Aad, G.Aakvaag, E.Abbott, B.Abdelhameed, S.Abeling, K.Abicht, N.J.Abidi, S.H.Aboelela, M.Aboulhorma, A.Abramowicz, H.Abreu, H.Abulaiti, Y.Acharya, B.S.Ackermann, A.Adam Bourdarios, C.Adamczyk, L.Addepalli, S.V.Addison, M.J.Adelman, J.Adiguzel, A.et al.2025-10-232025-10-232025Physical Review Letters, 2025; 134(6):061803-1-061803-240031-90071079-7114https://hdl.handle.net/2440/147969This Letter presents a search for highly ionizing magnetic monopoles in 262 μb⁻¹ of ultraperipheral Pb + Pb collision data at √sNN = 5.36 TeV collected by the ATLAS detector at the LHC. A new methodology that exploits the properties of clusters of hits reconstructed in the innermost silicon detector layers is introduced to study highly ionizing particles in heavy-ion data. No significant excess above the background, which is estimated using a data-driven technique, is observed. Using a nonperturbative semiclassical model, upper limits at 95% confidence level are set on the cross section for pair production of monopoles with a single Dirac magnetic charge in the mass range of 20–150 GeV. Depending on the model, monopoles with a single Dirac magnetic charge and mass below 80–120 GeV are excluded.enPublished by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by CERN.Particle production; Quantum electrodynamics; Hypothetical particles; Magnetic monopolesJournal article10.1103/physrevlett.134.061803729047Gallagher, J. [0000-0001-9284-6270]Jackson, P. [0000-0002-0847-402X]Kong, A.X.Y. [0000-0001-8063-8765]Oliver, J.L. [0000-0002-0713-6627]Pandya, H.D. [0000-0002-1199-945X]Potti, H. [0000-0002-0800-9902]Ruggeri, T.A. [0000-0001-9941-1966]Ting, E.X.L. [0000-0002-5886-6339]White, M.J. [0000-0001-5474-4580]