1 | //FJSTARTHEADER
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2 | // $Id: JHTopTagger.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/JHTopTagger.hh>
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32 | #include <fastjet/Error.hh>
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33 | #include <fastjet/JetDefinition.hh>
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34 | #include <fastjet/ClusterSequence.hh>
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35 | #include <sstream>
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36 | #include <limits>
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37 |
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38 | FASTJET_BEGIN_NAMESPACE
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39 |
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40 | using namespace std;
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41 |
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42 | //----------------------------------------------------------------------
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43 | // JHTopTagger class implementation
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44 | //----------------------------------------------------------------------
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45 |
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46 | LimitedWarning JHTopTagger::_warnings_nonca;
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47 |
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48 | //------------------------------------------------------------------------
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49 | // description of the tagger
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50 | string JHTopTagger::description() const{
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51 | ostringstream oss;
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52 | oss << "JHTopTagger with delta_p=" << _delta_p << ", delta_r=" << _delta_r
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53 | << ", cos_theta_W_max=" << _cos_theta_W_max
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54 | << " and mW = " << _mW;
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55 | oss << description_of_selectors();
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56 | return oss.str();
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57 | }
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58 |
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59 | //------------------------------------------------------------------------
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60 | // returns the tagged PseudoJet if successful, 0 otherwise
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61 | // - jet the PseudoJet to tag
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62 | PseudoJet JHTopTagger::result(const PseudoJet & jet) const{
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63 | // make sure that there is a "regular" cluster sequence associated
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64 | // with the jet. Note that we also check it is valid (to avoid a
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65 | // more criptic error later on)
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66 | if (!jet.has_valid_cluster_sequence()){
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67 | throw Error("JHTopTagger can only be applied on jets having an associated (and valid) ClusterSequence");
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68 | }
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69 |
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70 | // warn if the jet has not been clustered with a Cambridge/Aachen
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71 | // algorithm
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72 | if (jet.validated_cs()->jet_def().jet_algorithm() != cambridge_algorithm)
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73 | _warnings_nonca.warn("JHTopTagger should only be applied on jets from a Cambridge/Aachen clustering; use it with other algorithms at your own risk.");
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74 |
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75 |
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76 | // do the first splitting
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77 | vector<PseudoJet> split0 = _split_once(jet, jet);
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78 | if (split0.size() == 0) return PseudoJet();
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79 |
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80 | // now try a second splitting on each of the resulting objects
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81 | vector<PseudoJet> subjets;
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82 | for (unsigned i = 0; i < 2; i++) {
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83 | vector<PseudoJet> split1 = _split_once(split0[i], jet);
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84 | if (split1.size() > 0) {
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85 | subjets.push_back(split1[0]);
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86 | subjets.push_back(split1[1]);
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87 | } else {
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88 | subjets.push_back(split0[i]);
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89 | }
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90 | }
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91 |
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92 | // make sure things make sense
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93 | if (subjets.size() < 3) return PseudoJet();
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94 |
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95 | // now find the pair of objects closest in mass to the W
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96 | double dmW_min = numeric_limits<double>::max();
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97 | int ii=-1, jj=-1;
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98 | for (unsigned i = 0 ; i < subjets.size()-1; i++) {
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99 | for (unsigned j = i+1 ; j < subjets.size(); j++) {
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100 | double dmW = abs(_mW - (subjets[i]+subjets[j]).m());
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101 | if (dmW < dmW_min) {
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102 | dmW_min = dmW; ii = i; jj = j;
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103 | }
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104 | }
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105 | }
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106 |
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107 | // order the subjets in the following order:
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108 | // - hardest of the W subjets
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109 | // - softest of the W subjets
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110 | // - hardest of the remaining subjets
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111 | // - softest of the remaining subjets (if any)
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112 | if (ii>0) std::swap(subjets[ii], subjets[0]);
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113 | if (jj>1) std::swap(subjets[jj], subjets[1]);
