Chekhovsky, V.Hayrapetyan, A.Makarenko, V.Tumasyan, A.Adam, W.Andrejkovic, J. W.Druzhkin, D.2026-03-152026-03-1520250031-90071079-711410.1103/2ssw-wwyyhttps://doi.org/10.1103/2ssw-wwyyhttps://hdl.handle.net/20.500.14517/8902Luukka, Panja/0000-0003-2340-4641; Hall, Geoffrey/0000-0002-6299-8385; Pesaresi, Mark/0000-0002-9759-1083; Osterberg, Kenneth/0000-0003-4807-0414; Sastre, Javier/0000-0002-1654-2846; Tapper, Alexander/0000-0003-4543-864X; Grunewald, Martin/0000-0002-5754-0388; Tuominiemi, Jorma/0000-0003-0386-8633; Lorusso, Marco/0000-0003-4033-4956; Viinikainen, Jussi/0000-0003-2530-4265; Lampén, Tapio/0000-0002-8398-4249; Lindén, Tomas/0009-0002-4847-8882; Della Ricca, Giuseppe/0000-0003-2831-6982; Della Ricca, Giuseppe/0000-0003-2831-6982; Martikainen, Laura/0000-0003-1609-3515; Xie, Wei/0000-0003-1430-9191; Lorusso, Marco/0000-0003-4033-4956; Della Ricca, Giuseppe/0000-0003-2831-6982; Barroso Ferreira Filho, Mapse/0000-0003-3904-0571; Grunewald, Martin/0000-0002-5754-0388; El-Mahdy, Basma/0000-0002-1979-8548; Lampén, Tapio/0000-0002-8398-4249; Bartek, Rachel/0000-0002-1686-2882; Luukka, Panja/0000-0003-2340-4641; Voutilainen, Mikko/0000-0002-5200-6477; Lindén, Tomas/0009-0002-4847-8882; Giacomo, Bolini/0000-0001-5490-605X; Jang, Woojin/0000-0002-1571-9072The 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/openAccessArticle