1. Results from STAR Markus D. Oldenburg MPI Colloquium October 22, 2002 Munich, Germany For the STAR Collaboration

2. Markus D. OldenburgMPI Colloquium October 22, 20022 Outline Physics introduction STAR @ RHIC Analyses & Results –Particle spectra –Anisotropic Flow –Jets at RHIC –Ultra-Peripheral Collisions Summary Outlook

3. Markus D. OldenburgMPI Colloquium October 22, 20023 Phase Diagram for Nuclear Matter K. Rajagopol Study of nuclear matter under extreme conditions (high temperature and/or high pressure)

4. Markus D. OldenburgMPI Colloquium October 22, 20024 The R elativistic H eavy I on C ollider Two independent accelerator rings 3.83 km in circumference Accelerates everything from p to Au Running conditions: Au-Au 2001 55-56 bunches per ring (tested up to 110) 7.5 10 8 Au/bunch @ storage energy Storage energy: 100 GeV/A Peak luminosity: 5 10 26 cm -2 s -1 Running conditions: p p 2001 55 bunches per ring 0.8 10 11 p /bunch Energy/beam: 100 GeV Peak luminosity: 1.5 10 30 cm -2 s -1 Beam polarization ~ 25% ( AGS) Long Island STAR

5. The STAR experiment at RHIC STAR uses the worlds largest Time Projection Chamber

6. One of the first Au on Au Events at CM Energy of 200 GeV ASTAR

7. Markus D. OldenburgMPI Colloquium October 22, 20027 Spectra Measured vs. Centrality (impact parameter) Peripheral Collision x y z x y z (near) Central Collision X Y X Y central collision high multiplicity in CTB & low multiplicity in ZDcal

8. Markus D. OldenburgMPI Colloquium October 22, 20028 STAR Preliminary Bose-Einstein fits STAR Preliminary m t exponential fits K-K- Identified Particle Spectra at 200 GeV +, -, K +, K - spectra versus centrality (130 GeV/N data in nucl-ex/0206008 ) +

9. Markus D. OldenburgMPI Colloquium October 22, 20029 130 GeV data p Preliminary 200 GeV data gaussian fits Anti-Proton Spectra at 200/130 GeV/N Au + Au p + X p p and p-bar spectra versus centrality (130 GeV data in PRL 87 (2002))

10. Markus D. OldenburgMPI Colloquium October 22, 200210 Anti-Particle to Particle Ratios Excellent agreement between experiments at y = 0, s = 130 STAR results on the p/p ratio p-bar/p = 0.11 ± 0.01 @ 20 GeV p-bar/p = 0.71 ± 0.05 @ 130 GeV Previously reported as 0.60 ± 0.06 p-bar/p = 0.80 ± 0.05 @ 200 GeV p-bar/p ratios K+/K- ratios

11. Markus D. OldenburgMPI Colloquium October 22, 200211 Anti-Baryon/Baryon Ratios vs. s NN p+p p/p ISR In the early universe –p-bar/p ratio = 0.999999 At RHIC, pair-production increases with s Mid-rapidity region is not yet baryon-free! Pair production is larger than baryon transport 80% of protons from pair production 20% from initial baryon number transported over 5 units of rapidity _ _ _ _ _ _ STAR preliminary _ In HI collisions at RHIC, more baryons are pair produced than are brought in by the initial state

12. Markus D. OldenburgMPI Colloquium October 22, 200212 Particle Ratios at RHIC Good agreement between the 4 experiments STAR, PHOBOS, PHENIX, BRAHMS p/p= 0.71 ± 0.02(stat) ± 0.05 (sys) = 0.60 ± 0.04(stat) ± 0.06 (sys) = 0.64 ± 0.01(stat) ± 0.07 (sys) = 0.64 ± 0.04(stat) ± 0.06 (sys) / = 0.73 ± 0.03(stat) + / - = 0.83 ± 0.03(stat.)±0.05(sys.) K - / - = 0.15 ± 0.01 (stat) ± 0.02 (sys) K + / + = 0.16 ± 0.01 (stat) ± 0.02 (sys) / = 1.00 ± 0.01(stat) ± 0.02 (sys) = 0.95 ± 0.03(stat) ± 0.05 (sys) /h - = 0.021 ± 0.001 (stat) ± 0.005 (sys) /h - = 0.060 ± 0.001 (stat) ± 0.006 (sys) / h - = 0.043 ± 0.001 (stat) ± 0.004(sys) K 0 s / h - = 0.124 ± 0.001 (stat) ( K*+K* ) / 2 h - = 0.032 ± 0.003(stat.) ± 0.008 (sys.) 2 /( K*+K* ) = 0.64 ± 0.06 (stat) ± 0.16 (sys) K-/K + = 0.89 ± 0.008(stat) ± 0.05 (sys) = 0.91 ± 0.07(stat) ± 0.06 (sys) = 0.89 ± 0.07(stat) ± 0.05 (sys) K+/K-= 1.08 ± 0.03(stat) ± 0.22(sys) min. bias K -/ - = 0.15 ± 0.01 (stat) ± 0.02 (sys) K+/ + = 0.16 ± 0.01 (stat) ± 0.02 (sys) K*/K* = 0.92 ± 0.14(stat.)

