Making Quark Soup Out of Gold!

1. Making Quark Soup Out of Gold! Lanny Ray University of Texas at Austin October 13, 2004 Rice Colloquium

2. Outline: • Physics goals • How to accomplish these goals • Summary of global analysis • Probing the inner workings using correlations • Have we made the Quark Gluon Plasma at RHIC? • Conclusions and Acknowledgements Rice Colloquium

3. Physics Goals: This talk is about current efforts to better understand the strong interaction and strongly interacting matter, especially at very high energy density and temperature. Quantum Chromodynamics or QCD is the theory of the strong interaction. Electrodynamics: one charge, either positive or negative, carried by e. Strong force: three charges, RED or Anti-RED, GREEN or Anti-GREEN, BLUE or Anti-BLUE, carried by quarks (color), anti-quarks (anti-color) and gluons (color-anticolor combinations). Artist’s view of a nucleus Rice Colloquium

4. jet parton nucleon nucleon QCD is quite successful but in general is highly non-linear, and therefore very COMPLICATED. QCD verified in high energy, high momentum transfer scattering. Strong interaction systems are compact, color singlets, i.e. white, with color antisymmetric wave functions. Free or deconfined colored objects have not been observed. Can we better understand color confinement from experiment? Rice Colloquium

5. Phase Transition from hadron gas to “free” quarks and gluons? Numerical predictions of QCD using a 4D lattice approximation indicate a phase transition from bound hadrons (mesons and baryons) to color deconfined quark-gluon equilibrated matter – Quark Gluon Plasma (QGP). Tcrit~ 175 MeV Ecrit ~ 1-3 GeV/fm3 From: K.Kanaya, Nucl.Phys. A715, 233c (2003) (Quark Matter 2002). Rice Colloquium

6. early universe 250 quark-gluonplasma 200 RHIC Temperature Tchemical freezeout (MeV) SPS lattice QCD 150 deconfinement chiral restauration thermal freeze-out AGS 100 hadron gas SIS 50 neutron stars nuclei 0 0 200 400 600 800 1000 1200 Baryonic Potential B (MeV) P. Braun-Munzinger nucl-ex/0007021 Phase Diagram for the Strong Interaction Rice Colloquium

7. Phenomenology can be developed which characterizes the hot, dense medium at T > Tcrit Perhaps effective field theories will result: Equation of State: Temperature Pressure Density Opacity Viscosity • What are the effective degrees • of freedom and the effective • lagrangian, Leff? • Constituent quarks? • Current quarks? • Collective gluon states? • Diquarks? • Dressed q & g, etc.? Rice Colloquium

8. Big Bang! Can phenomenology of hot, dense hadronic matter improve our understanding of the very early universe Rice Colloquium

9. QGP? 1ms Rice Colloquium

10. How to Accomplish These Goals: To reach this new regime of temperature and energy density for strongly interacting matter theRelativistic Heavy Ion Collider (RHIC) was constructed along with four detectors to study ultra-relativistic collisions between gold nuclei. Rice Colloquium

11. Increasing the collision energy Few to ~100 GeV per nucleon E ~ A1/3log{sNN1/2} QGP? T Baryon debris goes forward down the beam pipe nuclei Hot, high energy density central region Net rB Rice Colloquium

12. Closer look at each stage of the collision: Rice Colloquium

13. A general view of RHIC collisions ? initial state pre-equilibrium QGP? hadronization decoupling time tLAB~5fm/c Beam direction Graphics from Steffen Bass and John Harris Rice Colloquium

14. The RHIC Facility at the Brookhaven National Lab BRAHMS PHOBOS RHIC PHENIX STAR Rice Colloquium

15. The STAR detector E-M Calorimeter Projection           Chamber Time of    Flight Rice Colloquium

16. About 2000 charged particles from a single collision! A typical, single Au+Au collision at STAR In a typical run period we obtain about 10M events like this. Rice Colloquium

