Nuclear Theory Seminars at Texas A&M: Spring 2014

Location: Cyclotron Conference Room (CYCL-300)

March 07, 4:00pm
      P. Hohler (Texas A&M University, College Station)
"Dileptons and Chiral Symmetry Restoration"

March 21, 4:00pm
      G. Vujanovic (McGill University, Montreal)
"Dileptons: Probing out-of-equilibrium properties of relativistic nuclear collisions with viscous hydrodynamics"

The current best description of the evolution of strongly interacting medium created in relativistic heavy ion collisions relies on viscous fluid dynamics. I will provide evidence that thermal dileptons are affected by the transport properties of the fluid and by non-equilibrium initial conditions of viscous hydrodynamics that hadronic observables are usually insensitive to. In fact, I will show that dilepton's flow harmonics can be used to investigate the magnitude of the shear-relaxation time as well as distinguish between possible initial shear-stress tensors.

April 14, 4:00pm
      S. Plumari (INFN Catania, Italy)
"Collective dynamics of the Quark-Gluon Plasma within a kinetic theory"
We discuss the build up of elliptic flow and high order harmonics v_n within a transport approach at fixed shear viscosity to entropy density ratio and with initial state fluctuations. We show, exploring the T dependence of eta/s, that a study of v_n in a wide p_T range allows to understand the difference behind the collective flows at LHC respect to RHIC. In particular we study the effect of a temperature dependent eta/s at different beam energies from RHIC for Au+Au at sqrt{s}= 62.4, 200 GeV to LHC energies for Pb+Pb at sqrt{s}= 2.76 TeV. We find that for the different beam energies considered the suppression of the elliptic flow due to the viscosity of the medium has different contaminations coming from the hadronic or QGP phase depending on the average energy of the system. In particular we show that it is possible to have a nearly invariant v_2(p_T) as observed experimetally only if eta/s has a behaviour typical of a phase transition with a fall and rise with the temperature. .

April 15, 4:00pm
      F. Scardina (INFN Catania, Italy)
"The puzzling relation between the RAA and the v2 for heavy mesons in a Boltzmann and in a Langevin approach"

The propagation of heavy flavour through the quark gluon plasma has been treated commonly within the framework of Langevin dynamics, i.e. assuming the heavy flavour momentum transfer is small or the scatterings are sufficiently forward peaked, small screening mass mD. We present a thorough study of the thermalization dynamics, average momentum evolution and of the approximations involved by Langevin equation by mean of a direct comparison with the full collisional integral within the framework of Boltzmann transport equation. We have carried out simulations using the two different approaches considering the dynamical evolution of a system consisting of heavy quarks within a bulk medium in equilibrium at fixed temperature. We have seen that unless the cross section is quite forward peaked or the mass to temperature ratio is quite large (Mq/T>8−10) there are significant differences in the evolution of the momentum spectra. In the case of bottom quarks we essentially find no differences for the time evolution of the momentum spectra between the Langevin and the Boltzmann dynamics independently of the the angular dependence of the cross section. Moreover we have performed simulations for realistic heavy Ion collisions at both RHIC and LHC energies and we have evaluated the nuclear suppression factor,R_AA , and the elliptic flow,v_2 , of the charm and bottom within the Langevin and the Boltzmann approach. We have compared the results obtained in both approaches which,for the case of charm quarks, can differ substantially leading to quite different values extracted for the the heavy quark diffusion coefficient. .

April 25, 4:00pm
      F. Geurts (Rice University, Houston)
"Dilepton Measurements at RHIC"

Dilepton measurements play an essential role in the study of hot and dense nuclear matter, created in relativistic heavy-ion collisions. Compared to hadrons, leptons have only little interaction with the strongly interacting system. Thus, dileptons provide ideal penetrating probes that allow the study of such a system throughout its space-time evolution. Depending on the dominating contributions in certain invariant mass ranges, these studies include the effects of chiral symmetry restoration, thermal radiation from the quark-gluon plasma, to effects of the medium on the heavy quarks that are created in the primordial processes. I will review dilepton measurements performed over a range of beam energies at the RHIC collider at Brookhaven National Lab and discuss these in the context of past SPS results as well ongoing and future activities at one of the main experiments at RHIC in an effort to further improve our understanding of hot and dense nuclear matter by means of these ideal penetrating probes..

June 06, 4:00pm
      B. Chen (Tsinghua University, Beijing)
"Heavy quarkonium suppression and production in heavy ion collisions"

Heavy quarkonium have long been considered as a good probe of the deconfined matter(QGP). Its suppression by color-screening is a strong evidence of QGP existence produced in heavy-ion collisions. But quarkonium regeneration through quark recombination in QGP makes it difficult to fully understand the quarkonium suppression mechanisms and extract hot deconfined medium information. Also, cold nuclear matter effects and feed-down contribution from other states makes the experimental data more challenging and even confusing. Here, based on the Boltzmann-type transport model, i will talk about the charmonium suppression and regeneration in the transverse and longitudinal direction with elastic and inelastic collisions, and B-hadron decay contribution to charmonium excited state(2S). Also, Upsilon suppression mechanism by QGP will be discussed briefly..

Previous seminars

Spring 2013
Spring 2012
Fall 2011
Spring 2011
Fall 2010
Spring 2010
Fall 2009
Spring 2009
Fall 2008
Spring 2008
Fall 2007
Spring 2007
Fall 2006
Spring 2006
Fall 2005
Spring 2005
Fall 2004
Spring 2004
Fall 2003

Nuclear theory group home page
Last updated: Jan 31/14
Maintained by Ralf Rapp