Many Thanks to Organizers! Collective Expansion in Relativistic Heavy Ion Collisions -- Search for the partonic EOS at RHIC Nu Xu Lawrence Berkeley National Laboratory Many Thanks to Organizers! J. Castillo, X. Dong, H. Huang, H.G. Ritter, K. Schweda, P. Sorensen, Z. Xu

Outline Introduction Energy loss - QCD at work Bulk properties - ∂PQCD - hadron spectra - elliptic flow v2 Summary and Outlook http://www4.rcf.bnl.gov/brahms/WWW/brahms.html http://www.phobos.bnl.gov/ http://www.phenix.bnl.gov/ http://www.star.bnl.gov/

Phase diagram of strongly interacting matter CERN-SPS, RHIC, LHC: high temperature, low baryon density AGS, GSI (SIS200): moderate temperature, high baryon density

Study of Nuclear Collisions Like… P.C. Sereno et al. Science, Nov. 13, 1298(1998). (Spinosaurid) High pT - QCD probes Bulk Properties

High-energy Nuclear Collisions time S. Bass Hadronization and Freeze-out Initial conditions Initial condition in high-energy nuclear collisions Cold-QCD-matter, small-x, high-parton density - parton structures in nucleon / nucleus Parton matter - QGP - The hot-QCD Initial high Q2 interactions Hard scattering production - QCD prediction Interactions with medium - deconfinement/thermalization Initial parton density Experimental approaches: Energy loss - ‘jet-quenching’ Elliptic flow - v2, radial flow Heavy flavor production, combination of 1) and 2)

High-energy Nuclear Collisions jets J/y, D W f X L p, K, K* D, p d, HBT Initial Condition - initial scatterings - baryon transfer - ET production - parton dof System Evolves - parton interaction - parton/hadron expansion Bulk Freeze-out - hadron dof - interactions stop partonic scatterings? early thermalization? Q2 TC Tch Tfo elliptic flow v2 time radial flow bT

Physics Goals at RHIC Identify and study the properties of matter with partonic degrees of freedom. Penetrating probes Bulk probes - direct photons, leptons - spectra, v1, v2 … - “jets” and heavy flavor - partonic collectivity - fluctuations jets - observed high pT hadrons (at RHIC, pT(min) > 3 GeV/c) collectivity - collective motion of observed hadrons, not necessarily reached thermalization among them. Hydrodynamic Flow Collectivity Local Thermalization = 

Collision Geometry z x beam Non-central Collisions Au + Au sNN = 200 GeV x Non-central Collisions beam 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 Collisions at RHIC Central Event STAR (real-time Level 3)

Charged Hadron Density 19.6 GeV 130 GeV 200 GeV Charged hadron pseudo-rapidity  PHOBOS Collaboration 1) High number of Nch indicates initial high density; 2) Mid-y, Nch  Npart  nuclear collisions are not incoherent; 3) Saturation model works Initial high parton density at RHIC PRL 85, 3100 (00); 91, 052303 (03); 88, 22302(02); 91, 052303 (03)

Energy Loss in A+A Collisions leading particle suppressed back-to-back jets disappear p+p Au + Au Nuclear Modification Factor:

Hadron Suppression at RHIC Hadron suppression in more central Au+Au collisions!

Jets Observation at RHIC  p+p collisions at RHIC Jet like events observed Au+Au collisions at RHIC Jets?

Suppression and Correlation In central Au+Au collisions: hadrons are suppressed and back-to-back ‘jets’ are disappeared. Different from p+p and d+Au collisions. Energy density at RHIC:  > 5 GeV/fm3 ~ 300 Parton energy loss: Bjorken 1982 (“Jet quenching”) Gyulassy & Wang 1992 …

Energy Loss and Equilibrium Leading hadrons Medium In Au +Au collision at RHIC: Suppression at the intermediate pT region - energy loss The energy loss leads to progressive equilibrium in Au+Au collisions STAR: nucl-ex/0404010

Parton Energy Loss (1) Measured spectra show evidence of suppression up to pT ~ 6 GeV/c; (2) Jet-like behavior observed in correlations: - hard scatterings in AA collisions - disappearance of back-to-back correlations “Partonic” Energy loss process leads to progressive equilibrium in the medium Next step: fix the partonic Equation of State, bulk properties

tds = dU + pdV Pressure, Flow, … s– entropy; p – pressure; U – energy; V – volume t = kBT, 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!

Transverse Flow Observables As a function of particle mass: Directed flow (v1) – early Elliptic flow (v2) – early Radial flow – integrated over whole evolution Note on collectivity: 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.

