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 | //STARTHEADER |
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5 | // $Id: JHTopTagger.hh 2689 2011-11-14 14:51:06Z soyez $ |
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6 | // |
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7 | // Copyright (c) 2005-2011, 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 and are described in hep-ph/0512210. If you use |
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19 | // FastJet as part of work towards a scientific publication, please |
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20 | // include a citation to the FastJet paper. |
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21 | // |
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22 | // FastJet is distributed in the hope that it will be useful, |
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23 | // but WITHOUT ANY WARRANTY; without even the implied warranty of |
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24 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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25 | // GNU General Public License for more details. |
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26 | // |
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27 | // You should have received a copy of the GNU General Public License |
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28 | // along with FastJet. If not, see <http://www.gnu.org/licenses/>. |
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29 | //---------------------------------------------------------------------- |
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30 | //ENDHEADER |
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31 | |
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32 | |
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33 | #include <fastjet/tools/TopTaggerBase.hh> |
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34 | #include <fastjet/CompositeJetStructure.hh> |
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35 | #include <fastjet/LimitedWarning.hh> |
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36 | |
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37 | FASTJET_BEGIN_NAMESPACE |
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38 | |
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39 | class JHTopTagger; |
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40 | class JHTopTaggerStructure; |
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41 | |
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42 | //---------------------------------------------------------------------- |
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43 | /// @ingroup tools_taggers |
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44 | /// \class JHTopTagger |
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45 | /// Class that helps perform boosted top tagging using the "Johns Hopkins" |
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46 | /// method from arXiv:0806.0848 (Kaplan, Rehermann, Schwartz |
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47 | /// and Tweedie) |
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48 | /// |
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49 | ///The tagger proceeds as follows: |
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50 | /// - start from a jet J obtained with the Cambridge/Aachen algorithm |
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51 | /// - undo the last iteration j -> j_1,j_2 (with pt_1>pt_2) until the |
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52 | /// two subjets satisfy pt_1 > delta_p pt_J (with pt_J the pt of |
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53 | /// the original jet) and |y_1 - y_2| + |phi_1 - phi_2| > delta_r. |
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54 | /// - if one of these criteria is not satisfied, carry on the |
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55 | /// procedure with j_1 (discarding j_2) |
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56 | /// - for each of the subjets found, repeat the procedure. If some |
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57 | /// new substructure is found, keep these 2 new subjets, otherwise |
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58 | /// keep the original subjet (found during the first iteration) |
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59 | /// - at this stage, one has at most 4 subjets. If one has less than |
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60 | /// 3, the tagger has failed. |
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61 | /// - reconstruct the W from the 2 subjets with a mass closest to the |
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62 | /// W mass |
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63 | /// - impose that the W helicity angle be less than a threshold |
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64 | /// cos_theta_W_max. |
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65 | /// |
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66 | /// \section input Input conditions |
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67 | /// |
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68 | /// - the original jet must have an associated (and valid) |
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69 | /// ClusterSequence |
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70 | /// - the tagger is designed to work with jets formed by the |
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71 | /// Cambridge/Aachen (C/A) algorithm; if a non-C/A jet is passed to |
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72 | /// the tagger, a warning will be issued |
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73 | /// |
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74 | /// \section Example |
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75 | /// |
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76 | /// A JHTopTagger can be used as follows: |
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77 | /// |
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78 | /// \code |
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79 | /// double delta_p = 0.10; // subjets must carry at least this fraction of the original jet's p_t |
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80 | /// double delta_r = 0.19; // subjets must be separated by at least this Manhattan distance |
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81 | /// double cos_theta_W_max = 0.7; // the maximal allowed value of the W helicity angle |
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82 | /// JHTopTagger top_tagger(delta_p, delta_r, cos_theta_W_max); |
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83 | /// // indicate the acceptable range of top, W masses (default: no limits) |
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84 | /// top_tagger.set_top_selector(SelectorMassRange(150,200)); |
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85 | /// top_tagger.set_W_selector (SelectorMassRange( 65, 95)); |
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86 | /// // now try and tag a jet |
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87 | /// PseudoJet top_candidate = top_tagger(jet); // jet should come from a Cambridge/Aachen clustering |
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88 | /// if (top_candidate != 0) { // successful tagging |
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89 | /// double top_mass = top_candidate.m(); |
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90 | /// double W_mass = top_candidate.structure_of<JHTopTagger>().W().m(); |
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91 | /// } |
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92 | /// \endcode |
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93 | /// |
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94 | /// The full set of information available from the structure_of<JHTopTagger>() |
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95 | /// call is |
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96 | /// |
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97 | /// - PseudoJet W() : the W subjet of the top candidate |
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98 | /// - PseudoJet non_W(): non-W subjet(s) of the top candidate (i.e. the b) |
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99 | /// - double cos_theta_W(): the W helicity angle |
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100 | /// - PseudoJet W1(): the harder of the two prongs of the W |
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101 | /// - PseudoJet W2(): the softer of the two prongs of the W |
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102 | /// |
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103 | /// The structure of the top_candidate can also be accessed through its |
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104 | /// pieces() function: |
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105 | /// |
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106 | /// - top_candidate.pieces()[0]: W |
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107 | /// - top_candidate.pieces()[1]: non_W |
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108 | /// |
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109 | /// The W itself has two pieces (corresponding to W1, W2). |
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110 | /// |
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111 | /// The existence of the first two of the structural calls (W(), |
