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.