| 1 | //STARTHEADER
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| 2 | // $Id$
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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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