Abstract
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.
Highlights
Vector-boson scattering (VBS) at a hadron collider usually refers to the interaction of massive vector bosons (W±, Z), radiated by partons of the incoming protons, which in turn are deflected from the beam direction and enter the volume of the particle detectors
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
A detailed study of the process pp → μ+νμe+νe jj + X at the Large Hadron Collider (LHC) has been presented, mainly focused on the EW production mechanism which involves the scattering of massive vector bosons
Summary
Vector-boson scattering (VBS) at a hadron collider usually refers to the interaction of massive vector bosons (W±, Z), radiated by partons (quarks) of the incoming protons, which in turn are deflected from the beam direction and enter the volume of the particle detectors. W+W+ scattering is the simplest VBS process to calculate, because the double-charge structure of the leptonic final state limits the number of partonic processes and total number of Feynman diagrams for each process. It possesses all features of VBS at the LHC and is representative of other VBS signatures. In the last few years, several next-to-leading-order (NLO) computations have become available for both the VBS process [7–13] and its QCD-induced irreducible background process [13–17] All these VBS computations rely on various approximations, typically neglecting contributions which are expected to be small in realistic experimental setups [12,18].
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