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//STARTHEADER
// $Id: RestFrameNSubjettinessTagger.cc 2689 2011-11-14 14:51:06Z soyez $
//
// 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/RestFrameNSubjettinessTagger.hh>
#include <fastjet/tools/Boost.hh>
#include <fastjet/ClusterSequence.hh>
#include <sstream>
using namespace std;
FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
//------------------------------------------------------------------------
// RestFrameNSubjettinessTagger class implementation
//------------------------------------------------------------------------
//------------------------------------------------------------------------
// tagger description
string RestFrameNSubjettinessTagger::description() const{
ostringstream oss;
oss << "RestFrameNSubjettiness tagger that performs clustering in the jet rest frame with "
<< _subjet_def.description()
<< ", supplemented with cuts tau_2 < " << _t2cut
<< " and cos(theta_s) < " << _costscut;
return oss.str();
}
//------------------------------------------------------------------------
// action on a single jet
// returns the tagged PseudoJet if successful, 0 otherwise
PseudoJet RestFrameNSubjettinessTagger::result(const PseudoJet & jet) const{
// make sure that the jet has constituents
if (!jet.has_constituents())
throw("The jet you try to tag needs to have accessible constituents");
// get the constituents and boost them into the rest frame of the jet
vector<PseudoJet> rest_input = jet.constituents();
for (unsigned int i=0; i<rest_input.size(); i++)
rest_input[i].unboost(jet);
ClusterSequence cs_rest(rest_input, _subjet_def);
vector<PseudoJet> subjets = (_use_exclusive)
? cs_rest.exclusive_jets(2)
: sorted_by_E(cs_rest.inclusive_jets());
// impose the cuts in the rest-frame
if (subjets.size()<2) return PseudoJet();
const PseudoJet &j0 = subjets[0];
const PseudoJet &j1 = subjets[1];
/// impose the cut on cos(theta_s)
double ct0 = (j0.px()*jet.px() + j0.py()*jet.py() + j0.pz()*jet.pz())
/sqrt(j0.modp2()*jet.modp2());
double ct1 = (j1.px()*jet.px() + j1.py()*jet.py() + j1.pz()*jet.pz())
/sqrt(j1.modp2()*jet.modp2());
if ((ct0 > _costscut) || (ct1 > _costscut)) return PseudoJet();
// ccompute the 2-subjettiness and impose the coresponding cut
double tau2 = 0.0;
for (unsigned int i=0; i<rest_input.size(); i++)
tau2 += min(dot_product(rest_input[i], j0),
dot_product(rest_input[i], j1));
tau2 *= (2.0/jet.m2());
if (tau2 > _t2cut) return PseudoJet();
// We have a positive tag,
// - boost everything back into the lab frame
// - record the info in the interface
// Note that in order to point to the correct Clustersequence, the
// subjets must be taken from the boosted one. We extract that
// through the history index of the rest-frame subjets
ClusterSequence * cs_structure = new ClusterSequence();
Boost boost(jet);
cs_structure->transfer_from_sequence(cs_rest, &boost);
PseudoJet subjet_lab1 = cs_structure->jets()[cs_rest.history()[subjets[0].cluster_hist_index()].jetp_index];
PseudoJet subjet_lab2 = cs_structure->jets()[cs_rest.history()[subjets[0].cluster_hist_index()].jetp_index];
PseudoJet result_local = join<StructureType>(subjet_lab1,subjet_lab2);
StructureType * s = (StructureType *) result_local.structure_non_const_ptr();
// s->_original_jet = jet;
s->_tau2 = tau2;
s->_costhetas = max(ct0, ct1);
// keep the rest-frame CS alive
cs_structure->delete_self_when_unused();
return result_local;
}
FASTJET_END_NAMESPACE
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