1 | //STARTHEADER |
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2 | // $Id: JHTopTagger.cc 999 2013-03-04 11:48:06Z pavel $ |
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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 | #include <fastjet/tools/JHTopTagger.hh> |
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30 | #include <fastjet/Error.hh> |
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31 | #include <fastjet/JetDefinition.hh> |
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32 | #include <fastjet/ClusterSequence.hh> |
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33 | #include <sstream> |
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34 | #include <limits> |
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35 | |
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36 | FASTJET_BEGIN_NAMESPACE |
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37 | |
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38 | using namespace std; |
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39 | |
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40 | //---------------------------------------------------------------------- |
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41 | // JHTopTagger class implementation |
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42 | //---------------------------------------------------------------------- |
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43 | |
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44 | LimitedWarning JHTopTagger::_warnings_nonca; |
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45 | |
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46 | //------------------------------------------------------------------------ |
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47 | // description of the tagger |
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48 | string JHTopTagger::description() const{ |
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49 | ostringstream oss; |
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50 | oss << "JHTopTagger with delta_p=" << _delta_p << ", delta_r=" << _delta_r |
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51 | << ", cos_theta_W_max=" << _cos_theta_W_max |
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52 | << " and mW = " << _mW; |
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53 | oss << description_of_selectors(); |
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54 | return oss.str(); |
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55 | } |
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56 | |
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57 | //------------------------------------------------------------------------ |
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58 | // returns the tagged PseudoJet if successful, 0 otherwise |
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59 | // - jet the PseudoJet to tag |
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60 | PseudoJet JHTopTagger::result(const PseudoJet & jet) const{ |
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61 | // make sure that there is a "regular" cluster sequence associated |
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62 | // with the jet. Note that we also check it is valid (to avoid a |
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63 | // more criptic error later on) |
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64 | if (!jet.has_valid_cluster_sequence()){ |
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65 | throw Error("JHTopTagger can only be applied on jets having an associated (and valid) ClusterSequence"); |
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66 | } |
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67 | |
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68 | // warn if the jet has not been clustered with a Cambridge/Aachen |
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69 | // algorithm |
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70 | if (! jet.validated_cs()->jet_def().jet_algorithm() == cambridge_algorithm) |
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71 | _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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72 | |
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73 | |
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74 | // do the first splitting |
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75 | vector<PseudoJet> split0 = _split_once(jet, jet); |
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76 | if (split0.size() == 0) return PseudoJet(); |
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77 | |
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78 | // now try a second splitting on each of the resulting objects |
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79 | vector<PseudoJet> subjets; |
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80 | for (unsigned i = 0; i < 2; i++) { |
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81 | vector<PseudoJet> split1 = _split_once(split0[i], jet); |
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82 | if (split1.size() > 0) { |
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83 | subjets.push_back(split1[0]); |
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84 | subjets.push_back(split1[1]); |
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85 | } else { |
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86 | subjets.push_back(split0[i]); |
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87 | } |
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88 | } |
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89 | |
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90 | // make sure things make sense |
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91 | if (subjets.size() < 3) return PseudoJet(); |
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92 | |
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93 | // now find the pair of objects closest in mass to the W |
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94 | double dmW_min = numeric_limits<double>::max(); |
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95 | int ii=-1, jj=-1; |
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96 | for (unsigned i = 0 ; i < subjets.size()-1; i++) { |
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97 | for (unsigned j = i+1 ; j < subjets.size(); j++) { |
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98 | double dmW = abs(_mW - (subjets[i]+subjets[j]).m()); |
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99 | if (dmW < dmW_min) { |
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100 | dmW_min = dmW; ii = i; jj = j; |
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101 | } |
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102 | } |
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103 | } |
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104 | |
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105 | // order the subjets in the following order: |
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106 | // - hardest of the W subjets |
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107 | // - softest of the W subjets |
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108 | // - hardest of the remaining subjets |
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109 | // - softest of the remaining subjets (if any) |
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110 | if (ii>0) std::swap(subjets[ii], subjets[0]); |
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111 | if (jj>1) std::swap(subjets[jj], subjets[1]); |
