Chekhovsky, V.Hayrapetyan, A.Makarenko, V.Tumasyan, A.Adam, W.Andrejkovic, J. W.Benato, L.2026-04-252026-04-2520250031-90071079-7114https://doi.org/10.1103/2ssw-wwyyhttps://hdl.handle.net/11486/8411The first observation of coherent phi(1020) meson photoproduction off heavy nuclei is presented using ultraperipheral lead-lead collisions at a center-of-mass energy per nucleon pair of 5.36 TeV. The data were collected by the CMS experiment and correspond to an integrated luminosity of 1.62 mu b(-1). The phi(1020) meson signals are reconstructed via the K+K- decay channel. The production cross section is presented as a function of the phi(1020) meson rapidity in the range 0.3 < vertical bar y vertical bar < 1.0, probing gluons that carry a fraction of the nucleon momentum (x) around 10(-4). The observed cross section exhibits little dependence on rapidity and is significantly suppressed, by a factor of similar to 5, compared to a baseline model that treats a nucleus as a collection of free nucleons. Theoretical models that incorporate the nuclear shadowing effect generally provide a better description of the phi(1020) data than those incorporating gluon saturation. This study establishes a powerful new tool for exploring nuclear effects and nuclear gluonic structure in the small-x regime at a unique energy scale bridging the perturbative and nonperturbative quantum chromodynamics domains.eninfo:eu-repo/semantics/openAccess#BAŞV!Article1352610.1103/2ssw-wwyy415574092-s2.0-105026120906Q1WOS:001654859300001Q10000-0003-2340-46410000-0003-4033-49560000-0002-6226-957X0000-0002-8087-31990000-0002-8398-42490000-0002-9270-56430000-0003-1803-0999