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JHTopTagger.hh
#ifndef __FASTJET_JH_TOP_TAGGER_HH__
#define __FASTJET_JH_TOP_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
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//
// 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
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//FJENDHEADER
#include "fastjet/tools/TopTaggerBase.hh"
#include "fastjet/CompositeJetStructure.hh"
#include "fastjet/LimitedWarning.hh"
FASTJET_BEGIN_NAMESPACE
class JHTopTagger;
class JHTopTaggerStructure;
//----------------------------------------------------------------------
/// @ingroup tools_taggers
/// \class JHTopTagger
/// Class that helps perform boosted top tagging using the "Johns Hopkins"
/// method from arXiv:0806.0848 (Kaplan, Rehermann, Schwartz
/// and Tweedie)
///
///The tagger proceeds as follows:
/// - start from a jet J obtained with the Cambridge/Aachen algorithm
/// - undo the last iteration j -> j_1,j_2 (with pt_1>pt_2) until the
/// two subjets satisfy pt_1 > delta_p pt_J (with pt_J the pt of
/// the original jet) and |y_1 - y_2| + |phi_1 - phi_2| > delta_r.
/// - if one of these criteria is not satisfied, carry on the
/// procedure with j_1 (discarding j_2)
/// - for each of the subjets found, repeat the procedure. If some
/// new substructure is found, keep these 2 new subjets, otherwise
/// keep the original subjet (found during the first iteration)
/// - at this stage, one has at most 4 subjets. If one has less than
/// 3, the tagger has failed.
/// - reconstruct the W from the 2 subjets with a mass closest to the
/// W mass
/// - impose that the W helicity angle be less than a threshold
/// cos_theta_W_max.
///
/// \section input Input conditions
///
/// - the original jet must have an associated (and valid)
/// ClusterSequence
/// - the tagger is designed to work with jets formed by the
/// Cambridge/Aachen (C/A) algorithm; if a non-C/A jet is passed to
/// the tagger, a warning will be issued
///
/// \section Example
///
/// A JHTopTagger can be used as follows:
///
/// \code
/// double delta_p = 0.10; // subjets must carry at least this fraction of the original jet's p_t
/// double delta_r = 0.19; // subjets must be separated by at least this Manhattan distance
/// double cos_theta_W_max = 0.7; // the maximal allowed value of the W helicity angle
/// JHTopTagger top_tagger(delta_p, delta_r, cos_theta_W_max);
/// // indicate the acceptable range of top, W masses (default: no limits)
/// top_tagger.set_top_selector(SelectorMassRange(150,200));
/// top_tagger.set_W_selector (SelectorMassRange( 65, 95));
/// // now try and tag a jet
/// PseudoJet top_candidate = top_tagger(jet); // jet should come from a Cambridge/Aachen clustering
/// if (top_candidate != 0) { // successful tagging
/// double top_mass = top_candidate.m();
/// double W_mass = top_candidate.structure_of<JHTopTagger>().W().m();
/// }
/// \endcode
///
/// The full set of information available from the structure_of<JHTopTagger>()
/// call is
///
/// - PseudoJet W() : the W subjet of the top candidate
/// - PseudoJet non_W(): non-W subjet(s) of the top candidate (i.e. the b)
/// - double cos_theta_W(): the W helicity angle
/// - PseudoJet W1(): the harder of the two prongs of the W
/// - PseudoJet W2(): the softer of the two prongs of the W
///
/// The structure of the top_candidate can also be accessed through its
/// pieces() function:
///
/// - top_candidate.pieces()[0]: W
/// - top_candidate.pieces()[1]: non_W
///
/// The W itself has two pieces (corresponding to W1, W2).
///
/// The existence of the first two of the structural calls (W(),
/// non_W()) and the fact that the top is made of two pieces (W,
/// non_W) are features that should be common to all taggers derived
/// from TopTaggerBase.
///
/// See also \subpage Example13 for a full usage example.
///
class JHTopTagger : public TopTaggerBase {
public:
/// default ctor
/// The parameters are the following:
/// \param delta_p fractional pt cut imposed on the subjets
/// (computed as a fraction of the original jet)
/// \param delta_r minimal distance between 2 subjets
/// (computed as |y1-y2|+|phi1-phi2|)
/// \param cos_theta_W_max the maximal value for the polarisation
/// angle of the W
/// \param mW the W mass
///
/// The default values of all these parameters are taken from
/// arXiv:0806:0848
JHTopTagger(const double delta_p=0.10, const double delta_r=0.19,
double cos_theta_W_max=0.7, double mW=80.4)
: _delta_p(delta_p), _delta_r(delta_r),
_cos_theta_W_max(cos_theta_W_max), _mW(mW){};
/// 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, or 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 JHTopTaggerStructure StructureType;
protected:
/// runs the Johns Hopkins decomposition procedure
std::vector<PseudoJet> _split_once(const PseudoJet & jet_to_split,
const PseudoJet & reference_jet) const;
double _delta_p, _delta_r, _cos_theta_W_max, _mW;
static LimitedWarning _warnings_nonca;
};
//------------------------------------------------------------------------
/// @ingroup tools_taggers
/// \class JHTopTaggerStructure
/// the structure returned by the JHTopTagger transformer.
