Dileptons from the nonequilibrium Quark-Gluon Plasma

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 $q\bar q\to\gamma^*$, $q\bar q\to\gamma^*+g$ and $qg\to\gamma^*q$($\bar q g\to\gamma^* \bar q$) 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 $\sim 1$ 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 $m_T$ spectra at intermediate masses (1 GeV $\le M \le$ 3 GeV) is approximately reproduced.Comment: 8 pages, 8 figures, to be published in the Proceedings of the 26th Winter Workshop on `Nuclear Dynamics', Ochto Rios, Jamaica, 2-9 January, 201

Measurement of the nuclear modification factor of electrons from heavy-flavour decays at mid-rapidity in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV with ALICE

We present results on inclusive electrons for 1.5 $< p_{\rm T} <$ 6 GeV/$c$ in {Pb-Pb} collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV measured with ALICE at the LHC and compare these to a cocktail of background electron sources. The excess of electrons beyond the cocktail at high momenta ({$p_{\rm T} >$ 3.5 GeV/$c$}) is attributed to electrons from heavy-flavour decays. The corresponding nuclear modification factor indicates heavy-flavour suppression by a factor of 1.5-4.Comment: 4 pages; 4 figures; QM 2011 proceeding

Elliptic and triangular flow of identified particles at ALICE

We report on the first measurements of elliptic and triangular flow for charged pions, kaons and anti-protons in lead-lead collisions at 2.76 TeV measured with the ALICE detector at the LHC. We compare the observed mass splitting of differential elliptic flow at LHC energies to RHIC measurements at lower energies and theory predictions. We test the quark coalescence picture with the quark number scaling of elliptic and triangular flow.Comment: 4 pages, 5 figures, Quark Matter 2011 conference proceeding

e+e- Pairs: a clock and a thermometer of heavy ion collisions

Recently, there is growing evidence that a new state of matter is formed in sqrt(s_NN)= 200 GeV Au+Au collisions at RHIC: a strongly coupled Quark Gluon Plasma of partonic degrees of freedom which develops a collective motion. Dilepton spectra are not affected by strong interaction and can therefore probe the whole time evolution of the collision. Thus they may be sensitive to onset of deconfinement, chiral symmetry restoration, as well as the production of thermal photons. The PHENIX experiment measured the production of e+e- pairs in p+p and Au+Au collisions at sqrt(s_NN)= 200 GeV. An enhanced dilepton yield in the mass range 150<m_ee<750 MeV/c^2 is measured. The excess increases faster with centrality than the number of participating nucleons and is concentrated at p_T<1GeV/c. At higher p_T the excess below 300 MeV/c^2 has been related to an enhanced production of direct photons possibly of thermal origin.Comment: Proceedings of Quark Matter 2008, 8 pages, 7 figure

Elliptic flow at high transverse momentum in Pb-Pb collisions at sNN=2.76\sqrt{s_{NN}} = 2.76 TeV with the ALICE experiment

An observable that can be used to better constrain the mechanism responsible for the parton energy loss is the elliptic azimuthal event anisotropy, $v_2$. We report on measurements of $v_2$ for inclusive and identified charged particles in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV recorded by the ALICE experiment at the LHC. $v_2$ is presented for a wide range of particle transverse momentum up to $p_T=20$ GeV/c. The particle $v_2$ is finite, positive and approximately constant for $p_T>8$ GeV/c. The proton $v_2$ is higher than that of the pion up to about $p_T=8$ GeV/c. The results are compared to the measurements at lower energy reported by RHIC experiments.Comment: 4 pages, QM 2011 proceeding

Low-mass dielectrons from the PHENIX experiment at RHIC

The production of the low-mass dielectrons is considered to be a powerful tool to study the properties of the hot and dense matter created in the ultra-relativistic heavy-ion collisions. We present the preliminary results on the first measurements of the low-mass dielectron continuum in Au+Au collisions and the phi meson production measured in Au+Au and d+Au collisions at sqrt{s_NN} = 200 GeV performed by the PHENIX experiment.Comment: 6 pages, 12 figures, conference proceedings for QNP06 (5-10 June, 2006, Madrid

Adipose-derived stem cells: true or false? A different point of view

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