Abstract
We estimate the production of electromagnetic radiation (real and virtual photons) from the early, pre-equilibrium, stage of relativistic heavy-ion collisions. The parton dynamics are obtained as a solution of the Boltzmann equation in the Fokker-Planck diffusion limit. The photon and dilepton rates are integrated and the obtained yields are compared with those from standard sources and with available experimental data. Non-equilibrium photon spectra are predicted for Pb+Pb at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
Highlights
The accepted theory of the strong nuclear interaction is quantum chromodynamics (QCD), a local gauge theory which admits a spontaneously broken chiral symmetry
The theoretical nature of the transition between degrees of freedom belonging, respectively, to the partonic and confined phases has only been recently identified as a rapid crossover, occurring at Tc ≈ 150 MeV, for zero baryon density [1]. This region is accessible to heavy-ion experiments performed at both the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC)
Experiments performed at these facilities have revealed an exotic form of matter: the quark-gluon plasma (QGP) [2]
Summary
The accepted theory of the strong nuclear interaction is quantum chromodynamics (QCD), a local gauge theory which admits a spontaneously broken chiral symmetry. The theoretical nature of the transition between degrees of freedom belonging, respectively, to the partonic and confined phases has only been recently identified as a rapid crossover, occurring at Tc ≈ 150 MeV, for zero baryon density [1] This region is accessible to heavy-ion experiments performed at both the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC). Notwithstanding the recent progress in relativistic fluid dynamics, relativistic heavy-ion collisions can still not be modeled ab initio: hybrid approaches need to be constructed Those typically consist of an initial state followed by the hydrodynamics phase which ends with a hadronic cascade and kinetic freeze-out, when interparticle distances exceed meanfree-paths while the interaction volume expands and cools.
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