1 //FJSTARTHEADER
2 // $Id: MassDropTagger.cc 4442 2020-05-05 07:50:11Z soyez $
3 //
4 // Copyright (c) 2005-2020, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
5 //
6 //----------------------------------------------------------------------
7 // This file is part of FastJet.
8 //
9 // FastJet is free software; you can redistribute it and/or modify
10 // it under the terms of the GNU General Public License as published by
11 // the Free Software Foundation; either version 2 of the License, or
12 // (at your option) any later version.
13 //
14 // The algorithms that underlie FastJet have required considerable
15 // development. They are described in the original FastJet paper,
16 // hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
17 // FastJet as part of work towards a scientific publication, please
18 // quote the version you use and include a citation to the manual and
19 // optionally also to hep-ph/0512210.
20 //
21 // FastJet is distributed in the hope that it will be useful,
22 // but WITHOUT ANY WARRANTY; without even the implied warranty of
23 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
24 // GNU General Public License for more details.
25 //
26 // You should have received a copy of the GNU General Public License
27 // along with FastJet. If not, see <http://www.gnu.org/licenses/>.
28 //----------------------------------------------------------------------
29 //FJENDHEADER
30
31 #include <fastjet/tools/MassDropTagger.hh>
32 #include <fastjet/ClusterSequence.hh>
33 #include <sstream>
34
35 FASTJET_BEGIN_NAMESPACE
36
37 LimitedWarning MassDropTagger::_warnings_nonca;
38 LimitedWarning MassDropTagger::_negative_mass_warning;
39
40 using namespace std;
41
42 //----------------------------------------------------------------------
43 // MassDropTagger class implementation
44 //----------------------------------------------------------------------
45
46 //------------------------------------------------------------------------
47 // description of the tagger
description() const48 string MassDropTagger::description() const{
49 ostringstream oss;
50 oss << "MassDropTagger with mu=" << _mu << " and ycut=" << _ycut;
51 return oss.str();
52 }
53
54 //------------------------------------------------------------------------
55 // returns the tagged PseudoJet if successful, 0 otherwise
56 // - jet the PseudoJet to tag
result(const PseudoJet & jet) const57 PseudoJet MassDropTagger::result(const PseudoJet & jet) const{
58 PseudoJet j = jet;
59
60 // issue a warning if the jet is not obtained through a C/A
61 // clustering
62 if ((! j.has_associated_cluster_sequence()) ||
63 (j.validated_cs()->jet_def().jet_algorithm() != cambridge_algorithm))
64 _warnings_nonca.warn("MassDropTagger should only be applied on jets from a Cambridge/Aachen clustering; use it with other algorithms at your own risk.");
65
66
67 PseudoJet j1, j2;
68 bool had_parents;
69
70 // we just ask that we can "walk" in the cluster sequence.
71 // appropriate errors will be thrown automatically if this is not
72 // the case
73 while ((had_parents = j.has_parents(j1,j2))) {
74 if (j.m2() <= 0) {
75 _negative_mass_warning.warn(
76 "MassDropTagger: parent (sub)jet has mass^2<=0; returning null jet");
77 return PseudoJet();
78 }
79 // make parent1 the more massive jet
80 if (j1.m2() < j2.m2()) std::swap(j1,j2);
81
82 // if we pass the conditions on the mass drop and its degree of
83 // asymmetry (kt_dist/m^2 > rtycut [where kt_dist/m^2 \sim
84 // z/(1-z)), then we've found something interesting, so exit the
85 // loop
86 if ( (j1.m2() < _mu*_mu*j.m2()) && (j1.kt_distance(j2) > _ycut*j.m2()) )
87 break;
88 else
89 j = j1;
90 }
91
92 if (!had_parents)
93 // no Higgs found, return an empty PseudoJet
94 return PseudoJet();
95
96 // create the result and its structure
97 PseudoJet result_local = j;
98 MassDropTaggerStructure * s = new MassDropTaggerStructure(result_local);
99 s->_mu = j1.m() / j.m();
100 s->_y = j1.kt_distance(j2)/j.m2();
101
102 result_local.set_structure_shared_ptr(SharedPtr<PseudoJetStructureBase>(s));
103
104 return result_local;
105 }
106
107 FASTJET_END_NAMESPACE
108
109