1 | #ifndef __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
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2 | #define __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
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3 |
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4 | //FJSTARTHEADER
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5 | // $Id: RestFrameNSubjettinessTagger.hh 4442 2020-05-05 07:50:11Z soyez $
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6 | //
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7 | // Copyright (c) 2005-2020, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
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8 | //
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9 | //----------------------------------------------------------------------
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10 | // This file is part of FastJet.
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11 | //
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12 | // FastJet is free software; you can redistribute it and/or modify
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13 | // it under the terms of the GNU General Public License as published by
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14 | // the Free Software Foundation; either version 2 of the License, or
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15 | // (at your option) any later version.
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16 | //
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17 | // The algorithms that underlie FastJet have required considerable
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18 | // development. They are described in the original FastJet paper,
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19 | // hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
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20 | // FastJet as part of work towards a scientific publication, please
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21 | // quote the version you use and include a citation to the manual and
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22 | // optionally also to hep-ph/0512210.
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23 | //
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24 | // FastJet is distributed in the hope that it will be useful,
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25 | // but WITHOUT ANY WARRANTY; without even the implied warranty of
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26 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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27 | // GNU General Public License for more details.
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28 | //
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29 | // You should have received a copy of the GNU General Public License
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30 | // along with FastJet. If not, see <http://www.gnu.org/licenses/>.
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31 | //----------------------------------------------------------------------
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32 | //FJENDHEADER
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33 |
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34 | #include <fastjet/PseudoJet.hh>
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35 | #include <fastjet/JetDefinition.hh>
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36 | #include <fastjet/CompositeJetStructure.hh>
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37 | #include <fastjet/tools/Transformer.hh>
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38 |
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39 | FASTJET_BEGIN_NAMESPACE
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40 |
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41 | class RestFrameNSubjettinessTagger;
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42 | class RestFrameNSubjettinessTaggerStructure;
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43 |
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44 | //----------------------------------------------------------------------
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45 | /// @ingroup tools_taggers
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46 | /// \class RestFrameNSubjettinessTagger
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47 | /// Class that helps perform 2-pronged boosted tagging using
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48 | /// a reclustering in the jet's rest frame, supplemented with a cut on N-subjettiness
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49 | /// (and a decay angle), as discussed by Ji-Hun Kim in arXiv:1011.1493.
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50 | ///
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51 | /// To tag a fat jet, the tagger proceeds as follows:
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52 | ///
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53 | /// - boost its constituents into the rest frame of the jet
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54 | ///
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55 | /// - recluster them using another jet definition (the original
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56 | /// choice was SISCone in spherical coordinates with R=0.6 and
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57 | /// f=0.75.
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58 | ///
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59 | /// - keep the 2 most energetic subjets (\f$q_{1,2}\f$) and compute
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60 | /// the 2-subjettiness
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61 | /// \f[
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62 | /// \tau_2^j = \frac{2}{m_{\rm jet}^2}\,
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63 | /// \sum_{k\in {\rm jet}} {\rm min}(q_1.p_k,q_2.p_k)
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64 | /// \f]
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65 | /// where the sum runs over the constituents of the jet.
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66 | ///
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67 | /// - require \f$\tau_2^j < \tau_2^{\rm cut}\f$ [0.08 by default]
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68 | ///
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69 | /// - impose that (in the rest frame of the fat jet), the angles
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70 | /// between the 2 most energetic subjets and the boost axis are
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71 | /// both large enough: \f$\cos(\theta_s)<c_\theta^{\rm cut}\f$
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72 | /// [0.8 by default]
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73 | ///
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74 | /// Note that in the original version, the jets to be tagged were reconstructed
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75 | /// using SISCone with R=0.8 and f=0.75. Also, b-tagging was imposed
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76 | /// on the 2 subjets found in the rest-frame tagging procedure.
