The ATLAS experiment at the Large Hadron Collider (LHC) pursues a wide and comprehensive program of searches for new physics Beyond the Standard Model (BSM). In this summary the results of two searches for new resonances in leptonic final states are presented. The data were recorded by the ATLAS experiment in proton–proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV during Run 2 of the LHC.
A search for a new heavy, charged $W'$ boson decaying into an electron or muon and a neutrino was conducted using an integrated luminosity of 79.8 fb$^{-1}$. As no excess of events above the Standard Model prediction is observed, the results are used to set upper limits on the $W'$ boson cross-section times branching ratio to an electron or muon and a neutrino as a function of the $W'$ mass. Assuming a $W'$ boson with the same couplings as the Standard Model $W$ boson, $W'$ masses below 5.6 TeV are excluded at the 95% confidence level.
A search for high-mass dielectron and dimuon resonances in the mass range of 250 GeV to 6 TeV was conducted using an integrated luminosity of 139 fb$^{-1}$. No significant deviation is observed, and upper limits are placed at the 95% confidence level on the fiducial cross-section times branching ratio for various resonance width hypotheses. For a set of benchmark models, the limits are converted into lower limits on the resonance mass and reach 4.5 TeV for the E$_6$-motivated $Z'_{\psi}$ boson.