Dilepton production in nucleus-nucleus collisions at top CERN Super Proton Synchrotron energy of 158AGeV within the parton-hadron-string dynamics transport approach

Abstract

Dilepton production in In+In collisions at 158 A·GeV is studied within the microscopic partonhadron-string dynamics (PHSD) transport approach that incorporates explicit partonic degrees-offreedom, dynamical hadronization as well as the more familiar hadronic dynamics in the final reaction stages. A comparison to the data of the NA60 Collaboration shows that the measured dilepton yield is well described by including the collisional broadening of vector mesons, while simultaneously accounting for the electromagnetic radiation of the strongly coupled quark-gluon plasma (sQGP) via off-shell quark-antiquark annihilation, quark annihilation with additional gluon Bremsstrahlung and the gluon-Compton scattering mechanisms. In particular, the spectra in the intermediate mass range (1 GeV ≤ M ≤ 2.5 GeV) are dominated by quark-antiquark annihilation in the nonperturbative QGP. Also, the observed softening of the transverse mass spectra at intermediate masses (1 GeV ≤ M ≤ 2.5 GeV) is approximately reproduced. Furthermore, for dileptons of low masses (M < 0.6 GeV), we find a sizeable contribution from the quark annihilation with additional gluon bremsstrahlung, thus providing another possible window for probing the properties of the sQGP.PACS numbers: 25.75.Cj, 25.75.Nq, 24.85.+p,

Measurements of dielectron production in Au + Au collisions atsNN=200GeV from the STAR experiment

“…± 0.9 (model) has been reported by the PHENIX collaboration [17]. Several theoretical calculations, which have successfully explained the SPS data [18][19][20][21] and the STAR data [22] previously, were unable to reproduce the magnitude of the low mass dielectron enhancement observed by PHENIX through expected vector meson contributions in the hadronic medium. The PHENIX measured IMR yields are consistent with the charm contribution from p + p scaled with the number of binary collisions.…”

“…The CERES measurements of e + e − spectra in Pb+Au collisions at the Super Proton Synchrotron (SPS) showed an enhancement in the mass region below ∼700 MeV/c 2 with respect to the hadron cocktail that included the vacuum line shape for the ρ meson [15]. High-statistics measurements from the NA60 experiment at √ s NN = 17.2 GeV suggested that this enhancement is consistent with in-medium broadening of the ρ-meson spectral function rather than a drop of its pole mass [16,[18][19][20][21]. Strikingly, after removal of correlated charm contributions, the NA60 collaboration also observed that the slope parameters of the dimuon transverse mass (m T ) spectrum showed a roughly linear increase with dimuon invariant mass below the φ-meson mass, followed by a sudden decline at higher masses.…”

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

“…The PHSD approach so far has been employed for dilepton production from pp to Au + Au collisions at SPS [6] and RHIC energies [7]. As in Refs.…”

Vector Meson Spectral Functions in a Coarse-Graining Approach

“…), is difficult here. Nevertheless, there have been some successful investigations with medium-effects implemented in transport models [16,[21][22][23]. However, problems such as the large variety of parameters, especially cross-sections and branching ratios for which little data is available, remain.…”

“…A completely different ansatz is used in transport models [14][15][16][17][18][19][20]. These approaches treat the dynamics microscopically and account for non-equilibrium, but the implementation of full medium effects, which were discussed above (i.e.…”