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112 | /// non_W()) and the fact that the top is made of two pieces (W, |
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113 | /// non_W) are features that should be common to all taggers derived |
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114 | /// from TopTaggerBase. |
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115 | /// |
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116 | /// See also \subpage Example13 for a full usage example. |
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117 | /// |
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118 | class JHTopTagger : public TopTaggerBase { |
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119 | public: |
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120 | /// default ctor |
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121 | /// The parameters are the following: |
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122 | /// \param delta_p fractional pt cut imposed on the subjets |
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123 | /// (computed as a fraction of the original jet) |
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124 | /// \param delta_r minimal distance between 2 subjets |
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125 | /// (computed as |y1-y2|+|phi1-phi2|) |
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126 | /// \param cos_theta_W_max the maximal value for the polarisation |
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127 | /// angle of the W |
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128 | /// \param mW the W mass |
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129 | /// |
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130 | /// The default values of all these parameters are taken from |
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131 | /// arXiv:0806:0848 |
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132 | JHTopTagger(const double delta_p=0.10, const double delta_r=0.19, |
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133 | double cos_theta_W_max=0.7, double mW=80.4) |
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134 | : _delta_p(delta_p), _delta_r(delta_r), |
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135 | _cos_theta_W_max(cos_theta_W_max), _mW(mW){}; |
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136 | |
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137 | /// returns a textual description of the tagger |
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138 | virtual std::string description() const; |
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139 | |
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140 | /// runs the tagger on the given jet and |
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141 | /// returns the tagged PseudoJet if successful, or a PseudoJet==0 otherwise |
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142 | /// (standard access is through operator()). |
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143 | /// \param jet the PseudoJet to tag |
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144 | virtual PseudoJet result(const PseudoJet & jet) const; |
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145 | |
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146 | // the type of the associated structure |
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147 | typedef JHTopTaggerStructure StructureType; |
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148 | |
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149 | protected: |
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150 | /// runs the Johns Hopkins decomposition procedure |
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151 | std::vector<PseudoJet> _split_once(const PseudoJet & jet_to_split, |
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152 | const PseudoJet & reference_jet) const; |
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153 | |
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154 | double _delta_p, _delta_r, _cos_theta_W_max, _mW; |
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155 | static LimitedWarning _warnings_nonca; |
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156 | }; |
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157 | |
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158 | |
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159 | //------------------------------------------------------------------------ |
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160 | /// @ingroup tools_taggers |
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161 | /// \class JHTopTaggerStructure |
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162 | /// the structure returned by the JHTopTagger transformer. |
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163 | /// |
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164 | /// See the JHTopTagger class description for the details of what |
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165 | /// is inside this structure |
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166 | /// |
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167 | class JHTopTaggerStructure : public CompositeJetStructure, public TopTaggerBaseStructure { |
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168 | public: |
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169 | /// ctor with pieces initialisation |
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170 | JHTopTaggerStructure(std::vector<PseudoJet> pieces_in, |
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171 | const JetDefinition::Recombiner *recombiner = 0) : |
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172 | CompositeJetStructure(pieces_in, recombiner), _cos_theta_w(0.0){} |
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173 | |
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174 | /// returns the W subjet |
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175 | inline const PseudoJet & W() const{ |
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176 | return _pieces[0]; |
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177 | } |
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178 | |
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179 | /// returns the first W subjet (the harder) |
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180 | inline PseudoJet W1() const{ |
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181 | assert(W().pieces().size()>0); |
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182 | return W().pieces()[0]; |
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183 | } |
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184 | |
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185 | /// returns the second W subjet |
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186 | inline PseudoJet W2() const{ |
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187 | assert(W().pieces().size()>1); |
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188 | return W().pieces()[1]; |
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189 | } |
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190 | |
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191 | /// returns the non-W subjet |
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192 | /// It will have 1 or 2 pieces depending on whether the tagger has |
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193 | /// found 3 or 4 pieces |
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194 | inline const PseudoJet & non_W() const{ |
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195 | return _pieces[1]; |
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196 | } |
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197 | |
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198 | /// returns the W helicity angle |
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199 | inline double cos_theta_W() const {return _cos_theta_w;} |
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200 | |
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201 | // /// returns the original jet (before tagging) |
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202 | // const PseudoJet & original() const {return _original_jet;} |
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203 | |
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204 | |
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205 | protected: |
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206 | double _cos_theta_w; ///< the W helicity angle |
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207 | //PseudoJet _W; ///< the tagged W |
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208 | //PseudoJet _non_W; ///< the remaining pieces |
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209 | // PseudoJet _original_jet; ///< the original jet (before tagging) |
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210 | |
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211 | // allow the tagger to set these |
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212 | friend class JHTopTagger; |
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213 | }; |
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214 | |
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215 | |
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216 | |
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217 | FASTJET_END_NAMESPACE |
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218 | |
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219 | #endif // __FASTJET_JH_TOP_TAGGER_HH__ |
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220 | |
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