Speakers
Description
Heavy ions accelerated at ultra-relativistic energies generate a strong electromagnetic field, leading to photon-photon and photonuclear interactions during the collision. The photoproduction of the J/$\psi$ vector meson has been widely studied in ultra-peripheral collisions with an impact parameter larger than twice the ion radius, where hadroproduction is negligible. In the last few years, this study was extended to heavy-ion collisions with nuclear overlap. The large intensity of the electromagnetic field and the unique kinematic features allowed for the observation of coherently photoproduced J/$\psi$ in peripheral and semi-central collisions, despite the growing contribution of the hadroproduction. J/$\psi$ originated through this mechanism are sensitive probes the nuclear gluon distributions at low Bjorken-$x$ values, and their production measurements might be used in the future to probe the fast-expanding quark-gluon plasma that it is formed during the collision.
The ALICE Collaboration measured the coherent J/$\psi$ photoproduction in Pb--Pb collisions with nuclear overlap at a center of mass energy per nucleon of 5.02 TeV, using the full Run 2 data sample. In this contribution we report on the final results at forward rapidity in the dimuon decay channel and the preliminary results at midrapidity in the dielectron decay channel. At forward rapidity the coherent J/$\psi$ cross section is measured in the centrality ranges 30-90% and 10-30%, although with limited statistical significance in the latter. An upper limit is provided in the centrality range 0-10%. The results are compared with a previous measurement at a lower center of mass energy per nucleon of 2.76 TeV. At midrapidity, the transverse momentum differential cross section was measured for the first time in the 50-70% and 70-90% centrality ranges, thanks to the excellent tracking resolution of the ALICE Time Projection Chamber. The comparison with the available model calculations will be presented as well.
| Submitted on behalf of a Collaboration? | Yes |
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