1 Questions about sQGP Carlos Arguello Columbia University 24 th Winter Workshop on Nuclear Dynamics April 10 th 2008

24th WWND 04/10/2008 Carlos Arguello Columbia University 2 Introduction Taken from “RHIC Physics in the Context of the Standard Model”, T.i Hirano

24th WWND 04/10/2008 Carlos Arguello Columbia University 3 Introduction As a Columbia student, I can’t escape from T.D. Lee’s influence. These are exciting times!

24th WWND 04/10/2008 Carlos Arguello Columbia University 4 The sQGP as an ideal fluid. sQGP has been claimed to behave as a (nearly) ideal fluid. What experimental data taken so far shows the strongest evidence for this nearly ideal fluid behavior? Do the estimates of the lower bound for viscosity from different theories (Uncertainty principle, AdS/CFT...) agree? Can we talk about surface tension on the sQGP?

24th WWND 04/10/2008 Carlos Arguello Columbia University 5 The sQGP as an ideal fluid Viscosity implies dissipation in the system. How does this modify the ideal hydrodynamic equations where energy- momentum tensor and the baryon current are conserved? The mean free path in fluids with low viscosity has to be very small compared with the system size. In the case of sQGP, can we define a mean free path for partons? Can we measure it?

24th WWND 04/10/2008 Carlos Arguello Columbia University 6 Thermalization process in sQGP “ The validity of ideal hydrodynamics requires local relaxation times towards thermal equilibrium which are much shorter than any macroscopic dynamical time scale... Only if the system is close to local thermal equilibrium, it’s thermodynamic properties are well defined.” Peter F. Kolb, Ulrich Heinz nucl-th/ Hydrodynamics seem to predict correctly several characteristics of the sQGP at low p T. J. Adams et al. (STAR), Phys. Rev. C 72, (2005).

24th WWND 04/10/2008 Carlos Arguello Columbia University 7 Thermalization process on sQGP From the experimental data can we conclude that indeed a thermalization process takes place in the sQGP? In case we have such a fast thermalization of the system, which is the mechanism responsible for it? M. Gyulassy, L. McLerran / Nuclear Physics A 750 (2005) 30–63 Does the sQGP have a blackbody radiation? Do we have experimental data for this type of radiation?

24th WWND 04/10/2008 Carlos Arguello Columbia University 8 Hydrodynamics model and Initial Conditions. With I.C. based on the CGC model, the elliptic flow V 2 is overestimated, while for Glauber initial conditions, the proposed model seems to explain accurately the experimental data...

24th WWND 04/10/2008 Carlos Arguello Columbia University 9 Hydrodynamics model and Initial Conditions. In order to predict the flow of the sQGP once formed using hydrodynamics, initial conditions over the system must be imposed. What initial conditions are imposed in the theoretical models in order to predict accurately the experimental data? How sensitive are the models used to describe the elliptic flow to this initial conditions?

24th WWND 04/10/2008 Carlos Arguello Columbia University 10 Jet Production “ Measurements of high p T hadron production in A+A collisions have revealed strong suppression of the single-particle inclusive yield compared to elementary p+p collisions. The suppression is commonly thought to arise from partonic energy loss in dense matter due to induced gluon radiation.” Taken from “Probing the QGP at RHIC” of Steffen A. Bass Nuclear Physics A 783 (2007) 1c–12c, T. Ullrich.

24th WWND 04/10/2008 Carlos Arguello Columbia University 11 Jet Production How does the energy given up from the outgoing jet to the bulk affect the local thermal equilibrium condition of the system? If the system remains in local thermal equilibrium while the jet passes through, how does the thermalization of the bulk take place?

24th WWND 04/10/2008 Carlos Arguello Columbia University 12 Jet Production Can we include a 4-current density in which the jet acts as a Dirac delta source, in analogy to what we do in E&M for point charges and the current density that they produce? What properties should this 4-current have? ?

24th WWND 04/10/2008 Carlos Arguello Columbia University 13 Transport coefficients in sQGP Can we calculate the dielectric tensor for the sQGP? Which sort of measurements must be carried out to get experimentally this tensor? Can we make a theorethical estimate of the heat conductivity for the sQGP? Reynolds number: In spite of having a very small shear viscosity, is the Reynolds number for the sQGP small enough in order to have laminar flow instead of turbulent one?

24th WWND 04/10/2008 Carlos Arguello Columbia University 14 Freeze Out Once the sQGP starts expanding (and cooling), how do we know when the hadronization process start (For what temperature does it start)? How does the hadronization process work? Is there a single process involved, or it can occur through different processes? How do we include this “boundary contition” (hadronization) in the hydrodynamics models used to describe the flow of the sQGP?

24th WWND 04/10/2008 Carlos Arguello Columbia University 15 sQG....Plasma??? One of the main properties of the electric plasma is the existence of a screening length (Debye Length): How do we define the screening length for the sQGP? Which properties does the sQGP have in common with the electronic plasma? Can we define every quantity used to describe the electronic plasma in the sQGP?

24th WWND 04/10/2008 Carlos Arguello Columbia University 16 It seems that we have still many open questions regarding the sQGP. That´s what makes this field so interesting. One last question I want to ask you is would be... Should I start learning string theory???? Thank You!!!