Hayrapetyan, A.Tumasyan, A.Adam, W.Andrejkovic, J. W.Benato, L.Bergauer, T.Druzhkin, D.2025-01-102025-01-1020240031-90071079-7114https://doi.org/10.1103/PhysRevLett.133.161805Navarrete Ramos, Efren/0000-0002-5180-4020; Rossi Tisbeni, Simone/0000-0001-6776-285X; Da Cruz E Silva, Cristovao/0000-0002-1231-3819; Della Ricca, Giuseppe/0000-0003-2831-6982; Radogna, Raffaella/0000-0002-1094-5038; Martinez Rivero, Celso/0000-0002-3224-956X; Cipriani, Marco/0000-0002-0151-4439; Asenov, Patrick/0000-0003-2379-9903; Battilana, Carlo/0000-0002-3753-3068; Hall, Geoffrey/0000-0002-6299-8385; Tapper, Alexander/0000-0003-4543-864X; Giommi, Luca/0000-0003-3539-4313; Moscatelli, Francesco/0000-0002-7676-3106; Grunewald, Martin/0000-0002-5754-0388; Colaleo, Anna/0000-0002-0711-6319; Pesaresi, Mark/0000-0002-9759-1083; Calderon, Dr. Alicia/0000-0002-7205-2040; Milosevic, Vukasin/0000-0002-1173-0696; Ligabue, Franco/0000-0002-1549-7107; Perez Adan, Danyer/0000-0003-3416-0726The first search for the Z boson decay to tau tau mu mu at the CERN LHC is presented, based on data collected by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb(-1). The data are compatible with the predicted background. For the first time, an upper limit at the 95% confidence level of 6.9 times the standard model expectation is placed on the ratio of the Z -> tau tau mu mu to Z -> 4 mu branching fractions. Limits are also placed on the six flavor-conserving four-lepton effective-field-theory operators involving two muons and two tau leptons, for the first time testing all such operators.eninfo:eu-repo/semantics/openAccessArticle10.1103/PhysRevLett.133.1618052-s2.0-85208290971