Measurement and effective field theory interpretation of the photon-fusion production cross section of a pair of W bosons in proton-proton collisions at s = 13 TeV

This analysis presents an observation of the photon-fusion production of W boson pairs using the CMS detector at the LHC. The total cross section of the W^+W^- production in photon fusion is measured using proton-proton collision data with an integrated luminosity of 138 fb^-1 collected with the CMS detector in 2016-2018 at a center-of-mass energy of s = 13 TeV. Events are selected in the final state with one isolated electron and one isolated muon, and no additional tracks associated with the electron-muon production vertex. The total and fiducial production cross sections are 643^+82-₇₈ fb and 3. 96^+0. 53-₀. ₅₁ fb, respectively, in agreement with the standard model predictions of 631 126 fb and 3. 87 0. 77 fb. This agreement enables stringent constraints to be imposed on anomalous quartic gauge couplings within a dimension-8 effective field theory framework.