1 | #ifndef __FASTJET_JH_TOP_TAGGER_HH__
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2 | #define __FASTJET_JH_TOP_TAGGER_HH__
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3 |
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4 | //FJSTARTHEADER
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5 | // $Id: JHTopTagger.hh 3433 2014-07-23 08:17:03Z salam $
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6 | //
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7 | // Copyright (c) 2005-2014, 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 |
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35 | #include <fastjet/tools/TopTaggerBase.hh>
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36 | #include <fastjet/CompositeJetStructure.hh>
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37 | #include <fastjet/LimitedWarning.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 JHTopTagger;
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42 | class JHTopTaggerStructure;
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43 |
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44 | //----------------------------------------------------------------------
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45 | /// @ingroup tools_taggers
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46 | /// \class JHTopTagger
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47 | /// Class that helps perform boosted top tagging using the "Johns Hopkins"
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48 | /// method from arXiv:0806.0848 (Kaplan, Rehermann, Schwartz
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49 | /// and Tweedie)
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50 | ///
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51 | ///The tagger proceeds as follows:
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52 | /// - start from a jet J obtained with the Cambridge/Aachen algorithm
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53 | /// - undo the last iteration j -> j_1,j_2 (with pt_1>pt_2) until the
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54 | /// two subjets satisfy pt_1 > delta_p pt_J (with pt_J the pt of
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55 | /// the original jet) and |y_1 - y_2| + |phi_1 - phi_2| > delta_r.
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56 | /// - if one of these criteria is not satisfied, carry on the
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57 | /// procedure with j_1 (discarding j_2)
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58 | /// - for each of the subjets found, repeat the procedure. If some
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59 | /// new substructure is found, keep these 2 new subjets, otherwise
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60 | /// keep the original subjet (found during the first iteration)
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61 | /// - at this stage, one has at most 4 subjets. If one has less than
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62 | /// 3, the tagger has failed.
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63 | /// - reconstruct the W from the 2 subjets with a mass closest to the
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64 | /// W mass
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65 | /// - impose that the W helicity angle be less than a threshold
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66 | /// cos_theta_W_max.
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67 | ///
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68 | /// \section input Input conditions
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69 | ///
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70 | /// - the original jet must have an associated (and valid)
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71 | /// ClusterSequence
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72 | /// - the tagger is designed to work with jets formed by the
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73 | /// Cambridge/Aachen (C/A) algorithm; if a non-C/A jet is passed to
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74 | /// the tagger, a warning will be issued
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75 | ///
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76 | /// \section Example
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77 | ///
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78 | /// A JHTopTagger can be used as follows:
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79 | ///
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80 | /// \code
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81 | /// double delta_p = 0.10; // subjets must carry at least this fraction of the original jet's p_t
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82 | /// double delta_r = 0.19; // subjets must be separated by at least this Manhattan distance
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83 | /// double cos_theta_W_max = 0.7; // the maximal allowed value of the W helicity angle
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84 | /// JHTopTagger top_tagger(delta_p, delta_r, cos_theta_W_max);
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85 | /// // indicate the acceptable range of top, W masses (default: no limits)
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86 | /// top_tagger.set_top_selector(SelectorMassRange(150,200));
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87 | /// top_tagger.set_W_selector (SelectorMassRange( 65, 95));
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88 | /// // now try and tag a jet
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89 | /// PseudoJet top_candidate = top_tagger(jet); // jet should come from a Cambridge/Aachen clustering
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90 | /// if (top_candidate != 0) { // successful tagging
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91 | /// double top_mass = top_candidate.m();
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92 | /// double W_mass = top_candidate.structure_of<JHTopTagger>().W().m();
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93 | /// }
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94 | /// \endcode
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95 | ///
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96 | /// The full set of information available from the structure_of<JHTopTagger>()
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97 | /// call is
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98 | ///
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99 | /// - PseudoJet W() : the W subjet of the top candidate
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100 | /// - PseudoJet non_W(): non-W subjet(s) of the top candidate (i.e. the b)
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101 | /// - double cos_theta_W(): the W helicity angle
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102 | /// - PseudoJet W1(): the harder of the two prongs of the W
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103 | /// - PseudoJet W2(): the softer of the two prongs of the W
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104 | ///
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105 | /// The structure of the top_candidate can also be accessed through its
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106 | /// pieces() function:
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107 | ///
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108 | /// - top_candidate.pieces()[0]: W
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109 | /// - top_candidate.pieces()[1]: non_W
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110 | ///
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111 | /// The W itself has two pieces (corresponding to W1, W2).
