A
bstract
A first study is presented of the cross section for the scattering of same-sign W boson pairs via the detection of a
τ
lepton. The data from proton-proton collisions at the center-of-mass energy of 13 TeV were collected by the CMS detector at the LHC, and correspond to an integrated luminosity of 138 fb
−1
. Events were selected that contain two jets with large pseudorapidity and large invariant mass, one
τ
lepton, one light lepton (e or
μ
), and significant missing transverse momentum. The measured cross section for electroweak same-sign WW scattering is
$${1.44}_{-0.56}^{+0.63}$$
times the standard model prediction. In addition, a search is presented for the indirect effects of processes beyond the standard model via the effective field theory framework, in terms of dimension-6 and dimension-8 operators.