The Quark Gluon Plasma what is it and why should it exist ?

1. The Quark Gluon Plasmawhat is it and why should it exist ?

2. time The first second of the universe from D.J. Schwarz, astro-ph/0303574 AP NP HEP

3. History of the early universe • The tools need to study the early history of the universe: • - Accelerator based high energy and nuclear experiments (LHC, RHIC) • Observational cosmology (LSST, HAWC, etc.)

4. Going back in time… Age Energy Matter in universe 0 1019 GeV grand unified theory of all forces 10-35 s 1014 GeV 1st phase transition (strong: q,g + electroweak: g, l,n) 10-10 s 102 GeV 2nd phase transition (strong: q,g + electro: g + weak: l,n) 10-5 s 0.2 GeV 3rd phase transition (strong:hadrons + electro:g + weak: l,n) 3 min. 0.1 MeV nuclei 6*105 years 0.3 eV atoms Now 3*10-4 eV = 3 K (13.7 billion years) RHIC, LHC & FAIR FRIB & FAIR

5. To understand the strong force and the phenomenon of confinement: Create and study a system of deconfined colored quarks (and gluons) quark-antiquark pair created from vacuum Analogies and differences between QED and QCD to study structure of an atom… electron F ~ 1/r2 …separate constituents Imagine our understanding of atoms or QED if we could not isolate charged objects!! nucleus neutral atom Confinement: fundamental & crucial (but not understood!) feature of strong force - colored objects (quarks) have  energy in normal vacuum F ~ r quark Strong color field Force grows with separation !!! “white” 0 (confined quarks) “white” proton (confined quarks) “white” proton

6. The main features of Quantum Chromodynamics (QCD) (Nobel Prize 2004) • Confinement • At large distances the effective coupling between quarks is large, resulting in confinement. • Free quarks are not observed in nature. • Asymptotic freedom • At short distances the effective coupling between quarks decreases logarithmically. • Under such conditions quarks and gluons appear to be quasi-free. • (Hidden) chiral symmetry • Connected with the quark masses • When confined quarks have a large dynamical mass - constituent mass • In the small coupling limit (some) quarks have small mass - current mass

7. Theoretical and computational QCDin vacuum and in medium In vacuum: - asymptotically free quarks have current mass - confined quarks have constituent mass - baryonic mass is sum of valence quark constituent masses Masses can be computed as a function of the evolving coupling strength or the ‘level of asymptotic freedom’, i.e. dynamic masses. B.Mueller (2004): New Discoveries at RHIC But the universe was not a vacuum at the time of hadronization, it was likely a plasma of quarks and gluons. Is the mass generation mechanism the same ?

8. The evolution of luminous matter Standard model is symmetric. All degrees of freedom are massless. Electro-weak symmetry breaking via Higgs field (Dm of W, Z, g) Mechanism to generate current quark masses (but does not explain their magnitude) QCD phase transition (I): chiral symmetry breaking via dynamical quarks. Mechanism to generate constituent quark masses (but does not explain hadronization) QCD phase transition (II): Confinement to hadrons. Mechanism to generate hadron properties (but does not explain hadron masses)

9. What can we do in the laboratory ? a.) Re-create the conditions as close as possible to the Big Bang, i.e. a condition of maximum density and minimum volume in an expanding macroscopic system. Is statistical thermodynamics applicable ? b.) Measure a phase transition, characterize the new phase, measure the de-excitation of the new phase into ‘ordinary’ matter – ‘do we come out the way went in ?’ (degrees of freedom, stable or metastable matter, homogeneity) c.) Learn about hadronization (how do particles acquire mass) – complementary to the Higgs search but with the same goal. The relevant theory is Quantum Chromo Dynamics

10. Generating a deconfined state • Present understanding of Quantum Chromodynamics (QCD) • heating • compression •  deconfined color matter ! Hadronic Matter (confined) Nuclear Matter (confined) Quark Gluon Plasma deconfined !

