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CASubJetTagger.hh
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30 
31 #ifndef __CASUBJET_TAGGER_HH__
32 #define __CASUBJET_TAGGER_HH__
33 
34 #include <fastjet/PseudoJet.hh>
35 #include <fastjet/WrappedStructure.hh>
36 #include <fastjet/tools/Transformer.hh>
37 #include "fastjet/LimitedWarning.hh"
38 
39 FASTJET_BEGIN_NAMESPACE
40 
41 class CASubJetTagger;
42 class CASubJetTaggerStructure;
43 
44 //----------------------------------------------------------------------
45 /// @ingroup tools_taggers
46 /// \class CASubJetTagger
47 /// clean (almost parameter-free) tagger searching for the element in
48 /// the clustering history that maximises a chosen distance
49 ///
50 /// class to help us get a clean (almost parameter-free) handle on
51 /// substructure inside a C/A jet. It follows the logic described in
52 /// arXiv:0906.0728 (and is inspired by the original Cambridge
53 /// algorithm paper in its use of separate angular and dimensionful
54 /// distances), but provides some extra flexibility.
55 ///
56 /// It searches for all splittings that pass a symmetry cut (zcut) and
57 /// then selects the one with the largest auxiliary scale choice
58 /// (e.g. jade distance of the splitting, kt distance of the
59 /// splitting, etc.)
60 ///
61 /// By default, the zcut is calculated from the fraction of the child
62 /// pt carried by the parent jet. If one calls set_absolute_z_cut the
63 /// fraction of transverse momentum will be computed wrt the original
64 /// jet.
65 ///
66 /// original code copyright (C) 2009 by Gavin Salam, released under
67 /// the GPL.
68 ///
69 /// \section desc Options
70 ///
71 /// - the distance choice: options are
72 /// kt2_distance : usual min(kti^2,ktj^2)DeltaR_{ij}^2
73 /// jade_distance : kti . ktj DeltaR_{ij}^2 (LI version of jade)
74 /// jade2_distance : kti . ktj DeltaR_{ij}^4 (LI version of jade * DR^2)
75 /// plain_distance : DeltaR_{ij}^2
76 /// mass_drop_distance : m_jet - max(m_parent1,m_parent2)
77 /// dot_product_distance: parent1.parent2
78 /// (kt2_distance by default)
79 ///
80 /// - the z cut (0 by default)
81 ///
82 /// - by calling set_absolute_z_cut(), one can ask that the pt
83 /// fraction if calculated wrt the original jet
84 ///
85 /// - by calling set_dr_min(drmin), one can ask that only the
86 /// recombinations where the 2 objects are (geometrically) distant
87 /// by at least drmin are kept in the maximisation.
88 ///
89 /// \section input Input conditions
90 ///
91 /// - the jet must have been obtained from a Cambridge/Aachen cluster
92 /// sequence
93 ///
94 /// \section output Output/structure
95 ///
96 /// - the element of the cluster sequence maximising the requested
97 /// distance (and satisfying the zcut) is returned.
98 ///
99 /// - if the original jet has no parents, it will be returned
100 ///
101 /// - the value of the "z" and distance corresponding to that history
102 /// element are stored and accessible through
103 /// result.structure_of<CASubJetTagger>().z();
104 /// result.structure_of<CASubJetTagger>().distance();
105 ///
106 class CASubJetTagger : public Transformer {
107 public:
108 
109  /// the available choices of auxiliary scale with respect to which
110  /// to order the splittings
111  enum ScaleChoice {
112  kt2_distance, //< usual min(kti^2,ktj^2)DeltaR_{ij}^2
113  jade_distance, //< kti . ktj DeltaR_{ij}^2 (LI version of jade)
114  jade2_distance, //< kti . ktj DeltaR_{ij}^4 (LI version of jade * DR^2)
115  plain_distance, //< DeltaR_{ij}^2
116  mass_drop_distance, //< m_jet - max(m_parent1,m_parent2)
117  dot_product_distance //< parent1.parent2
118  };
119 
120  /// just constructs
121  CASubJetTagger(ScaleChoice scale_choice = jade_distance,
122  double z_threshold = 0.1)
123  : _scale_choice(scale_choice), _z_threshold(z_threshold),
124  _dr2_min(0.0), _absolute_z_cut(false){};
125 
126  /// sets a minimum delta R below which spliting will be ignored
127  /// (only relevant if set prior to calling run())
128  void set_dr_min(double drmin) {_dr2_min = drmin*drmin;}
129 
130  /// returns a textual description of the tagger
131  virtual std::string description() const;
132 
133  /// If (abs_z_cut) is set to false (the default) then for a
134  /// splitting to be considered, each subjet must satisfy
135  ///
136  /// p_{t,sub} > z_threshold * p_{t,parent}
137  ///
138  /// whereas if it is set to true, then each subject must satisfy
139  ///
140  /// p_{t,sub} > z_threshold * p_{t,original-jet}
141  ///
142  /// where parent is the immediate parent of the splitting, and
143  /// original jet is the one supplied to the run() function.
