Influence of the electromagnetic fields on hadronic observables in proton-induced collisions

L Oliva,E Bratkovskaya,P Moreau,V Voronyuk

doi:10.1088/1742-6596/1667/1/012032

Abstract

We investigate proton-gold collisions at top RHIC energy GeV within the Parton-Hadron-String Dynamics (PHSD) approach, focusing on the influence of the electromagnetic fields on final hadronic observable. We discuss the space-time distribution of the magnetic and electric field components, showing that the electric field Ex along the impact parameter direction is comparable in magnitude to the magnetic field By perpendicular to the reaction plane. We discuss the effect of these fields on the directed flow υ1 of pions and kaons. While there is no visible effect of electromagnetic fields in 5% central collisions, the result for collisions at fixed impact parameter clearly indicates an electromagnetically-induced splitting in the v1 of positively and negatively charged mesons; the effect, driven by the huge Ex component, is larger for kaons than to pions and increases with the impact parameter of the collision.

Highlights

The recent experimental and theoretical results on high-multiplicity events in small systems, such as proton-proton and proton-nucleus collisions, seems to indicate the formation of short-lived droplets of Quark-Gluon Plasma (QGP) [1], which give rise to final-state momentum anisotropies comparable in magnitude to those found in collisions between two heavy ions
The Parton-Hadron-String Dynamics (PHSD) approach is a covariant dynamical model for strongly interacting particles whose time evolution, both in the partonic and in the hadronic phase, is governed by off-shell transport equations, which are derived from the Kadanoff-Baym equations for non-equilibrium Green functions [7, 8]
PHSD includes the dynamical formation and evolution of the retarded electromagnetic fields (EMF) and its influence on quasi-particle as well as the back-reaction of particle dynamics on the fields [2, 6, 10]; the off-shell transport equation are supplemented by the Maxwell equations for the electric field E and the magnetic field B

Summary

Introduction

The recent experimental and theoretical results on high-multiplicity events in small systems, such as proton-proton and proton-nucleus collisions, seems to indicate the formation of short-lived droplets of Quark-Gluon Plasma (QGP) [1], which give rise to final-state momentum anisotropies comparable in magnitude to those found in collisions between two heavy ions. Among the Fourier coefficients of the particle azimuthal distribution the directed flow v1, which refers to a collective sidewards deflection of particles, is a promising probe for the electromagnetic fields (EMF) produced in the collision [2, 3, 4]. Extremely intense magnetic fields are produced in non-central relativistic heavy-ion collisions mainly due to the motion of spectator charges [5, 6, 10], with a maximum magnitude at top RHIC and LHC energies of about |eBy| ∼ 5−50 m2π, corresponding to ∼ 1018 − 1019 Gauss.

Remainder of the PHSD model

Space-time distributions of electromagnetic field