Impact of temperature dependence of the energy loss on jet quenching observables

The quenching of jets (particles with $p_T>>T, \Lambda_{QCD}$) in ultra-relativistic heavy-ion collisions has been one of the main prediction and discovery at RHIC. We have studied, by a simple jet quenching modeling, the correlation between different observables like the nuclear modification factor \Rapt, the elliptic flow $v_2$ and the ratio of quark to gluon suppression $R_{AA}(quark)/R_{AA}(gluon)$. We show that the relation among these observables is strongly affected by the temperature dependence of the energy loss. In particular the large $v_2$ and and the nearly equal \Rapt of quarks and gluons can be accounted for only if the energy loss occurs mainly around the temperature $T_c$ and the flavour conversion is significant.Finally we point out that the efficency in the conversion of the space eccentricity into the momentum one ($v_2$) results to be quite smaller respect to the one coming from elastic scatterings in a fluid with a viscosity to entropy density ratio $4\pi\eta/s=1$.Comment: 7 pages, 8 figures, Workshop WISH 201

Elliptic Flow from Non-equilibrium Initial Condition with a Saturation Scale

A current goal of relativistic heavy ion collisions experiments is the search for a Color Glass Condensate as the limiting state of QCD matter at very high density. In viscous hydrodynamics simulations, a standard Glauber initial condition leads to estimate $4\pi \eta/s \sim 1$, while a Color Glass Condensate modeling leads to at least a factor of 2 larger $\eta/s$. Within a kinetic theory approach based on a relativistic Boltzmann-like transport simulation, we point out that the out-of-equilibrium initial distribution proper of a Color Glass Condensate reduces the efficiency in building-up the elliptic flow. Our main result at RHIC energy is that the available data on $v_2$ are in agreement with a $4\pi \eta/s \sim 1$ also for Color Glass Condensate initial conditions, opening the possibility to describe self-consistently also higher order flow, otherwise significantly underestimated, and to pursue further the search for signatures of the Color Glass Condensate.Comment: 6 pages, 4 figures. // Title changed, some discussion added, main conclusions unchanged. Version accepted for publication on Phys. Lett.

Shear viscosity and chemical equilibration of the QGP

We have investigated, in the frame work of the transport approach, different aspects of the QGP created in Heavy Ion Collisions at RHIC and LHC energies. The shear viscosity $\eta$ has been calculated by using the Green-Kubo relation at the cascade level. We have compared the numerical results for $\eta$ obtained from the Green-Kubo correlator with the analytical formula in both the Relaxation Time Approximation (RTA) and the Chapman-Enskog approximation (CE). From this comparison we show that in the range of temperature explored in a Heavy Ion collision the RTA underestimates the viscosity by about a factor of 2, while a good agreement is found between the CE approximation and Gree-Kubo relation already at first order of approximation. The agreement with the CE approximation supplies an analytical formula that allows to develop kinetic transport theory at fixed shear viscosity to entropy density ratio, $\eta/s$. We show some results for the build up of anisotropic flows $v_{2}$ in a transport approach at fixed shear viscosity to entropy density ratio, $\eta/s$. We study the impact of a T-dependent $\eta/s(T)$ on the generation of the elliptic flows at both RHIC and LHC. We show that the transport approach provides, in a unified way, a tool able to naturally describe the $v_{2}(p_{T})$ in a wide range of $p_{T}$, including also the description of the rise and fall and saturation of the $v_{2}(p_{T})$ observed at LHC. Finally, we have studied the evolution of the quark-gluon composition employing a Boltzmann-Vlasov transport approach that include: the mean fields dynamics, associated to the quasi-particle model, and the elastic and inelastic collisions for massive quarks and gluons. Following the chemical evolution from an initial gluon dominated plasma we predict a quark dominance close to $T_{C}$ paving the way to an hadronization via quark coalescence.Comment: 15 pages, 10 figures, Invited Talk given by S. Plumari at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

Anisotropic flows and shear viscosity of the Quark-Gluon plasma within a transport approach

In this talk we discuss the build up of elliptic flow v2 and high order harmonics v3, v4 and v5 for a fluid at fixed η/s by mean of an event-by-event transport approach. We discuss the effect of the η/s ratio on the build up of the vn(pT). In particular we study the effect of a temperature dependent η/s for two different beam energies: RHIC for Au+Au at p s = 200GeV and LHC for Pb+ Pb at p s = 2.76 TeV. We find that for the two different beam energies considered t he suppression of the vn(pT) due to the viscosity of the medium have different contributions coming from the cross over or QGP phase. In ultra-central collisions the vn(pT) show a strong sensitivity to the η/s ratio in the QGP phase and this sensitivity increase with the increase of the order of the harmonic

The elliptic flow and the shear viscosity of the QGP within a kinetic approach

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

Air Traffic Management Technology Demonstration-1 Concept of Operations (ATD-1 ConOps), Version 3.0

This document describes the goals, benefits, technologies, and procedures of the Concept of Operations (ConOps) for the Air Traffic Management (ATM) Technology Demonstration #1 (ATD-1), and provides an update to the previous versions of the document [ref 1 and ref 2]