Results from BRAHMS, PHENIX, and STAR experiments Hadron Spectra From RHIC mid-rapidity, p+p and Au+Au collisions at 200 GeV 5% 10-20% 20-40% 40-60% 60-80% (ss) centrality (usd) (ssd) (sss) Results from BRAHMS, PHENIX, and STAR experiments

Compare with Model Results Model results fit to , K, p spectra well, but over predicted <pT> for multi-strange hadrons - Do they freeze-out earlier? Phys. Rev. C69 034909 (04); Phys. Rev. Lett. 92, 112301(04); 92, 182301(04); P. Kolb et al., Phys. Rev. C67 044903(03)

Thermal fits: Tfo vs. < bT > 200GeV Au + Au collisions 1) p, K, and p change smoothly from peripheral to central collisions. 2) At the most central collisions, <T> reaches 0.6c. 3) Multi-strange particles ,  are found at higher Tfo (T~Tch) and lower <T>  Sensitive to early partonic stage!  How about v2? STAR: NPA715, 458c(03); PRL 92, 112301(04); 92, 182301(04). Chemical Freeze-out: inelastic interactions stop Kinetic Freeze-out: elastic interactions stop

Anisotropy Parameter v2 coordinate-space-anisotropy  momentum-space-anisotropy y py x px Now I will discuss the event anisotropy. The idea behind the measurement is the following: For non-central collisions, as shown here, the overlapped region looks like a ellipsoid. Sometimes this is called elliptical flow. The space anisotropy is defined as … After collisions, the space anisotropy is converted into momentum anisotropy. Experimentally we use the v2 parameter to characterize it. As I said, the conversion from space to momentum anisotropy is through collisions – may be partons at early time, and may be hadrons. So we think this variable should be sensitive to the initial conditions and the equation of state. We will hear more on this later during the conference. Initial/final conditions, EoS, degrees of freedom

v2 at Low pT P. Huovinen, private communications, 2004 - At low pT, hydrodynamic model fits well for minimum bias events indicating early thermalization in Au+Au collisions at RHIC! - More theory work needed to understand details: such as centrality dependence of v2; consistency between spectra and v2 …

v2 at All pT v2, the spectra of multi- strange hadrons, and the PHENIX: PRL91, 182301(03) STAR: PRL92, 052302(04) Models: R. Fries et al, PRC68, 044902(03), Hwa, nucl-th/0406072 v2, the spectra of multi- strange hadrons, and the scaling of the number of constituent quarks  Partonic collectivity has been attained at RHIC!  Deconfinement, model dependently, has been attained at RHIC! Next question is the thermalization of light flavors at RHIC: - v2 of charm hadrons - J/ distributions !!

Nuclear Modification Factor 1) Baryon vs. meson effect! 2) Hadronization via coalescence 3) Parton thermalization (model) - (K0, ): PRL92, 052303(04); NPA715, 466c(03); - R. Fries et al, PRC68, 044902(03)

Bulk Freeze-out Systematics The additional increase in bT is likely due to partonic pressure at RHIC. 1) v2 self-quenching, hydrodynamic model works at low pT 2) Multi-strange hadron freeze-out earlier, Tfo~ Tch 3) Multi-strang hadron show strong v2

Partonic Collectivity at RHIC 1) Copiously produced hadrons freeze-out: Tfo = 100 MeV, T = 0.6 (c) > T(SPS) 2)* Multi-strange hadrons freeze-out: Tfo = 160-170 MeV (~ Tch), T = 0.4 (c) 3)** Multi-strange v2: Multi-strange hadrons  and  flow! 4)*** Constituent Quark scaling: Seems to work for v2 and RAA (RCP) Partonic (u,d,s) collectivity at RHIC!

Summary & Outlook Charged multiplicity - high initial density (2) Parton energy loss - QCD at work (3) Collectivity - pressure gradient ∂PQCD  Deconfinement and Partonic collectivity Open issues - partonic (u,d,s) thermalization - heavy flavor v2 and spectra - di-lepton and thermal photon spectra

Equation of State With given degrees of freedom, the EOS - the system response to the changes of the thermal condition - is fixed by its p and T or . Energy density  GeV/fm3 Equation of state: EOS I : relativistic ideal gas: p = /3 EOS H: resonance gas: p ~ /6 EOS Q: Maxwell construction: Tcrit= 165 MeV, B1/4 = 0.23 GeV lat=1.15 GeV/fm3 P. Kolb et al., Phys. Rev. C62, 054909 (2000).

Phase diagram of strongly interacting matter LHC RHIC GSI CERN-SPS, RHIC, LHC: high temperature, low baryon density AGS, GSI (SIS200): moderate temperature, high baryon density

RHIC @ Brookhaven National Laboratory PHOBOS BRAHMS PHENIX h STAR

Experiments @ LHC B: The beauty of the Swiss rivers and mountains, especially the river, the Geneva lake! Oh, but the girl that cathe one’s breath.

ALICE: dedicated HI experiment CMS: pp experiment with HI program

International Accelerator Facility for Beams of Ions and Antiprotons at Darmstadt Key features: Intense, high-quality secondary beams of rare isotopes and antiprotons 2012: first beam $$$$: ~ 109 Euro SIS 100 Tm SIS 200 (250) Tm 23 (29) AGeV U 60 (75) GeV p Antiproton storage ring: Hadron Spectroscopy Ion and Laser Induced Plasmas: High Energy Density in Matter Structure of Nuclei far from Stability Polarized anti-proton proton collisions, nucleon structure Compressed Baryonic Matter