Abstract
A measurement of vector boson scattering and constraints on anomalous quartic gauge couplings from events with two Z bosons and two jets are presented. The analysis is based on a data sample of proton–proton collisions at s=13 TeV collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb−1. The search is performed in the fully leptonic final state ZZ→ℓℓℓ′ℓ′, where ℓ,ℓ′=e or μ. The electroweak production of two Z bosons in association with two jets is measured with an observed (expected) significance of 2.7 (1.6) standard deviations. A fiducial cross section for the electroweak production is measured to be σEW(pp→ZZjj→ℓℓℓ′ℓ′jj)=0.40−0.16+0.21(stat)−0.09+0.13(syst) fb, which is consistent with the standard model prediction. Limits on anomalous quartic gauge couplings are determined in terms of the effective field theory operators T0, T1, T2, T8, and T9. This is the first measurement of vector boson scattering in the ZZ channel at the LHC.
Highlights
Weak vector boson scattering (VBS) plays a central role in the standard model (SM) and is a key process to probe the non-Abelian gauge structure of the electroweak (EW) interaction
The discovery of a scalar boson at the CERN LHC [3,4] with gauge couplings compatible with those predicted for the SM Higgs boson [5] provides evidence that contributions from the exchange of this boson may be responsible for preserving unitarity at high energies, as predicted in the SM
Many models of physics beyond the SM alter the couplings of vector bosons, and the effects can be parametrized in an effective field theory approach [6]
Summary
Weak vector boson scattering (VBS) plays a central role in the standard model (SM) and is a key process to probe the non-Abelian gauge structure of the electroweak (EW) interaction. The qq → VVjj process can be mediated through the strong interaction (bottom right in Fig. 1), which leads to the same final state as the VBS signal, resulting in an irreducible background. Despite a low cross section, a small Z → ll branching fraction, and a large irreducible QCD background, this channel provides a favorable laboratory to study EWSB because all final-state particles are reconstructed. The clean leptonic final state results in a small reducible background, where one or more of the reconstructed lepton candidates originate from the misidentification of jet fragments. This channel provides a precise knowledge of the scattering energy. The selected lll′l′jj events are used to constrain aQGCs described by the operators T0, T1, and T2 as well as the neutralcurrent operators T8 and T9 [7]
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