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RestFrameNSubjettinessTagger.hh
#ifndef __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
#define __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
//FJSTARTHEADER
// $Id$
//
// Copyright (c) 2005-2021, 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. They are described in the original FastJet paper,
// hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
// FastJet as part of work towards a scientific publication, please
// quote the version you use and include a citation to the manual and
// optionally also to hep-ph/0512210.
//
// 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/>.
//----------------------------------------------------------------------
//FJENDHEADER
#include "fastjet/PseudoJet.hh"
#include "fastjet/JetDefinition.hh"
#include "fastjet/CompositeJetStructure.hh"
#include "fastjet/tools/Transformer.hh"
FASTJET_BEGIN_NAMESPACE
class RestFrameNSubjettinessTagger;
class RestFrameNSubjettinessTaggerStructure;
//----------------------------------------------------------------------
/// @ingroup tools_taggers
/// \class RestFrameNSubjettinessTagger
/// Class that helps perform 2-pronged boosted tagging using
/// a reclustering in the jet's rest frame, supplemented with a cut on N-subjettiness
/// (and a decay angle), as discussed by Ji-Hun Kim in arXiv:1011.1493.
///
/// To tag a fat jet, the tagger proceeds as follows:
///
/// - boost its constituents into the rest frame of the jet
///
/// - recluster them using another jet definition (the original
/// choice was SISCone in spherical coordinates with R=0.6 and
/// f=0.75.
///
/// - keep the 2 most energetic subjets (\f$q_{1,2}\f$) and compute
/// the 2-subjettiness
/// \f[
/// \tau_2^j = \frac{2}{m_{\rm jet}^2}\,
/// \sum_{k\in {\rm jet}} {\rm min}(q_1.p_k,q_2.p_k)
/// \f]
/// where the sum runs over the constituents of the jet.
///
/// - require \f$\tau_2^j < \tau_2^{\rm cut}\f$ [0.08 by default]
///
/// - impose that (in the rest frame of the fat jet), the angles
/// between the 2 most energetic subjets and the boost axis are
/// both large enough: \f$\cos(\theta_s)<c_\theta^{\rm cut}\f$
/// [0.8 by default]
///
/// Note that in the original version, the jets to be tagged were reconstructed
/// using SISCone with R=0.8 and f=0.75. Also, b-tagging was imposed
/// on the 2 subjets found in the rest-frame tagging procedure.
///
/// \section desc Options
///
/// The constructor has the following arguments:
/// - The first argument is the jet definition to be used to
/// recluster the constituents of the jet to be filtered (in the
/// rest frame of the tagged jet).
/// - The second argument is the cut on tau_2 [0.08 by default]
/// - The 3rd argument is the cut on cos(theta_s) [0.8 by default]
/// - If the 4th argument is true, 2 exclusive rest-frame jets will
/// be considered in place of the 2 most energetic inclusive jets
///
/// \section input Input conditions
///
/// - the original jet must have constituents
///
/// \section output Output/structure
///
/// - the 2 subjets are kept as pieces if some substructure is found,
/// otherwise a single 0-momentum piece
/// - the tau2 and maximal cos(theta_s) values computed during the
/// tagging can be obtained via the resulting jet's structure_of<...>()
/// function
///
class RestFrameNSubjettinessTagger : public Transformer{
public:
/// ctor with arguments (see the class description above)
RestFrameNSubjettinessTagger(const JetDefinition subjet_def,
const double tau2cut=0.08,
const double costhetascut=0.8,
const bool use_exclusive = false)
: _subjet_def(subjet_def), _t2cut(tau2cut), _costscut(costhetascut),
_use_exclusive(use_exclusive){};
/// returns a textual description of the tagger
virtual std::string description() const;
/// runs the tagger on the given jet and
/// returns the tagged PseudoJet if successful, a PseudoJet==0 otherwise
/// (standard access is through operator()).
virtual PseudoJet result(const PseudoJet & jet) const;
/// the type of Structure returned
typedef RestFrameNSubjettinessTaggerStructure StructureType;
protected:
JetDefinition _subjet_def;
double _t2cut, _costscut;
bool _use_exclusive;
};
//------------------------------------------------------------------------
/// @ingroup tools_taggers
/// \class RestFrameNSubjettinessTaggerStructure
/// the structure returned by the RestFrameNSubjettinessTagger transformer.
///
/// See the RestFrameNSubjettinessTagger class description for the details of
/// what is inside this structure
///
class RestFrameNSubjettinessTaggerStructure : public CompositeJetStructure{
public:
/// ctor with pieces initialisation
RestFrameNSubjettinessTaggerStructure(const std::vector<PseudoJet> & pieces_in) :
CompositeJetStructure(pieces_in), _tau2(0.0), _costhetas(1.0){}
/// returns the associated N-subjettiness
inline double tau2() const{return _tau2;}
/// returns the associated angle with the boosted axis
inline double costhetas() const {return _costhetas;}
// /// returns the original jet (before tagging)
// const PseudoJet & original() const {return _original_jet;}
protected:
double _tau2; ///< the value of the N-subjettiness
double _costhetas; ///< the minimal angle between the dijets
///< and the boost axis
// PseudoJet _original_jet; ///< the original jet (before tagging)
// allow the tagger to set these
friend class RestFrameNSubjettinessTagger;
};
FASTJET_END_NAMESPACE
#endif // __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
fastjet::CompositeJetStructure::CompositeJetStructure
CompositeJetStructure()
default ctor
Definition CompositeJetStructure.hh:54
fastjet::JetDefinition
class that is intended to hold a full definition of the jet clusterer
Definition JetDefinition.hh:250
fastjet::PseudoJet
Class to contain pseudojets, including minimal information of use to jet-clustering routines.
Definition PseudoJet.hh:68
fastjet::RestFrameNSubjettinessTaggerStructure
the structure returned by the RestFrameNSubjettinessTagger transformer.
Definition RestFrameNSubjettinessTagger.hh:137
fastjet::RestFrameNSubjettinessTaggerStructure::_costhetas
double _costhetas
the minimal angle between the dijets and the boost axis
Definition RestFrameNSubjettinessTagger.hh:154
fastjet::RestFrameNSubjettinessTaggerStructure::tau2
double tau2() const
returns the associated N-subjettiness
Definition RestFrameNSubjettinessTagger.hh:144
fastjet::RestFrameNSubjettinessTaggerStructure::costhetas
double costhetas() const
returns the associated angle with the boosted axis
Definition RestFrameNSubjettinessTagger.hh:147
fastjet::RestFrameNSubjettinessTaggerStructure::_tau2
double _tau2
the value of the N-subjettiness
Definition RestFrameNSubjettinessTagger.hh:153
fastjet::RestFrameNSubjettinessTaggerStructure::RestFrameNSubjettinessTaggerStructure
RestFrameNSubjettinessTaggerStructure(const std::vector< PseudoJet > &pieces_in)
ctor with pieces initialisation
Definition RestFrameNSubjettinessTagger.hh:140
fastjet::RestFrameNSubjettinessTagger::StructureType
RestFrameNSubjettinessTaggerStructure StructureType
the type of Structure returned
Definition RestFrameNSubjettinessTagger.hh:120
fastjet::RestFrameNSubjettinessTagger::RestFrameNSubjettinessTagger
RestFrameNSubjettinessTagger(const JetDefinition subjet_def, const double tau2cut=0.08, const double costhetascut=0.8, const bool use_exclusive=false)
ctor with arguments (see the class description above)
Definition RestFrameNSubjettinessTagger.hh:104
fastjet::Transformer::Transformer
Transformer()
default ctor
Definition Transformer.hh:74