Can we obtain a "new femtoscopy" on the basis of electromagnetic effects?

TL;DR

This paper reviews electromagnetic effects on charged pion emission in heavy ion collisions, proposing a new method to study the space-time evolution of the created matter through electromagnetic charge splitting and spectral distortions.

Contribution

It introduces electromagnetic effects as a novel tool to probe the space-time evolution and decoupling time of the hot dense matter in heavy ion collisions.

Findings

Electromagnetic effects cause charge splitting in pion flow.

Spectral distortions reveal the distance between pion formation zone and spectators.

Estimated pion decoupling time aligns with HBT measurements.

Abstract

We review our studies of spectator-induced electromagnetic (EM) effects on charged pion emission in ultrarelativistic heavy ion collisions. These effects are found to consist in the electromagnetic {charge splitting} of pion directed flow as well as very large distortions in spectra and ratios of produced charged particles. As it emerges from our analysis, they offer sensitivity to the actual distance $d_E$ between the pion formation zone at freeze-out and the spectator matter. As a result, this gives a new possibility of studying the space-time evolution of dense and hot matter created in the course of the collision. Having established that $d_E$ traces the longitudinal evolution of the system and therefore rapidly decreases as a function of pion rapidity, we investigate the latter finding in view of pion feed-over from intermediate resonance production. As a result we obtain a first estimate of the pion decoupling time from EM effects which we compare to existing HBT data. We conclude that spectator-induced EM interactions can serve as a new tool for studying the space-time characteristics and longitudinal evolution of the system.