After the First Discoveries at RHIC

1. After the First Discoveries at RHIC Hideki Hamagaki Center for Nuclear Study (CNS) University of Tokyo

2. Primary Goal of Study with High-Energy Heavy-Ion Collisions • Understand hadronic matter under extreme conditions • Basic QCD property; confinement & chiral symmetry • Relevance to Early universe Our knowledge of QCD matter has been limited to the region at T ~ 0 and r/r0～1 Phys.Rev. D72 (2005) 034004 • High-energy heavy-ion collision provides extreme conditions • Accelerators • Cosmic rays After the First Discoveries at RHIC

3. Accelerators (GeV) 1000 100 10 1 CERN SPS 1986~ ECM=17GeV CERN LHC 2009~ ECM=5500GeV LBL Bevalac 1974~1993 ECM=2GeV BNL RHIC 2000~ ECM=200GeV BNL AGS 1986~ ECM=5GeV 1970 1980 1990 2000 2010 2020 After the First Discoveries at RHIC

4. Spectator -- beam fragment Participant Spectator -- target fragment Gross Features of High-Energy Heavy-Ion Collisions • nuclei = Lorentz contracted disks (d~2R/g) • participant-spectator picture works well • classical trajectory • participant region is geometrically determined • Specification of ‘Centrality’ is a Must to characterize the collisions After the First Discoveries at RHIC

5. Initial Processes in High-Energy Heavy-Ion Collisions • Collisions in high energy • between partons (quarks and gluons) in the colliding nucleons • Two competing processes in the initial stage • hard process • large-Q2 scattering between partons • pQCD calculation • becomes prominent in high energy • soft process • dominant in the low-energy collisions • multi-particle production with low-pT • non-perturbative After the First Discoveries at RHIC

6. Color Glass Condensate (CGC) becomes important at high gluon density; central subject at LHC) Characteristics of Hard Process • jet & single photon production • production yield; proportional to number of binary collisions between nucleons (<- Glauber model) • with known nuclear effects • Cronin effect • Nuclear shadowing effect • Nuclear modification factor After the First Discoveries at RHIC

7. RHIC and the Experiments • New York State, USA • Long Island • Brookhaven National Lab. RHIC • 2 independent rings • 3.83 km circumference • CMS energy • Au + Au: up to 200 A GeV • p + p: 500 GeV (polarized) • two programs: Heavy Ion and SPIN • BRAHMS, PHOBOS • Small collaborations (~100) • Large h but small f coverage • STAR , PHENIX • Big collaborations (~500) • Small h but large f coverage After the First Discoveries at RHIC

8. Japanese group in PHENIX • Two Japanese groups have been participating in the PHENIX experiment • Heavy ion: Japan-US collaboration in High Energy Physics • SPIN: RIKEN SPIN project After the First Discoveries at RHIC

9. RHIC Physics Runs First Au + Au collisionsat √sNN = 56 GeV June 12, 2000 • RUN-1: June ~ Sep.4, 2000 • Au+Au: (sNN)1/2 = 132 GeV • RUN-2: Aug. 2001 ~ Jan. 2002 • Au+Au, p+p: (sNN)1/2 = 200 GeV • RUN-3: Jan. 2003 ~ May 2004 • d+Au, p+p：(sNN)1/2 = 200 GeV • RUN-4: Jan. 2004 ~ May 2004 • Au+Au, p+p: (sNN)1/2 = 200, 63 GeV • RUN-5: Jan. 2005 ~May 2005 • Cu+Cu: (sNN)1/2 = 200, 63 GeV • p+p: (s)1/2 = 200 GeV • RUN-6: Feb. 2006 ~June 2006 • p+p: (s)1/2 = 200 GeV, 63 GeV • RUN-7: Mar. 2007~June 2007 • Au+Au, p+p: (sNN)1/2 = 200 GeV • RUN-8: Nov.29 2007~Mar. 2008 • d+Au, p+p: (sNN)1/2 = 200 GeV,... After the First Discoveries at RHIC

10. p p Energy loss in plasma The First Major Discovery at RHIC • Strong suppression of pion yield at high-pT in central Au+Au collisions • most high-pT pions are from jet fragmentation • Strong jet energy loss >>> Evidence of formation of high-density matter Hot dense medium After the First Discoveries at RHIC

11. Reaction plane The Second Major Discovery at RHIC • Large anisotropy in angular distribution in azimuth • hydro-dynamical behavior ~ consistent with hydro with no viscosity => perfect liquid Spatial anisotropy --->>> Momentum anisotropy After the First Discoveries at RHIC

12. Top Story 2005 According to American Institut of Physics, the top physics story in 2005 was the discovery of the perfect liquid After the First Discoveries at RHIC

13. Leading hadrons Medium Where has all the energy gone? 4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig • Collective excitation, analogous to shock wave? --- having been sought since BEVALAC era STAR, PRL 90 (2003) 082302 After the First Discoveries at RHIC

14. PHENIX preliminary Sideward Particle Emission • Clear change from back-to-back correlation to sideward correlation with increase of centrality After the First Discoveries at RHIC

15. Event by event deflection of jets Cone like structure in each event 13  13  13   0   12 0   12 12 Origin of Sideward Peak • Jet deflection • Cone-like structure 3-particle correlation data by STAR indicates cone-like particle emission After the First Discoveries at RHIC

