Directed flow in asymmetric nucleus-nucleus collisions and the inverse Landau-Pomeranchuk-Migdal effect

TL;DR

This paper investigates the electric field effects in asymmetric nucleus collisions by analyzing charge-dependent directed flow, incorporating the inverse Landau-Pomeranchuk-Migdal effect, and comparing results with experimental data to predict energy-dependent behaviors.

Contribution

It introduces the incorporation of the inverse Landau-Pomeranchuk-Migdal effect into the PHSD model to better describe charge-dependent flow in asymmetric collisions.

Findings

Inclusion of iLPM effect aligns PHSD results with STAR data.

Instant charge appearance overestimates charge splitting.

Charge splitting is predicted to increase at lower energies.

Abstract

It is proposed to identify a strong electric field - created during relativistic collisions of asymmetric nuclei - via the observation of pseudorapidity and transverse momentum distributions of hadrons with the same mass but opposite charge. The results of detailed calculations within the Parton-Hadron String Dynamics (PHSD) approach for the charge-dependent directed flow $v_1$ are presented for semi-central Cu+Au collision at $\sqrt{s_{NN}}=200$ GeV incorporating the inverse Landau-Pomeranchuk-Migdal (iLPM) effect, which accounts for a delay in the electromagnetic interaction with the charged degree of freedom. Including the iLPM effect we achieve a reasonable agreement of the PHSD results for the charge splitting in $v_1(p_T)$ in line with the recent measurements of the STAR Collaboration for Cu+Au collisions at $\sqrt{s_{NN}}=200$ GeV while an instant appearance and coupling of electric charges at the hard collision vertex overestimates the splitting by about a factor of 10. We predict that the iLPM effect should practically disappear at energies of $\sqrt{s_{NN}} \approx$9 GeV, which should lead to a significantly larger charge splitting of $v_1$ at the future FAIR/NICA facilities.