1 | //FJSTARTHEADER
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2 | // $Id: CASubJetTagger.cc 4442 2020-05-05 07:50:11Z soyez $
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3 | //
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4 | // Copyright (c) 2005-2020, 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 | #include <fastjet/tools/CASubJetTagger.hh>
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32 | #include <fastjet/ClusterSequence.hh>
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33 |
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34 | #include <algorithm>
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35 | #include <cmath>
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36 | #include <sstream>
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37 |
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38 | using namespace std;
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39 |
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40 | FASTJET_BEGIN_NAMESPACE
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41 |
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42 |
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43 | LimitedWarning CASubJetTagger::_non_ca_warnings;
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44 |
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45 | // the tagger's description
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46 | //----------------------------------------------------------------------
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47 | string CASubJetTagger::description() const{
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48 | ostringstream oss;
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49 | oss << "CASubJetTagger with z_threshold=" << _z_threshold ;
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50 | if (_absolute_z_cut) oss << " (defined wrt original jet)";
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51 | oss << " and scale choice ";
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52 | switch (_scale_choice) {
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53 | case kt2_distance: oss << "kt2_distance"; break;
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54 | case jade_distance: oss << "jade_distance"; break;
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55 | case jade2_distance: oss << "jade2_distance"; break;
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56 | case plain_distance: oss << "plain_distance"; break;
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57 | case mass_drop_distance: oss << "mass_drop_distance"; break;
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58 | case dot_product_distance: oss << "dot_product_distance"; break;
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59 | default:
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60 | throw Error("unrecognized scale choice");
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61 | }
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62 |
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63 | return oss.str();
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64 | }
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65 |
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66 | // run the tagger on the given cs/jet
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67 | // returns the tagged PseudoJet if successful, 0 otherwise
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68 | //----------------------------------------------------------------------
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69 | PseudoJet CASubJetTagger::result(const PseudoJet & jet) const{
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70 | // make sure that the jet results from a Cambridge/Aachen clustering
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71 | if (jet.validated_cs()->jet_def().jet_algorithm() != cambridge_algorithm)
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72 | _non_ca_warnings.warn("CASubJetTagger should only be applied on jets from a Cambridge/Aachen clustering; use it with other algorithms at your own risk");
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73 |
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74 | // recurse in the jet to find the max distance
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75 | JetAux aux;
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76 | aux.jet = PseudoJet();
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77 | aux.aux_distance = -numeric_limits<double>::max();
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78 | aux.delta_r = 0.0;
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79 | aux.z = 1.0;
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80 | _recurse_through_jet(jet, aux, jet); // last arg remains original jet
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81 |
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82 | // create the result and its associated structure
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83 | PseudoJet result_local = aux.jet;
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84 |
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85 | // the tagger is considered to have failed if aux has never been set
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86 | // (in which case it will not have parents).
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87 | if (result_local == PseudoJet()) return result_local;
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88 |
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89 | // otherwise sort out the structure
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90 | CASubJetTaggerStructure * s = new CASubJetTaggerStructure(result_local);
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91 | // s->_original_jet = jet;
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92 | s->_scale_choice = _scale_choice;
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93 | s->_distance = aux.aux_distance;
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94 | s->_absolute_z = _absolute_z_cut;
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95 | s->_z = aux.z;
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96 |
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97 | result_local.set_structure_shared_ptr(SharedPtr<PseudoJetStructureBase>(s));
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98 |
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99 | return result_local;
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100 | }
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101 |
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102 |
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103 | ///----------------------------------------------------------------------
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104 | /// work through the jet, establishing a distance at each branching
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105 | inline void CASubJetTagger::_recurse_through_jet(const PseudoJet & jet, JetAux &aux, const PseudoJet & original_jet) const {
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106 |
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107 | PseudoJet parent1, parent2;
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108 | if (! jet.has_parents(parent1, parent2)) return;
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109 |
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110 | /// make sure the objects are not _too_ close together
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111 | if (parent1.squared_distance(parent2) < _dr2_min) return;
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112 |
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113 | // distance
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114 | double dist=0.0;
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115 | switch (_scale_choice) {
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116 | case kt2_distance:
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117 | // a standard (LI) kt distance
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118 | dist = parent1.kt_distance(parent2);
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119 | break;
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120 | case jade_distance:
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121 | // something a bit like a mass: pti ptj Delta R_ij^2
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122 | dist = parent1.perp()*parent2.perp()*parent1.squared_distance(parent2);
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123 | break;
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124 | case jade2_distance:
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125 | // something a bit like a mass*deltaR^2: pti ptj Delta R_ij^4
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126 | dist = parent1.perp()*parent2.perp()*pow(parent1.squared_distance(parent2),2);
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127 | break;
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128 | case plain_distance:
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129 | // Delta R_ij^2
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130 | dist = parent1.squared_distance(parent2);
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131 | break;
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132 | case mass_drop_distance:
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133 | // Delta R_ij^2
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134 | dist = jet.m() - std::max(parent1.m(),parent2.m());
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135 | break;
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136 | case dot_product_distance:
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137 | // parent1 . parent2
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138 | // ( = jet.m2() - parent1.m2() - parent2.m() in a
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139 | // 4-vector recombination scheme)
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140 | dist = dot_product(parent1, parent2);
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141 | break;
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142 | default:
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143 | throw Error("unrecognized scale choice");
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144 | }
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145 |
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146 | // check the z cut
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147 | bool zcut1 = true;
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148 | bool zcut2 = true;
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149 | double z2 = 0.0;
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150 |
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151 | // not very efficient -- sort out later
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152 | if (parent1.perp2() < parent2.perp2()) std::swap(parent1,parent2);
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153 |
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154 | if (_absolute_z_cut) {
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155 | z2 = parent2.perp() / original_jet.perp();
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156 | zcut1 = parent1.perp() / original_jet.perp() >= _z_threshold;
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157 | } else {
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158 | z2 = parent2.perp()/(parent1.perp()+parent2.perp());
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159 | }
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160 | zcut2 = z2 >= _z_threshold;
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161 |
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162 | if (zcut1 && zcut2){
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163 | if (dist > aux.aux_distance){
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164 | aux.jet = jet;
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165 | aux.aux_distance = dist;
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166 | aux.delta_r = sqrt(parent1.squared_distance(parent2));
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167 | aux.z = z2; // the softest
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168 | }
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169 | }
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170 |
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171 | if (zcut1) _recurse_through_jet(parent1, aux, original_jet);
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172 | if (zcut2) _recurse_through_jet(parent2, aux, original_jet);
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173 | }
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174 |
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175 | FASTJET_END_NAMESPACE
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