16. * * * * * High pT (1) f f q q Df 13 12 12 Normal Jet (unmodified) Same Side Assoc. pTs (2,3) Deflected Jet _ Away Side (scattered jet axis) = Cone Jet D q* (medium excitation) D = 3-Particle Correlations at PHENIX Df* Dq* PHENIX Preliminary After the First Discoveries at RHIC

17. Trying to Reproduce Mach Cone in Hot QCD Matter Relevant dynamical quantities: • g2Q projectile color charge • mD screening mass • cs2 (= dp/de) sound speed • p = e/3 -> cs2 = 1/3 • Gs = 4h/3sT: attentuation length • Gs = (4/3)(1/4p)(1/T) = 1/3pT QM08: B. Mueller, M. Asakawa, R.B. Neufeld, C. Nonaka , J. Ruppert After the First Discoveries at RHIC

18. (4p) Perfect Fluids? • Conjectured lower quantum limit • Derived first in (P. Kovtun, D.T. Son, A.O. Starinets, Phys. Rev. Lett. 94:111601, 2005) • AdS/CFT (Anti de Sitter space / Conformal Field Theory) correspondence (J. Maldacena: Adv. Theor. Math. Phys. 2, 231, 1998) • “ordinary” fluids • water (at normal conditions) • h/s ~ 380 ћ/4p • helium (at l point) • h/s ~ 9 ћ/4p • Need observables that are sensitive to shear stress • Damping (flow, fluctuations, heavy quark motion) ~ h/s After the First Discoveries at RHIC

19. Heavy Flavor • Production of charm (and bottom) is a hard process • leading order at low x = ’’gluon fusion’’ • Ncoll scaling should hold, with known nuclear effects of nuclear shadowing and kT broadening • Interaction is considered to be weaker • gluon bremsstrahlung is suppressed at forward angles (dead cone effect); q < mQ/EQ • How to measure • “exclusive” is favorable, but difficult in heavy ion collisions • semi-leptonic decay  measure electrons/muons After the First Discoveries at RHIC

20. In Au+Au Collisions at sNN = 200 GeV • Binary scaling of total e± yield from heavy-flavor decays • Expected from heavy-quark production via hard scattering • High pT e± suppression increasing with centrality • Energy loss Phys.Rev.Lett.98:172301,2007 After the First Discoveries at RHIC

21. RAA and v2 of non-photonic Electrons • At pT > 4 GeV/c • b/(c+b) > 0.5 • RAA continues dropping • (New) v2 result stays high -> bottom seems to interact strongly as charm ... need further study to make it quantitative Large yield suppression and significant v2 After the First Discoveries at RHIC

22. Viscosity from Heavy Flavor Data • Strongly suppressed & significant v2 implies high density & small diffusion coefficient • DHQx2pT ~ 4-6 • Rapp & van Hees (PRC 71, 034907 (2005)) • D ~ 6 h/(e+P) • Moore & Teaney (PRC 71, 064904 (2005)) • e+P = Ts at mB = 0 --> h/s = (1.3-2.0)/4p = Very close to conjectured limit PHENIX : PRL98, 172301 (2007) After the First Discoveries at RHIC

23. R. Lacey et al.: PRL 98:092301, 2007 S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006 H.-J. Drescher et al.: arXiv:0704.3553 pTfluctuations STAR v2 PHOBOS v2 PHENIX & STAR conjectured quantum limit Compilation of Estimates • Estimates of h/s based on flow and fluctuation data • Indicate small value as well • Close to conjectured limit • Significantly below h/s of helium (4ph/s ~ 9) After the First Discoveries at RHIC

24. Summary • First major discoveries at RHIC • Parton energy loss -- high density matter • Hydrodynamical flow -- perfect liquid(?) • Many interesting results afterward • Mach cone-like structure -- shock wave? • Energy-loss and thermalization of heavy flavor • Anomalous baryon/meson ratio -- recombination picture • Thermal photons in p-p & HI collisions • Low-mass lepton-pairs in HI collisions • Charm to bottom ratio • J/y systematics After the First Discoveries at RHIC

25. Outlook • Good d + Au run in RUN8 -- we will soon have high-statistics results for cold nuclear matter effect • Au + Au run for low-mass e+e- pairs with HBD (PHENIX) • Charm and bottom identification with VTX silicon tracker • Energy scan (to lower energy) for critical point search • SPIN PROGRAM -- DG and W After the First Discoveries at RHIC

26. Backups

27. Initial energy density CMS energy Why do we need Higher Energy? With collisions at higher energy • High initial energy density • Large margin at RHIC and LHC • Longer duration time of QGP • Description of space-time evolution becomes simpler • Higher particle density  shorter mean free path • chemical & thermal equilibrium • Hydro-dynamical description may become possible  comparison with models becomes reliable • Availability of hard probes • jet & hard photon • heavy flavor After the First Discoveries at RHIC

28. Nuclear Effects • Cronin effect spA(pT) = spp(pT) Aa(pT) a (pT) > 1 in the high pT • small-angle multiple scattering of partons in the initial stage • kT broadening • Nuclear shadowing • modification of parton structure function in case of nuclei • large depletion in small x After the First Discoveries at RHIC

29. t dN dy dET dy mT pr02A2/3t0 1 pr02A2/3t0 t0 e = = z Soft Process • non-perturbative  phenomenological description • string model • confinement potential kx with string tension k ~ 1 GeV/fm • Bjorken’s picture • Boost invariance  space-time evolution is determined by proper time • string trajectory = hyperbola • string fragmentation at a certain proper time  particle production After the First Discoveries at RHIC