Coherent J/$\ddot{I}ˆ$ photoproduction at midrapidity in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

Abstract

The coherent J/$\ddot{I}ˆ$ photoproduction cross section is measured for the first time at midrapidity in peripheral to semicentral Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. The centrality differential cross section $\mathrm{d}\ddot{I}ƒ/\mathrm{d}y$ is reported for the centrality range 40-90%, together with the doubly-differential cross section ${\mathrm{d}}^2\ddot{I}ƒ/\mathrm{d}y\mathrm{d}{p}_{\mathrm{T}}$, extracted in two peripheral centrality classes. The J/$\ddot{I}ˆ$ mesons are reconstructed in the dielectron channel, in the rapidity interval $|y|<0.9$ using the ALICE central barrel detectors. The J/$\ddot{I}ˆ$ cross section at midrapidity is statistically compatible to the earlier ALICE measurement at forward rapidity and at the same centre-of-mass energy, and shows only a mild centrality dependence over the covered range. Several sets of theoretical calculations taking into account the hadronic overlap in the collisions but ignoring possible final-state effects from a hot expanding medium are found to give a fairly good description of the current measurements within uncertainties.

23 pages, 3 captioned figures, 1 table, authors from page 17, figures at http://alice-publications.web.cern.ch/node/11308