PT Journal AU ATLAS Collaboration (Aad, Gea Aikot, A Amos, KR Aparisi Pozo, JA Bailey, AJ Bouchhar, N Cabrera Urban, S Cantero, J Cardillo, F Castillo Gimenez, V Chitishvili, M Costa, MJ Didenko, M Escobar, C Fiorini, L Fullana Torregrosa, E Fuster, J Garcia, C Garcia Navarro, JE Gomez Delegido, AJ Gonzalez de la Hoz, S Gonzalvo Rodriguez, GR Guerrero Rojas, JGR Lacasta, C Marti-Garcia, S Martinez Agullo, P Miralles Lopez, M Mitsou, VA Monsonis Romero, L Moreno Llacer, M Munoz Perez, D Navarro-Gonzalez, J Poveda, J Prades Ibañez, A Rubio Jimenez, A Ruiz-Martinez, A Sabatini, P Salt, J Sanchez Sebastian, V Sayago Galvan, I Senthilkumar, V Soldevila, U Sanchez, J Torro Pastor, E Valero, A Valiente Moreno, E Valls Ferrer, JA Varriale, L Villaplana Perez, M Vos, M TI Search for lepton-flavour violation in high-mass dilepton final states using 139 fb−1 of pp collisions at root s= 13 TeV with the ATLAS detector SO Journal of High Energy Physics JI J. High Energy Phys. PY 2023 BP 082 EP 49pp VL 10 IS 10 DI 10.1007/JHEP10(2023)082 AB A search is performed for a heavy particle decaying into different-flavour, dilepton final states, using 139 fb−1 of proton-proton collision data at = 13 TeV collected in 2015–2018 by the ATLAS detector at the Large Hadron Collider. Final states with electrons, muons and hadronically decaying tau leptons are considered (eμ, eτ or μτ). No significant excess over the Standard Model predictions is observed. Upper limits on the production cross-section are set as a function of the mass of a Z′ boson, a supersymmetric τ-sneutrino, and a quantum black-hole. The observed 95% CL lower mass limits obtained on a typical benchmark model Z′ boson are 5.0 TeV (eμ), 4.0 TeV (eτ), and 3.9 TeV (μτ), respectively. ER