Perturbative Corrections in SHERPA

Abstract

The use of Monte Carlo event generators for the simulation of LHC collider experiments, has in recent years driven a demand for greater accuracy of predictions in such generators.
This thesis will be concerned with the addition of certain perturbative corrections in the event generator SHERPA.
In this vein a framework for the automatic calculation of the real correction terms is presented, based on the the subtraction mechanism of of Frixione, Kunszt and Signer.
This resulting framework is implemented in the matrix element generator Amegic, which will then allow the calculation of the real components of an NLO QCD for any process; this can be supplemented with virtual corrections to provide a full NLO QCD prediction. This implementation is then rigorously tested and found to be consistent with known NLO results.
This subtraction framework is then utilized to perform a series of tests on the relative efficiency of the FKS and Catani Seymour subtraction methods; these tests are conducted over multiple processes and the affect of the multiplicity of the state is investigated.In addition the contribution of photon induced processes to lepton and W boson production is discussed, taking into account contributions from the QED part of parton distribution functions and from equivalent photons in the Weizsaecker Williams approximation. Typically these processes contribute on the per cent level compared to standard quark and gluon-induced processes; however, when applying various cuts this picture may change and the photon induced processes may become significant.