Abstract
We propose a new method of investigating the space-time evolution of meson production in heavy ion collisions, by making use of spectator-induced electromagnetic (“Coulomb”) effects. The presence of two nuclear remnants (“spectator systems”) in the non-central collision generates a strong Coulomb field, which modifies the trajectories of charged final state hadrons. This results in charge-dependent azimuthal anisotropies in final state meson emission. In our approach, this effect can be computed numerically by means of a high-statistics Monte Carlo simulation, using the distance between the meson formation zone and the spectator system as free parameter. Our simulation correctly describes the electromagnetic effect on azimuthal anisotropies observed for π + and π − mesons in Au+Au collisions at lower RHIC energy, known from data recently reported by the STAR Collaboration. Similarly to our earlier studies of spectator-induced electromagnetic effects, also in the present study we find that these effects offer sensitivity to the position of the meson formation zone with respect to the spectator system. Therefore, we conclude that they can serve as a new tool to investigate the space-time evolution of meson production, and the dynamics of the heavy ion collision.
Highlights
In relativistic heavy ion collisions in the energy regime of at least a few GeV per participating nucleon pair, two main elements of the heavy ion reaction are differentiated
In the present paper we focus on the electromagnetic effect which the spectator systems induce on positive and negative pions in the region of central rapidities, in the context of the new experimental data provided by the STAR Collaboration [6]
This, as schematically illustrated in figure 3, reflects the longitudinal evolution of the system created in the course of the heavy ion collision
Summary
In relativistic heavy ion collisions in the energy regime of at least a few GeV per participating nucleon pair, two main elements of the heavy ion reaction are differentiated. Directed flow in heavy ion collisions is subject of intensive studies as it is supposed to reflect collective phenomena occurring in the collision; it reflects the collective sidewards motion of the emitted particles It is defined as the first Fourier coefficient of the azimuthal distribution of the particles with respect to the reaction plane [3]: v1 ≡ cos(φ − ΨRP) ,. Our analysis of charged pion directed flow in Pb+Pb collisions [4] demonstrated that the spectator-induced electromagnetic effect results in very large absolute values of v1 for positive pions at target and beam rapidities, in agreement with data from the WA98 experiment [5]. In the present paper we focus on the electromagnetic effect which the spectator systems induce on positive and negative pions in the region of central rapidities, in the context of the new experimental data provided by the STAR Collaboration [6]
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