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112 | if (subjets[0].perp2() < subjets[1].perp2()) std::swap(subjets[0], subjets[1]); |
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113 | if ((subjets.size()>3) && (subjets[2].perp2() < subjets[3].perp2())) |
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114 | std::swap(subjets[2], subjets[3]); |
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115 | |
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116 | // create the result and its structure |
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117 | const JetDefinition::Recombiner *rec |
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118 | = jet.associated_cluster_sequence()->jet_def().recombiner(); |
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119 | |
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120 | PseudoJet W = join(subjets[0], subjets[1], *rec); |
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121 | PseudoJet non_W; |
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122 | if (subjets.size()>3) { |
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123 | non_W = join(subjets[2], subjets[3], *rec); |
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124 | } else { |
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125 | non_W = join(subjets[2], *rec); |
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126 | } |
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127 | PseudoJet result_local = join<JHTopTaggerStructure>(W, non_W, *rec); |
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128 | JHTopTaggerStructure *s = (JHTopTaggerStructure*) result_local.structure_non_const_ptr(); |
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129 | s->_cos_theta_w = _cos_theta_W(result_local); |
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130 | |
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131 | // if the polarisation angle does not pass the cut, consider that |
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132 | // the tagging has failed |
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133 | // |
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134 | // Note that we could perhaps ensure this cut before constructing |
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135 | // the result structure but this has the advantage that the top |
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136 | // 4-vector is already available and does not have to de re-computed |
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137 | if (s->_cos_theta_w >= _cos_theta_W_max || |
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138 | ! _top_selector.pass(result_local) || ! _W_selector.pass(W) |
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139 | ) { |
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140 | result_local *= 0.0; |
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141 | } |
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142 | |
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143 | return result_local; |
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144 | |
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145 | // // old version |
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146 | // PseudoJet result = join<JHTopTaggerStructure>(subjets, *rec); |
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147 | // JHTopTaggerStructure *s = (JHTopTaggerStructure*) result.structure_non_const_ptr(); |
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148 | // // s->_original_jet = jet; |
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149 | // s->_W = join(subjets[0], subjets[1], *rec); |
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150 | // if (subjets.size()>3) |
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151 | // s->_non_W = join(subjets[2], subjets[3], *rec); |
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152 | // else |
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153 | // s->_non_W = join(subjets[2], *rec); |
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154 | // s->_cos_theta_w = _cos_theta_W(result); |
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155 | // |
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156 | // // if the polarisation angle does not pass the cut, consider that |
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157 | // // the tagging has failed |
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158 | // // |
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159 | // // Note that we could perhaps ensure this cut before constructing |
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160 | // // the result structure but this has the advantage that the top |
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161 | // // 4-vector is already available and does not have to de re-computed |
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162 | // if (s->_cos_theta_w >= _cos_theta_W_max) |
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163 | // return PseudoJet(); |
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164 | // |
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165 | // return result; |
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166 | } |
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167 | |
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168 | // runs the Johns Hopkins decomposition procedure |
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169 | vector<PseudoJet> JHTopTagger::_split_once(const PseudoJet & jet_to_split, |
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170 | const PseudoJet & reference_jet) const{ |
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171 | PseudoJet this_jet = jet_to_split; |
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172 | PseudoJet p1, p2; |
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173 | vector<PseudoJet> result_local; |
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174 | while (this_jet.has_parents(p1, p2)) { |
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175 | if (p2.perp2() > p1.perp2()) std::swap(p1,p2); // order with hardness |
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176 | if (p1.perp() < _delta_p * reference_jet.perp()) break; // harder is too soft wrt original jet |
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177 | if ( (abs(p2.rap()-p1.rap()) + abs(p2.delta_phi_to(p1))) < _delta_r) break; // distance is too small |
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178 | if (p2.perp() < _delta_p * reference_jet.perp()) { |
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179 | this_jet = p1; // softer is too soft wrt original, so ignore it |
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180 | continue; |
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181 | } |
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182 | //result.push_back(this_jet); |
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183 | result_local.push_back(p1); |
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184 | result_local.push_back(p2); |
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185 | break; |
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186 | } |
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187 | return result_local; |
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188 | } |
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189 | |
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190 | |
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191 | |
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192 | |
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193 | FASTJET_END_NAMESPACE |
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194 | |
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