The VII-th International Conference on the Initial Stages of High-Energy Nuclear Collisions : Initial Stages 2023

New ALICE results of the energy dependence of coherent photoproduction of $J/\psi$ in ultra-peripheral Pb--Pb collisions

Jun 20, 2023, 4:50 PM

20m

Aud. 3 (H.C. Ørsted)

Oral Physics at low-x and gluon saturation Parallel Session 4

Speaker

Joakim Nystrand (University of Bergen (NO))

Description

Photon-induced reactions in ultra-peripheral collisions (UPCs) of heavy nuclei at the LHC have been studied using the ALICE detector for several years. The ALICE detector can measure the photoproduction cross section for vector mesons at various rapidities, centre-of-mass energies and collision systems. Beyond the recent ALICE studies of the rapidity and momentum transfer dependence of coherent $J/\psi$ photoproduction, new results on coherent $J/\psi$ measurements with forward neutron tagging will be presented for the first time. The coherent production of $J/\psi$ accompanied by electromagnetic nuclear dissociation (EMD) has been performed in a large range of the $J/\psi$ rapidity covering $0<|y|<4$, with the $J/\psi$ reconstructed through its decay channels into a lepton pair. Having cross sections in a given rapidity but with different configurations of EMD allows for the extraction of the energy dependence of this process in the range $17< W_{\rm\gamma Pb} < 920$ GeV, where $W_{\rm\gamma Pb}$ is the centre-of-mass energy per nucleon of the photon-lead system. This range corresponds to a Bjorken-$x$ interval of about three orders of magnitude $1.1\times 10^{-5}< x <3.3\times 10^{-2}$, covering an explored kinematic region of great interest.
In this talk we will discuss the impact of these measurements in testing our understanding of perturbative quantum chromodynamics at large energies by comparing the ALICE data to theoretical predictions of this process.

Presentation materials

nystrand.pdf