Collectivity in Ultra-Peripheral Pb+Pb Collisions at the Large Hadron Collider

TL;DR

This paper presents comprehensive (3+1)D dynamical simulations of ultra-peripheral Pb+Pb collisions at the LHC, demonstrating fluid-like behavior in photon-nucleus interactions and comparing results with experimental data.

Contribution

It introduces a novel theoretical framework for simulating collectivity in ultra-peripheral collisions, extending analysis across different system sizes and collision types.

Findings

Reproduces experimental flow coefficients in ultra-peripheral collisions.

Shows fluid behavior can emerge in photon-nucleus interactions.

Provides a unified model for particle production across various collision systems.

Abstract

We present the first full (3+1)D dynamical simulations of ultra-peripheral Pb+Pb collisions at the Large Hadron Collider. Extrapolating from p+Pb collisions, we explore whether a quasi-real photon $\gamma^*$ interacting with the lead nucleus in an ultra-peripheral collision can create a many-body system exhibiting fluid behavior. Assuming strong final-state interactions, we provide model results for charged hadron multiplicity, identified particle mean transverse momenta, and charged hadron anisotropic flow coefficients, and compare them with experimental data from the ALICE and ATLAS collaborations. The elliptic flow hierarchy between p+Pb and $\gamma^*$+Pb collisions is dominated by the difference in longitudinal flow decorrelations and reproduces the experimental data well. We have demonstrated that our theoretical framework provides a quantitative tool to study particle production and collectivity for all system sizes, ranging from central heavy-ion collisions to small asymmetric collision systems at the Relativistic Heavy-Ion Collider and the Large Hadron Collider and even at the future Electron-Ion Collider.