The general purpose event generators, Pythia, Herwig and Sherpa, work well for most processes at the LHC, but there is still room for improvement. The development of models is often done outside the three main programs, although the resulting code typically is interfaced to plug in to one or more of them. A special class of such programs involves parton shower models where the standard collinear evolution is amended by so-called small-x resummation. Two such programs are explicitly included in this project:

• Ariadne/DIPSY is based on dipole formulation of parton showers where the initial-state shower is based on evolutionin impact-parameter space. This program is also able to model collisions involving heavy-ion collision. Such collisions are well integrated parts on the LHC program, but none of the three main programs have the capability of fully simulating them.
• HEJ is based on a high-energy version of collinear factorization, where small-x resummation is added in the limit of multi-Regge kinematics. The program needs to be interfaced to final state showers to get the full modeling of the resulting jets. So far there exists a simplified interface to Ariadne, and another more sophisticated interface is being developed. Work is also ongoing on merging NLO partonic samples within the HEJ formalism.

Besides developing these two programs, the Plugin project will act as an interface to theorists in the wider community working on special models for parts of the event generating chain. The project is led by Leif Lonnblad in Lund, with Jeppe Andersen and Jennifer Smillie of the Durham team, with ESRs in Lund and Durham.