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Questions about sQGP

Carlos Arguello

Columbia University

24th Winter Workshop on Nuclear Dynamics

April 10th 2008

24th WWND04/10/2008

Carlos ArguelloColumbia University 2

Introduction

Taken from Taken from “RHIC Physics in the Context of the Standard Model”“RHIC Physics in the Context of the Standard Model”, , TT..i i HiranoHirano

24th WWND04/10/2008

Carlos ArguelloColumbia University 3

IntroductionAs a Columbia student, I can’t escape from T.D. Lee’s influence.

These are exciting times!

24th WWND04/10/2008

Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia 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/0305084

Hydrodynamics seem to predict correctly several characteristics of the sQGP at low pT.

J. Adams et al. (STAR), Phys. Rev. C 72, 014904 (2005).

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Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia University 8

Hydrodynamics model and Initial Conditions.

With I.C. based on the CGC model, the elliptic flow V2 is overestimated, while for Glauber initial conditions, the proposed model seems to explain accurately the experimental data...

24th WWND04/10/2008

Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia University 10

Jet Production

“Measurements of high pT 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 WWND04/10/2008

Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia 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 WWND04/10/2008

Carlos ArguelloColumbia 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!!!