Implementation of the spherical version of the SISCone algorithm (plugin for fastjet v2.1 upwards) More...

#include <fastjet/SISConeSphericalPlugin.hh>

Inherits fastjet::SISConeBasePlugin.

Public Types
enum	SplitMergeScale { SM_E, SM_Etilde }
	enum for the different split-merge scale choices; Note that order must be the same as in siscone More...

Public Member Functions
	SISConeSphericalPlugin (double cone_radius_in, double overlap_threshold_in, int n_pass_max_in=0, double protojet_Emin_in=0.0, bool caching_in=false, SplitMergeScale split_merge_scale_in=SM_Etilde, double split_merge_stopping_scale_in=0.0)
	Main constructor for the SISConeSpherical Plugin class.

double	protojet_Emin () const
	minimum energy for a protojet to be considered in the split-merge step of the algorithm

double	protojet_or_ghost_Emin () const
	return the scale to be passed to SISCone as the protojet_Emin – if we have a ghost separation scale that is above the protojet_ptmin, then the ghost_separation_scale becomes the relevant one to use here

SplitMergeScale	split_merge_scale () const
	indicates scale used in split-merge

void	set_split_merge_scale (SplitMergeScale sms)
	sets scale used in split-merge

bool	split_merge_use_E_weighted_splitting () const
	indicate if the splittings are done using the anti-kt distance

void	set_split_merge_use_E_weighted_splitting (bool val)

virtual bool	supports_ghosted_passive_areas () const
	overload the default as we don't provide support for passive areas. More...

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: More...

virtual bool	is_spherical () const
	returns true because this plugin is intended for spherical geometries (i.e. More...

Protected Member Functions
virtual void	reset_stored_plugin () const

Detailed Description

Implementation of the spherical version of the SISCone algorithm (plugin for fastjet v2.1 upwards)

SISConeSphericalPlugin is a plugin for fastjet (v2.1 upwards) that provides an interface to the seedless infrared safe cone jet finder by Gregory Soyez and Gavin Salam.

This is the version of SISCone using spherical coordinates. Compared to the original cylindrical version:

Particles are within a cone if their opening angle relative to the centre of the cone is less than R
The split-merge step uses the total energy in the protojet as the ordering and overlap-measure variable
The IR safety of the split-merge step is not guaranteed for events consisting of two back-to-back identical heavy particles that decay. This is because of potential degeneracies in the ordering for the split-merge step.

For moderate values of R the problem should not be too severe (or may even be absent for some values of the overlap parameter), however the user should be aware of the issue.

The default split-merge scale may change at a later date to resolve this issue.

SISCone uses geometrical techniques to exhaustively consider all possible distinct cones. It then finds out which ones are stable and sends the result to the Tevatron Run-II type split-merge procedure for overlapping cones.

Four parameters govern the "physics" of the algorithm:

the cone_radius (this should be self-explanatory!)
the overlap_threshold is the parameter which dictates how much two jets must overlap (E_overlap/min(E1,E2)) if they are to be merged
Not all particles are in stable cones in the first round of searching for stable cones; one can therefore optionally have the the jet finder carry out additional passes of searching for stable cones among particles that were in no stable cone in previous passes — the maximum number of passes carried out is n_pass_max. If this is zero then additional passes are carried out until no new stable cones are found.
Protojet Emin: protojets that are below this Emin (default = 0) are discarded before each iteration of the split-merge loop.

One parameter governs some internal algorithmic shortcuts:

if "caching" is turned on then the last event clustered by siscone is stored – if the current event is identical and the cone_radius and n_pass_max are identical, then the only part of the clustering that needs to be rerun is the split-merge part, leading to significant speed gains; there is a small (O(N) storage and speed) penalty for caching, so it should be kept off (default) if only a single overlap_threshold is used.

The final jets can be accessed by requestion the inclusive_jets(...) from the ClusterSequence object. Note that these PseudoJets have their user_index() set to the index of the pass in which they were found (first pass = 0). NB: This does not currently work for jets that consist of a single particle.

For further information on the details of the algorithm see the SISCone paper, arXiv:0704.0292 [JHEP 0705:086,2007].

For documentation about the implementation, see the siscone/doc/html/index.html file.

Definition at line 94 of file SISConeSphericalPlugin.hh.

Member Enumeration Documentation

◆ SplitMergeScale

enum fastjet::SISConeSphericalPlugin::SplitMergeScale

enum for the different split-merge scale choices; Note that order must be the same as in siscone

Enumerator
SM_E	Energy (IR unsafe with momentum conservation)
SM_Etilde	sum_{i jet} E_i [1+sin^2(theta_iJ)]

Definition at line 99 of file SISConeSphericalPlugin.hh.

Member Function Documentation

◆ supports_ghosted_passive_areas()

virtual bool fastjet::SISConeSphericalPlugin::supports_ghosted_passive_areas ( ) const

inlinevirtual

overload the default as we don't provide support for passive areas.

Reimplemented from fastjet::JetDefinition::Plugin.

Definition at line 148 of file SISConeSphericalPlugin.hh.

◆ run_clustering()

void fastjet::SISConeSphericalPlugin::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: