1 | //STARTHEADER |
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2 | // $Id: CASubJetTagger.hh 2616 2011-09-30 18:03:40Z salam $ |
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3 | // |
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4 | // Copyright (c) 2005-2011, 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 and are described in hep-ph/0512210. If you use |
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16 | // FastJet as part of work towards a scientific publication, please |
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17 | // include a citation to the FastJet paper. |
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18 | // |
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19 | // FastJet is distributed in the hope that it will be useful, |
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20 | // but WITHOUT ANY WARRANTY; without even the implied warranty of |
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21 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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22 | // GNU General Public License for more details. |
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23 | // |
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24 | // You should have received a copy of the GNU General Public License |
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25 | // along with FastJet. If not, see <http://www.gnu.org/licenses/>. |
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26 | //---------------------------------------------------------------------- |
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27 | //ENDHEADER |
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28 | |
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29 | #ifndef __CASUBJET_TAGGER_HH__ |
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30 | #define __CASUBJET_TAGGER_HH__ |
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31 | |
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32 | #include <fastjet/PseudoJet.hh> |
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33 | #include <fastjet/WrappedStructure.hh> |
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34 | #include <fastjet/tools/Transformer.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 CASubJetTagger; |
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40 | class CASubJetTaggerStructure; |
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41 | |
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42 | //---------------------------------------------------------------------- |
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43 | /// @ingroup tools_taggers |
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44 | /// \class CASubJetTagger |
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45 | /// clean (almost parameter-free) tagger searching for the element in |
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46 | /// the clustering history that maximises a chosen distance |
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47 | /// |
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48 | /// class to help us get a clean (almost parameter-free) handle on |
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49 | /// substructure inside a C/A jet. It follows the logic described in |
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50 | /// arXiv:0906.0728 (and is inspired by the original Cambridge |
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51 | /// algorithm paper in its use of separate angular and dimensionful |
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52 | /// distances), but provides some extra flexibility. |
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53 | /// |
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54 | /// It searches for all splittings that pass a symmetry cut (zcut) and |
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55 | /// then selects the one with the largest auxiliary scale choice |
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56 | /// (e.g. jade distance of the splitting, kt distance of the |
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57 | /// splitting, etc.) |
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58 | /// |
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59 | /// By default, the zcut is calculated from the fraction of the child |
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60 | /// pt carried by the parent jet. If one calls set_absolute_z_cut the |
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61 | /// fraction of transverse momentum will be computed wrt the original |
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62 | /// jet. |
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63 | /// |
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64 | /// original code copyright (C) 2009 by Gavin Salam, released under |
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65 | /// the GPL. |
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66 | /// |
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67 | /// \section desc Options |
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68 | /// |
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69 | /// - the distance choice: options are |
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70 | /// kt2_distance : usual min(kti^2,ktj^2)DeltaR_{ij}^2 |
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71 | /// jade_distance : kti . ktj DeltaR_{ij}^2 (LI version of jade) |
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72 | /// jade2_distance : kti . ktj DeltaR_{ij}^4 (LI version of jade * DR^2) |
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73 | /// plain_distance : DeltaR_{ij}^2 |
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74 | /// mass_drop_distance : m_jet - max(m_parent1,m_parent2) |
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75 | /// dot_product_distance: parent1.parent2 |
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76 | /// (kt2_distance by default) |
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77 | /// |
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78 | /// - the z cut (0 by default) |
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79 | /// |
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80 | /// - by calling set_absolute_z_cut(), one can ask that the pt |
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81 | /// fraction if calculated wrt the original jet |
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82 | /// |
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83 | /// - by calling set_dr_min(drmin), one can ask that only the |
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84 | /// recombinations where the 2 objects are (geometrically) distant |
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85 | /// by at least drmin are kept in the maximisation. |
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86 | /// |
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87 | /// \section input Input conditions |
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88 | /// |
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89 | /// - the jet must have been obtained from a Cambridge/Aachen cluster |
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90 | /// sequence |
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91 | /// |
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92 | /// \section output Output/structure |
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93 | /// |
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94 | /// - the element of the cluster sequence maximising the requested |
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95 | /// distance (and satisfying the zcut) is returned. |
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96 | /// |
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97 | /// - if the original jet has no parents, it will be returned |
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98 | /// |
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99 | /// - the value of the "z" and distance corresponding to that history |
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100 | /// element are stored and accessible through |
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101 | /// result.structure_of<CASubJetTagger>().z(); |
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102 | /// result.structure_of<CASubJetTagger>().distance(); |
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103 | /// |
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104 | class CASubJetTagger : public Transformer { |
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105 | public: |
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106 | |
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107 | /// the available choices of auxiliary scale with respect to which |
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108 | /// to order the splittings |
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109 | enum ScaleChoice { |
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110 | kt2_distance, //< usual min(kti^2,ktj^2)DeltaR_{ij}^2 |
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111 | jade_distance, //< kti . ktj DeltaR_{ij}^2 (LI version of jade) |
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112 | jade2_distance, //< kti . ktj DeltaR_{ij}^4 (LI version of jade * DR^2) |
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113 | plain_distance, //< DeltaR_{ij}^2 |
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114 | mass_drop_distance, //< m_jet - max(m_parent1,m_parent2) |
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115 | dot_product_distance //< parent1.parent2 |
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116 | }; |
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117 | |
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118 | /// just constructs |
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119 | CASubJetTagger(ScaleChoice scale_choice = jade_distance, |
