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MassDropTagger.hh
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30 
31 #ifndef __FASTJET_MASS_DROP_TAGGER_HH__
32 #define __FASTJET_MASS_DROP_TAGGER_HH__
33 
34 #include <fastjet/tools/Transformer.hh>
35 #include <fastjet/LimitedWarning.hh>
36 #include <fastjet/WrappedStructure.hh>
37 
38 FASTJET_BEGIN_NAMESPACE
39 
40 class MassDropTagger;
41 class MassDropTaggerStructure;
42 
43 //----------------------------------------------------------------------
44 /// @ingroup tools_taggers
45 /// \class MassDropTagger
46 /// Class that helps perform 2-pronged boosted tagging using
47 /// the "mass-drop" technique (with asymmetry cut) introduced by Jonathan
48 /// Butterworth, Adam Davison, Mathieu Rubin and Gavin Salam in
49 /// arXiv:0802.2470 in the context of a boosted Higgs search.
50 ///
51 /// The tagger proceeds as follows:
52 ///
53 /// 0. start from a jet obtained from with the Cambridge/Aachen
54 /// algorithm
55 ///
56 /// 1. undo the last step of the clustering step j -> j1 + j2 (label
57 /// them such as j1 is the most massive).
58 ///
59 /// 2. if there is a mass drop, i.e. m_j1/m_j < mu_cut, and the
60 /// splitting is sufficiently symmetric, \f${\rm
61 /// min}(p_{tj1}^2,p_{tj2}^2)\Delta R_{j1,j2}^2 > y_{\rm cut}
62 /// m_j^2\f$, keep j as the result of the tagger (with j1 and j2
63 /// its 2 subjets)
64 ///
65 /// 3. otherwise, redefine j to be equal to j1 and return to step 1.
66 ///
67 /// Note that in the original proposal, j1 and j2 are both required
68 /// to be b-tagged and a filter (with Rfilt=min(0.3,Rbb/2) and
69 /// n_filt=3) is also applied to j to obtain the final "Higgs candidate".
70 /// See the example \subpage Example12 for details.
71 ///
72 /// \section desc Options
73 ///
74 /// The constructor has the following arguments:
75 /// - The first argument is the minimal mass drop that is required (mu_cut) [0.67
76 /// by default]
77 /// - The second argument is the asymmetry cut (y_cut) [0.09 by default]
78 ///
79 /// \section input Input conditions
80 ///
81 /// - one must be able to successively "uncluster" the original jet
82 /// using "has_parents"
83 ///
84 /// \section output Output/structure
85 ///
86 /// - the 2 subjets are kept as pieces if some substructure is found,
87 /// otherwise a single 0-momentum piece is returned
88 /// - the 'mu' and 'y' values corresponding to the unclustering step
89 /// that passed the tagger's cuts
90 ///
91 /// See also \subpage Example12 for a usage example.
92 class MassDropTagger : public Transformer{
93 public:
94  /// default ctor
95  MassDropTagger(const double mu=0.67, const double ycut=0.09) : _mu(mu), _ycut(ycut){};
96 
97  /// returns a textual description of the tagger
98  virtual std::string description() const;
99 
100  /// runs the tagger on the given jet and
101  /// returns the tagged PseudoJet if successful, a PseudoJet==0 otherwise
102  /// (standard access is through operator()).
103  /// \param jet the PseudoJet to tag
104  virtual PseudoJet result(const PseudoJet & jet) const;
105 
106  /// the type of the associated structure
108 
109 protected:
110  double _mu, _ycut;
111  static LimitedWarning _warnings_nonca;
112 };
113 
114 
115 //------------------------------------------------------------------------
116 /// @ingroup tools_taggers
117 /// \class MassDropTaggerStructure
118 /// the structure returned by the MassDropTagger transformer.
119 ///
120 /// See the MassDropTagger class description for the details of what
121 /// is inside this structure
122 ///
124 public:
125  /// ctor with initialisation
126  /// \param pieces the pieces of the created jet
127  /// \param rec the recombiner from the underlying cluster sequence
128  MassDropTaggerStructure(const PseudoJet & result_jet) :
129  WrappedStructure(result_jet.structure_shared_ptr()), _mu(0.0), _y(0.0){}
130 
131  /// returns the mass-drop ratio, pieces[0].m()/jet.m(), for the splitting
132  /// that triggered the mass-drop condition
133  inline double mu() const{return _mu;}
134 
135  /// returns the value of y = (squared kt distance) / (squared mass) for the
136  /// splitting that triggered the mass-drop condition
137  inline double y() const {return _y;}
138 
139 // /// returns the original jet (before tagging)
140 // const PseudoJet & original() const {return _original_jet;}
141 
142 protected:
143  double _mu; ///< the value of the mass-drop parameter
144  double _y; ///< the value of the asymmetry parameter
145 // PseudoJet _original_jet; ///< the original jet (before tagging)
146 
147  // allow the tagger to set these
148  friend class MassDropTagger;
149 };
150 
151 
152 
153 FASTJET_END_NAMESPACE
154 
155 #endif // __FASTJET_MASS_DROP_TAGGER_HH__
156 
double mu() const
returns the mass-drop ratio, pieces[0].m()/jet.m(), for the splitting that triggered the mass-drop co...
double y() const
returns the value of y = (squared kt distance) / (squared mass) for the splitting that triggered the ...
MassDropTagger(const double mu=0.67, const double ycut=0.09)
default ctor
MassDropTaggerStructure StructureType
the type of the associated structure
This wraps a (shared) pointer to an underlying structure.
Base (abstract) class for a jet transformer.
Definition: Transformer.hh:71
the structure returned by the MassDropTagger transformer.
class to provide facilities for giving warnings up to some maximum number of times and to provide glo...
Class that helps perform 2-pronged boosted tagging using the "mass-drop" technique (with asymmetry cu...
double _y
the value of the asymmetry parameter
MassDropTaggerStructure(const PseudoJet &result_jet)
ctor with initialisation
Class to contain pseudojets, including minimal information of use to jet-clustering routines...
Definition: PseudoJet.hh:67
double _mu
the value of the mass-drop parameter