Collectivity in Ultraperipheral Pb+Pb Collisions at the Large Hadron Collider

Area of Science:

• Nuclear Physics
• High-Energy Physics
• Quantum Chromodynamics

Background:

• Ultra-peripheral collisions (UPCs) probe fundamental interactions.
• Heavy-ion collisions create quark-gluon plasma.
• Understanding fluid behavior in smaller systems is crucial.

Purpose of the Study:

• To perform the first full (3+1)D dynamical simulations of UPC Pb+Pb collisions.
• To investigate if quasireal photon-lead nucleus interactions create fluid-like systems.
• To compare model predictions with ALICE and ATLAS experimental data.

Main Methods:

• Full (3+1)D dynamical simulations.
• Extrapolation from proton-lead (p+Pb) collisions.
• Modeling strong final-state interactions.

Main Results:

• Charged hadron multiplicity, identified particle mean transverse momenta, and anisotropic flow coefficients were calculated.
• Elliptic flow hierarchy in p+Pb and photon-Pb (γ*+Pb) collisions was reproduced.
• Model results align well with experimental data from ALICE and ATLAS.

Conclusions:

• The theoretical framework quantitatively studies particle production and collectivity.
• This approach is applicable to all system sizes, from heavy-ion to small asymmetric collisions.
• The study validates the fluid behavior of photon-nucleus systems in UPCs.