Precision Simulations for Future Colliders

Abstract

Future particle colliders will usher in a new era of precision physics. It will be crucial that the theory community can provide highly precise predictions forthese experiments. In particular, for future e+e− colliders the theoretical calculations will need to improve by a factor 2-100, depending on the observable. In this thesis,we will present the theoretical improvements implemented in the SHERPA event generator for e+e− physics. We will concentrate on the treatment of QED radiation within the framework of Yennie, Frautschi and Suura resummation and discuss its impact on future colliders. In particular, we shall show how initial state radiation can be resummed in a process-independent manner to all orders in the QED coupling.We find that the resummation alone is not sufficient, and the inclusion of fixed-order corrections improves the perturbative description substantially. We will apply these corrections to the study of e+e−→ff,e+e−→W+W− and e+e−→ZH processes at a future lepton-lepton collider, and discuss the impact of the QED corrections.In the second part of this thesis we will consider precision calculation of W/Z+jet at a future hadron-hadron colliders, namely the HE-LHC/FCC-hh. The theoretical modelling of these processes is crucial for controlling the background in many beyond the standard model searches. The processes are calculated up to next-to-next-to-leading order in the QCD coupling αs. A detailed and robust study of the associated scale and shape uncertainties is presented.