We use a relativistic transport approach to study the role of a temperature dependent shear viscosity to entropy density ratio, η/s(T), on the build-up of the elliptic flow, v2. The recent results ...from = 62.4GeV at RHIC up to 2.76 TeV at LHC have shown an intriguing property of the v2(pT), which appears to be nearly invariant with energy. We show that in our transport approach this surprising behavior can be described by a particular temperature dependence of η/s(T), typical of matter that undergoes a phase transition or a cross-over, with a rise and fall and the minimum close to critical temperature Tc.
The two key observables related to heavy quarks that have been measured in experiments are the nuclear suppression factor RAA and the elliptic flow ν2. The simultaneous reproduction of these two ...observables is a puzzle which have challenged all the existing models. We discuss two ingredients responsible for addressing a large part of such a puzzle: the temperature dependence of the energy loss and the full solution of the Boltzmann collision integral for the scattering between the heavy quarks and the particle of the bulk.
A current goal of relativistic heavy ion collisions experiments is to understand the impact of initial non-equilibrium on final observables. A Color Glass Condensate (CGC) as the limiting state of ...QCD matter at very high density implies initial non-thermal distribution at least for momenta below the saturation scale. In viscous hydrodynamics simulations, a standard Glauber initial condition leads to estimate 4pieta/s ~ 1, while employing the Kharzeev-Levin-Nardi (KLN) modeling of the CGC leads to at least a factor of 2 larger eta/s. Within a kinetic theory approach based on a relativistic Boltzmann-like transport simulation, our main result is that the out-of-equilibrium initial distribution in p-space reduces the efficiency in building-up the elliptic flow. At RHIC energy we find the available data on v sub(2) are in agreement with a 4pieta/s ~ 1 also for KLN initial conditions.
Collective Flows in a Transport Approach Plumari, S; Baran, V; Toro, M Di ...
Journal of physics. Conference series,
01/2011, Letnik:
270, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We introduce a transport approach at fixed shear viscosity to entropy ratio η/s to study the generation of collective flows in ultra-relativistic heavy-ion collisions. Transport theory supplies a ...covariant approach valid also at large η/s and at intermediate transverse momentum pT, where deviations from equilibrium is no longer negligible. Such an approach shows that at RHIC energies a temperature dependent η/s enhances significantly the v4/v22 respect to the case of constant η/s. Furthermore if NJL chiral dynamics is self-consistently implemented we show that it does not modify the relation between v2 and η/s.
In Ultra-relativistic Heavy-Ion Collisions (HICs) very strong initial electro-magnetic (E.M.) fields are created: the order of magnitude of the magnetic field is about 1019Gauss, the most intense ...field in the Universe, even larger than that of a magnetar. These fields rapidly decrease in time, inducing a drift of particles in the reaction plane. The resulting flow is odd under charge exchange and this allows to distinguish it from the large vorticity of the bulk matter due to the initial angular momentum conservation. Conjointly charm quarks, thanks to their large mass Mc≫ΛQCD, are produced in hard partonic processes at formation time τf≈1/(2MHQ) which is comparable with the time scale when the E.M. field attains its maximum value. Moreover, with a mass of Mc≈1.3GeV there should be no mixing with the chiral magnetic dynamics and the condition Mc≫T allows charm quarks to have sufficiently large thermalization time, so that they can probe the entire phase-space evolution of the QGP retaining the initial kick given by the E.M. field. We show that such E.M. field entails a transverse motion of charm quarks resulting in a splitting of directed flow v1 of D and D‾ mesons of few percent, i.e. much larger compared to the measured pion one.
We analyse the hadron-quark phase transition in neutron stars by confronting the hadronic Equation of State (EoS) obtained according to the microscopic Brueckner-Hartree-Fock many body theory, with ...the quark matter EoS derived within the Field Correlator Method. In particular, the latter EoS is only parametrized in terms of the gluon condensate and the large distance quark-antiquark potential, so that the comparison of the results of this analysis with the most recent measurements of heavy neutron star masses provides some physical constraints on these two parameters.
Strongly interacting matter manifests a very rich dynamical behavior and the associated phase diagram was intensively explored through heavy ions collisions during the last years. Around Fermi ...energies the nuclear multifragmentation shows up analogies with the liquid-gas phase transition. Within a microscopic transport model based on Boltzmann-Nordheim-Vlasov equation we investigate the kinetics of this process as well as the features related to the two-component character of the nuclear matter. The evolution of the fragmentation mechanism with the centrality and the role of various instabilities are also discussed. At ultra-relativistic energies recent results from RHIC and LHC experiments evidenced the manifestation of quarks and gluons degrees of freedom during the evolution of the hot fireball created in these collisions. Based on a relativistic transport model we inquire upon the role of chiral symmetry breaking on the collective features of expanding quark-gluon plasma.
The two-Equation of State (EoS) model is used to describe the hadron-quark phase transition in asymmetric matter formed at high density in heavy-ion collisions. For the quark phase, the three-flavor ...Nambu–Jona-Lasinio (NJL) effective theory is used to investigate the influence of dynamical quark mass effects on the phase transition. At variance to the MIT-Bag results, with fixed current quark masses, the main important effect of the chiral dynamics is the appearance of an end point for the coexistence zone. We show that a first order hadron-quark phase transition may take place in the region T (50 – 80) MeV and ρB (2 – 4)ρ0, which is possible to be probed in the new planned facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From isospin properties of the mixed phase some possible signals are suggested. The importance of chiral symmetry and dynamical quark mass on the hadron-quark phase transition is stressed.
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