );
ptrhad2->setLabVertex( cluPtr2->vertex() ); // set hadron vertex position to the
// parent cluster position.
// cluPtr2->addChild(ptrhad2);
pstep->addDecayProduct(cluPtr2, ptrhad2);
} else {
// Create the new cluster which is the redefinitions of the cluster
// partner (cluster "2") used in the reshuffling procedure of the
// light cluster (cluster "1").
// The rationale of this is to preserve completely all of the information.
ClusterPtr cluPtr2new = ClusterPtr();
if (part3 && part4) cluPtr2new = new_ptr(Cluster(part3,part4));
cluPtr2new->set5Momentum( pclu2 );
cluPtr2new->setVertex( cluPtr2->vertex() );
// cluPtr2->addChild( cluPtr2new );
pstep->addDecayProduct(cluPtr2, cluPtr2new);
redefinedClusters.push_back( cluPtr2new );
// Set consistently the momenta of the two components of the second cluster
// after the reshuffling. To do that we first calculate the momenta of the
// constituents in the initial cluster rest frame; then we boost them back
// in the lab but using this time the new cluster rest frame. Finally we store
// these information in the new cluster. Notice that we do *not* set
// consistently also the momenta of the (eventual) particles pointed by the
// two components: that's because we do not need to do so, being the momentum
// an explicit private member of the class Component (which is set equal
// to the momentum of the eventual particle pointed only in the constructor,
// but then later should not necessary be the same), and furthermore it allows
// us not to loose any information, in the sense that we can always, later on,
// to find the original momenta of the two components before the reshuffling.
Lorentz5Momentum p3 = part3->momentum();
p3.boost( - (cluPtr2->momentum()).boostVector() ); // from LAB to clu2 (old) frame
p3.boost( pclu2.boostVector() ); // from clu2 (new) to LAB frame
Lorentz5Momentum p4 = part4->momentum();
p4.boost( - (cluPtr2->momentum()).boostVector() ); // from LAB to clu2 (old) frame
p4.boost( pclu2.boostVector() ); // from clu2 (new) to LAB frame
cluPtr2new->particle(0)->set5Momentum(p3);
cluPtr2new->particle(1)->set5Momentum(p4);
// Sanity check (normally skipped) to see if the energy-momentum is conserved.
if ( HERWIG_DEBUG_LEVEL >= HwDebug::minimal_Hadronization ) {
Lorentz5Momentum sumMomentaComponents = Lorentz5Momentum();
for(int i = 0; i<cluPtr2new->numComponents(); i++)
sumMomentaComponents += cluPtr2new->particle(i)->momentum();
Lorentz5Momentum diff = sumMomentaComponents - cluPtr2new->momentum();
Energy ediff = fabs( diff.m() );
if ( ediff > 1e-3*GeV ) {
generator()->logWarning( Exception("LightClusterDecayer::reshuffling "
"***Energy-momentum NOT conserved: clu2new***",
Exception::warning) );
if ( HERWIG_DEBUG_LEVEL >= HwDebug::full_Hadronization ) {
generator()->log() << " ===> " << endl
<< " sumMomentaComponents = " << sumMomentaComponents << endl
<< " momentumClu2 = " << cluPtr2new->momentum() << endl
<< " diff = " << diff << endl << endl;
}
}
}
} // end of if ( ! normalSecondCluster )
return true;
}

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