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

作者：Acharya, S.; Adamova, D.; Adler, A.; Adolfsson, J.; Rinella, G. Aglieri; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; Akbar, Z.; Akindinov, A.; Al-Turany, M.; Albuquerque, D. S. D.; Aleksandrov, D.; Alessandro, B.; Alfanda, H. M.; Molina, R. Alfaro; Ali, B.; Ali, Y.; Alici, A.; Alizadehvandchali, N.; Alkin, A.; Alme, J.; Alt, T.; Altenkamper, L.; Altsybeev, I; Anaam, M. N.; Andrei, C.; Andreou, D.; Andronic, A.; Anguelov, V; Antinori, F.; Antonioli, P.; Anuj, C.; Apadula, N.

来源：European Physical Journal C, 2021, 81(8): 712.

DOI：10.1140/epjc/s10052-021-09437-6

• DIFFRACTIVE PHOTOPRODUCTION
• PSI(2S) MESONS
• NUCLEUS
• PHYSICS

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