### Title: Mapping the Electromagnetic Fields of Heavy-Ion Collisions with the Breit-Wheeler Process

Ultra-relativistic heavy-ion collisions are expected to produce the strongest electromagnetic fields ($10^{13}-10^{16}$ Tesla) in the known Universe. These highly-Lorentz contracted fields can manifest themselves as linearly polarized quasi-real photons that interact via the Breit-Wheeler process. In this talk I will discuss recent experimental measurements that have spurred significant theoretical progress in our understanding of dilepton production in ultra-peripheral heavy ion collisions. Specifically, we now know that the energy and momentum distribution of the produced dileptons carry information about the strength and spatial distribution of the colliding fields. Moreover, the recent observation of quantum correlations between the interacting photon’s spin (polarization) and momentum provides a clear connection to the semi-classical electromagnetic field distribution, thus making it possible to measure the magnetic field produced in heavy ion collisions for the first time. I’ll end the talk with a look at how current and future measurements can be used to constraining the magnetic field and explore how they may provide novel input for the discussion of emergent magnetohydrodynamical phenomena driven by event-by-event fluctuations of the magnetic field.

Online here: https://hit.lbl.gov/#h.vyruxndze0en