[d7d2da3] | 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/RestFrameNSubjettinessTagger.hh>
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| 30 | #include <fastjet/tools/Boost.hh>
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| 31 | #include <fastjet/ClusterSequence.hh>
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| 32 | #include <sstream>
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| 33 |
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| 34 | using namespace std;
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| 35 |
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| 36 | FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
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| 37 |
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| 38 | //------------------------------------------------------------------------
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| 39 | // RestFrameNSubjettinessTagger class implementation
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| 40 | //------------------------------------------------------------------------
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| 41 |
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| 42 | //------------------------------------------------------------------------
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| 43 | // tagger description
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| 44 | string RestFrameNSubjettinessTagger::description() const{
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| 45 | ostringstream oss;
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| 46 | oss << "RestFrameNSubjettiness tagger that performs clustering in the jet rest frame with "
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| 47 | << _subjet_def.description()
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| 48 | << ", supplemented with cuts tau_2 < " << _t2cut
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| 49 | << " and cos(theta_s) < " << _costscut;
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| 50 | return oss.str();
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| 51 | }
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| 52 |
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| 53 |
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| 54 | //------------------------------------------------------------------------
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| 55 | // action on a single jet
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| 56 | // returns the tagged PseudoJet if successful, 0 otherwise
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| 57 | PseudoJet RestFrameNSubjettinessTagger::result(const PseudoJet & jet) const{
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| 58 | // make sure that the jet has constituents
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| 59 | if (!jet.has_constituents())
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| 60 | throw("The jet you try to tag needs to have accessible constituents");
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| 61 |
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| 62 | // get the constituents and boost them into the rest frame of the jet
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| 63 | vector<PseudoJet> rest_input = jet.constituents();
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| 64 | for (unsigned int i=0; i<rest_input.size(); i++)
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| 65 | rest_input[i].unboost(jet);
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| 66 |
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| 67 | ClusterSequence cs_rest(rest_input, _subjet_def);
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| 68 | vector<PseudoJet> subjets = (_use_exclusive)
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| 69 | ? cs_rest.exclusive_jets(2)
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| 70 | : sorted_by_E(cs_rest.inclusive_jets());
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| 71 |
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| 72 | // impose the cuts in the rest-frame
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| 73 | if (subjets.size()<2) return PseudoJet();
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| 74 |
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| 75 | const PseudoJet &j0 = subjets[0];
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| 76 | const PseudoJet &j1 = subjets[1];
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| 77 |
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| 78 | /// impose the cut on cos(theta_s)
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| 79 | double ct0 = (j0.px()*jet.px() + j0.py()*jet.py() + j0.pz()*jet.pz())
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| 80 | /sqrt(j0.modp2()*jet.modp2());
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| 81 | double ct1 = (j1.px()*jet.px() + j1.py()*jet.py() + j1.pz()*jet.pz())
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| 82 | /sqrt(j1.modp2()*jet.modp2());
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| 83 | if ((ct0 > _costscut) || (ct1 > _costscut)) return PseudoJet();
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| 84 |
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| 85 | // ccompute the 2-subjettiness and impose the coresponding cut
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| 86 | double tau2 = 0.0;
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| 87 | for (unsigned int i=0; i<rest_input.size(); i++)
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| 88 | tau2 += min(dot_product(rest_input[i], j0),
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| 89 | dot_product(rest_input[i], j1));
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| 90 |
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| 91 | tau2 *= (2.0/jet.m2());
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| 92 |
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| 93 | if (tau2 > _t2cut) return PseudoJet();
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| 94 |
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| 95 | // We have a positive tag,
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| 96 | // - boost everything back into the lab frame
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| 97 | // - record the info in the interface
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| 98 | // Note that in order to point to the correct Clustersequence, the
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| 99 | // subjets must be taken from the boosted one. We extract that
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| 100 | // through the history index of the rest-frame subjets
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| 101 | ClusterSequence * cs_structure = new ClusterSequence();
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| 102 | Boost boost(jet);
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| 103 | cs_structure->transfer_from_sequence(cs_rest, &boost);
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| 104 | PseudoJet subjet_lab1 = cs_structure->jets()[cs_rest.history()[subjets[0].cluster_hist_index()].jetp_index];
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| 105 | PseudoJet subjet_lab2 = cs_structure->jets()[cs_rest.history()[subjets[0].cluster_hist_index()].jetp_index];
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| 106 |
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| 107 | PseudoJet result_local = join<StructureType>(subjet_lab1,subjet_lab2);
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| 108 | StructureType * s = (StructureType *) result_local.structure_non_const_ptr();
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| 109 | // s->_original_jet = jet;
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| 110 | s->_tau2 = tau2;
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| 111 | s->_costhetas = max(ct0, ct1);
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| 112 |
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| 113 | // keep the rest-frame CS alive
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| 114 | cs_structure->delete_self_when_unused();
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| 115 |
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| 116 | return result_local;
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| 117 | }
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| 118 |
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| 119 |
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| 120 | FASTJET_END_NAMESPACE
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