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[en] In order to cope with increased experimental accuracy of the LHC era, the accuracy of theoretical predictions has to be increased as well. For this task, sophisticated tools for automated computation, namely matrix-element generators and Monte-Carlo event generators, have to take next-to-leading order effects into account. A hadronic initial state like protons at the LHC however incorporates computational challenges such as infrared initial state divergences. A possibility to substract these divergencies is the Frixione-Kunszt-Signer (FKS) subtraction scheme whose implementation in Whizard is currently being validated. In this talk I will show details of the implementation and validation of the FKS subtraction, particularly the initial state splittings and regions, using as a prime example computed by Whizard the simplest process where all these components are needed, namely pp Zj+X at QCD NLO.
[en] This summarizes the talk given at the LCWS 2019 conference in Sendai, Japan, on the progress of the WHIZARD event generator in terms of new physics features and technical improvements relevant for the physics programme of future lepton and especially linear colliders. It takes as a reference the version 2.8.2 released in October 2019, and also takes into account the development until version 2.8.3 to be released in February 2020.
[en] Vector-boson scattering processes are of great importance for the current run-II and future runs of the Large Hadron Collider. The presence of triple and quartic gauge couplings in the process gives access to the gauge sector of the Standard Model (SM) and possible new-physics contributions there. To test any new-physics hypothesis, sound knowledge of the SM contributions is necessary, with a precision which at least matches the experimental uncertainties of existing and forthcoming measurements. In this article we present a detailed study of the vector-boson scattering process with two positively-charged leptons and missing transverse momentum in the final state. In particular, we first carry out a systematic comparison of the various approximations that are usually performed for this kind of process against the complete calculation, at LO and NLO QCD accuracy. Such a study is performed both in the usual fiducial region used by experimental collaborations and in a more inclusive phase space, where the differences among the various approximations lead to more sizeable effects. Afterwards, we turn to predictions matched to parton showers, at LO and NLO: we show that on the one hand, the inclusion of NLO QCD corrections leads to more stable predictions, but on the other hand the details of the matching and of the parton-shower programs cause differences which are considerably larger than those observed at fixed order, even in the experimental fiducial region. We conclude with recommendations for experimental studies of vector-boson scattering processes. (orig.)