Charge-dependent Flow Induced by Magnetic and Electric Fields in Heavy Ion Collisions

TL;DR

This paper studies how magnetic and electric fields influence charge-dependent flow patterns in heavy ion collisions, using hydrodynamic simulations to reveal effects on directed, elliptic, and radial flows.

Contribution

It demonstrates the combined effects of electromagnetic fields and Coulomb forces on charge-dependent flow observables in heavy ion collisions, with detailed simulation results.

Findings

Charge-odd directed flow $oldsymbol{ ext{Δ}v_1}$ induced by magnetic and electric fields.

Charge-odd triangular flow $oldsymbol{ ext{Δ}v_3}$ with similar origin.

Electric fields from net charge density influence radial and elliptic flow $oldsymbol{ ext{Δ}v_2}$.

Abstract

We investigate the charge-dependent flow induced by magnetic and electric fields in heavy ion collisions. We simulate the evolution of the expanding cooling droplet of strongly coupled plasma hydrodynamically, using the iEBE-VISHNU framework, and add the magnetic and electric fields as well as the electric currents they generate in a perturbative fashion. We confirm the previously reported effect of the electromagnetically induced currents, that is a charge-odd directed flow $\Delta v_1$ that is odd in rapidity, noting that it is induced by magnetic fields (\`a la Faraday and Lorentz) and by electric fields (the Coulomb field from the charged spectators). In addition, we find a charge-odd $\Delta v_3$ that is also odd in rapidity and that has a similar physical origin. We furthermore show that the electric field produced by the net charge density of the plasma drives rapidity-even charge-dependent contributions to the radial flow $\langle p_T \rangle$ and the elliptic flow $\Delta v_2$. Although their magnitudes are comparable to the charge-odd $\Delta v_1$ and $\Delta v_3$, they have a different physical origin, namely the Coulomb forces within the plasma.