1 //FJSTARTHEADER 2 // $Id: MassDropTagger.hh 4442 2020-05-05 07:50:11Z soyez $ 3 // 4 // Copyright (c) 2005-2020, Matteo Cacciari, Gavin P. Salam and Gregory Soyez 5 // 6 //---------------------------------------------------------------------- 7 // This file is part of FastJet. 8 // 9 // FastJet is free software; you can redistribute it and/or modify 10 // it under the terms of the GNU General Public License as published by 11 // the Free Software Foundation; either version 2 of the License, or 12 // (at your option) any later version. 13 // 14 // The algorithms that underlie FastJet have required considerable 15 // development. They are described in the original FastJet paper, 16 // hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use 17 // FastJet as part of work towards a scientific publication, please 18 // quote the version you use and include a citation to the manual and 19 // optionally also to hep-ph/0512210. 20 // 21 // FastJet is distributed in the hope that it will be useful, 22 // but WITHOUT ANY WARRANTY; without even the implied warranty of 23 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 24 // GNU General Public License for more details. 25 // 26 // You should have received a copy of the GNU General Public License 27 // along with FastJet. If not, see <http://www.gnu.org/licenses/>. 28 //---------------------------------------------------------------------- 29 //FJENDHEADER 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 MassDropTagger(const double mu=0.67,const double ycut=0.09)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 107 typedef MassDropTaggerStructure StructureType; 108 109 protected: 110 double _mu, _ycut; 111 static LimitedWarning _warnings_nonca; 112 static LimitedWarning _negative_mass_warning; 113 }; 114 115 116 //------------------------------------------------------------------------ 117 /// @ingroup tools_taggers 118 /// \class MassDropTaggerStructure 119 /// the structure returned by the MassDropTagger transformer. 120 /// 121 /// See the MassDropTagger class description for the details of what 122 /// is inside this structure 123 /// 124 class MassDropTaggerStructure : public WrappedStructure{ 125 public: 126 /// ctor with initialisation 127 /// \param pieces the pieces of the created jet 128 /// \param rec the recombiner from the underlying cluster sequence MassDropTaggerStructure(const PseudoJet & result_jet)129 MassDropTaggerStructure(const PseudoJet & result_jet) : 130 WrappedStructure(result_jet.structure_shared_ptr()), _mu(0.0), _y(0.0){} 131 132 /// returns the mass-drop ratio, pieces[0].m()/jet.m(), for the splitting 133 /// that triggered the mass-drop condition mu() const134 inline double mu() const{return _mu;} 135 136 /// returns the value of y = (squared kt distance) / (squared mass) for the 137 /// splitting that triggered the mass-drop condition y() const138 inline double y() const {return _y;} 139 140 // /// returns the original jet (before tagging) 141 // const PseudoJet & original() const {return _original_jet;} 142 143 protected: 144 double _mu; ///< the value of the mass-drop parameter 145 double _y; ///< the value of the asymmetry parameter 146 // PseudoJet _original_jet; ///< the original jet (before tagging) 147 148 // allow the tagger to set these 149 friend class MassDropTagger; 150 }; 151 152 153 154 FASTJET_END_NAMESPACE 155 156 #endif // __FASTJET_MASS_DROP_TAGGER_HH__ 157 158