17. STAR kinematics and acceptance: Full h charged particle distribution measured by the PHOBOS experiment (www.phobos.bnl.gov) Definitions: y Beam direction STAR pt x z STAR TPC acceptance Rice Colloquium

18. Challenges: • Big science, large collaborations • High energy Au+Au collisions are messy. • The most interesting stage of the collision is hidden from direct observation behind a veil of hadronization, hadro-chemistry, and hadron rescattering. • Several signals of color deconfinement proposed, but none are “smoking guns.” RHIC has been operating for four years; I will summarize major highlights for global properties of RHIC collision systems. Rice Colloquium

19. Summary of Global Analysis Particle Distributions Spectra are thermal (B.E. or M.B.) distributions plus hard scattering which causes power law behavior at higher pt central From: Adler et al. (STAR Collaboration), Phys. Rev. Lett. 89, 202301 (2002). centrality peripheral Rice Colloquium

20. Identical Charged Pion Quantum Interferometry Rice Colloquium

21. p- Analysis reveals correlation lengths of an expanding source Rside side Rout out long Rlong The decreasing correlation lengths with increasing pair momentum indicate an expanding medium. Compilation from: M. Lisa et al., PRL 84, 2798 (2000) R. Soltz et al., to be sub PRC C. Adler et al., PRL 87, 082301 I.G. Bearden et al., EJP C18, 317 (2000) Rice Colloquium

22. midrapidity : |h| < 1.0 z STAR Model PRL 86 (2001) 402 y Peripheral  Central x Azimuthal Anisotropy – Elliptic Flow Measures:  response of the system to early pressure  the system’s ability to convert original spatial anisotropy into momentum anisotropy typical minimum bias event - “almond” Rice Colloquium

23. ? Azimuthal correlationsin Au+Au at 200 GeV peripheral central pedestal and flow subtracted Phys Rev Lett 90, 082302 p-p and peripheral Au+Au similar Suppression of away-side jet; requires high gluon density Rice Colloquium

24. Summary of bulk properties of final stages of Au+Au collisions at RHIC Energy density ~ 5-7 GeV/fm3 = 30-40 times rnuc which is well above Lattice QCD predictions for a phase transition ~1-3 GeV/fm3. -- highest man-made energy density so far! Very high initial pressure High gluon density ~ 1000/unit rapidity Decoupling T ~ 110 MeV = 1.3 trillion K Matter is expanding outward at ½c. Radius ~ 12 fm, twice that of gold nucleus. Total lifetime ~ 10 fm/c = 3x10-23 s Longitudinal “Hubble” expansion Transverse collective expansion plus random thermal motion Two-dimensional, hydrodynamics with hadron-QGP phase transition describes most of the bulk properties of RHIC collisions. Rice Colloquium

25. Probing the inner workings using correlations Correlation measurements provide a window into the internal dynamics of the hot, dense medium: Two-particle correlation in momentum space Two-particle density “sibling pair” Single-particle densities: mixed event pair mixed pair sibling pair Define ratio of densities of the number of pairs of particles: STAR reports these normalized ratios Rice Colloquium

26. Proton+proton reference: • Two-Component Model: • Longitudinal color string fragmentation • Transverse semi-hard parton scattering and fragmentation • Local charge, momentum cons. charge-ordering local momentum conservation pt,2 Semi-hard parton scattering “minijet” (min-bias) pt,1 p-p 200 GeV pt,2 minijets Longitudinal color string fragmentation “soft” particles Transverse rapidity pt,1 Rice Colloquium

27. LS US CI Proton-Proton Correlations in h,f Space: Semi-hard minijets STAR preliminary Like sign pairs fD=f1-f2 hD=h1-h2 Unlike sign pairs Beam f Collision “event” in h,f Charge Independent (CI = all charged pairs) Rice Colloquium

28. Soft, longitudinal string fragmentation in p-p Manifest as strong, charge-dependent correlations + HBT Charge ordering along h - + - Local momentum conservation + Like-sign, near-side correlations Unlike-sign, away-side correlations Charge dependent, CD = LS-US, strong negative correlations on hD. STAR preliminary Rice Colloquium

