Phenomenology of photon and di-lepton production in relativistic nuclear collisions

TL;DR

This paper reviews recent theoretical insights into photon and dilepton production in relativistic heavy-ion collisions, highlighting in-medium effects, QGP contributions, and the photon elliptic flow puzzle at RHIC and LHC energies.

Contribution

It provides a comprehensive overview of the current understanding of electromagnetic emissions and flow phenomena in heavy-ion collisions, emphasizing the roles of hadronic and partonic sources.

Findings

Dilepton spectra at low mass show in-medium vector meson broadening.

High-mass dilepton yield is dominated by QGP contributions.

The large photon v2 observed at RHIC and LHC remains an open puzzle.

Abstract

We discuss the latest theoretical results on direct photon and dilepton production from relativistic heavy-ion collisions. While the dilepton spectra at low invariant mass show in-medium effects like a collisional broadening of the vector meson spectral functions, the dilepton yield at high invariant masses (above 1.1 GeV) is dominated by QGP contributions for central heavy-ion collisions at relativistic energies. The present status of the photon $v_2$ "puzzle" - a large elliptic flow $v_2$ of the direct photons experimentally observed at RHIC and LHC energies - is also addressed. The role of hadronic and partonic sources for the photon spectra and $v_2$ is considered as well as the possibility to subtract the QGP signal from the experimental observables.