Implementation of the MidPoint algorithm from CDF (plugin for fastjet-v2.1 upwards) More...

#include <CDFMidPointPlugin.hh>

Inheritance diagram for fastjet::CDFMidPointPlugin:

Collaboration diagram for fastjet::CDFMidPointPlugin:

Public Types
enum	SplitMergeScale { SM_pt, SM_Et, SM_mt, SM_pttilde }
	the choice of scale to be used in the split-merge step
Public Member Functions
	CDFMidPointPlugin (double seed_threshold, double cone_radius, double cone_area_fraction, int max_pair_size, int max_iterations, double overlap_threshold, SplitMergeScale sm_scale=SM_pt)
	A CDFMidPointPlugin constructor that looks like the one provided by CDF.
	CDFMidPointPlugin (double cone_radius, double overlap_threshold, double seed_threshold=1.0, double cone_area_fraction=1.0)
	a compact constructor
double	seed_threshold () const
double	cone_radius () const
double	cone_area_fraction () const
int	max_pair_size () const
int	max_iterations () const
double	overlap_threshold () const
virtual std::string	description () const
	return a textual description of the jet-definition implemented in this plugin
virtual void	run_clustering (ClusterSequence &) const
	given a ClusterSequence that has been filled up with initial particles, the following function should fill up the rest of the ClusterSequence, using the following member functions of ClusterSequence:
virtual double	R () const
	the plugin mechanism's standard way of accessing the jet radius

Detailed Description

Implementation of the MidPoint algorithm from CDF (plugin for fastjet-v2.1 upwards)

A plugin for fastjet-v2.1 that provides an interface to the CDF midpoint algorithm

CDFMidPointPlugin is a plugin for fastjet (v2.1 upwards) that provides an interface to the CDF version of Run-II iterative cone algorithm with midpoint seeds (also known as the Iterative Legacy Cone Algorithm, ILCA).

The CDF code has been taken from Joey Huston's webpage http://www.pa.msu.edu/~huston/Les_Houches_2005/Les_Houches_SM.html

Note that the CDF midpoint code contains options that go beyond those described in the Tevatron run-II document (hep-ex/0005012), notably search-cones, as described in hep-ph/0111434, and midpoints bewteen multiplets of stable cones.

Additionally, the version of the CDF midpoint code distributed here has been modified by the FastJet authors, so as to allow one to choose the scale used in the split-merge step.

Definition at line 68 of file CDFMidPointPlugin.hh.

Constructor & Destructor Documentation

fastjet::CDFMidPointPlugin::CDFMidPointPlugin	(	double	seed_threshold,
		double	cone_radius,
		double	cone_area_fraction,
		int	max_pair_size,
		int	max_iterations,
		double	overlap_threshold,
		SplitMergeScale	sm_scale = `SM_pt`
	)		`[inline]`

A CDFMidPointPlugin constructor that looks like the one provided by CDF.

Its arguments should have the following meaning:

seed_threshold: minimum pt for a particle to be considered a seed of the iteration.

cone_radius: standard meaning

cone_area_fraction: stable-cones are searched for with a radius Rsearch = R * sqrt(cone_area_fraction), and then expanded to size R afterwards; note (hep-ph/0610012) that this introduces IR unsafety at NLO for X+2-jet observables (where X any hard object).

max_pair_size: "midpoints" can be added between pairs of stable cones, triplets of stable cones, etc.; max_pair_size indicates the maximum number of stable cones that are assembled when adding midpoints.

max_iterations: the maximum number of iterations to carry out when looking for a stable cone.

overlap_threshold: if (overlapping_Et)/(Et_of_softer_protojet) < overlap_threshold, overlapping jets are split, otherwise they are merged.

sm_scale: a choice for the scale to be used in the split-merge step (both for ordering the momenta and quantifying the overlap); the three options are

. SM_pt: pt (default -- source of small IR safety issue in purely hadronic events)

. SM_Et: Et (not boost invariant, reduces to mt at zero rapidity and to pt and infinite rapidity)

. SM_mt: transverse mass = sqrt(m^2+pt^2)

Definition at line 113 of file CDFMidPointPlugin.hh.

