Theory seminar (11am): Oscar Garcia-Montero: A new phenomenology of the early stages of Heavy-Ion Collisions

Thursday 15 May 2025, 11:00 → 12:00 Europe/Amsterdam

Veltman Centre (Nikhef)

Describing the complex space-time evolution of heavy-ion collisions (HICs), is a challenging task in theoretical nuclear physics. Nowadays, the standard procedure adapted for collisions at high center of mass (c.m.) energies, the so-called Standard Model of HICs, describes the dynamics in terms of multistage evolution models. During the first stage, the initial energy and charge deposition in the collision is followed by a short epoch of far-from-equilibrium dynamics, before the quark-gluon plasma (QGP) relaxes towards equilibrium and expands hydrodynamically. By now it has been established that —  even when using various different microscopic theories — the onset of hydrodynamic behavior typically occurs on the time scale of a single equilibrium relaxation time $\sim (4\pi \eta /s)/T_{\mathrm{e}\mathrm{q}}$, as determined by the specific shear viscosity $\eta /s$ and (effective, local) temperature of the system.

The idea of using dilepton measurements to construct a phenomenology of the early pre-equilibrium phase of heavy-ion collisions has been recently posed, as electromagnetic probes are the only probes which retain the information of these early stages, and hence, of the thermalization of QCD in Heavy Ion Collisions. In this seminar, I will give a brief introduction to ultra-relativistic Heavy Ion Collisions with emphasis on its early stages and their hydrodynamization. Furthermore I will present the advances in the creation of an electromagnetic phenomenology of the early stages. This includes our new work, in which we use QCD kinetic theory to compute dilepton production coming from the pre-equilibrium phase of the Quark-Gluon Plasma created in high-energy heavy-ion collisions, and demonstrate that the dilepton spectrum exhibits a simple scaling in terms of the specific shear viscosity  and entropy density, which can be derived from dimensional analysis in the presence of a pre-equilibrium attractor.

NIKHEF_GarciaMontero.pdf