Mass effect and coherence in medium-induced QCD radiation off a qqˉq {\bar q} antenna

The medium-induced one-gluon radiation spectrum off a massive quark-antiquark ($q {\bar q}$) antenna traversing a colored QCD medium is calculated in this contribution. The gluon spectrum off the antenna computed at first order in the opacity expansion is collinear finite but infrared divergent, which is different from the result obtained from an independent emitter which is both infrared and collinear finite. The interference between emitters dominates the soft gluon radiation when the antenna opening angle is small and the emitted gluon is soft, whereas the antenna behaves like a superposition of independent emitters when the opening angle is large and the radiated gluon is hard. As a phenomenological consequence, we investigate the energy lost by the projectiles due to the radiation. In general, the size of the mass effects is similar in both cases.Comment: 4 pages, 1 figure, Proceedings of Quark Matter 2011, Annecy, Franc

PHENIX first measurement of the J/psi elliptic flow parameter v2 in Au+Au collisions at sqrt(sNN) = 200 GeV

Recent results indicate that the J/psi suppression pattern differs with rapidity showing a larger suppression at forward rapidity. J/psi suppression mechanisms based on energy density (such as color screening, interaction with co-movers, etc.) predict the opposite trend. On the other hand, it is expected that more c\bar{c} pairs should be available to form quarkonia at mid-rapidity via recombination. Some models provide a way to differentiate J/psi production from initially produced c\bar{c} pairs and final state recombination of uncorrelated pairs, via the rapidity and transverse momentum dependence of the elliptic flow (v2). During 2007 data taking at RHIC, a large sample of Au+Au collisions at sqrt(sNN)=200 GeV was collected. The statistics has been increased compared to previous 2004 data set, thus allowing a more precise measurement of the J/psi production at both mid and forward rapidity. Furthermore, the PHENIX experiment benefited from the addition of a new detector, which improves the reaction plane resolution and allows us to measure the J/psi v2. Comparing this measurement to the positive D-mesons v2 (through non-photonic electron decays) will help constraining the J/psi production mechanisms and getting a more precise picture of the proportion of J/psi coming from direct production or charm quark coalescence. Details on how the J/psi v2 is measured at both rapidities are presented. The J/psi v2 as a function of transverse momentum are compared to existing models.Comment: 4 pages, 3 figures, Quark Matter 2008 proceeding

Monte Carlo Tools for Jet Quenching

A thorough understanding of jet quenching on the basis of multi-particle final states and jet observables requires new theoretical tools. This talk summarises the status and propects of the theoretical description of jet quenching in terms of Monte Carlo generators.Comment: proceedings of the 22nd International Conference on Ultra-Relativistic Nucleus Nucleus Collisions (Quark Matter 2011

Equation of state at FAIR energies and the role of resonances

Two microscopic models, UrQMD and QGSM, are used to extract the effective equation of state (EOS) of locally equilibrated nuclear matter produced in heavy-ion collisions at energies from 11.6 AGeV to 160 AGeV. Analysis is performed for the fixed central cubic cell of volume V = 125 fm**3 and for the expanding cell that followed the growth of the central area with uniformly distributed energy. For all reactions the state of local equilibrium is nearly approached in both models after a certain relaxation period. The EOS has a simple linear dependence P/e = c_s**2 with 0.12 < c_s**2 < 0.145. Heavy resonances are shown to be responsible for deviations of the c_s**2(T) and c_s**2(mu_B) from linear behavior. In the T-mu_B and T-mu_S planes the EOS has also almost linear dependence and demonstrates kinks related not to the deconfinement phase transition but to inelastic freeze-out in the system.Comment: SQM2008 proceedings, 6 page

Future Experiments in Relativistic Heavy Ion Collisions

The measurements at RHIC have revealed a new state of matter, which needs to be further characterized in order to better understand its implications for the early evolution of the universe and QCD. I will show that, in the near future, complementary key measurements can be performed at RHIC, LHC, and FAIR. I will focus on results than can be obtained using identified particles, a probe which has been the basis for this conference over the past three decades. The sophisticated detectors, built and planned, for all three accelerator facilities enable us to measure leptons, photons, muons as well as hadrons and resonances of all flavors almost equally well, which makes these experiments unprecedented precision tools for the comprehensive understanding of the physics of the early universe.Comment: 10 pages, 4 figures, Proceedings for Summary Talk at SQM 2007, Levoca, Slovakia, June 24-29, 200

Microscopic models and effective equation of state in nuclear collisions at FAIR energies

Two microscopic models, UrQMD and QGSM, were employed to study the formation of locally equilibrated hot and dense nuclear matter in heavy-ion collisions at energies from 11.6 AGeV to 160 AGeV. Analysis was performed for the fixed central cubic cell of volume V = 125 fm**3 and for the expanding cell which followed the growth of the central area with uniformly distributed energy. To decide whether or not the equilibrium was reached, results of the microscopic calculations were compared to that of the statistical thermal model. Both dynamical models indicate that the state of kinetic, thermal and chemical equilibrium is nearly approached at any bombarding energy after a certain relaxation period. The higher the energy, the shorter the relaxation time. Equation of state has a simple linear dependence P = a(sqrt{s})*e, where a = c_s**2 is the sound velocity squared. It varies from 0.12 \pm 0.01 at E_{lab} = 11.6 AGeV to 0.145 \pm 0.005 at E_{lab} = 160 AGeV. Change of the slope in a(sqrt{s}) behavior occurs at E_{lab} = 40 AGeV and can be assigned to the transition from baryon-rich to meson-dominated matter. The phase diagrams in the T - mu_B plane show the presence of kinks along the lines of constant entropy per baryon. These kinks are linked to the inelastic (i.e. chemical) freeze-out in the system.Comment: 14 pages, REVTE

Jet quenching pattern at LHC in PYQUEN model

The first LHC data on high transverse momentum hadron and dijet spectra in PbPb collisions at center-of-mass energy 2.76 TeV per nucleon pair are analyzed in the frameworks of PYQUEN jet quenching model. The presented studies for the nuclear modification factor of high-pT hadrons and the imbalance in dijet transverse energy support the supposition that the intensive wide-angular ("out-of-cone") medium-induced partonic energy loss is seen in central PbPb collisions at the LHC.Comment: 5 pages including 4 figures as EPS-files; prepared using LaTeX package for publication in the European Physical Journal

Quarkonia Production in Hot and Cold Matters

Quarkonia were predicted to be suppressed in the "hot" deconfined matter known as the Quark Gluon Plasma (QGP), but they were also seen to suffer from "cold" nuclear matter effects (parton shadowing, nuclear absorption...). Both at SPS and RHIC, suppression beyond nuclear effects was observed, but the rapidity dependence of the RHIC result is not easy to interpret. I review here the current status of these results, their possible interpretations and the new measurements that could provide insights on quarkonia suppression. Some of them were presented at this conference.Comment: 8 pages, 4x2 figures, to appear in the proceedings of Quark Matter 2008: 20th International Conference on Ultra-Relativistic Nucleus Nucleus Collisions (QM 2008), Jaipur, India, 4-10 Feb 2008. Version 3 accepted by editor. Figure 3 correcte