FastJet  3.0.6
MassDropTagger.hh
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28 
29 #ifndef __FASTJET_MASS_DROP_TAGGER_HH__
30 #define __FASTJET_MASS_DROP_TAGGER_HH__
31 
32 #include <fastjet/tools/Transformer.hh>
33 #include <fastjet/LimitedWarning.hh>
34 #include <fastjet/WrappedStructure.hh>
35 
36 FASTJET_BEGIN_NAMESPACE
37 
38 class MassDropTagger;
39 class MassDropTaggerStructure;
40 
41 //----------------------------------------------------------------------
42 /// @ingroup tools_taggers
43 /// \class MassDropTagger
44 /// Class that helps perform 2-pronged boosted tagging using
45 /// the "mass-drop" technique (with asymmetry cut) introduced by Jonathan
46 /// Butterworth, Adam Davison, Mathieu Rubin and Gavin Salam in
47 /// arXiv:0802.2470 in the context of a boosted Higgs search.
48 ///
49 /// The tagger proceeds as follows:
50 ///
51 /// 0. start from a jet obtained from with the Cambridge/Aachen
52 /// algorithm
53 ///
54 /// 1. undo the last step of the clustering step j -> j1 + j2 (label
55 /// them such as j1 is the most massive).
56 ///
57 /// 2. if there is a mass drop, i.e. m_j1/m_j < mu_cut, and the
58 /// splitting is sufficiently symmetric, \f${\rm
59 /// min}(p_{tj1}^2,p_{tj2}^2)\Delta R_{j1,j2}^2 > y_{\rm cut}
60 /// m_j^2\f$, keep j as the result of the tagger (with j1 and j2
61 /// its 2 subjets)
62 ///
63 /// 3. otherwise, redefine j to be equal to j1 and return to step 1.
64 ///
65 /// Note that in the original proposal, j1 and j2 are both required
66 /// to be b-tagged and a filter (with Rfilt=min(0.3,Rbb/2) and
67 /// n_filt=3) is also applied to j to obtain the final "Higgs candidate".
68 /// See the example \subpage Example12 for details.
69 ///
70 /// \section desc Options
71 ///
72 /// The constructor has the following arguments:
73 /// - The first argument is the minimal mass drop that is required (mu_cut) [0.67
74 /// by default]
75 /// - The second argument is the asymmetry cut (y_cut) [0.09 by default]
76 ///
77 /// \section input Input conditions
78 ///
79 /// - one must be able to successively "uncluster" the original jet
80 /// using "has_parents"
81 ///
82 /// \section output Output/structure
83 ///
84 /// - the 2 subjets are kept as pieces if some substructure is found,
85 /// otherwise a single 0-momentum piece is returned
86 /// - the 'mu' and 'y' values corresponding to the unclustering step
87 /// that passed the tagger's cuts
88 ///
89 /// See also \subpage Example12 for a usage example.
90 class MassDropTagger : public Transformer{
91 public:
92  /// default ctor
93  MassDropTagger(const double mu=0.67, const double ycut=0.09) : _mu(mu), _ycut(ycut){};
94 
95  /// returns a textual description of the tagger
96  virtual std::string description() const;
97 
98  /// runs the tagger on the given jet and
99  /// returns the tagged PseudoJet if successful, a PseudoJet==0 otherwise
100  /// (standard access is through operator()).
101  /// \param jet the PseudoJet to tag
102  virtual PseudoJet result(const PseudoJet & jet) const;
103 
104  /// the type of the associated structure
106 
107 protected:
108  double _mu, _ycut;
109  static LimitedWarning _warnings_nonca;
110 };
111 
112 
113 //------------------------------------------------------------------------
114 /// @ingroup tools_taggers
115 /// \class MassDropTaggerStructure
116 /// the structure returned by the MassDropTagger transformer.
117 ///
118 /// See the MassDropTagger class description for the details of what
119 /// is inside this structure
120 ///
122 public:
123  /// ctor with initialisation
124  /// \param pieces the pieces of the created jet
125  /// \param rec the recombiner from the underlying cluster sequence
126  MassDropTaggerStructure(const PseudoJet & result_jet) :
127  WrappedStructure(result_jet.structure_shared_ptr()), _mu(0.0), _y(0.0){}
128 
129  /// returns the mass-drop ratio, pieces[0].m()/jet.m(), for the splitting
130  /// that triggered the mass-drop condition
131  inline double mu() const{return _mu;}
132 
133  /// returns the value of y = (squared kt distance) / (squared mass) for the
134  /// splitting that triggered the mass-drop condition
135  inline double y() const {return _y;}
136 
137 // /// returns the original jet (before tagging)
138 // const PseudoJet & original() const {return _original_jet;}
139 
140 protected:
141  double _mu; ///< the value of the mass-drop parameter
142  double _y; ///< the value of the asymmetry parameter
143 // PseudoJet _original_jet; ///< the original jet (before tagging)
144 
145  // allow the tagger to set these
146  friend class MassDropTagger;
147 };
148 
149 
150 
151 FASTJET_END_NAMESPACE
152 
153 #endif // __FASTJET_MASS_DROP_TAGGER_HH__
154 
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:69
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:65
double _mu
the value of the mass-drop parameter