Monte Carlo Models at the Lhc

In this contribution the new event generation framework SHERPA will be presented, which aims at a full simulation of events at current and future high-energy experiments. Some first results exemplify its capabilities. Experiments at particle colliders are the most prominent way of testing the basic structure of matter at shortest distances and the dynamics underlying the interactions of its fundamental constituents at the energy frontier. These tests, however, become increasingly precise; the number of processes as well as the complexity of the phenomena involved require an increasingly careful planning of the experimental strategy and more and highly sophisticated analysis tools. In order to compare theoretical predictions with actual experimental results, simulation programs, also known as event generators, have become one of the most central tools. Over the past decades, these programs have been significantly improved in terms of physics content and they have grown to highly evolved computer code. In view of the next generation of collider experiments it is apparent that also the development of event generators have to keep pace with the new great challenges posed by them. Apart from physics issues, reflecting the rising complexity of the experiments, transparency and maintenance of these codes start to become an important issue. In order to meet these increasingly demanding requirements, a number of new codes are being constructed at the moment. These include the completely new write-ups in C++ of the well-known Fortran programs Herwig [1]and Pythia [2].Both Herwig++ [3] and Pythia7 [4] rely on a common event generation framework called ThePEG [5] and concentrate on the specific implementation of physics models for different aspects of event simulation. ThePEG, in turn, incorporates the organisation and structure of event generation itself. Another, completely independent approach is represented by the package SHERPA [6], also written in C++. In the remainder of this contribution, this new event generator will be presented in more detail; for details concerning the status of the two other C++-based event generators, cf. the respective presentations by L. Lönnblad and S. Gieseke. One of the construction paradigms of SHERPA is the clear separation of specific physics implementation and the more abstract rules defining the interplay of the different physics modules. To exemplify this, consider the case of potentially different codes for the description of hard scattering matrix elements. The SHERPA framework provides an interface called Matrix Element Handler to steer these codes. In turn, this interface is used …