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 #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
 //  (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
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 //  optionally also to hep-ph/0512210.
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 //  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.
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 //  You should have received a copy of the GNU General Public License
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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__
 

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