Dilepton radiation by vector mesons and off-shell partons in the hot and dense medium

TL;DR

This paper models dilepton production in heavy-ion collisions by incorporating off-shell vector mesons and partons within the dynamical quasiparticle framework, successfully matching experimental data and revealing the roles of various processes in different mass ranges.

Contribution

It introduces off-shell cross sections for dilepton production derived from the DQPM and implements them into the PHSD transport approach, providing a comprehensive description of the sQGP evolution and dilepton spectra.

Findings

Low mass dilepton spectra are explained by vector meson broadening.

Intermediate mass spectra are dominated by off-shell q-qbar annihilation, Bremsstrahlung, and gluon-Compton scattering.

The model reproduces the softening of mT spectra at intermediate masses.

Abstract

According to the dynamical quasiparticle model (DQPM) - matched to reproduce lattice QCD results in thermodynamic limit, - the constituents of the strongly interacting quark-gluon plasma (sQGP) are massive and off-shell quasi-particles (quarks and gluons) with broad spectral functions. In order to address the electromagnetic radiation of the sQGP, we derive off-shell cross sections of q+qbar->gamma*, q+qbar->gamma*+glue and q+glue->gamma*+q(qbar+glue->gamma*qbar) reactions taking into account the effective propagators for quarks and gluons from the DQPM. Dilepton production in In+In collisions at 158 AGeV is studied by implementing these processes into the parton-hadron-string dynamics (PHSD) transport approach. The microscopic PHSD transport approach describes the full evolution of the heavy-ion collision: from the dynamics of quasi-particles in the sQGP phase (when the local energy density is above ~1 GeV/fm^3) through hadronization and to the following hadron interactions and off-shell propagation after the hadronization. A comparison to the data of the NA60 Collaboration shows that the low mass dilepton spectra are well described by including a collisional broadening of vector mesons, while the spectra in the intermediate mass range are dominated by off-shell quark-antiquark annihilation, quark Bremsstrahlung and gluon-Compton scattering in the nonperturbative QGP. In particular, the observed softening of the mT spectra at intermediate masses (1 GeV < M < 3 GeV) is approximately reproduced.