Open charm and dileptons from relativistic heavy-ion collisions

TL;DR

This study investigates the sources of dileptons in heavy-ion collisions across a wide energy range, highlighting the dominance of charm decays at high energies and the potential to observe QGP signals at lower energies using the PHSD transport approach.

Contribution

It introduces a fully microscopic treatment of charm dynamics and their semileptonic decays in the PHSD model, providing new insights into dilepton sources in heavy-ion collisions.

Findings

Charm decays dominate intermediate-mass dileptons at high energies (>40 GeV)

QGP radiation can be clearly observed at lower energies (8-20 GeV)

Predictions for dilepton spectra at 5.02 TeV are provided

Abstract

Dileptons are considered as one of the cleanest signals of the quark-gluon plasma (QGP), however, the QGP radiation is masked by many 'background' sources from either hadronic decays or semileptonic decays from correlated charm pairs. In this study we investigate the relative contribution of these channels in heavy-ion collisions from $\sqrt{s_{\rm NN}}=$ 8 GeV to 5 TeV with a focus on the competition between the thermal QGP radiation and the semileptonic decays from correlated $D-$meson pairs. As a 'tool' we employ the parton-hadron-string dynamics (PHSD) transport approach to study dilepton spectra in Pb+Pb (Au+Au) collisions in a wide energy range incorporating for the first time a fully microscopic treatment of the charm dynamics and their semileptonic decays. We find that the dileptons from correlated $D-$meson decays dominate the 'thermal' radiation from the QGP in central Pb+Pb collisions at the intermediate masses (1.2 GeV $< M <$ 3 GeV) for $\sqrt{s_{\rm NN}} > $ 40 GeV, while for $\sqrt{s_{\rm NN}}=$ 8 to 20 GeV the contribution from $D,{\bar D}$ decays to the intermediate mass dilepton spectra is subleading such that one should observe a rather clear signal from the QGP radiation. We, furthermore, study the $p_T$-spectra and the $R_{AA}(p_T)$ of single electrons at different energies as well as the excitation function of the inverse slope of the $m_T$- spectra for intermediate-mass dileptons from the QGP and from charm decays. We find moderate but characteristic changes in the inverse slope parameter for $\sqrt{s_{\rm NN}} > $ 20 GeV which can be observed experimentally in high statistics data. Additionally, we provide detailed predictions for dilepton spectra from Pb+Pb collisions at $\sqrt{s_{\rm NN}} = $ 5.02 TeV.