Updated 2006-10-01

To the best of my understanding, the Optimal Jet Definition
together with its fast Fortran-77 implementation Optimal Jet Finder
(versions OJF_014 and later) solves the problem of
jet definition. |

It was crucial for the success of the
project that the algorithm design of the OJF library (except the last
addition described in hep-ph/0301185) was performed using the software
development platform BlackBox Component Builder (www.oberon.ch)
based on the ultra-modern, component- and object-oriented, statically
type-safe, modular, efficiently compilable programming language Component
Pascal. It is is a refinement of the revolutionary Oberon(-2) from the
language design workshop of Niklaus Wirth, the celebrated author of Pascal
and Modula-2.
A unique combination of features makes For more about Oberon and its potential in scientific computations see http://cern.ch/oberon.day and hep-ph/0202033. |

The public code is here (including a C++ version). It's now official:

D.Yu. Grigoriev, E. Jankowski, F.V. Tkachov: *
Towards a
standard jet definition* hep-ph/0301185
(Phys. Rev. Let. 91 (2003) 061801)

D.Yu. Grigoriev, E. Jankowski, F.V. Tkachov: *
Optimal Jet
Finder* hep-ph/0301226
(Comp. Phys. Commun. 155 (2003) 42-64)

The picture below conveys an idea of how superiorly better OJF behaves ar large particle multiplicities (red) than kT/KTCLUS
(black).

The vertical axis is time in 1/100 sec per one reconstruction for kT, and for
one minimization for OJF.

The horizontal axis is the number of particles per event.

Further pictures can be found at http://www.phys.ualberta.ca/~ejankows/jets/graphs.html

A related important result is
the method of **quasi-optimal observables**:

F.V. Tkachov, Approaching the parameter estimation quality of maximum likelihood
via generalized moments, physics/0001019.

For references to earlier work dealing with an important special case discovered earlier by other authors, see the Jan. 2003 update of F.V. Tkachov, hep-ph/0210116.

The method of quasi-optimal observables offers **a straightforward deterministic
recipe **for construction of observables for theoretically optimal (i.e.
corresponding to the Fisher-Frechet-Rao-Cramer limit) estimation of a given
parameter.

A number of straightforward algorithmic implementations immediately
come to mind.

A universal algorithm based on this (something like MINUIT)
could be very useful.