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114 | if (subjets[0].perp2() < subjets[1].perp2()) std::swap(subjets[0], subjets[1]);
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115 | if ((subjets.size()>3) && (subjets[2].perp2() < subjets[3].perp2()))
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116 | std::swap(subjets[2], subjets[3]);
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117 |
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118 | // create the result and its structure
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119 | const JetDefinition::Recombiner *rec
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120 | = jet.associated_cluster_sequence()->jet_def().recombiner();
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121 |
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122 | PseudoJet W = join(subjets[0], subjets[1], *rec);
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123 | PseudoJet non_W;
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124 | if (subjets.size()>3) {
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125 | non_W = join(subjets[2], subjets[3], *rec);
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126 | } else {
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127 | non_W = join(subjets[2], *rec);
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128 | }
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129 | PseudoJet result_local = join<JHTopTaggerStructure>(W, non_W, *rec);
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130 | JHTopTaggerStructure *s = (JHTopTaggerStructure*) result_local.structure_non_const_ptr();
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131 | s->_cos_theta_w = _cos_theta_W(result_local);
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132 |
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133 | // if the polarisation angle does not pass the cut, consider that
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134 | // the tagging has failed
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135 | //
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136 | // Note that we could perhaps ensure this cut before constructing
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137 | // the result structure but this has the advantage that the top
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138 | // 4-vector is already available and does not have to de re-computed
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139 | if (s->_cos_theta_w >= _cos_theta_W_max ||
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140 | ! _top_selector.pass(result_local) || ! _W_selector.pass(W)
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141 | ) {
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142 | result_local *= 0.0;
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143 | }
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144 |
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145 | return result_local;
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146 |
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147 | // // old version
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148 | // PseudoJet result = join<JHTopTaggerStructure>(subjets, *rec);
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149 | // JHTopTaggerStructure *s = (JHTopTaggerStructure*) result.structure_non_const_ptr();
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150 | // // s->_original_jet = jet;
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151 | // s->_W = join(subjets[0], subjets[1], *rec);
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152 | // if (subjets.size()>3)
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153 | // s->_non_W = join(subjets[2], subjets[3], *rec);
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154 | // else
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155 | // s->_non_W = join(subjets[2], *rec);
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156 | // s->_cos_theta_w = _cos_theta_W(result);
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157 | //
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158 | // // if the polarisation angle does not pass the cut, consider that
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159 | // // the tagging has failed
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160 | // //
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161 | // // Note that we could perhaps ensure this cut before constructing
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162 | // // the result structure but this has the advantage that the top
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163 | // // 4-vector is already available and does not have to de re-computed
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164 | // if (s->_cos_theta_w >= _cos_theta_W_max)
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165 | // return PseudoJet();
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166 | //
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167 | // return result;
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168 | }
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169 |
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170 | // runs the Johns Hopkins decomposition procedure
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171 | vector<PseudoJet> JHTopTagger::_split_once(const PseudoJet & jet_to_split,
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172 | const PseudoJet & reference_jet) const{
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173 | PseudoJet this_jet = jet_to_split;
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174 | PseudoJet p1, p2;
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175 | vector<PseudoJet> result_local;
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176 | while (this_jet.has_parents(p1, p2)) {
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177 | if (p2.perp2() > p1.perp2()) std::swap(p1,p2); // order with hardness
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178 | if (p1.perp() < _delta_p * reference_jet.perp()) break; // harder is too soft wrt original jet
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179 | if ( (abs(p2.rap()-p1.rap()) + abs(p2.delta_phi_to(p1))) < _delta_r) break; // distance is too small
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180 | if (p2.perp() < _delta_p * reference_jet.perp()) {
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181 | this_jet = p1; // softer is too soft wrt original, so ignore it
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182 | continue;
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183 | }
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184 | //result.push_back(this_jet);
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185 | result_local.push_back(p1);
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186 | result_local.push_back(p2);
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187 | break;
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188 | }
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189 | return result_local;
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190 | }
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191 |
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192 |
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193 |
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194 |
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195 | FASTJET_END_NAMESPACE
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196 |
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