Intermediate mass dileptons as pre-equilibrium probes in heavy ion collisions

• DOI: 10.1016/j.physletb.2021.136626
• Publication Date: 2021-09-06T11:51:44Z
• Authors: Maurice Coquet; Xiaojian Du; Jean-Yves Ollitrault; Sören Schlichting; Michael Winn
• Keywords: Drell-Yan process; heavy ion: scattering; [PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th]; Nuclear Theory; dilepton: production; dilepton: mass; QC1-999; density: ratio; FOS: Physical sciences; anisotropy; [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex]; 01 natural sciences; 7. Clean energy; High Energy Physics - Experiment; Nuclear Theory (nucl-th); High Energy Physics - Experiment (hep-ex); High Energy Physics - Phenomenology (hep-ph); quantum chromodynamics; 0103 physical sciences; [PHYS.HEXP]Physics [physics]/High Energy Physics - Experiment [hep-ex]; quark antiquark: annihilation; Nuclear Experiment (nucl-ex); Nuclear Experiment; background; Physics; nucleus nucleus: scattering; quark: momentum spectrum; heavy quark: semileptonic decay; High Energy Physics - Phenomenology; [PHYS.HPHE]Physics [physics]/High Energy Physics - Phenomenology [hep-ph]; viscosity: density; entropy: density

The production of dileptons with an invariant mass in the range 1 GeV < M < 5 GeV provides unique insight into the approach to thermal equilibrium in ultrarelativistic nucleus-nucleus collisions. In this mass range, they are produced through the annihilation of quark-antiquark pairs in the early stages of the collision. They are sensitive to the anisotropy of the quark momentum distribution, and also to the quark abundance, which is expected to be underpopulated relative to thermal equilibrium. We take into account both effects based on recent theoretical developments in QCD kinetic theory, and study how the dilepton mass spectrum depends on the shear viscosity to entropy ratio that controls the equilibration time. We evaluate the background from the Drell-Yan process and argue that future detector developments can suppress the additional background from semileptonic decays of heavy flavors.<br/>10 pages, 7 figures; computation of the effective area is defined more rigorously, figures are updated accordingly. Added paragraph on page 7, discussing the impact of inhomogeneities in transverse density profile. Added paragraph in the conclusion on page 9, on fitting the invariant mass spectrum with a power function<br/>