Vector Boson Scattering prospective studies in the ZZ fully leptonic decay channel for the High-Luminosity and High-Energy LHC upgrades

Prospective studies for the vector boson scattering (VBS) in the ZZ channel at the HL-LHC are presented, where the Z bosons are identified and measured through their leptonic decays, $\ell = e, \mu$. The results obtained from the 2016 analysis with an integrated luminosity of $36~\mathrm{fb}^{-1}$ are projected to the HL-LHC luminosity of $3000~\mathrm{fb}^{-1}$ and center-of-mass energy of 14 TeV, taking into account the increased acceptance of the CMS detector. The projected uncertainty in the VBS ZZ cross section is 8.5--10.3$\%$ depending on the lepton $\eta$ coverage and assumptions made for the systematic uncertainties. A study is performed to separate the longitudinal polarization ($\mathrm{Z_L}$) from the dominant transverse polarizations. The expected sensitivity for the VBS $\mathrm{Z_LZ_L}$ fraction is $1.4$ standard deviations. The foreseen upgrade coverage of up to $\vert \eta \vert = 3(2.8)$ for electrons (muons) leads to a $13\%$ improvement in sensitivity compared to the Run 2 acceptance. Extending the coverage for electrons up to $\vert \eta \vert = 4$ would result in a modest increase in the sensitivity. Finally, the HE-LHC option would allow to bring the sensitivity at the 5$\sigma$ level for this process.