Hydrodynamic modeling of a pure-glue initial scenario in high-energy hadron and heavy-ion collisions

TL;DR

This paper models the early pure-glue state in high-energy collisions using hydrodynamics, showing that suppressed early quark production affects dilepton yields and elliptic flows, offering potential experimental signatures.

Contribution

It introduces a hydrodynamic approach to simulate a pure-glue initial state in high-energy collisions, highlighting observable effects on dilepton and photon elliptic flows.

Findings

Suppression of early quarks reduces thermal dilepton yield.

Modest impact on direct photon p_T-distribution.

Enhanced elliptic flows of photons and dileptons as signatures of pure-glue initial state.

Abstract

Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. The comparable hydrodynamic simulations of heavy-ion collisions for (2+1)-flavor and Yang-Mills equations of state performed by using three different hydrodynamic codes are presented. Assuming slow chemical equilibration of quarks, the spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy of $\sqrt{s_{_{\rm NN}}} = 2.76$ TeV. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the $p_T$-distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state. Calculations based on Bjorken hydrodynamics suggest that collisions of small systems at intermediate energies available at RHIC or future FAIR facilities may show stronger effects associated with initial pure gluodynamic evolution.