29. Comparing p-p and Au-Au Correlations in Transverse Momentum Space Au-Au 130 GeV mid-central (nucl-ex/0408012 ) p-p 200 GeV All Charges Evolution of soft medium; dissipation of minijet structure to lower pt. Au-Au Peripheral Au-Au Central Rice Colloquium

30. Charge-independent correlations onh,fspace for Au-Au Rice Colloquium

31. All Charges h,f correlations for 130 GeV Au-Au: Central (correlation amplitude per final state hadron) Features: peak at small relative angles cos(fD) - soft momentum conservation cos(2fD) - elliptic anisotropy STAR preliminary Peripheral Rice Colloquium

32. STAR preliminary Subtract cos(fD) and cos(2fD): central • Notable Results: • Absence of away-side, hD • dependent structure from • soft string fragmentation • beginning in most peripheral bin. • Elongation along hD • Narrowing along fD peripheral p-p 200 GeV Rice Colloquium

33. Possible interpretation… Au Soft, away-side recoil, cos(fD) Interaction with longitudinally expanding color fluid drags pre-hadronic matter associated with semi-hard partonic scattering along pseudorapidity. (See: Armesto, Salgado, Wiedemann, hep-ph/0405301.) minijet Au But note that actual, central events have several 10s of these minijets poking out! Rice Colloquium

34. Charge dependent (like-unlike sign pairs) h,f correlations for 62 GeV Au-Au p-p 200 GeV STAR preliminary Au-Au Peripheral Gaussian to exponential _ opaque medium Rice Colloquium Evolution from 1D string fragmentation to at least 2D hadronization Au-Au Central

35. Possible interpretation… If Au+Au collisions were simply a superposition of independent pp collisions, then we would expect to see one-dimensional charge-ordering on hD. Au But the system evolves to… Au + - - - + - + + + - - - + - Au + A system with two-dimensional charge-ordering on h,f, implying that the 1D color strings have “melted” to form a 2(+)D colored medium. + - + Au Rice Colloquium

36. What about theoretical predictions or phenomenological models? Generally, there are no theoretical or phenomenological models which describe any of these correlation results. A model (Hijing) by Wang and Gyulassy [Phys. Rev. D44, 3501 (1991)] based on the high energy jet fragmentation code Pythia, produces some minijet structure like we observe but none of the dissipation effects, strong interaction with the medium, or 2D hadronization geometry we observe. Rice Colloquium

37. Have we made the QGP at RHIC? (a personal, non-STAR opinion) • The matter produced: • appears hot enough • has high enough energy density • is in approximate thermal equilibrium • is strongly self-interacting • dissipates energy like crazy • appears to hadronize in the bulk • But, • it does not last as long as expected which we do not understand; • we have not yet seen color screening effects which await • results from PHENIX (www.phenix.bnl.gov) on J/Y suppression; • we cannot yet rule out a dense medium of compact color • singlet objects. • I am hopeful but I believe it is premature to declare victory. Rice Colloquium

38. Conclusions and Acknowledgements However I cannot over emphasize the fact that: • RHIC is a non-perturbative QCD test facility, searching for the LQCD predicted Quark Gluon Plasma, but RHIC is also studying this hot, dense hadronic matter which may be similar to primordial Big Bang matter. • This field is data driven, theory is way behind. • Experimental results will eventually lead to better phenomenological models. • Ultimately, RHIC data may lead to effective field theories, based on QCD, which are calculable for hot, dense, non-perturbative matter. Given what we know now, what do RHIC events look like? Rice Colloquium

39. An updated view of possible deconfined system at fixed time in the lab of about 5 fm/c minijets Au Au Incoming nuclei Minijets based on correlations per final state particle in Au-Au assuming about 3-5 hadrons per minijet from p-p; colors indicate strong charge carriers, mainly gluons. Rice Colloquium

