Chekhovsky, V.Hayrapetyan, A.Makarenko, V.Tumasyan, A.Adam, W.Andrejkovic, J. W.Druzhkin, D.2026-01-102026-01-1020250031-90071079-7114https://doi.org/10.1103/2ssw-wwyyXie, Wei/0000-0003-1430-9191; Bartek, Rachel/0000-0002-1686-2882; Sastre, Javier/0000-0002-1654-2846; Pesaresi, Mark/0000-0002-9759-1083; Hall, Geoffrey/0000-0002-6299-8385; Giacomo, Bolini/0000-0001-5490-605X; Grunewald, Martin/0000-0002-5754-0388; Jang, Woojin/0000-0002-1571-9072; Grunewald, Martin/0000-0002-5754-0388The 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/openAccessArticle10.1103/2ssw-wwyy2-s2.0-105026120906