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  • Coherent $$\mathrm{J}/\psi ...
    Adamová, D.; Agnello, M.; Ali, B.; Andrei, C.; Antonioli, P.; Arcelli, S.; Basu, S.; Belokurova, S.; Berdnikova, A.; Bhattacharya, P.; Bombara, M.; Butt, J. B.; Bysiak, S. A.; Calvo Villar, E.; Camerini, P.; Caron, R.; Chattopadhyay, S.; Christensen, C. H.; Clai, G.; Collu, A.; Cormier, T. M.; Cui, P.; Damas, F. P. A.; Danisch, M. C.; Das, S.; Evdokimov, S.; Figiel, J.; Finogeev, D.; Flor, F.; Foka, P.; Gaardhøje, J. J.; Gianotti, P.; Glässel, P.; Graham, K. L.; Guzman, I. B.; Harton, A.; Innocenti, G. M.; Ivanov, V.; Jaelani, S.; Keidel, R.; Khanzadeev, A.; Kim, H.; Kirsch, S.; Kisel, I.; Klein, J.; Kovalenko, O.; Králik, I.; Kravčáková, A.; Kurepin, A. B.; Lai, Y. S.; Lien, J.; Lindenstruth, V.; Lofnes, I. M.; Malinina, L.; Mandaglio, G.; García, G. Martínez; Masera, M.; Melikyan, Y.; Mihaylov, D. L.; Modak, A.; Noferini, F.; Pachmayer, Y.; Paić, G.; Peitzmann, T.; Peng, X.; Pezzi, R. P.; Reichelt, P.; Riegler, W.; Rogochaya, E.; Rohr, D.; Rojas, P. F.; Rui, R.; Sahoo, B.; Saini, J.; Schiaua, C.; Shabetai, A.; Sharma, N.; Silva, T. F. D.; Sitta, M.; Sputowska, I.; Stiefelmaier, S. F.; Sugitate, T.; Szabo, A.; Telesca, A.; Timmins, A. R.; Toppi, M.; Tripathy, T.; Vino, G.; Volkel, B.; Voloshin, S. A.; Vorobyev, I.; Wagner, B.; Wessels, J. P.; Yokoyama, H.; Yoon, J. H.; Zaviyalov, N.; Zbroszczyk, H.; Zhang, S.; Zhu, Y.; Zichichi, A.

    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.