Azimuthal Asymmetry of Prompt Photons in Nuclear Collisions

TL;DR

This paper investigates the initial-stage azimuthal asymmetry of prompt photons in nuclear collisions, attributing it to multiple parton interactions and nuclear density gradients, using the light-cone dipole formalism.

Contribution

It introduces a novel calculation of azimuthal asymmetry originating from initial parton interactions, applicable to various collision types at RHIC energies.

Findings

Azimuthal asymmetry arises from initial parton interactions and nuclear density gradients.

The model successfully predicts azimuthal asymmetry in prompt photon production across different collision systems.

The approach highlights the significance of initial state effects in azimuthal asymmetry measurements.

Abstract

The azimuthal elliptic asymmetry v2 observed in heavy ion collisions, is usually associated with properties of the medium created in the final state. We compute the azimuthal asymmetry which is due to multiple interactions of partons at the initial stage of nuclear collisions, and which is also present in $pA$ collisions. In our approach the main source of azimuthal asymmetry is the combination of parton multiple interactions with the steep variation of the nuclear density at the edge of nuclei. We apply the light-cone dipole formalism to compute the azimuthal asymmetry of prompt photons yield from parton-nucleus, proton-nucleus and nucleus-nucleus collisions at the RHIC energy.