11. Expectations from Lattice QCD /T4 ~ # degrees of freedom confined: few d.o.f. deconfined: many d.o.f. TC ≈ 173 MeV ≈ 21012 K ≈ 130,000T[Sun’s core] C  0.7 GeV/fm3

12. The phase diagram of QCD Early universe quark-gluon plasma critical point ? Tc Temperature colour superconductor hadron gas nucleon gas nuclei CFL r0 Neutron stars vacuum baryon density

13. PHOBOS BRAHMS RHIC Au+Au @ sNN=200 GeV PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC) 1 mile v = 0.99995c

14. Study all phases of a heavy ion collision If the QGP was formed, it will only live for 10-21 s !!!! BUT does matter come out of this phase the same way it went in ???

15. Study all phases of a heavy ion collision If the QGP was formed, it will only live for 10-21 s !!!! BUT does matter come out of this phase the same way it went in ???

16. Proving the existence of a new phase of matterCan we prove that we have a phase thatbehaves different than elementary pp collisions ? Three steps: a.) prove that the phase is partonic b.) prove that the phase is collective c.) prove that the phase characteristics (state variables) are different from the QCD vacuum

17. Proof (a) for partonic medium creationShooting a high momentum particle through a dense medium idea: p+p collisions @ same sNN = 200 GeV as reference p p ?: what happens in Au+Au to jets which pass through medium? • Prediction: scattered quarks radiate energy (~ GeV/fm) in the colored medium: • “quenches” high pT particles • “kills” jet partner on other side ? Au+Au

18. RAA and high-pT suppression STAR, nucl-ex/0305015 pQCD + Shadowing + Cronin energy loss pQCD + Shadowing + Cronin + Energy Loss • Deduced initial gluon density at t0 = 0.2 fm/c dNglue/dy ≈ 800-1200 • ≈ 15 GeV/fm3, eloss = 15*cold nuclear matter (compared to HERMES eA)(e.g. X.N. Wang nucl-th/0307036) SYSTEM NEEDS TO BE PARTONIC

19. Y Directed flow Elliptic flow Time X Proof (b): is the matter behaving collective ? elliptic (anisotropic)flow Flow Mid-central collision Y Out-of-plane In-plane Reaction plane Flow X Dashed lines: hard sphere radii of nuclei

20. Proof (c): new phase leads to new matter production mechanismThe medium consists of constituent quarks ?Massive quasiparticles instead of current quarks ? baryons mesons

21. z y x Elliptic flow exists and its magnitude is described by ideal hydrodynamics ! Strong collective flow: elliptic expansion with mass ordering Hydrodynamics: strong coupling, small mean free path: many interactions NOT plasma-like system behaves liquid-like

22. A surprise: ideal liquid behavior First time in heavy-ion collisions we created a system which is in quantitativeagreement with ideal hydrodynamic model. The new phase behaves like an ideal liquid rather than a plasma. Not anticipated. In stark contrast to pQCD.

23. ? How strong is the coupling ? Simple pQCD processes do not generate sufficient interaction strength. Navier-Stokes type calculation of viscosity yield a near perfect liquid Viscous force ~ 0. We have made a sQGP not the anticipated wQGP.

24. Experimental verification at RHIC RB, J.Phys.G35:044504 (2008) Lacey et al., PRL 98 (2007) 092301 The quantum limit has been reached at RHIC and has been independently verified in several measurements of collective effects

25. Lessons from RHIC: The Quark SoupAIP ScienceStory of 2006 Hirano, Gyulassy (2006)

26. A three prong approach: lower energy better facility higher energy The future is bright RHIC-II: RHIC upgrade with higher luminosity and upgraded detectors LHC: Large Hadron Collider with ALICE, CMS, ATLAS FAIR: Facility for Antiproton & Ion Reseach

27. Measuring pp/AA in all LHC experiments • ALICE • Dedicated & most versatile heavy ion detector • Important for particle identified fragmentation measurements in pp • CMS/ATLAS • Dedicated & most versatile p+p detectors • Important for calorimeter based jet measurements in A+A.