NLO QCD Programs

I am working on a set of programs implementing the Catani-Seymour subtraction algorithm for calculating Next to Leading Order corrections to jet cross-sections in perturbative QCD.

EVENT2 is a program for two- and three-jet events in e+e- annihilation. It offers several advantages over the standard EVENT program of Kunszt and Nason, briefly: full event orientation is retained; Z exchange is included; different partonic final states and colour are labelled correctly. A preliminary version (0.2) is here together with a brief set of notes describing it.
A prepreliminary update is also available, version 0.3, but the notes have not yet been updated accordingly.

DISENT is a program for (1+1)- and (2+1)-jet events in deep inelastic scattering. A preliminary version (0.1) is here together with a brief set of notes describing it.
There was an important bug found in version 0.0. If you used that version, you are strongly advised to rerun with version 0.1. The differences are typically of order 1% for most quantities, but could be larger depending on the kinematic cuts made. In order to quickly assess the importance of the bug, there is also a program that simply integrates the term that was wrong (it runs about three times quicker than the full program).
Thomas Hadig has set up a common interface for NLO DIS programs, which so far works for DISENT and DISASTER.

If you use these programs please let me know, as they are bound to keep changing for a while, partly in response to your comments.

The demonstration versions of these programs use Torbjorn Sjöstrand's GBOOK package, heavily modified by me over the years. To be honest, I can't even remember all the changes I've made, but the important ones are: switched to DOUBLE PRECISION throughout; made the max number and size of histograms compile-time parameters, and improved safety against asking for non-existent histograms; written an interface to SLAC's TOPDRAWER program. Of course the latter is not much use to you if you don't use TOPDRAWER, but the format is very simple (it is just a list of X Y Y-ERROR points) so it would be straightforward to change to any other format. You can get my version here.

There is a brief Letter describing the algorithm, and the full paper goes in to all the gory details.
It has also been described in various conference proceedings: Rheinsberg, Rome and HERA.

Mike Seymour