Observation of photon-induced W+W− production in pp collisions at s=13 TeV using the ATLAS detector

Abstract

This letter reports the observation of photon-induced production of W-boson pairs, γ γ → W W. The analysis uses 139 fb −1 of LHC proton-proton collision data taken at √ s = 13 TeV recorded by the ATLAS experiment during the years 2015-2018. The measurement is performed selecting one electron and one muon, corresponding to the decay of the diboson system as W W → e ± νμ ∓ ν final state. The background-only hypothesis is rejected with a significance of well above 5 standard deviations consistent with the expectation from Monte Carlo simulation. A cross section for the γ γ → W W process of 3.13 ± 0.31(stat.) ± 0.28(syst.) fb is measured in a fiducial volume close to the acceptance of the detector, by requiring an electron and a muon of opposite signs with large dilepton transverse momentum and exactly zero additional charged particles. This is found to be in agreement with the Standard Model prediction.

White Paper on Forward Physics, BFKL, Saturation Physics and Diffraction

“…Unlike the two previous instances, the γγ → W + W − process is induced at tree-level in the SM via the triple γW W and quartic couplings γγW W in the electroweak sector [501]. The process has been observed already by the ATLAS Collaboration without the use of proton tagging by focusing on the purely leptonic decay channel [502]. However, in order to probe a region of phase-space that is sensitive to modifications of the SM interactions (high-mass modifications specifically), the proton tagging technique is necessary [500].…”

Search for low-mass leptoquarks using the llqq final states in Pb-Pb ultra-peripheral collisions

“…If we have real data samples, we can apply further requirements to suppress the background due to the hadronic Pb-Pb interactions: 1) no additional charged tracks in the inner detector and no additional energy deposit from neutral particles in the calorimeters as used in refs. [78,79]; 2) no significant energy deposit in the Zero Degree Calorimeters [80] for the ATLAS detector (because the Pb nuclei are intact in UPCs) as used in ref. [81]; JHEP08(2021)071…”