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//STARTHEADER
// $Id: MassDropTagger.cc 3249 2013-10-28 15:06:25Z salam $
//
// Copyright (c) 2005-2011, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
//
//----------------------------------------------------------------------
// This file is part of FastJet.
//
// FastJet is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// The algorithms that underlie FastJet have required considerable
// development and are described in hep-ph/0512210. If you use
// FastJet as part of work towards a scientific publication, please
// include a citation to the FastJet paper.
//
// FastJet is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with FastJet. If not, see <http://www.gnu.org/licenses/>.
//----------------------------------------------------------------------
//ENDHEADER
#include <fastjet/tools/MassDropTagger.hh>
#include <fastjet/ClusterSequence.hh>
#include <sstream>
FASTJET_BEGIN_NAMESPACE
LimitedWarning MassDropTagger::_warnings_nonca;
using namespace std;
//----------------------------------------------------------------------
// MassDropTagger class implementation
//----------------------------------------------------------------------
//------------------------------------------------------------------------
// description of the tagger
string MassDropTagger::description() const{
ostringstream oss;
oss << "MassDropTagger with mu=" << _mu << " and ycut=" << _ycut;
return oss.str();
}
//------------------------------------------------------------------------
// returns the tagged PseudoJet if successful, 0 otherwise
// - jet the PseudoJet to tag
PseudoJet MassDropTagger::result(const PseudoJet & jet) const{
PseudoJet j = jet;
// issue a warning if the jet is not obtained through a C/A
// clustering
if ((! j.has_associated_cluster_sequence()) ||
(j.validated_cs()->jet_def().jet_algorithm() != cambridge_algorithm))
_warnings_nonca.warn("MassDropTagger should only be applied on jets from a Cambridge/Aachen clustering; use it with other algorithms at your own risk.");
PseudoJet j1, j2;
bool had_parents;
// we just ask that we can "walk" in the cluster sequence.
// appropriate errors will be thrown automatically if this is not
// the case
while ((had_parents = j.has_parents(j1,j2))) {
// make parent1 the more massive jet
if (j1.m2() < j2.m2()) std::swap(j1,j2);
// if we pass the conditions on the mass drop and its degree of
// asymmetry (kt_dist/m^2 > rtycut [where kt_dist/m^2 \sim
// z/(1-z)), then we've found something interesting, so exit the
// loop
if ( (j1.m2() < _mu*_mu*j.m2()) && (j1.kt_distance(j2) > _ycut*j.m2()) )
break;
else
j = j1;
}
if (!had_parents)
// no Higgs found, return an empty PseudoJet
return PseudoJet();
// create the result and its structure
PseudoJet result_local = j;
MassDropTaggerStructure * s = new MassDropTaggerStructure(result_local);
// s->_original_jet = jet;
s->_mu = (j.m2()!=0.0) ? sqrt(j1.m2()/j.m2()) : 0.0;
s->_y = (j.m2()!=0.0) ? j1.kt_distance(j2)/j.m2() : 0.0;
result_local.set_structure_shared_ptr(SharedPtr<PseudoJetStructureBase>(s));
return result_local;
}
FASTJET_END_NAMESPACE
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