Searching for New Heavy Neutral Gauge Bosons using Vector Boson Fusion Processes at the LHC

Abstract: New massive resonances are predicted in many extensions to the Standard Model (SM) of particle physics and constitutes one of the most promising searches for new physics at the LHC. We present a feasibility study to search for new heavy neutral gauge bosons using vector boson fusion (VBF) processes, which become especially important as the LHC probes higher collision energies. In particular, we consider the possibility that the discovery of a $Z'$ boson may have eluded searches at the LHC. The coupling of the $Z'$ boson to the SM quarks can be small, and thus the $Z'$ would not be discoverable by the searches conducted thus far. In the context of a simplified phenomenological approach, we consider the $Z'\to\tau\tau$ and $Z'\to\mu\mu$ decay modes to show that the requirement of a dilepton pair combined with two high $p_{T}$ forward jets with large separation in pseudorapidity and with large dijet mass is effective in reducing SM backgrounds. The expected exclusion bounds (at 95\% confidence level) are $m(Z') < 1.8$ TeV and $m(Z') < 2.5$ TeV in the $\tau\tau j_{f}j_{f}$ and $\mu\mu j_{f}j_{f}$ channels, respectively, assuming 1000 fb$^{-1}$ of 13 TeV data from the LHC. The use of the VBF topology to search for massive neutral gauge bosons provides a discovery reach with expected significances greater than 5$\sigma$ (3$\sigma$) for $Z'$ masses up to 1.4 (1.6) TeV and 2.0 (2.2) TeV in the $\tau\tau j_{f}j_{f}$ and $\mu\mu j_{f}j_{f}$ channels.