The FastJet package, written by Matteo Cacciari, Gavin Salam and Gregory Soyez, provides fast native implementations of many sequential recombination algorithms, including the longitudinally invariant kt [1,2] longitudinally invariant inclusive Cambridge/Aachen [3,4] and anti-kt [7] jet finders. It also provides a uniform interface to external jet finders (notably SISCone [5]) via a plugin mechanism. Native jet-finding is based on the geometrical methods described in Phys. Lett. B 641 (2006) 57 [hep-ph/0512210] and [6]. In order to use the N ln N strategy for the kt (and other) jet finder(s), you will also need to install CGAL. This is useful mainly for heavy-ion multiplicities (N > 20000).

FastJet also includes tools for calculating jet areas [8] and performing background (pileup/UE) subtraction [9] and for jet substructure analyses [10].

FastJet is made available under the GNU public license (v2 or later). While this license grants you considerable freedom, please bear in mind that FastJet's use falls under guidelines similar to those that are standard for Monte Carlo event generators. In particular, if you use this code as part of work towards a scientific publication, whether directly or as contained within another program (e.g. Delphes, SpartyJet, Rivet, LHC collaboration software frameworks, ...), you should include a citation to

M. Cacciari, G.P. Salam and G. Soyez, Eur.Phys.J. C72 (2012) 1896 [arXiv:1111.6097] and, optionally,
M. Cacciari and G.P. Salam, Phys. Lett. B 641 (2006) 57 [hep-ph/0512210].

[get LaTeX for citation]

The original papers describing the jet algorithms and methods that you use within FastJet should also be cited separately.

Comments on FastJet are welcome. To be kept informed of new releases, you are strongly encouraged to subscribe to the low-volume fastjet-announce mailing list. Bug reports and feature requests should be sent to

The FastJet web pages are hosted by the LPTHE.

Some useful references

  1. S. Catani, Y. L. Dokshitzer, M. H. Seymour and B. R. Webber, Nucl. Phys. B 406 (1993) 187.
  2. S. D. Ellis and D. E. Soper, Phys. Rev. D 48 (1993) 3160 [arXiv:hep-ph/9305266].
  3. Y.L. Dokshitzer, G.D. Leder, S. Moretti and B.R. Webber, JHEP 9708 (1997) 001 [arXiv:hep-ph/9707323].
  4. M. Wobisch and T. Wengler, arXiv:hep-ph/9907280 and DESY-THESIS-2000-049
  5. G. P. Salam and G. Soyez, JHEP 0705 (2007) 086 [arXiv:0704.0292 [hep-ph]].
  6. G. P. Salam and M. Cacciari, "Jet clustering in particle physics, via a dynamic nearest neighbour graph implemented with CGAL", LPTHE-06-02, unpublished note.
  7. M. Cacciari, G. P. Salam and G. Soyez, "The anti-kt jet clustering algorithm", JHEP 0804 (2008) 063 [arXiv:0802.1189].
  8. M. Cacciari, G. P. Salam and G. Soyez, "The catchment area of jets", JHEP 0804 (2008) 005 [arXiv:0802.1188].
  9. M. Cacciari, G. P. Salam, "Pileup subtraction using jet areas", Phys.Lett.B 659 (2008) 119 [arXiv:0707.1378].
  10. A. Abdesselam et al., "Boosted objects: A Probe of beyond the Standard Model physics", Eur.Phys.J. C71 (2011) 1661 [arXiv:1012.5412].