Measurements of $W^+W^- + \geq1$ jet production cross sections with the ATLAS detector

Measurements of cross sections for the production of pairs of oppositely charged $W$ bosons provide an important test of the Standard Model (SM), in particular electroweak theory and perturbative quantum chromodynamics. $WW$ production can additionally be a dominant background for measurements of Higgs boson production, and in searches for physics beyond the SM. In contrast to most previous measurements that have focused on $WW$ production in the absence of hadronic jets, due to the higher obtainable precision, here a measurement of $WW$ production in association with at least one hadronic jet is presented. This is motivated by an expected improved precision of fully inclusive $WW$ production cross sections in a future combined measurement, and additionally by an enhanced sensitivity to the linear effects of dimension-6 effective field theory operators with respect to the jet veto case. In this measurement, fiducial and differential cross sections are obtained using data collected in $\sqrt{s} = 13$ TeV collisions at the ATLAS detector, corresponding to an integrated luminosity of 139 fb$^{-1}$. Events are selected with exactly one electron and one muon of opposite charge and at least one hadronic jet with a transverse momentum of $p_{\mathrm{T}}$ > 30 GeV and a pseudo rapidity of $|\eta|$ < 4.5. Background contributions are estimated using a combination of simulation and data-driven techniques. The dominant background from $t\bar{t}$ events is precisely estimated using a data-driven method that significantly reduces experimental and modeling uncertainties. Differential results are used to place constraints on a dimension-6 effective field theory coefficient.