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RestFrameNSubjettinessTagger.hh
1 #ifndef __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
2 #define __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
3 
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5 // $Id: RestFrameNSubjettinessTagger.hh 3433 2014-07-23 08:17:03Z salam $
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33 
34 #include <fastjet/PseudoJet.hh>
35 #include <fastjet/JetDefinition.hh>
36 #include <fastjet/CompositeJetStructure.hh>
37 #include <fastjet/tools/Transformer.hh>
38 
39 FASTJET_BEGIN_NAMESPACE
40 
41 class RestFrameNSubjettinessTagger;
42 class RestFrameNSubjettinessTaggerStructure;
43 
44 //----------------------------------------------------------------------
45 /// @ingroup tools_taggers
46 /// \class RestFrameNSubjettinessTagger
47 /// Class that helps perform 2-pronged boosted tagging using
48 /// a reclustering in the jet's rest frame, supplemented with a cut on N-subjettiness
49 /// (and a decay angle), as discussed by Ji-Hun Kim in arXiv:1011.1493.
50 ///
51 /// To tag a fat jet, the tagger proceeds as follows:
52 ///
53 /// - boost its constituents into the rest frame of the jet
54 ///
55 /// - recluster them using another jet definition (the original
56 /// choice was SISCone in spherical coordinates with R=0.6 and
57 /// f=0.75.
58 ///
59 /// - keep the 2 most energetic subjets (\f$q_{1,2}\f$) and compute
60 /// the 2-subjettiness
61 /// \f[
62 /// \tau_2^j = \frac{2}{m_{\rm jet}^2}\,
63 /// \sum_{k\in {\rm jet}} {\rm min}(q_1.p_k,q_2.p_k)
64 /// \f]
65 /// where the sum runs over the constituents of the jet.
66 ///
67 /// - require \f$\tau_2^j < \tau_2^{\rm cut}\f$ [0.08 by default]
68 ///
69 /// - impose that (in the rest frame of the fat jet), the angles
70 /// between the 2 most energetic subjets and the boost axis are
71 /// both large enough: \f$\cos(\theta_s)<c_\theta^{\rm cut}\f$
72 /// [0.8 by default]
73 ///
74 /// Note that in the original version, the jets to be tagged were reconstructed
75 /// using SISCone with R=0.8 and f=0.75. Also, b-tagging was imposed
76 /// on the 2 subjets found in the rest-frame tagging procedure.
77 ///
78 /// \section desc Options
79 ///
80 /// The constructor has the following arguments:
81 /// - The first argument is the jet definition to be used to
82 /// recluster the constituents of the jet to be filtered (in the
83 /// rest frame of the tagged jet).
84 /// - The second argument is the cut on tau_2 [0.08 by default]
85 /// - The 3rd argument is the cut on cos(theta_s) [0.8 by default]
86 /// - If the 4th argument is true, 2 exclusive rest-frame jets will
87 /// be considered in place of the 2 most energetic inclusive jets
88 ///
89 /// \section input Input conditions
90 ///
91 /// - the original jet must have constituents
92 ///
93 /// \section output Output/structure
94 ///
95 /// - the 2 subjets are kept as pieces if some substructure is found,
96 /// otherwise a single 0-momentum piece
97 /// - the tau2 and maximal cos(theta_s) values computed during the
98 /// tagging can be obtained via the resulting jet's structure_of<...>()
99 /// function
100 ///
102 public:
103  /// ctor with arguments (see the class description above)
105  const double tau2cut=0.08,
106  const double costhetascut=0.8,
107  const bool use_exclusive = false)
108  : _subjet_def(subjet_def), _t2cut(tau2cut), _costscut(costhetascut),
109  _use_exclusive(use_exclusive){};
110 
111  /// returns a textual description of the tagger
112  virtual std::string description() const;
113 
114  /// runs the tagger on the given jet and
115  /// returns the tagged PseudoJet if successful, a PseudoJet==0 otherwise
116  /// (standard access is through operator()).
117  virtual PseudoJet result(const PseudoJet & jet) const;
118 
119  /// the type of Structure returned
121 
122 protected:
123  JetDefinition _subjet_def;
124  double _t2cut, _costscut;
125  bool _use_exclusive;
126 };
127 
128 
129 //------------------------------------------------------------------------
130 /// @ingroup tools_taggers
131 /// \class RestFrameNSubjettinessTaggerStructure
132 /// the structure returned by the RestFrameNSubjettinessTagger transformer.
133 ///
134 /// See the RestFrameNSubjettinessTagger class description for the details of
135 /// what is inside this structure
136 ///
138 public:
139  /// ctor with pieces initialisation
140  RestFrameNSubjettinessTaggerStructure(const std::vector<PseudoJet> & pieces_in) :
141  CompositeJetStructure(pieces_in), _tau2(0.0), _costhetas(1.0){}
142 
143  /// returns the associated N-subjettiness
144  inline double tau2() const{return _tau2;}
145 
146  /// returns the associated angle with the boosted axis
147  inline double costhetas() const {return _costhetas;}
148 
149 // /// returns the original jet (before tagging)
150 // const PseudoJet & original() const {return _original_jet;}
151 
152 protected:
153  double _tau2; ///< the value of the N-subjettiness
154  double _costhetas; ///< the minimal angle between the dijets
155  ///< and the boost axis
156 // PseudoJet _original_jet; ///< the original jet (before tagging)
157 
158  // allow the tagger to set these
159  friend class RestFrameNSubjettinessTagger;
160 };
161 
162 FASTJET_END_NAMESPACE
163 #endif // __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
164 
Class that helps perform 2-pronged boosted tagging using a reclustering in the jet's rest frame...
RestFrameNSubjettinessTaggerStructure(const std::vector< PseudoJet > &pieces_in)
ctor with pieces initialisation
the structure returned by the RestFrameNSubjettinessTagger transformer.
RestFrameNSubjettinessTaggerStructure StructureType
the type of Structure returned
Base (abstract) class for a jet transformer.
Definition: Transformer.hh:71
The structure for a jet made of pieces.
double tau2() const
returns the associated N-subjettiness
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)
Class to contain pseudojets, including minimal information of use to jet-clustering routines...
Definition: PseudoJet.hh:67
class that is intended to hold a full definition of the jet clusterer
double costhetas() const
returns the associated angle with the boosted axis
double _costhetas
the minimal angle between the dijets and the boost axis