Open charm and dileptons from relativistic heavy-ion collisions

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 √ sNN = 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 √ sNN > 40 GeV, while for √ sNN = 8 to 20 GeV the contribution from D,D decays to the intermediate mass dileptonspectra is subleading such that one should observe a rather clear signal from the QGP radiation. We, furthermore, study the pT -spectra and the RAA(pT ) of single electrons at different energies as well as the excitation function of the inverse slope of the mT -spectra for intermediate-mass dileptons from the QGP and from charm decays. We find moderate but characteristic changes in the inverse slope parameter for √ sNN > 20 GeV which can be observed experimentally in high statistics data.Additionally, we provide detailed predictions for dilepton spectra from Pb+Pb collisions at √ sNN = 5.02 TeV.

Measurement of dielectron production in central Pb-Pb collisions at sNN=2.76TeV

“…The second model from Song et al [64] is based on the Parton-Hadron-String Dynamics (PHSD) transport approach. The contribution of thermal dielectrons from the partonic phase is calculated assuming that the degrees of freedom in the QGP are massive off-shell strongly interacting quasiparticles.…”

High density matter physics at J-PARC-HI

“…However, the cc production is highly suppressed at J-PARC energy because of kinematical limit. Therefore, this mass region is ideal for observing the thermal radiation from the matter at this energy [12].…”

Electromagnetic probes of the quark‐gluon plasma

“…Figure shows the dielectron mass spectra from partonic interactions in the QGP (a) and from the semi‐leptonic decays of pairs (b) in central Pb + Pb collisions at at mid‐pseudorapidity ∣ η e ∣ < 1 for the leptons. We mention that the contribution from the hadronic channels increases only moderately with collision energy (in line with the hadron abundance) (Song et al ), while the contribution from the QGP rises more steeply (in line with the enhanced space–time volume of the QGP phase) and that from pairs increases most dramatically. Accordingly, the contribution from heavy flavor is small at low‐energy collisions but becomes more and more important with increasing collision energy in competition with the production from the QGP channels.…”

“…The dilepton production from hadronic and partonic channels in central Pb + Pb (or Au + Au) collisions has been calculated by including also the contribution from the semi‐leptonic decays of heavy flavors in PHSD on a fully microscopic level. We recall that also the cross‐sections for dilepton production have been calculated by employing the same propagators and couplings as incorporated in the partonic dynamics in PHSD (Song et al ). We find that even in central Pb + Pb collisions at to 20 GeV, the contribution from mesons to the intermediate mass dilepton spectra is subleading and one should have a rather clear signal from the QGP radiation, whereas at the top RHIC energy this contribution overshines the intermediate‐mass dileptons from the QGP.…”

“…Dilepton production in the QGP—as created in early stages of heavy‐ion collisions—is calculated by implementing these off‐shell processes into the PHSD transport approach on the basis of the same partonic propagators as used for the time evolution of the partonic system. For a review on electromagnetic production channels within PHSD, we refer the reader to Linnyk et al () and for the details of the dilepton cross‐sections from off‐shell partonic channels to the Appendix in Song et al ().…”