                                                       :
    _seed_threshold     (seed_threshold     ),    
    _cone_radius        (cone_radius        ),
    _cone_area_fraction (cone_area_fraction ),
    _max_pair_size      (max_pair_size      ),
    _max_iterations     (max_iterations     ),
    _overlap_threshold  (overlap_threshold  ),
    _sm_scale           (sm_scale)             {}

fastjet::CDFMidPointPlugin::CDFMidPointPlugin	(	double	cone_radius,
		double	overlap_threshold,
		double	seed_threshold = `1.0`,
		double	cone_area_fraction = `1.0`
	)		`[inline]`

a compact constructor

NB: as of version 2.4, the default value for the overlap_threshold threshold has been removed, to avoid misleading people into using the value of 0.5 without thinking, which is known to have adverse effects in high-noise environments. A recommended value is 0.75.

Definition at line 136 of file CDFMidPointPlugin.hh.

                                                        : 
    _seed_threshold     (seed_threshold     ),    
    _cone_radius        (cone_radius        ),
    _cone_area_fraction (cone_area_fraction ),
    _max_pair_size      (2                  ),
    _max_iterations     (100                ),
    _overlap_threshold  (overlap_threshold  ),
    _sm_scale           (SM_pt)                {}

Member Function Documentation

void fastjet::CDFMidPointPlugin::run_clustering ( ClusterSequence & ) const [virtual]

given a ClusterSequence that has been filled up with initial particles, the following function should fill up the rest of the ClusterSequence, using the following member functions of ClusterSequence:

plugin_do_ij_recombination(...)
plugin_do_iB_recombination(...)

Implements fastjet::JetDefinition::Plugin.

Definition at line 87 of file CDFMidPointPlugin.cc.

References fastjet::ClusterSequence::jets(), fastjet::ClusterSequence::plugin_record_iB_recombination(), and fastjet::ClusterSequence::plugin_record_ij_recombination().

                                                                        {
 
  // create the physics towers needed by the CDF code
  vector<PhysicsTower> towers;
  towers.reserve(clust_seq.jets().size());
  for (unsigned i = 0; i < clust_seq.jets().size(); i++) {
    LorentzVector fourvect(clust_seq.jets()[i].px(),
                           clust_seq.jets()[i].py(),
                           clust_seq.jets()[i].pz(),
                           clust_seq.jets()[i].E());
    PhysicsTower tower(fourvect);
    // misuse one of the indices for tracking, since the MidPoint
    // implementation doesn't seem to make use of these indices
    tower.calTower.iEta = i;
    towers.push_back(tower);
  }

  // prepare the CDF algorithm
  MidPointAlgorithm m(_seed_threshold,_cone_radius,_cone_area_fraction,
                      _max_pair_size,_max_iterations,_overlap_threshold,
                      MidPointAlgorithm::SplitMergeScale(_sm_scale));
    
  // run the CDF algorithm
  std::vector<Cluster> jets;
  m.run(towers,jets);


  // now transfer the jets back into our own structure -- we will
  // mimic the cone code with a sequential recombination sequence in
  // which the jets are built up by adding one particle at a time
  for(vector<Cluster>::const_iterator jetIter = jets.begin(); 
                                      jetIter != jets.end(); jetIter++) {
    const vector<PhysicsTower> & tower_list = jetIter->towerList;
    int jet_k = tower_list[0].calTower.iEta;
  
    int ntow = int(jetIter->towerList.size());
    for (int itow = 1; itow < ntow; itow++) {
      int jet_i = jet_k;
      // retrieve our misappropriated index for the jet
      int jet_j = tower_list[itow].calTower.iEta;
      // do a fake recombination step with dij=0
      double dij = 0.0;
      clust_seq.plugin_record_ij_recombination(jet_i, jet_j, dij, jet_k);
    }
  
    // NB: put a sensible looking d_iB just to be nice...
    double d_iB = clust_seq.jets()[jet_k].perp2();
    clust_seq.plugin_record_iB_recombination(jet_k, d_iB);
  }


  // following code is for testing only
  //cout << endl;
  //for(vector<Cluster>::const_iterator jetIter = jets.begin(); 
  //                                    jetIter != jets.end(); jetIter++) {
  //  cout << jetIter->fourVector.pt() << " " << jetIter->fourVector.y() << endl;
  //}
  //cout << "-----------------------------------------------------\n";
  //vector<PseudoJet> ourjets(clust_seq.inclusive_jets());
  //for (vector<PseudoJet>::const_reverse_iterator ourjet = ourjets.rbegin();
  //     ourjet != ourjets.rend(); ourjet++) {
  //  cout << ourjet->perp() << " " << ourjet->rap() << endl;
  //}
  //cout << endl;
}

The documentation for this class was generated from the following files:

plugins/CDFCones/fastjet/CDFMidPointPlugin.hh
plugins/CDFCones/CDFMidPointPlugin.cc

Public Types

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation