Improved constraints on the mixing and mass of $Z^{\prime }$ bosons from resonant diboson searches at the LHC at $\sqrt{s}=13$ TeV and predictions for Run II

Abstract

New neutral vector bosons $Z^{\prime }$ 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 $E_6$, left-right symmetric $Z_{\mathrm{LRS}}^{\prime }$ and the sequential standard model $Z_{\mathrm{SSM}}^{\prime }$. For these benchmark models we calculate and present theoretical expectations for different values of the $Z^{\prime }$ mass $M_2$ and mixing parameter $\xi$. 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 $Z$-$Z^{\prime }$ mixing angle and the $Z^{\prime }$ mass, which we determine by using data from $pp$ collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the CERN LHC, with integrated luminosity of $\sim$ 36 fb${}^{-1}$. By comparing the experimental limits to the theoretical predictions for the total cross section of $Z^{\prime }$ 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 $\times 10^{-4}$, 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 $M_2$-$\xi$ 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.

Comments: 16 pages, some figures. arXiv admin note: text overlap with arXiv:1707.02717, arXiv:1406.6776. v2: version to appear in PRD