FastJet 3.0.2
EECambridgePlugin.cc
00001 //STARTHEADER
00002 // $Id: EECambridgePlugin.cc 2577 2011-09-13 15:11:38Z salam $
00003 //
00004 // Copyright (c) 2007-2011, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
00005 //
00006 //----------------------------------------------------------------------
00007 // This file is part of FastJet.
00008 //
00009 //  FastJet is free software; you can redistribute it and/or modify
00010 //  it under the terms of the GNU General Public License as published by
00011 //  the Free Software Foundation; either version 2 of the License, or
00012 //  (at your option) any later version.
00013 //
00014 //  The algorithms that underlie FastJet have required considerable
00015 //  development and are described in hep-ph/0512210. If you use
00016 //  FastJet as part of work towards a scientific publication, please
00017 //  include a citation to the FastJet paper.
00018 //
00019 //  FastJet is distributed in the hope that it will be useful,
00020 //  but WITHOUT ANY WARRANTY; without even the implied warranty of
00021 //  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00022 //  GNU General Public License for more details.
00023 //
00024 //  You should have received a copy of the GNU General Public License
00025 //  along with FastJet. If not, see <http://www.gnu.org/licenses/>.
00026 //----------------------------------------------------------------------
00027 //ENDHEADER
00028 
00029 // fastjet stuff
00030 #include "fastjet/ClusterSequence.hh"
00031 #include "fastjet/EECambridgePlugin.hh"
00032 #include "fastjet/NNH.hh"
00033 
00034 // other stuff
00035 #include <sstream>
00036 #include <limits>
00037 
00038 FASTJET_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh
00039 
00040 using namespace std;
00041 
00042 //----------------------------------------------------------------------
00043 /// class to help run an e+e- Cambridge algorithm
00044 class EECamBriefJet {
00045 public:
00046   void init(const PseudoJet & jet) {
00047     double norm = 1.0/sqrt(jet.modp2());
00048     nx = jet.px() * norm;
00049     ny = jet.py() * norm;
00050     nz = jet.pz() * norm;
00051   }
00052 
00053   double distance(const EECamBriefJet * jet) const {
00054     double dij = 1 - nx*jet->nx
00055                    - ny*jet->ny
00056                    - nz*jet->nz;
00057     return dij;
00058   }
00059 
00060   double beam_distance() const {
00061     return numeric_limits<double>::max();
00062   }
00063 
00064 private:
00065   double nx, ny, nz;
00066 };
00067 
00068 
00069 string EECambridgePlugin::description () const {
00070   ostringstream desc;
00071   desc << "EECambridge plugin with ycut = " << ycut() ;
00072   return desc.str();
00073 }
00074 
00075 void EECambridgePlugin::run_clustering(ClusterSequence & cs) const {
00076   int njets = cs.jets().size();
00077   NNH<EECamBriefJet> nnh(cs.jets());
00078 
00079   double Q2 = cs.Q2(); 
00080 
00081   while (njets > 0) {
00082     int i, j, k;
00083     // here we get a minimum based on the purely angular variable from the NNH class
00084     // (called dij there, but vij in the Cambridge article (which uses dij for 
00085     // a kt distance...)
00086     double vij = nnh.dij_min(i, j); // i,j are return values...
00087 
00088     // next we work out the dij (ee kt distance), and based on its
00089     // value decide whether we have soft-freezing (represented here by
00090     // a "Beam" clustering) or not
00091     double dij;
00092     if (j >= 0) {
00093       double scale = min(cs.jets()[i].E(), cs.jets()[j].E());
00094       dij = 2 * vij * scale * scale;
00095       if (dij > Q2 * ycut()) {
00096         // we'll call the softer partner a "beam" jet
00097         if (cs.jets()[i].E() > cs.jets()[j].E()) std::swap(i,j);
00098         j = -1;
00099       }
00100     } else {
00101       // for the last particle left, just use yij = 1
00102       dij = Q2;
00103     }
00104     
00105     if (j >= 0) {
00106       cs.plugin_record_ij_recombination(i, j, dij, k);
00107       nnh.merge_jets(i, j, cs.jets()[k], k);
00108     } else {
00109       cs.plugin_record_iB_recombination(i, dij);
00110       nnh.remove_jet(i);
00111     }
00112     njets--;
00113   }
00114     
00115 }
00116 
00117 FASTJET_END_NAMESPACE      // defined in fastjet/internal/base.hh
 All Classes Namespaces Files Functions Variables Typedefs Enumerations Enumerator Friends