Prospects for the measurement of the $W^{\pm}W^{\pm}$ scattering cross section and extraction of the longitudinal scattering component in $pp$ collisions at the High-Luminosity LHC with the ATLAS experiment}

Prospects for measuring the \ssWW vector boson scattering process with 3000\ifb of proton-proton collisions at $\sqrt{s}$ = 14 TeV at the High-Luminosity Large Hadron Collider are studied. Events containing two same-sign leptons, missing transverse momentum, and at least two jets are analysed using simulated events parameterised to take into account the expected detector effects, and the typically-data-driven backgrounds arising from charge misidentification and jets faking leptons are also included using the parameterisation functions. The cross section for the electroweak production process is extracted from a fit to the dijet invariant mass distribution, and an expected total uncertainty of 6% is achieved. We find the purely longitudinal scattering component can be extracted with an expected significance of 1.8$\sigma$ from a binned likelihood fit to the dijet azimuthal separation distribution.