Speaker
Description
We present the first study of coherent exclusive J/psi photoproduction in ultraperipheral collisions (UPCs) of heavy and intermediate ions at the LHC in the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD and make predictions for the J/psi rapidity distributions for the cases of lead (Pb) and oxygen (O) beams. We confirm the general expectation of a dramatic role of NLO corrections, quantify the significant uncertainties associated with used nuclear PDFs and the choice of hard scale, and determine an "optimal scale" allowing for a simultaneously good description of all available Run 1 and Run 2 LHC data on J/psi photoproduction in Pb-Pb UPCs. One of the major results of our study is the counter-intuitive observation that at central rapidities,
the cross section is dominated by the quark contribution since the gluon one largely cancels in the sum of the (leading-order) LO and the NLO terms. To better control the theoretical uncertainties, we advocate the use of the ratio of UPC cross sections on oxygen and lead, for which we make detailed predictions.
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