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77 | ///
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78 | /// \section desc Options
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79 | ///
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80 | /// The constructor has the following arguments:
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81 | /// - The first argument is the jet definition to be used to
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82 | /// recluster the constituents of the jet to be filtered (in the
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83 | /// rest frame of the tagged jet).
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84 | /// - The second argument is the cut on tau_2 [0.08 by default]
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85 | /// - The 3rd argument is the cut on cos(theta_s) [0.8 by default]
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86 | /// - If the 4th argument is true, 2 exclusive rest-frame jets will
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87 | /// be considered in place of the 2 most energetic inclusive jets
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88 | ///
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89 | /// \section input Input conditions
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90 | ///
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91 | /// - the original jet must have constituents
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92 | ///
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93 | /// \section output Output/structure
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94 | ///
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95 | /// - the 2 subjets are kept as pieces if some substructure is found,
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96 | /// otherwise a single 0-momentum piece
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97 | /// - the tau2 and maximal cos(theta_s) values computed during the
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98 | /// tagging can be obtained via the resulting jet's structure_of<...>()
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99 | /// function
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100 | ///
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101 | class RestFrameNSubjettinessTagger : public Transformer{
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102 | public:
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103 | /// ctor with arguments (see the class description above)
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104 | RestFrameNSubjettinessTagger(const JetDefinition subjet_def,
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105 | const double tau2cut=0.08,
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106 | const double costhetascut=0.8,
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107 | const bool use_exclusive = false)
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108 | : _subjet_def(subjet_def), _t2cut(tau2cut), _costscut(costhetascut),
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109 | _use_exclusive(use_exclusive){};
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110 |
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111 | /// returns a textual description of the tagger
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112 | virtual std::string description() const;
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113 |
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114 | /// runs the tagger on the given jet and
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115 | /// returns the tagged PseudoJet if successful, a PseudoJet==0 otherwise
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116 | /// (standard access is through operator()).
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117 | virtual PseudoJet result(const PseudoJet & jet) const;
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118 |
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119 | /// the type of Structure returned
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120 | typedef RestFrameNSubjettinessTaggerStructure StructureType;
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121 |
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122 | protected:
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123 | JetDefinition _subjet_def;
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124 | double _t2cut, _costscut;
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125 | bool _use_exclusive;
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126 | };
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127 |
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128 |
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129 | //------------------------------------------------------------------------
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130 | /// @ingroup tools_taggers
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131 | /// \class RestFrameNSubjettinessTaggerStructure
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132 | /// the structure returned by the RestFrameNSubjettinessTagger transformer.
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133 | ///
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134 | /// See the RestFrameNSubjettinessTagger class description for the details of
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135 | /// what is inside this structure
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136 | ///
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137 | class RestFrameNSubjettinessTaggerStructure : public CompositeJetStructure{
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138 | public:
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139 | /// ctor with pieces initialisation
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140 | RestFrameNSubjettinessTaggerStructure(const std::vector<PseudoJet> & pieces_in) :
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141 | CompositeJetStructure(pieces_in), _tau2(0.0), _costhetas(1.0){}
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142 |
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143 | /// returns the associated N-subjettiness
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144 | inline double tau2() const{return _tau2;}
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145 |
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146 | /// returns the associated angle with the boosted axis
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147 | inline double costhetas() const {return _costhetas;}
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148 |
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149 | // /// returns the original jet (before tagging)
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150 | // const PseudoJet & original() const {return _original_jet;}
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151 |
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152 | protected:
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153 | double _tau2; ///< the value of the N-subjettiness
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154 | double _costhetas; ///< the minimal angle between the dijets
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155 | ///< and the boost axis
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156 | // PseudoJet _original_jet; ///< the original jet (before tagging)
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157 |
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158 | // allow the tagger to set these
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159 | friend class RestFrameNSubjettinessTagger;
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160 | };
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161 |
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162 | FASTJET_END_NAMESPACE
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163 | #endif // __FASTJET_RESTFRAMENSUBJETTINESS_TAGGER_HH__
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164 |
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