2. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 1 The `Big Bang’ in the Laboratory -- The Physics of High-energy Nuclear Collisions The `Big Bang’ in the Laboratory -- The Physics of High-energy Nuclear Collisions Nu Xu Lawrence Berkeley National Laboratory (1) Introduction (2) Some recent results at RHIC (3) Summary J. Castillo, X. Dong, H. Huang, H.G. Ritter, K. Schweda, P. Sorensen, A. Tai, Z. Xu

3. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 2 strongly interaction gluons and quarks confined inside hadrons States of Matter Q G P Compressing - new form of matter with partonic d.o.f. - nucleon boundary irrelevant Ordinary matter atom nucleus Heating heavy ion collisions

4. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 3 1) Two (at least) thermodynamic phase transitions in nuclear matter: –“Liquid Gas” –Hadron gas  QGP / chiral symmetry restoration 2) Problems / Opportunities: –Finite size effects –Is there equilibrium? –Measurement of state variables ( , T, S, p, …) –Migration of nuclear system through phase diagram Nuclear Matter Phase Diagram NUCLEAR SCIENCE, A Teacher’s Guide to the Nuclear Science Wall Chart, Figure 9-2

5. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 4 Create QGP in the laboratory H 2 O Conventional plasma: Quark-Gluon plasma T ~ 300 KT ~ 2 million KT ~ 2 trillion K

6. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 5 Quark Gluon Plasma 1)Theory SM: LQCD predictions 2)Cosmology: Parton - Hadron transition 3)Astrophysics:Core of dense star Can we make it with a controlled manner to establish the properties of QCD at high energy and particle densities? Source: Michael Turner, National Geographic (1996)

7. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 6 QCD confinement potential T < T conf T > T conf constant potential linear potential r V(r,T) The potential between quarks is a function of distance. It also depends on the temperature. 1) At low temperature, the potential increases linearly with the distance between quarks  quarks are confined; 2) At high temperature, the confinement potential is ‘melted’  quarks are ‘free’ (larger than that from p+p collisions); 3) LGT calculation predicted a fast- cross over temperature T C = 160 - 170 MeV.

8. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 7 QCD on Lattice Lattice calculations predict T C ~ 170 MeV 1) Large increase in  a fast cross cover ! 2) Does not reach ideal, non-interaction S. Boltzmann limit !  many body interactions  Collective modes  Quasi-particles are necessary 3) T C ~ 170 MeV robust! Z. Fodor et al, JHEP 0203:014(02) Z. Fodor et al, hep-lat/0204001 C.R. Allton et al, hep-lat/0204010 F. Karsch, Nucl. Phys. A698, 199c(02).

9. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 8 High-energy nuclear collisions S. Bass Experimental approaches: Energy loss - ‘jet-quenching’ Elliptic flow - v 2, radial flow Charm - productions plus the combination (1) and (2) Hadronization and Freeze-out Initial conditions (1)Initial condition in high-energy nuclear collisions (2)Cold-QCD-matter, small-x, high-parton density - parton structures in nucleon / nucleus Parton matter - QGP - The hot-QCD Initial high Q 2 interactions (1)Hard scattering production - QCD prediction (2)Interactions with medium - deconfinement/thermalization (3)Initial parton density

10. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 9 Identify and study the properties of the matter with partonic degrees of freedom. Probing Characterizing - direct photons, leptons - spectra, v 1, v 2 … - jets and heavy flavor - partonic collectivity - fluctuations Physics Goals at RHIC

11. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 10 Blue Ring (clockwise) Yellow Ring ARC Four Experiments: BRAHMSPHENIX PHOBOSSTAR ~ 1200 physicists: high energy/nuclear Started in the Summer of 2000 ~ 200 publications (summer ‘04)

12. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 11 People at RHIC More than 1000 people from around the world Brazil, Canada, China, Croatia, Denmark, France, Germany, India, Israel, Japan, Korea, Norway, Poland, Russia, Sweden, UK, USA

13. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 12 STAR PHOBOS PHENIX BRAHMS

14. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 13 Variable definitions 1)Transverse momentum: p T = (p x +p y ) 1/2 2)Transverse mass: m T =(p T 2 +mass 2 ) 1/2 3)Rapidity: y = 1/2 log[(E+p z )/(E-p z )] 4)Pseudo-rapidity:  = -log tan(  /2) = y| mass=0 cos  = p z /p 5) Impact parameter b: distance between the centers of the two nuclei 6) Geometrical cross section:  =  b 2,  total =  (2R) 2

15. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 14 Peripheral Event STAR Au + Au Collisions at 130 GeV (real-time Level 3)

16. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 15 STAR Mid-Central Event Au + Au Collisions at 130 GeV (real-time Level 3)

17. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 16 Au + Au Collisions at RHIC STAR Central Event (real-time Level 3)

18. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 17 Collision Geometry, Flow x z Non-central Collisions Number of participants: number of incoming nucleons in the overlap region Number of binary collisions: number of inelastic nucleon-nucleon collisions Charged particle multiplicity  collision centrality Reaction plane: x-z plane Au + Au  s NN = 200 GeV

19. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 18 Global: Charge hadron density 19.6 GeV 130 GeV 200 GeV Charged hadron pseudo-rapidity  1) High number of N ch indicates initial high density; 2) Mid-y, N ch  N part  nuclear collisions are not incoherent; Important for high density and thermalization. PRL 85, 3100 (00); 91, 052303 (03); 88, 22302 (02), 91, 052303 (03) PHOBOS Collaboration

20. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 19 Energy loss in A+A collisions Nuclear Modification Factor: back-to-back jets disappear leading particle suppressed p+p Au + Au

21. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 20 Jet Quenching Hadron suppression at intermediate p T, caused by energy loss of energetic objects, - ‘Jet quenching’!

22. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 21 d+Au Au+Au d+Au comparison Observed suppression in Au+Au collisions is due to final state interactions, most likely via parton-parton interactions! QCD predictions: Bjorken 1982 Gyulassy and Wang 1992

23. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 22 Jets at RHIC p+p collisions at RHIC Jet like events observed Au+Au collisions at RHIC Jets?

24. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 23 Suppression and correlation Hadron suppression and disappearance of back-to-back ‘jet’ are correlated!

25. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 24 Energy loss and equilibrium Leading hadrons Medium In Au +Au collision at RHIC: - Suppression at the intermediate p T region - energy loss cause by the final state interactions - The energy loss leads to progressive equilibrium in Au+Au collisions STAR: nucl-ex/0404010

26. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 25 Lesson learned I. - QCD at work (1) High rapidity density for produced hadrons. Necessary for energy loss and equilibrium; (2) Spectra at intermediate p T show evidence of suppression up to p T ~ 6 GeV/c; (3) Jet-like behavior observed in correlations: - hard scatterings in AA collisions - disappearance of back-to-back correlations êEnergy loss process leads to progressive equilibrium in the medium Next step: fix the partonic Equation of State

27. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 26 Pressure, Flow, …  d  = dU + pdV  – entropy; p – pressure; U – energy; V – volume  = k B T, thermal energy per dof In high-energy nuclear collisions, interaction among constituents and density distribution will lead to: pressure gradient  collective flow  number of degrees of freedom (dof)  Equation of State (EOS)  No thermalization is needed – pressure gradient only depends on the density gradient and interactions.  Space-time-momentum correlations!

28. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 27 Transverse flow observables As a function of particle mass: Directed flow (v 1 ) – early Elliptic flow (v 2 ) – early Radial flow – integrated over whole evolution Note on collectivity: 1) Effect of collectivity is accumulative – final effect is the sum of all processes. 2) Thermalization is not needed to develop collectivity - pressure gradient depends on density gradient and interactions.

29. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 28 Hadron spectra from RHIC p+p and Au+Au collisions at 200 GeV sss ss uud ud

30. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 29 Hadron production & chemical freeze-out 1) Chemical fits well for all hadron ratios at RHIC: T ch = 160 ± 10 MeV  B = 25 ± 5 MeV  S = 1 ± 0.05 Necessary for QGP! 2) The temperature parameter T ch is close to the critical temperature T C predicted by LGT calculations  chemical equilibrium at the phase boundary (?) 3) Since 1999, much work in this direction Review: P. Braun-Munzinger et al. nucl-th/0304013

31. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 30 Phase dirgram: data and predictions 1) Chemical fit well to all hadron ratios at RHIC: T ch = 160 ± 10 MeV  B = 25 ± 5 MeV  S = 1 ± 0.05 Necessary for QGP! 2) The temperature parameter T ch is close to the critical temperature T C predicted by LGT calculations  chemical equilibrium at the phase boundary 3) Since 1999, many work in this direction Review: P. Braun-Munzinger et al. nucl-th/0304013

32. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 31 Thermal model fit Source is assumed to be: –Local thermal equilibrated –Boosted radically random boosted E.Schnedermann, J.Sollfrank, and U.Heinz, Phys. Rev. C48, 2462(1993)

33. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 32 Compare with hydrodynamic model - Hydrodynamic model fit to pion, Kaon, and proton spectra; - over predicted the values of for multi-strange hadrons

34. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 33 Blast wave fits: T fo vs. 1) , K, and p change smoothly from peripheral smoothly from peripheral to central collisions. to central collisions. 2) For the most central collisions, reaches collisions, reaches 0.6c. 0.6c. 3) Multi-strange particles ,  are found at higher T  are found at higher T and lower and lower  Sensitive to early partonic stage!  Sensitive to early partonic stage!  How about v 2 ?  How about v 2 ? STAR: NPA715, 458c(03); PRL 92, 112301(04); 92, 182301(04). 200GeV Au + Au collisions

35. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 34 y x pypy pxpx coordinate-space-anisotropy  momentum-space-anisotropy Anisotropy parameter v 2 Initial/final conditions, EoS, degrees of freedom

36. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 35 v 2 at low p T - At low p T, hydrodynamic model fits well the v 2 from minimum bias events indicating of early thermalization in Au+Au collisions at RHIC! - More theory work needed to understand the details, such as the centrality dependence of v 2, mass dependence… P. Huovinen, private communications, 2004

37. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 36 Partonic collectivity at RHIC From v 2, hadron spectra, and the scaling properties:  Partonic collectivity has been attained at RHIC!  Deconfinement, model dependently, has been attained at RHIC! Next question is the thermalization: - v 2 of charm hadrons - J/  yield, distributions PHENIX: PRL91, 182301(03) STAR: PRL92, 052302(04)

38. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 37 Nuclear modification factor 1) Baryon vs. meson effect! 2) Hadronization via coalescence 3) Deconfinement at RHIC - (K 0,  ): PRL92, 052303(04); NPA715, 466c(03); - R. Fries et al, PRC68, 044902(03); - Hwa and Yang, J. Phys.G30, S1117(04); PRC70, 024905(04)

39. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 38 Freeze-out systematics The additional increase in  T is likely due to partonic pressure at RHIC. 1) Smaller baryon chemical potential  B = 25 MeV with T ch = 160 MeV 2) Stronger transverse flow,  T = 0.6(c)

40. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 39 Lesson learned II -  P QCD at RHIC 1) Freeze-out of the copiously produced hadrons: T fo = 100 MeV,  T = 0.6 (c) >  T (SPS) 2)* Freeze-out of the multi-strange hadrons: T fo = 170 MeV (~ T ch ),  T = 0.4 (c) 3)** v 2 of the multi-strange hadrons: Multi-strange hadrons  and  flow! 4)*** Constituent Quark scaling: Seems to work for v 2 and R AA (R CP )  Partonic (u,d,s) collectivity at RHIC

41. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 40 Summary (1) Flavor equilibration - necessary for QGP (2) Jet energy loss - QCD at work (3) Collectivity - pressure gradient ∂P QCD Deconfinement and Partonic collectivity First time ever, re-produced partonic matter in the laboratory since big bang.

42. Department of Physics, Oregon University, 7 October, 2004 Nu Xu //Nxu/tex3/TALK/2004/10OU 41 P hase diagram of strongly interacting matter CERN-SPS, RHIC, LHC: high temperature, low baryon density AGS, GSI (SIS200): moderate temperature, high baryon density GSI200 RHIC LHC Discover QGP and more!