///
/// See the JHTopTagger class description for the details of what
/// is inside this structure
///
class JHTopTaggerStructure : public CompositeJetStructure, public TopTaggerBaseStructure {
public:
/// ctor with pieces initialisation
JHTopTaggerStructure(std::vector<PseudoJet> pieces_in,
const JetDefinition::Recombiner *recombiner = 0) :
CompositeJetStructure(pieces_in, recombiner), _cos_theta_w(0.0){}
/// returns the W subjet
inline const PseudoJet & W() const{
return _pieces[0];
}
/// returns the first W subjet (the harder)
inline PseudoJet W1() const{
assert(W().pieces().size()>0);
return W().pieces()[0];
}
/// returns the second W subjet
inline PseudoJet W2() const{
assert(W().pieces().size()>1);
return W().pieces()[1];
}
/// returns the non-W subjet
/// It will have 1 or 2 pieces depending on whether the tagger has
/// found 3 or 4 pieces
inline const PseudoJet & non_W() const{
return _pieces[1];
}
/// returns the W helicity angle
inline double cos_theta_W() const {return _cos_theta_w;}
// /// returns the original jet (before tagging)
// const PseudoJet & original() const {return _original_jet;}
protected:
double _cos_theta_w; ///< the W helicity angle
//PseudoJet _W; ///< the tagged W
//PseudoJet _non_W; ///< the remaining pieces
// PseudoJet _original_jet; ///< the original jet (before tagging)
// allow the tagger to set these
friend class JHTopTagger;
};
FASTJET_END_NAMESPACE
#endif // __FASTJET_JH_TOP_TAGGER_HH__
fastjet::CompositeJetStructure::_pieces
std::vector< PseudoJet > _pieces
the pieces building the jet
Definition CompositeJetStructure.hh:140
fastjet::CompositeJetStructure::pieces
virtual std::vector< PseudoJet > pieces(const PseudoJet &jet) const override
returns the pieces
Definition CompositeJetStructure.cc:120
fastjet::CompositeJetStructure::CompositeJetStructure
CompositeJetStructure()
default ctor
Definition CompositeJetStructure.hh:54
fastjet::JHTopTaggerStructure
the structure returned by the JHTopTagger transformer.
Definition JHTopTagger.hh:169
fastjet::JHTopTaggerStructure::non_W
const PseudoJet & non_W() const
returns the non-W subjet It will have 1 or 2 pieces depending on whether the tagger has found 3 or 4 ...
Definition JHTopTagger.hh:196
fastjet::JHTopTaggerStructure::W2
PseudoJet W2() const
returns the second W subjet
Definition JHTopTagger.hh:188
fastjet::JHTopTaggerStructure::cos_theta_W
double cos_theta_W() const
returns the W helicity angle
Definition JHTopTagger.hh:201
fastjet::JHTopTaggerStructure::W
const PseudoJet & W() const
returns the W subjet
Definition JHTopTagger.hh:177
fastjet::JHTopTaggerStructure::JHTopTaggerStructure
JHTopTaggerStructure(std::vector< PseudoJet > pieces_in, const JetDefinition::Recombiner *recombiner=0)
ctor with pieces initialisation
Definition JHTopTagger.hh:172
fastjet::JHTopTaggerStructure::_cos_theta_w
double _cos_theta_w
the W helicity angle
Definition JHTopTagger.hh:208
fastjet::JHTopTaggerStructure::W1
PseudoJet W1() const
returns the first W subjet (the harder)
Definition JHTopTagger.hh:182
fastjet::JHTopTagger::JHTopTagger
JHTopTagger(const double delta_p=0.10, const double delta_r=0.19, double cos_theta_W_max=0.7, double mW=80.4)
default ctor The parameters are the following:
Definition JHTopTagger.hh:134
fastjet::JetDefinition::Recombiner
An abstract base class that will provide the recombination scheme facilities and/or allow a user to e...
Definition JetDefinition.hh:491
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::PseudoJet
Class to contain pseudojets, including minimal information of use to jet-clustering routines.
Definition PseudoJet.hh:68
fastjet::TopTaggerBaseStructure
class that specifies the structure common to all top taggers
Definition TopTaggerBase.hh:96