40. The STAR Collaboration Brazil: Universidade de Sao Paulo China: IHEP – Beijing IMP - Lanzou IPP – Wuhan USTC SINR – Shanghai Tsinghua University Great Britain: University of Birmingham France: IReS Strasbourg SUBATECH - Nantes Germany: MPI – Munich University of Frankfurt India: IOP - Bhubaneswar VECC - Calcutta Panjab University University of Rajasthan Jammu University IIT - Bombay VECC – Kolcata Poland: Warsaw University of Tech. Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino U.S. Laboratories: Argonne Berkeley Brookhaven U.S. Universities: UC Berkeley UC Davis UC Los Angeles Carnegie Mellon Creighton University Indiana University Kent State University Michigan State University City College of New York Ohio State University Penn. State University Purdue University Rice University Texas A&M UT Austin U. of Washington Wayne State University Yale University Rice Colloquium

41. The University of Texas High Energy Heavy Ion Nuclear Physics Group http://www.rhip.utexas.edu Faculty and Research Staff: G. W. Hoffmann, C. F. Moore, Lanny Ray, Jo Schambach Graduate Students:Michael Daugherity, Kohei Kajimoto, Cody McCain UT STAR Ph.D.s: Curtis Lansdell, Bum Choi, Aya Ishihara, Yiqun Wang Rice Colloquium

42. Extra Slides Rice Colloquium

43. Can we better understand color confinement from experiment? Effective quark-antiquark interaction potential r q g q as ~ 1 non-perturbative Color Confinement “Coulomb”-like interaction, as small, perturbative Asymptotic Freedom (2004 Nobel Prize in Physics – Wilczek, Gross, Politzer) Rice Colloquium

44. Atomic Nucleus protons Energy units: eV, electron Volt - atoms MeV =106 eV - nuclei GeV = 109 eV - nucleons mesons (carriers of the nuclear force) neutrons gluons (carriers of the strong force) quarks Rice Colloquium

45. Hadronic matter (anything containing quarks and gluons) at finite temperature and/or increased net baryon density can be produced in the laboratory via heavy ion collisions. Few 100 MeV per nucleon The collision compresses the matter to higher density and somewhat higher temperature. QGP? T nuclei Net rB Rice Colloquium

46. red Colors quark gluon gluon anti- quark anti- quark magenta yellow gluon gluon gluon gluon blue green quark quark cyan gluon gluon anti- quark Rice Colloquium

47. Chiral Symmetry Restoration? Lattice QCD also predicts that the Chiral symmetry invariance of the Basic QCD Lagrangian, which is Spontaneously broken in the hadonic States of QCD, is restored in QCD Systems above the critical temperature Tc. One consequence is that mass degeneracy in meson multiplets, such as the pseudoscalar pion and rho mesons, will be restored. r mass p- p+ Chrially symmetric, degenerate pseudoscalar states p0 T > Tc T = 0 Rice Colloquium

48. What is the color screening distance in hot matter Above Tc? This is the QCD analog to the Debeye Screening length in atomic physics. Rice Colloquium

49. Phase Transition from hadron gas to “free” quarks and gluons? Numerical predictions of QCD using a 4D lattice approximation indicate a phase transition from bound hadrons (mesons and baryons) to color deconfined quark-gluon equilibrated matter – Quark Gluon Plasma (QGP). From: K.Kanaya, Nucl.Phys. A715, 233c (2003) (QM2002) Rice Colloquium

50. Chemical decoupling temperature and potential inferred from particle ratios and resonances for a thermal model fit Central K+/K- • Chemical freeze-out • parameters • Tch = 179±4 MeV • mB = 51±4 MeV BRAHMS PHENIX PHOBOS STAR X+/X- p-/p+ p/p L/L K+/p+ K-/p- p/p+ K+/h- Ratio (chemical fit) K-/h- p/p- K0s/h- K*0/h- L/h- L/h- f/h- X-/h- Model: M.Kaneta, Thermal Fest (BNL, Jul 2001), N.Xu and M.Kaneta, nucl-ex/0104021 X+/h- Ratio (data) Rice Colloquium