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  • Coherent $$\ rm {NN}}}~=~5....
    ALICE Collaboration; S. Acharya; G. Aglieri Rinella; S. Ahmad; B. Ali; L. Aphecetche; H. Appelshäuser; R. Averbeck; A. Balbino; A. Baldisseri; R. Bellwied; L. Bianchi; H. Borel; H. Bossi; L. Bratrud; M. Bregant; G. E. Bruno; J. M. M. Camacho; P. Chochula; C. H. Christensen; G. Clai; G. Contin; M. R. Cosentino; P. Crochet; S. De; V. N. Eikeland; D. Elia; M. R. Ersdal; A. Feliciello; V. J. G. Feuillard; D. Finogeev; C. Garabatos; M. Germain; A. Harlenderova; A. Harton; P. Hauer; S. T. Heckel; H. Helstrup; T. Herman; B. Hohlweger; H. Hushnud; M. S. Islam; M. Ivanov; N. Jacazio; B. Kileng; S. Klein; C. Kobdaj; A. Kravčáková; P. Larionov; T. Lazareva; M. Lettrich; X. Li; C. Lippmann; V. Loginov; M. Malaev; V. Manzari; A. Margotti; S. Masciocchi; Y. Miake; A. N. Mishra; L. A. P. Moreno; T. Mrnjavac; J. W. Myrcha; B. Naik; P. Nomokonov; J. Norman; P. Nowakowski; J. Pazzini; I. Pshenichnov; S. Qiu; L. Quaglia; R. Raniwala; S. S. Räsänen; P. Roy; R. Rui; A. Rybicki; B. Sahoo; V. Samsonov; A. Shabetai; A. I. Sheikh; B. Singh; R. Singh; S. F. Stiefelmaier; D. Thomas; W. H. Trzaska; K. Ullaland; E. N. Umaka; A. Uras; P. Vande Vyvre; D. Varga; O. Vázquez Doce; M. Verweij; T. Virgili; G. Volpe; B. von Haller; J. Vrláková; J. H. Yoon; C. Zampolli; M. Zhalov; Y. Zhi

    The European physical journal. C, Particles and fields, 08/2021, Letnik: 81, Številka: 8
    Journal Article

    Abstract The coherent photoproduction of $$\mathrm{J}/\psi $$ J / ψ and $${\uppsi '}$$ ψ ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy $$\sqrt{s_{\mathrm {NN}}}~=~5.02$$ s NN = 5.02  TeV  with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The $$\mathrm{J}/\psi $$ J / ψ is reconstructed using the dilepton ( $$l^{+} l^{-}$$ l + l - ) and proton–antiproton decay channels, while for the $${\uppsi '}$$ ψ ′   the dilepton and the $$l^{+} l^{-} \pi ^{+} \pi ^{-}$$ l + l - π + π - decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 $$\mu {\mathrm{b}}^{-1}$$ μ b - 1 . The results are compared with theoretical models for coherent $$\mathrm{J}/\psi $$ J / ψ and $${\uppsi '}$$ ψ ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around $$6\times 10^{-4}$$ 6 × 10 - 4 , such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent $$\mathrm{J}/\psi $$ J / ψ cross section including ALICE measurements at forward rapidity. The ratio of $${\uppsi '}$$ ψ ′ to $$\mathrm{J}/\psi $$ J / ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.