Dilepton production in proton-proton and Pb+Pb collisions atsNN=2.76TeV

Abstract

We study ${e}^{+}{e}^{\ensuremath{-}}$ pair production in proton-proton and central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=2.76$ TeV within two models: an extended statistical hadronization model (SHM) and the Parton-Hadron-String Dynamics (PHSD) transport approach. We find that the PHSD calculations roughly agree with the dilepton spectrum from hadronic sources with the ``cocktail'' estimates from the statistical hadronization model matched to available data at Large Hadron Collider energies. The dynamical simulations within the PHSD show a moderate increase of the low-mass dilepton yield essentially due to the in-medium modification of the $\ensuremath{\rho}$ meson. Furthermore, pronounced traces of the partonic degrees of freedom are found in the PHSD results in the intermediate-mass regime. The dilepton production from the strongly interacting quark-gluon plasma (sQGP) exceeds that from the semileptonic decays of open charm and bottom mesons. Additionally, we observe that a transverse momentum cut of 1 GeV/$c$ further suppresses the relative contribution of the heavy-meson decays to the dilepton yield, such that the sQGP radiation strongly dominates the spectrum for masses from 1 to 3 GeV, allowing a closer look at the electromagnetic emissivity of the partonic plasma in the early phase of $\mathrm{Pb}+\mathrm{Pb}$ collisions.