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MassDropTagger.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.
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// development. They are described in the original FastJet paper,
// hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
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#ifndef __FASTJET_MASS_DROP_TAGGER_HH__
#define __FASTJET_MASS_DROP_TAGGER_HH__
#include "fastjet/tools/Transformer.hh"
#include "fastjet/LimitedWarning.hh"
#include "fastjet/WrappedStructure.hh"
FASTJET_BEGIN_NAMESPACE
class MassDropTagger;
class MassDropTaggerStructure;
//----------------------------------------------------------------------
/// @ingroup tools_taggers
/// \class MassDropTagger
/// Class that helps perform 2-pronged boosted tagging using
/// the "mass-drop" technique (with asymmetry cut) introduced by Jonathan
/// Butterworth, Adam Davison, Mathieu Rubin and Gavin Salam in
/// arXiv:0802.2470 in the context of a boosted Higgs search.
///
/// The tagger proceeds as follows:
///
/// 0. start from a jet obtained from with the Cambridge/Aachen
/// algorithm
///
/// 1. undo the last step of the clustering step j -> j1 + j2 (label
/// them such as j1 is the most massive).
///
/// 2. if there is a mass drop, i.e. m_j1/m_j < mu_cut, and the
/// splitting is sufficiently symmetric, \f${\rm
/// min}(p_{tj1}^2,p_{tj2}^2)\Delta R_{j1,j2}^2 > y_{\rm cut}
/// m_j^2\f$, keep j as the result of the tagger (with j1 and j2
/// its 2 subjets)
///
/// 3. otherwise, redefine j to be equal to j1 and return to step 1.
///
/// Note that in the original proposal, j1 and j2 are both required
/// to be b-tagged and a filter (with Rfilt=min(0.3,Rbb/2) and
/// n_filt=3) is also applied to j to obtain the final "Higgs candidate".
/// See the example \subpage Example12 for details.
///
/// \section desc Options
///
/// The constructor has the following arguments:
/// - The first argument is the minimal mass drop that is required (mu_cut) [0.67
/// by default]
/// - The second argument is the asymmetry cut (y_cut) [0.09 by default]
///
/// \section input Input conditions
///
/// - one must be able to successively "uncluster" the original jet
/// using "has_parents"
///
/// \section output Output/structure
///
/// - the 2 subjets are kept as pieces if some substructure is found,
/// otherwise a single 0-momentum piece is returned
/// - the 'mu' and 'y' values corresponding to the unclustering step
/// that passed the tagger's cuts
///
/// See also \subpage Example12 for a usage example.
class MassDropTagger : public Transformer{
public:
/// default ctor
MassDropTagger(const double mu=0.67, const double ycut=0.09) : _mu(mu), _ycut(ycut){};
/// 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()).
/// \param jet the PseudoJet to tag
virtual PseudoJet result(const PseudoJet & jet) const;
/// the type of the associated structure
typedef MassDropTaggerStructure StructureType;
protected:
double _mu, _ycut;
static LimitedWarning _warnings_nonca;
static LimitedWarning _negative_mass_warning;
};
//------------------------------------------------------------------------
/// @ingroup tools_taggers
/// \class MassDropTaggerStructure
/// the structure returned by the MassDropTagger transformer.
///
/// See the MassDropTagger class description for the details of what
/// is inside this structure
///
class MassDropTaggerStructure : public WrappedStructure{
public:
/// ctor with initialisation
/// \param pieces the pieces of the created jet
/// \param rec the recombiner from the underlying cluster sequence
MassDropTaggerStructure(const PseudoJet & result_jet) :
WrappedStructure(result_jet.structure_shared_ptr()), _mu(0.0), _y(0.0){}
/// returns the mass-drop ratio, pieces[0].m()/jet.m(), for the splitting
/// that triggered the mass-drop condition
inline double mu() const{return _mu;}
/// returns the value of y = (squared kt distance) / (squared mass) for the
/// splitting that triggered the mass-drop condition
inline double y() const {return _y;}
// /// returns the original jet (before tagging)
// const PseudoJet & original() const {return _original_jet;}
protected:
double _mu; ///< the value of the mass-drop parameter
double _y; ///< the value of the asymmetry parameter
// PseudoJet _original_jet; ///< the original jet (before tagging)
// allow the tagger to set these
friend class MassDropTagger;
};
FASTJET_END_NAMESPACE
#endif // __FASTJET_MASS_DROP_TAGGER_HH__
fastjet::LimitedWarning
class to provide facilities for giving warnings up to some maximum number of times and to provide glo...
Definition LimitedWarning.hh:54
fastjet::MassDropTaggerStructure
the structure returned by the MassDropTagger transformer.
Definition MassDropTagger.hh:124
fastjet::MassDropTaggerStructure::_y
double _y
the value of the asymmetry parameter
Definition MassDropTagger.hh:145
fastjet::MassDropTaggerStructure::_mu
double _mu
the value of the mass-drop parameter
Definition MassDropTagger.hh:144
fastjet::MassDropTaggerStructure::MassDropTaggerStructure
MassDropTaggerStructure(const PseudoJet &result_jet)
ctor with initialisation
Definition MassDropTagger.hh:129
fastjet::MassDropTaggerStructure::y
double y() const
returns the value of y = (squared kt distance) / (squared mass) for the splitting that triggered the ...
Definition MassDropTagger.hh:138
fastjet::MassDropTaggerStructure::mu
double mu() const
returns the mass-drop ratio, pieces[0].m()/jet.m(), for the splitting that triggered the mass-drop co...
Definition MassDropTagger.hh:134
fastjet::MassDropTagger::MassDropTagger
MassDropTagger(const double mu=0.67, const double ycut=0.09)
default ctor
Definition MassDropTagger.hh:95
fastjet::MassDropTagger::StructureType
MassDropTaggerStructure StructureType
the type of the associated structure
Definition MassDropTagger.hh:107
fastjet::PseudoJet
Class to contain pseudojets, including minimal information of use to jet-clustering routines.
Definition PseudoJet.hh:68
fastjet::Transformer::Transformer
Transformer()
default ctor
Definition Transformer.hh:74
fastjet::WrappedStructure::WrappedStructure
WrappedStructure(const SharedPtr< PseudoJetStructureBase > &to_be_shared)
default ctor the argument is the structure we need to wrap
Definition WrappedStructure.hh:57