Sirunyan, A. M.Işıldak, Bora2023-08-032023-08-032022-01-190031-9007http://hdl.handle.net/10679/8553https://doi.org/10.1103/PhysRevLett.128.032001The first evidence for X(3872) production in relativistic heavy ion collisions is reported. The X(3872) production is studied in lead-lead (Pb-Pb) collisions at a center-of-mass energy of √ s NN = 5.02     TeV per nucleon pair, using the decay chain X ( 3872 ) → J / ψ π + π − → μ + μ − π + π − . The data were recorded with the CMS detector in 2018 and correspond to an integrated luminosity of 1.7     nb − 1 . The measurement is performed in the rapidity and transverse momentum ranges | y | < 1.6 and 15 < p T < 50     GeV / c . The significance of the inclusive X(3872) signal is 4.2 standard deviations. The prompt X(3872) to ψ 2 S yield ratio is found to be ρ Pb − Pb = 1.08 ± 0.49 ( stat ) ± 0.52 ( syst ) , to be compared with typical values of 0.1 for p p collisions. This result provides a unique experimental input to theoretical models of the X(3872) production mechanism, and of the nature of this exotic state.engAttribution 4.0 InternationalopenAccesshttp://creativecommons.org/licenses/by/4.0/article128300074879980000210.1103/PhysRevLett.128.0320012-s2.0-85123710396