Coherent J/ψ and ψ photoproduction at midrapidity in ultra-peripheral Pb–Pb collisions at √sNN = 5.02 TeV

• Main Authors: Rinella, G. Aglieri, Bai, X, Balbino, A, Barret, V, Bauri, D, Bellini, F, Biro, G, Blidaru, M.B, Boca, G, Bombara, M, Calvo Villar, Villar, Cicalo, C, Cormier, T.M, Costa, F, Das, P, Dubey, A.K, Dubla, A, Ersdal, Magnus Rentsch, Fasel, M, Feliciello, A, Finogeev, D, Funicello, N, Furget, C, Ghosh, J, Giacalone, M, Glaenzer, A.M.C, Görlich, L, Grigoras, C, Grosso, R, Guernane, R, Hetland, K.F, Hornung, S, Hosokawa, R, Huang, C, Hushnud, H, Kileng, Bjarte, Kim, E.J, Kisel, I, Konopka, P.J, Kovalenko, V, Králik, I, Krivda, M, Kurashvili, P, Kurepin, A, Kweon, M.J, Kwon, J.Y, La Pointe, Pointe, Langøy, Rune, Martin, N.A, Masera, M, Micheletti, L, Mishra, A.N, Modak, A, Moravcova, Z, Munzer, R.H, Musa, L, Nesterov, D, Nikulin, S, Noferini, F, Silva, A. C. Oliveira Da, Otwinowski, J, Park, J, Pei, H, Peresunko, D, Pestov, Y, Pinto, C, Puccio, M, Raniwala, R, Raniwala, S, Richert, T, Rode, S.P, Rueda, O.V, Saha, S.K, Sahoo, S, Scomparin, E, Senyukov, S, Seo, J.J, Silvermyr, D, Smirnov, N, Suaide, A.A.P, Sugitate, T, Suljic, M, Sultanov, R, Sumberia, V, Szarka, I, Takahashi, J, Terlizzi, L, Tersimonov, G, Trubnikov, V, Turrisi, R, Ullaland, Kjetil, Urioni, M, Vázquez Doce, Doce, Wagner, Boris, Wessels, J.P, Yang, Shiming, Yoo, I.-K, Zampolli, C, Zhalov, M, Zhi, Y
• Format: Article
• Language: English

The coherent photoproduction of J/ψJ/ψ and ψ′ψ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN−−−√ = 5.02sNN = 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 J/ψJ/ψ is reconstructed using the dilepton (l+l−l+l−) and proton–antiproton decay channels, while for the ψ′ψ′ the dilepton and the l+l−π+π−l+l−π+π− decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 μb−1μb−1. The results are compared with theoretical models for coherent J/ψJ/ψ and ψ′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 6×10−46×10−4, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J/ψJ/ψ cross section including ALICE measurements at forward rapidity. The ratio of ψ′ψ′ to J/ψJ/ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.