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120 | double z_threshold = 0.1) |
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121 | : _scale_choice(scale_choice), _z_threshold(z_threshold), |
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122 | _dr2_min(0.0), _absolute_z_cut(false){}; |
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123 | |
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124 | /// sets a minimum delta R below which spliting will be ignored |
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125 | /// (only relevant if set prior to calling run()) |
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126 | void set_dr_min(double drmin) {_dr2_min = drmin*drmin;} |
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127 | |
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128 | /// returns a textual description of the tagger |
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129 | virtual std::string description() const; |
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130 | |
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131 | /// If (abs_z_cut) is set to false (the default) then for a |
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132 | /// splitting to be considered, each subjet must satisfy |
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133 | /// |
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134 | /// p_{t,sub} > z_threshold * p_{t,parent} |
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135 | /// |
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136 | /// whereas if it is set to true, then each subject must satisfy |
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137 | /// |
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138 | /// p_{t,sub} > z_threshold * p_{t,original-jet} |
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139 | /// |
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140 | /// where parent is the immediate parent of the splitting, and |
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141 | /// original jet is the one supplied to the run() function. |
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142 | /// |
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143 | /// Only relevant is called prior to run(). |
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144 | void set_absolute_z_cut(bool abs_z_cut=true) {_absolute_z_cut = abs_z_cut;} |
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145 | |
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146 | /// runs the tagger on the given jet and |
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147 | /// returns the tagged PseudoJet if successful, or a PseudoJet==0 otherwise |
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148 | /// (standard access is through operator()). |
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149 | virtual PseudoJet result(const PseudoJet & jet) const; |
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150 | |
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151 | /// the type of Structure returned |
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152 | typedef CASubJetTaggerStructure StructureType; |
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153 | |
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154 | protected: |
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155 | /// class that contains the result internally |
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156 | class JetAux { |
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157 | public: |
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158 | PseudoJet jet; //< the subjet (immediate parent of splitting) |
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159 | double aux_distance; //< the auxiliary distance between its two subjets |
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160 | double delta_r; //< the angular distance between its two subjets |
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161 | double z; //< the transverse momentum fraction |
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162 | }; |
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163 | |
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164 | |
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165 | void _recurse_through_jet(const PseudoJet & current_jet, |
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166 | JetAux &aux_max, |
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167 | const PseudoJet & original_jet) const; |
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168 | |
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169 | ScaleChoice _scale_choice; |
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170 | double _z_threshold; |
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171 | double _dr2_min; |
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172 | bool _absolute_z_cut; |
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173 | |
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174 | static LimitedWarning _non_ca_warnings; |
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175 | }; |
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176 | |
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177 | |
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178 | //------------------------------------------------------------------------ |
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179 | /// @ingroup tools_taggers |
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180 | /// the structure returned by a CASubJetTagger |
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181 | /// |
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182 | /// Since this is directly an element of the ClusterSequence, we keep |
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183 | /// basically the original ClusterSequenceStructure (wrapped for |
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184 | /// memory-management reasons) and add information about the pt |
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185 | /// fraction and distance of the subjet structure |
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186 | class CASubJetTaggerStructure : public WrappedStructure{ |
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187 | public: |
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188 | /// default ctor |
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189 | /// \param result_jet the jet for which we have to keep the |
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190 | /// structure |
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191 | CASubJetTaggerStructure(const PseudoJet & result_jet) |
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192 | : WrappedStructure(result_jet.structure_shared_ptr()){} |
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193 | |
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194 | /// returns the scale choice asked for the maximisation |
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195 | CASubJetTagger::ScaleChoice scale_choice() const {return _scale_choice;} |
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196 | |
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197 | /// returns the value of the distance measure (corresponding to |
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198 | /// ScaleChoice) for this jet's splitting |
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199 | double distance() const {return _distance;} |
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200 | |
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201 | /// returns the pt fraction contained by the softer of the two component |
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202 | /// pieces of this jet (normalised relative to this jet) |
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203 | double z() const {return _z;} |
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204 | |
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205 | /// returns the pt fraction contained by the softer of the two component |
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206 | /// pieces of this jet (normalised relative to the original jet) |
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207 | bool absolute_z() const {return _absolute_z;} |
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208 | |
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209 | // /// returns the original jet (before tagging) |
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210 | // const PseudoJet & original() const {return _original_jet;} |
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211 | |
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212 | protected: |
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213 | CASubJetTagger::ScaleChoice _scale_choice; ///< the user scale choice |
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214 | double _distance; ///< the maximal distance associated with the result |
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215 | bool _absolute_z; ///< whether z is computed wrt to the original jet or not |
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216 | double _z; ///< the transverse momentum fraction |
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217 | // PseudoJet _original_jet; ///< the original jet (before tagging) |
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218 | |
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219 | friend class CASubJetTagger; ///< to allow setting the internal information |
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220 | }; |
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221 | |
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222 | FASTJET_END_NAMESPACE |
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223 | |
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224 | #endif // __CASUBJET_HH__ |
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