  Measuring longitudinally polarised vector boson scattering in WW channel is a
promising way to investigate unitarity restoration with the Higgs mechanism and
to search for possible physics beyond the Standard Model. In order to perform
such a measurement, it is crucial to develop an efficient reconstruction of the
full W boson kinematics in leptonic decays with the focus on polarisation
measurements. We investigated several approaches, from traditional ones up to
advanced deep neural network structures, and we compared their ability to
reconstruct the W boson reference frame and to consequently measure the
longitudinal fraction W_L in both semi-leptonic and di-leptonic WW decay
channels.
