1 | //FJSTARTHEADER
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2 | // $Id: MassDropTagger.hh 4354 2018-04-22 07:12:37Z salam $
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3 | //
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4 | // Copyright (c) 2005-2018, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
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5 | //
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6 | //----------------------------------------------------------------------
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7 | // This file is part of FastJet.
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8 | //
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9 | // FastJet is free software; you can redistribute it and/or modify
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10 | // it under the terms of the GNU General Public License as published by
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11 | // the Free Software Foundation; either version 2 of the License, or
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12 | // (at your option) any later version.
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13 | //
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14 | // The algorithms that underlie FastJet have required considerable
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15 | // development. They are described in the original FastJet paper,
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16 | // hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
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17 | // FastJet as part of work towards a scientific publication, please
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18 | // quote the version you use and include a citation to the manual and
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19 | // optionally also to hep-ph/0512210.
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20 | //
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21 | // FastJet is distributed in the hope that it will be useful,
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22 | // but WITHOUT ANY WARRANTY; without even the implied warranty of
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23 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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24 | // GNU General Public License for more details.
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25 | //
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26 | // You should have received a copy of the GNU General Public License
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27 | // along with FastJet. If not, see <http://www.gnu.org/licenses/>.
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28 | //----------------------------------------------------------------------
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29 | //FJENDHEADER
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30 |
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31 | #ifndef __FASTJET_MASS_DROP_TAGGER_HH__
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32 | #define __FASTJET_MASS_DROP_TAGGER_HH__
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33 |
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34 | #include <fastjet/tools/Transformer.hh>
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35 | #include <fastjet/LimitedWarning.hh>
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36 | #include <fastjet/WrappedStructure.hh>
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37 |
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38 | FASTJET_BEGIN_NAMESPACE
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39 |
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40 | class MassDropTagger;
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41 | class MassDropTaggerStructure;
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42 |
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43 | //----------------------------------------------------------------------
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44 | /// @ingroup tools_taggers
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45 | /// \class MassDropTagger
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46 | /// Class that helps perform 2-pronged boosted tagging using
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47 | /// the "mass-drop" technique (with asymmetry cut) introduced by Jonathan
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48 | /// Butterworth, Adam Davison, Mathieu Rubin and Gavin Salam in
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49 | /// arXiv:0802.2470 in the context of a boosted Higgs search.
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50 | ///
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51 | /// The tagger proceeds as follows:
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52 | ///
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53 | /// 0. start from a jet obtained from with the Cambridge/Aachen
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54 | /// algorithm
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55 | ///
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56 | /// 1. undo the last step of the clustering step j -> j1 + j2 (label
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57 | /// them such as j1 is the most massive).
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58 | ///
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59 | /// 2. if there is a mass drop, i.e. m_j1/m_j < mu_cut, and the
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60 | /// splitting is sufficiently symmetric, \f${\rm
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61 | /// min}(p_{tj1}^2,p_{tj2}^2)\Delta R_{j1,j2}^2 > y_{\rm cut}
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62 | /// m_j^2\f$, keep j as the result of the tagger (with j1 and j2
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63 | /// its 2 subjets)
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64 | ///
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65 | /// 3. otherwise, redefine j to be equal to j1 and return to step 1.
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66 | ///
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67 | /// Note that in the original proposal, j1 and j2 are both required
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68 | /// to be b-tagged and a filter (with Rfilt=min(0.3,Rbb/2) and
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69 | /// n_filt=3) is also applied to j to obtain the final "Higgs candidate".
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70 | /// See the example \subpage Example12 for details.
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71 | ///
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72 | /// \section desc Options
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73 | ///
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74 | /// The constructor has the following arguments:
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75 | /// - The first argument is the minimal mass drop that is required (mu_cut) [0.67
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76 | /// by default]
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77 | /// - The second argument is the asymmetry cut (y_cut) [0.09 by default]
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78 | ///
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79 | /// \section input Input conditions
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80 | ///
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81 | /// - one must be able to successively "uncluster" the original jet
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82 | /// using "has_parents"
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83 | ///
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84 | /// \section output Output/structure
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85 | ///
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86 | /// - the 2 subjets are kept as pieces if some substructure is found,
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87 | /// otherwise a single 0-momentum piece is returned
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88 | /// - the 'mu' and 'y' values corresponding to the unclustering step
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89 | /// that passed the tagger's cuts
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90 | ///
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91 | /// See also \subpage Example12 for a usage example.
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92 | class MassDropTagger : public Transformer{
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93 | public:
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94 | /// default ctor
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95 | MassDropTagger(const double mu=0.67, const double ycut=0.09) : _mu(mu), _ycut(ycut){};
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96 |
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97 | /// returns a textual description of the tagger
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98 | virtual std::string description() const;
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99 |
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100 | /// runs the tagger on the given jet and
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101 | /// returns the tagged PseudoJet if successful, a PseudoJet==0 otherwise
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102 | /// (standard access is through operator()).
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103 | /// \param jet the PseudoJet to tag
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104 | virtual PseudoJet result(const PseudoJet & jet) const;
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105 |
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106 | /// the type of the associated structure
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107 | typedef MassDropTaggerStructure StructureType;
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108 |
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109 | protected:
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110 | double _mu, _ycut;
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111 | static LimitedWarning _warnings_nonca;
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112 | static LimitedWarning _negative_mass_warning;
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113 | };
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114 |
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115 |
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116 | //------------------------------------------------------------------------
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117 | /// @ingroup tools_taggers
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118 | /// \class MassDropTaggerStructure
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119 | /// the structure returned by the MassDropTagger transformer.
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120 | ///
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121 | /// See the MassDropTagger class description for the details of what
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122 | /// is inside this structure
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123 | ///
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124 | class MassDropTaggerStructure : public WrappedStructure{
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125 | public:
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126 | /// ctor with initialisation
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127 | /// \param pieces the pieces of the created jet
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128 | /// \param rec the recombiner from the underlying cluster sequence
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129 | MassDropTaggerStructure(const PseudoJet & result_jet) :
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130 | WrappedStructure(result_jet.structure_shared_ptr()), _mu(0.0), _y(0.0){}
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131 |
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132 | /// returns the mass-drop ratio, pieces[0].m()/jet.m(), for the splitting
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133 | /// that triggered the mass-drop condition
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134 | inline double mu() const{return _mu;}
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135 |
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136 | /// returns the value of y = (squared kt distance) / (squared mass) for the
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137 | /// splitting that triggered the mass-drop condition
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138 | inline double y() const {return _y;}
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139 |
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140 | // /// returns the original jet (before tagging)
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141 | // const PseudoJet & original() const {return _original_jet;}
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142 |
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143 | protected:
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144 | double _mu; ///< the value of the mass-drop parameter
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145 | double _y; ///< the value of the asymmetry parameter
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146 | // PseudoJet _original_jet; ///< the original jet (before tagging)
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147 |
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148 | // allow the tagger to set these
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149 | friend class MassDropTagger;
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150 | };
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151 |
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152 |
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153 |
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154 | FASTJET_END_NAMESPACE
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155 |
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156 | #endif // __FASTJET_MASS_DROP_TAGGER_HH__
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157 |
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