144  ///
145  /// Only relevant is called prior to run().
146  void set_absolute_z_cut(bool abs_z_cut=true) {_absolute_z_cut = abs_z_cut;}
147 
148  /// runs the tagger on the given jet and
149  /// returns the tagged PseudoJet if successful, or a PseudoJet==0 otherwise
150  /// (standard access is through operator()).
151  virtual PseudoJet result(const PseudoJet & jet) const;
152 
153  /// the type of Structure returned
155 
156 protected:
157  /// class that contains the result internally
158  class JetAux {
159  public:
160  PseudoJet jet; //< the subjet (immediate parent of splitting)
161  double aux_distance; //< the auxiliary distance between its two subjets
162  double delta_r; //< the angular distance between its two subjets
163  double z; //< the transverse momentum fraction
164  };
165 
166 
167  void _recurse_through_jet(const PseudoJet & current_jet,
168  JetAux &aux_max,
169  const PseudoJet & original_jet) const;
170 
171  ScaleChoice _scale_choice;
172  double _z_threshold;
173  double _dr2_min;
174  bool _absolute_z_cut;
175 
176  static LimitedWarning _non_ca_warnings;
177 };
178 
179 
180 //------------------------------------------------------------------------
181 /// @ingroup tools_taggers
182 /// the structure returned by a CASubJetTagger
183 ///
184 /// Since this is directly an element of the ClusterSequence, we keep
185 /// basically the original ClusterSequenceStructure (wrapped for
186 /// memory-management reasons) and add information about the pt
187 /// fraction and distance of the subjet structure
189 public:
190  /// default ctor
191  /// \param result_jet the jet for which we have to keep the
192  /// structure
193  CASubJetTaggerStructure(const PseudoJet & result_jet)
194  : WrappedStructure(result_jet.structure_shared_ptr()){}
195 
196  /// returns the scale choice asked for the maximisation
197  CASubJetTagger::ScaleChoice scale_choice() const {return _scale_choice;}
198 
199  /// returns the value of the distance measure (corresponding to
200  /// ScaleChoice) for this jet's splitting
201  double distance() const {return _distance;}
202 
203  /// returns the pt fraction contained by the softer of the two component
204  /// pieces of this jet (normalised relative to this jet)
205  double z() const {return _z;}
206 
207  /// returns the pt fraction contained by the softer of the two component
208  /// pieces of this jet (normalised relative to the original jet)
209  bool absolute_z() const {return _absolute_z;}
210 
211 // /// returns the original jet (before tagging)
212 // const PseudoJet & original() const {return _original_jet;}
213 
214 protected:
215  CASubJetTagger::ScaleChoice _scale_choice; ///< the user scale choice
216  double _distance; ///< the maximal distance associated with the result
217  bool _absolute_z; ///< whether z is computed wrt to the original jet or not
218  double _z; ///< the transverse momentum fraction
219 // PseudoJet _original_jet; ///< the original jet (before tagging)
220 
221  friend class CASubJetTagger; ///< to allow setting the internal information
222 };
223 
224 FASTJET_END_NAMESPACE
225 
226 #endif // __CASUBJET_HH__
void set_absolute_z_cut(bool abs_z_cut=true)
If (abs_z_cut) is set to false (the default) then for a splitting to be considered, each subjet must satisfy.
double _z
the transverse momentum fraction
CASubJetTagger::ScaleChoice scale_choice() const
returns the scale choice asked for the maximisation
the structure returned by a CASubJetTagger
This wraps a (shared) pointer to an underlying structure.
Base (abstract) class for a jet transformer.
Definition: Transformer.hh:71
CASubJetTagger(ScaleChoice scale_choice=jade_distance, double z_threshold=0.1)
just constructs
class that contains the result internally
clean (almost parameter-free) tagger searching for the element in the clustering history that maximis...
class to provide facilities for giving warnings up to some maximum number of times and to provide glo...
ScaleChoice
the available choices of auxiliary scale with respect to which to order the splittings ...
double distance() const
returns the value of the distance measure (corresponding to ScaleChoice) for this jet's splitting ...
void set_dr_min(double drmin)
sets a minimum delta R below which spliting will be ignored (only relevant if set prior to calling ru...
CASubJetTaggerStructure(const PseudoJet &result_jet)
default ctor
bool absolute_z() const
returns the pt fraction contained by the softer of the two component pieces of this jet (normalised r...
double z() const
returns the pt fraction contained by the softer of the two component pieces of this jet (normalised r...
Class to contain pseudojets, including minimal information of use to jet-clustering routines...
Definition: PseudoJet.hh:67
bool _absolute_z
whether z is computed wrt to the original jet or not
CASubJetTaggerStructure StructureType
the type of Structure returned
CASubJetTagger::ScaleChoice _scale_choice
the user scale choice
double _distance
the maximal distance associated with the result