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112 | ///
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113 | /// The existence of the first two of the structural calls (W(),
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114 | /// non_W()) and the fact that the top is made of two pieces (W,
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115 | /// non_W) are features that should be common to all taggers derived
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116 | /// from TopTaggerBase.
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117 | ///
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118 | /// See also \subpage Example13 for a full usage example.
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119 | ///
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120 | class JHTopTagger : public TopTaggerBase {
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121 | public:
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122 | /// default ctor
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123 | /// The parameters are the following:
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124 | /// \param delta_p fractional pt cut imposed on the subjets
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125 | /// (computed as a fraction of the original jet)
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126 | /// \param delta_r minimal distance between 2 subjets
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127 | /// (computed as |y1-y2|+|phi1-phi2|)
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128 | /// \param cos_theta_W_max the maximal value for the polarisation
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129 | /// angle of the W
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130 | /// \param mW the W mass
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131 | ///
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132 | /// The default values of all these parameters are taken from
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133 | /// arXiv:0806:0848
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134 | JHTopTagger(const double delta_p=0.10, const double delta_r=0.19,
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135 | double cos_theta_W_max=0.7, double mW=80.4)
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136 | : _delta_p(delta_p), _delta_r(delta_r),
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137 | _cos_theta_W_max(cos_theta_W_max), _mW(mW){};
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138 |
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139 | /// returns a textual description of the tagger
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140 | virtual std::string description() const;
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141 |
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142 | /// runs the tagger on the given jet and
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143 | /// returns the tagged PseudoJet if successful, or a PseudoJet==0 otherwise
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144 | /// (standard access is through operator()).
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145 | /// \param jet the PseudoJet to tag
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146 | virtual PseudoJet result(const PseudoJet & jet) const;
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147 |
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148 | // the type of the associated structure
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149 | typedef JHTopTaggerStructure StructureType;
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150 |
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151 | protected:
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152 | /// runs the Johns Hopkins decomposition procedure
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153 | std::vector<PseudoJet> _split_once(const PseudoJet & jet_to_split,
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154 | const PseudoJet & reference_jet) const;
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155 |
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156 | double _delta_p, _delta_r, _cos_theta_W_max, _mW;
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157 | static LimitedWarning _warnings_nonca;
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158 | };
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159 |
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160 |
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161 | //------------------------------------------------------------------------
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162 | /// @ingroup tools_taggers
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163 | /// \class JHTopTaggerStructure
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164 | /// the structure returned by the JHTopTagger transformer.
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165 | ///
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166 | /// See the JHTopTagger class description for the details of what
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167 | /// is inside this structure
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168 | ///
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169 | class JHTopTaggerStructure : public CompositeJetStructure, public TopTaggerBaseStructure {
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170 | public:
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171 | /// ctor with pieces initialisation
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172 | JHTopTaggerStructure(std::vector<PseudoJet> pieces_in,
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173 | const JetDefinition::Recombiner *recombiner = 0) :
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174 | CompositeJetStructure(pieces_in, recombiner), _cos_theta_w(0.0){}
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175 |
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176 | /// returns the W subjet
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177 | inline const PseudoJet & W() const{
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178 | return _pieces[0];
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179 | }
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180 |
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181 | /// returns the first W subjet (the harder)
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182 | inline PseudoJet W1() const{
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183 | assert(W().pieces().size()>0);
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184 | return W().pieces()[0];
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185 | }
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186 |
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187 | /// returns the second W subjet
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188 | inline PseudoJet W2() const{
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189 | assert(W().pieces().size()>1);
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190 | return W().pieces()[1];
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191 | }
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192 |
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193 | /// returns the non-W subjet
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194 | /// It will have 1 or 2 pieces depending on whether the tagger has
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195 | /// found 3 or 4 pieces
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196 | inline const PseudoJet & non_W() const{
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197 | return _pieces[1];
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198 | }
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199 |
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200 | /// returns the W helicity angle
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201 | inline double cos_theta_W() const {return _cos_theta_w;}
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202 |
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203 | // /// returns the original jet (before tagging)
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204 | // const PseudoJet & original() const {return _original_jet;}
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205 |
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206 |
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207 | protected:
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208 | double _cos_theta_w; ///< the W helicity angle
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209 | //PseudoJet _W; ///< the tagged W
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210 | //PseudoJet _non_W; ///< the remaining pieces
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211 | // PseudoJet _original_jet; ///< the original jet (before tagging)
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212 |
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213 | // allow the tagger to set these
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214 | friend class JHTopTagger;
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215 | };
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216 |
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217 |
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218 |
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219 | FASTJET_END_NAMESPACE
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220 |
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221 | #endif // __FASTJET_JH_TOP_TAGGER_HH__
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222 |
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