Anomalous quartic gauge couplings and unitarization for the vector boson scattering process pprightarrow W^+W^+jjXrightarrow ell ^+nu _ell ell ^+nu _ell jjX

Genessis Perez,Marco Sekulla,Dieter Zeppenfeld

doi:10.1140/epjc/s10052-018-6230-1

Genessis Perez, Marco Sekulla + Show 1 more

Open Access

https://doi.org/10.1140/epjc/s10052-018-6230-1

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Abstract

Weak vector boson scattering (VBS) at the LHC provides an excellent source of information on the structure of quartic gauge couplings and possible effects of physics beyond the SM in electroweak symmetry breaking. Parameterizing deviations from the SM within an effective field theory at tree level, the dimension-8 operators, which are needed for sufficiently general modeling, lead to unphysical enhancements of cross sections within the accessible energy range of the LHC. Preservation of unitarity limits is needed for phenomenological studies of the VVjj events which signify VBS. Here we develop a numerical unitarization scheme for the full off-shell VBS processes and apply it to same-sign W scattering, i.e. processes like qqrightarrow qqW^+W^+. The scheme is implemented within the Monte Carlo program VBFNLO, including leptonic decay of the weak bosons and NLO QCD corrections. Distributions differentiating between higher dimensional operators are discussed.

Highlights

We introduce a variant of the T/K-matrix unitarization scheme [12,14], called the longitudinal operator OS1 (Tu) unitarization below, for general combinations of operators within vector boson scattering (VBS), for arbitrary space-like virtualities of the incoming vector bosons, and describe its implementation in the Monte Carlo generator VBFNLO [15,16,17]
Because of the large energy reach of hadron colliders, which spans from low energies and momentum transfers where the pure
effective field theory (EFT) description is valid, to regions of phase space where the polynomial growth of partial wave amplitudes with energy exceeds unitarity limits, the naive EFT description must be generalized to a model which respects unitarity bounds

Summary

Introduction

We introduce a variant of the T/K-matrix unitarization scheme [12,14], called Tu unitarization below, for general combinations of operators within VBS, for arbitrary space-like virtualities of the incoming vector bosons, and describe its implementation in the Monte Carlo generator VBFNLO [15,16,17].

Effective field theory description of anomalous quartic gauge couplings

Unitarity for VBS: going off-shell

Implementation of unitarization: the Tu model

Consequences for LHC physics

Discussion and conclusions