Probing dense matter at extremely high temperature

1. Probing dense matter at extremely high temperature Rudolph C. Hwa University of Oregon Jiao Tong University, Shanghai, China April 20, 2009

3. 1012K Outline High temperature. How high? 1000K? 106? 109? How do we get there? How do we probe it? What do we know so far? What are new very recently? What can be expected in the future?

8. Relativistic Heavy Ion Collider 100 +100 GeV (Au+Au) LHC Large Hadron Collider 2.75 + 2.75 TeV (Pb+Pb) RHIC

9. PHOBOS BRAHMS PHENIX STAR

10. STAR detector

15. lumpy initial conditions and a QGP expansion collision evolution particle detectors expansion and cooling kinetic freeze-out distributions and correlations of produced particles lumpy initial energy density hadronization QGP phase quark and gluon degrees of freedom collision overlap zone quantum fluctuations  ~ 1015 fm/c  ~ 10 fm/c  ~ 0 fm/c 0~1 fm/c 15

17. pseudorapidity azimuthal angle transverse momentum Collision geometry

18. Au + Au sNN = 200 GeV Collision geometrycentrality very peripheral very central c=0-0.05

19. pT  z y x Non-central collision py px (Npart) Azimuthal variation in non-central collisions

20. How can we probe such a medium? z y x Non-central collision Example: X-ray We need a penetrating probe.

22. We can’t shoot a probe through the dense medium, as in X-ray diagnostic. It must come from within. pT L ~ size of biological molecules For good resolution we need  << L In nuclear collisions the transverse size of collision zone is about 10 fm (10-12cm). For  << 1 fm, we need p = h/  >> 1 GeV At RHIC cm energy of a nucleon is 100 GeV, but it is the momentum-transfer scale that measures the small-distance resolution:

23. low intermediate high pT 2 6 jet Jet production in pp collision parton nucleon nucleon jet soft semi-hard hard relativistic hydrodynamics no reliable theory perturbative Quantum Chromo Dynamics (quarks, gluons) -- partons

24. What do we see at high pT? Au+Au  0 + anything pT (GeV/c)

28. So the pT of the detected jet in AA collision is lower than a similar jet in pp collision. pp AA That is a suppression effect pT Jet quenching In the transverse plane a hard scattering can occur anywhere If the hot medium is sQGP, the partons that traverse it lose energy.

29. trigger associated particle How do we know that the suppression is due to parton interaction with QGP as the medium? A more revealing way to see its properties is to examine the azimuthal dependence of jet production Dihadron correlations

30. STAR Striking final state effects preliminary 20-60% central trigger out-of-plane trigger in-plane Dihadron correlations in Df PRL 91, 072304

31. absorbed undamped to detector If there is severe damping on the away side, then most observed jets are produced near the surface.

32. away near centrality c=0.05 c=0.5 Back-to-back jets Hwa-Yang 0812.2205 Not measurable: initial parton momenta k, k’ parton momenta at surfaces q, q’ Measurable:trigger momentum pt associated particle (same side) pa associated particle (away side) pb

33. Away Yield per trigger Near

34. L-t t if we fix the length L Much less energy loss on the near side Suppression factor Energy loss1- More energy loss on the away side

35. It is only possible to fix the centrality c. Some paths are long Some are short The problem is that the path length L cannot be fixed experimentally. Data integrates over all points of interaction. Tangential jets dominate.

36. associates “jet-axis” trigger (T2) primary trigger (T1) -2 -1 2 0 1 3 4 5 associates Dominance by tangential jets! Df STAR has recent data on Dijets Au+Au centrality comparison T1: pT>5 GeV/c, T2: pT>4 GeV/c, A: pT>1.5 GeV/c 1 _dN_ Ntrigd(Df ) T2A1_T1 12% Central 40-60% MB 60-80% MB 2 0 STAR Preliminary • Df projection: no significant centrality dependence • No modification of away-side jet

37. Very hard to probe the interior of dense medium --- if the thickness cannot be controlled. That’s the problem with jet-jet correlation. So let’s move on to the medium response to jets.

38. Δφ 2. Effect of jets on medium. Trigger trigger direction Assoc. ridge Δη A ridge is discovered on the near side. distribution of particles associated with the trigger Jet-medium interaction 1. Effect of medium on jets. Jet

39. Trigger Trigger   irrelevant very relevant Dependence of ridge yield on the trigger azimuthal angle restrict ||<0.7 What is the direction of the trigger T?

40. A. Feng (STAR): 6 5 4 in-plane fS=0 out-of-plane fS=90o 3 Dependence of ridge yield on 2 1 Out-of-plane assoc 3<pTtrig<4, 1.5<pTtrig<2.0 GeV/c Ridge In-plane STAR Preliminary Jet New data presented at QM08

41. medium probe Correlated emission model (CEM) Chiu-Hwa PRC(09) Strong ridge formation when trigger and flow directions match.

42.  Sound wave Heating Away side jet Trigger jet Shock wave? What is on the away-side direction? Do you believe it? This is an active area of current research.

43. At LHC, cm energy is increased over RHIC by factor of 27. Energy density is expected to increase by < 10. Tinitial ………………………………………………………. < 2. It is hard to hold the dense matter together for long to thermalize. Large pT range will increase by > 20. Good ground to test pQCD. There are wide variations in extrapolation to higher energies. Ex. Most people predict p/ < 0.5 for 10<pT<20 GeV/c. We (RH & CBYang) predict 5 < p/ < 20.

44. Most significant advance will be either to confirm conventional wisdom or to validate unconventional ideas. I hope that I can tell you which next time. Thank you!