Jet Finders
 
 
Pythia comes with three built-in 
jet finders, ClusterJet for e^+e^- events 
and SlowJet and CellJetfor hadron collider ones. 
Especially the latter is not so well matched to the standards of its field, 
however. (But it is closely related to the anti-kT algorithm, 
so is also not completely disconnected [Cac08].) 
 
 
SlowJet can do jet finding according to the current-day 
kT, Cambridge/Aachen and anti-kT algorithms. 
It can be run in two modes. The original one is a native implementation 
which, as the name indicates, is rather slow. However, with the release 
of the fjcore code from FastJet 
[Cac06, Cac12], the default mode has become to use the 
fjcore methods. This is transparent to the user. 
 
 
FastJet
 
 
SlowJet does not exhaust all the posssibilities of the 
fjcore code, so users are welcome to extend on the existing 
functionality by a direct usage of the fjcore methods. 
 
 
Missing from fjcore is a number of aspects, such as 
jet areas functionality, background estimation, access to other algorithms 
via plugins, interface to CGAL and tools such as filters and taggers. 
Therefore, for more sophisticated jet studies the complete 
FastJet package needs to be linked. This is foreseen in the 
configure file in the examples subdirectory, and the 
main212.cc and main213.cc programs contain 
examples how it can be used with Pythia events. (Even if 
these examples do not go beyond the functionality that 
SlowJet can offer.) 
 
 
The latter program makes use of the 
include/Pythia8Plugins/FastJet3.h 
header file, contributed by Gavin Salam. This allows simple input 
of a Pythia particle into a FastJet one, 
either retaining only the four-momentum or the full particle information. 
Thereby more sophisticated selectors become possible at the 
FastJet level. This code could be duplicated, with trivial 
modifications, to augment the fjcore package functionality 
in an identical manner, should the need arise.