%0 Journal Article %T Observation of the γγ → ττ Process in Pb plus Pb Collisions and Constraints on the τ-Lepton Anomalous Magnetic Moment with the ATLAS Detector %A ATLAS Collaboration (Aad, G. et al %A Amos, K. R. %A Aparisi Pozo, J. A. %A Bailey, A. J. %A Cabrera Urban, S. %A Cantero, J. %A Cardillo, F. %A Castillo Gimenez, V. %A Costa, M. J. %A Didenko %A Escobar, C. %A Fiorini, L. %A Fullana Torregrosa, E. %A Fuster, J. %A Garcia, C. %A Garcia Navarro, J. E. %A Gomez Delegido, A. J. %A Gonzalez de la Hoz, S. %A Gonzalvo Rodriguez, G. R. %A Guerrero Rojas, J. G. R. %A Higon-Rodriguez, E. %A Lacasta, C. %A Lozano Bahilo, J. J. %A Marti-Garcia, S. %A Martinez Agullo, P. %A Miralles Lopez, M. %A Mitsou, V. A. %A Monsonis Romero, L. %A Moreno Llacer, M. %A Munoz Perez, D. %A Navarro-Gonzalez, J. %A Poveda, J. %A Prades Ibañez, A. %A Rubio Jimenez, A. %A Ruiz-Martinez, A. %A Sabatini, P. %A Salt, J. %A Sanchez Sebastian, V. %A Sayago Galvan, I. %A Senthilkumar, V. %A Soldevila, U. %A Sanchez, J. %A Torro Pastor, E. %A Valero, A. %A Valls Ferrer, J. A. %A Varriale, L. %A Villaplana Perez, M. %A Vos, M. %J Physical Review Letters %D 2023 %V 131 %N 15 %I Amer Physical Soc %@ 0031-9007 %G English %F ATLASCollaborationAad_etal2023 %O WOS:001094306100001 %O exported from refbase (https://references.ific.uv.es/refbase/show.php?record=5837), last updated on Mon, 18 Dec 2023 08:45:05 +0000 %X This Letter reports the observation of tau-lepton-pair production in ultraperipheral lead-lead collisions Pb + Pb -> Pb(gamma gamma -> tau tau)Pb and constraints on the tau-lepton anomalous magnetic moment a(tau). The dataset corresponds to an integrated luminosity of 1.44 nb(-1) of LHC Pb + Pb collisions at root(NN)-N-s = 5.02 TeV recorded by the ATLAS experiment in 2018. Selected events contain one muon from a t-lepton decay, an electron or charged-particle track(s) from the other tau-lepton decay, little additional central-detector activity, and no forward neutrons. The gamma gamma -> tau tau process is observed in Pb + Pb collisions with a significance exceeding 5 standard deviations and a signal strength of mu(tau tau) = 1.03(-0.05)(+0.06) assuming the standard model value for a(tau). To measure a(tau), a template fit to the muon transverse-momentum distribution from tau-lepton candidates is performed, using a dimuon (gamma gamma -> μmu) control sample to constrain systematic uncertainties. The observed 95% confidence-level interval for a(tau) is -0.057 < a(tau) < 0.024. %R 10.1103/PhysRevLett.131.151802 %U https://arxiv.org/abs/2204.13478 %U https://doi.org/10.1103/PhysRevLett.131.151802 %P 151802-23pp