## Jet Finders

`Pythia` comes with three built-in jet finders, `ClusterJet` for e^+e^- events and `SlowJet` and `CellJet`for 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 but, as the name indicates, is is rather slow, especially when compared with the `FastJet` alternative.

### FastJet

For realistic jet studies the `FastJet` package [Cac06] has become a standard. Several different jet options are available, such as kT, Cambridge/Aachen, anti-kT and SISCone.

Linking to `FastJet` is foreseen in the configure file in the `examples` subdirectory, and the `main71.cc` and `main72.cc` programs contain examples how it can be used with `Pythia` events.

The latter program makes use of the `include/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.