Report on Progress in Physics: Observation of the Breit-Wheeler Process and Vacuum Birefringence in Heavy-Ion Collisions

TL;DR

This report reviews decades of experimental efforts to observe the Breit-Wheeler process and vacuum birefringence in high-energy collisions, highlighting recent STAR results and future testing opportunities in quantum electrodynamics.

Contribution

It summarizes key theoretical and experimental developments in observing the Breit-Wheeler process and vacuum birefringence, emphasizing recent collider experiment achievements and challenges.

Findings

Observation of the Breit-Wheeler process in collider experiments

Detection of vacuum birefringence signatures

Advancements in detector capabilities for unambiguous identification

Abstract

This Report reviews the effort over several decades to observe the linear Breit-Wheeler process ($\gamma\gamma \rightarrow e^+e^-$) and vacuum birefringence in high-energy particle and heavy-ion collider experiment. This Report, motivated by STAR's recent observations, attempts to summarize the key issues related to the interpretation of polarized $\gamma\gamma \rightarrow l^+l^-$ measurements in high-energy experiments. To that end, we start by reviewing the historical context and essential theoretical developments, before focusing on the decades of progress made in high-energy collider experiments. Special attention is given to the evolution in experimental approaches in response to various challenges and the demanding detector capabilities required to unambiguously identify the linear Breit-Wheeler process and to detect the signatures of vacuum birefringence. We close the report with a discussion, followed by a look at near-future opportunities for utilizing these discoveries and for testing QED in previously unexplored regimes.