New neutral vector bosons Z decaying to charged gauge boson pairs W + W − are predicted in many scenarios of new physics, including models with an extended gauge sector such as E6, leftright symmetric Z LRS and the sequential standard model Z SSM . For these benchmark models we calculate and present theoretical expectations for different values of the Z mass M2 and mixing parameter ξ. Our results are based on the narrow width approximation which allows to make a convenient comparison of experiment to theoretical benchmark models. The diboson production allows to place stringent constraints on the Z-Z mixing angle and the Z mass, which we determine by using data from pp collisions at √ s = 13 TeV recorded by the ATLAS detector at the CERN LHC, with integrated luminosity of ∼ 36 fb −1 . By comparing the experimental limits to the theoretical predictions for the total cross section of Z resonant production and its subsequent decay into W + W − pairs, we show that the derived constraints on the mixing angle for the benchmark models are of the order of a few ×10 −4 , i.e., greatly improved with respect to those derived from the global analysis of electroweak data. We combine the limits derived from diboson production data with those obtained from the Drell-Yan process in order to significantly extend the exclusion region in the M2-ξ parameter plane. Also, we demonstrate that further improvement on the constraining of this mixing can be achieved through analysis of the full set of Run II data. * boboilya@yandex.by † Per.Osland@uib.no ‡ pankov@ictp.it arXiv:1809.08933v2 [hep-ph]

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Abstract. We consider the sensitivity of the International Linear Collider (ILC) to probe Z − Z mixing and Z mass by the reaction e + e − → W + W − with longitudinally polarized e + e − beams. We perform here a generic analysis of the deviations of the differential cross section from the Standard Model prediction, and apply it to a specific class of extended weak gauge models called as 'minimal-Higgs' models.