13. Markus D. OldenburgMPI Colloquium October 22, 200213 Chemical Freeze-out (thermal model) (P. Braun-Munzinger et al.: hep-ph/105229) Thermal model fits Compare to QCD on Lattice: T c = 154 ± 8 MeV (N f =3) T c = 173 ± 8 MeV (N f =2) (ref. Karsch QM01) Assume:- Thermally and chemically equilibrated fireball at hadro-chemical freeze-out Recipe:- Grand canonical ensemble to describe partition function density of particles of species i - Fixed by constraints: Volume V, strangeness chemical potential S, and isospin input: measured particle ratios output: temperature T and baryo-chemical potential B

14. Markus D. OldenburgMPI Colloquium October 22, 200214 Putting STAR on the Phase Diagram Final-state analysis suggests RHIC reaches the phase boundary Hadron yields cannot probe higher temperatures /N ~ 1 GeV (J. Cleymans and K. Redlich, Phys. Rev. Lett., 81, 5284, 1998) Lattice results Neutron STAR We know where we are on the phase diagram but now we want to know what other features are on the diagram

15. Markus D. OldenburgMPI Colloquium October 22, 200215 Chemical and Kinetic Freeze-out Chemical freeze-out (first) –End of inelastic interactions –Number of each particle species is frozen Useful data –Particle yields Kinetic freeze-out (later) –End of elastic interactions –Particle momenta are frozen Useful data –Transverse momentum distributions –and Effective temperatures space time inelastic interactions Chemical freeze-out elastic interactions Kinetic freeze-out blue beamyellow beam

16. Markus D. OldenburgMPI Colloquium October 22, 200216 Transverse Flow The transverse radial expansion of the source (flow) adds kinetic energy to the particle distribution. So the classical expression for E Tot suggests a linear relationship - K -K - p Au+Au at 200 GeV STAR Preliminary Slopes decrease with mass. and the effective temperature increase with mass. T 575 MeV T 310 MeV T 215 MeV

17. Markus D. OldenburgMPI Colloquium October 22, 200217 Kinetic Freezeout from Transv. Flow (RHIC) = 0.55 ± 0.1 c T KFO (RHIC) = 100 ± 10 MeV Explosive Transverse Expansion at RHIC High Pressure T th [GeV] [c] STAR PHENIX

18. Markus D. OldenburgMPI Colloquium October 22, 200218 Anisotropic Flow Look at peripheral collisions Overlap region is not symmetric in coordinate space Almond shaped overlap region –Easier for particles to emerge in the direction of x-z plane –Larger area shines to the side x y z pxpx pypy y x Spatial anisotropy Momemtum anisotropy –Interactions among constituents generate a pressure which transforms the initial spatial anisotropy into the observed momentum anisotropy Perform a Fourier decomposition of the momentum space particle distributions in the x-y plane –v n is the n-th harmonic Fourier coefficient of the distribution of particles with repsect to the reaction plane v 1 : directed flow v 2 : elliptic flow

19. Markus D. OldenburgMPI Colloquium October 22, 200219 PRL 86, (2001) 402 more central v 2 vs. Centrality (130 GeV) v 2 is large –6% in peripheral collisions –Smaller for central collisions Hydro calculations are in reasonable agreement with the data –In contrast to lower collision energies where hydro over- predicts anisotropic flow Anisotropic flow is developed by rescattering –Data suggests early time history –Quenched at later times Anisotropic transverse flow is large at RHIC Hydro predictions

20. Markus D. OldenburgMPI Colloquium October 22, 200220 v 2 vs. p t and Particle Mass (130 GeV) The mass dependence is reproduced by hydrodynamic models –Hydro assumes local thermal equilibrium –At early times –Followed by hydrodynamic expansion PRL 86, 402 (2001) & nucl-ex/0107003 Hydro does a very good job D. Teaney et al., QM2001 Proc. P. Huovinen et al., nucl-th/0104020

21. Markus D. OldenburgMPI Colloquium October 22, 200221 v 2 for, K, K 0, p and Preliminary

22. Markus D. OldenburgMPI Colloquium October 22, 200222 v 2 for High p t Particles (130 GeV) pQCD inelastic energy loss + parameterized hydro component (M. Gyulassy, I. Vitev and X.N. Wang, PRL 86 (2001) 2537) –value of v 2 at high p t sensitive to the initial gluon density –saturation and decrease of v 2 as a function of p t at higher p t data starts to deviate from hydrodynamics at p t > 2 GeV/c Adler et al., nucl-ex/0206006 Data is in qualitative agreement with jet-quenching scenario

23. Markus D. OldenburgMPI Colloquium October 22, 200223 Centrality dependence of v 2 (p t ) v 2 is saturated at high p t and it does not come back down as rapidly as expected What does v 2 do at very high p t ? 200 GeV (preliminary) 130 GeV peripheral central

24. Markus D. OldenburgMPI Colloquium October 22, 200224 v 2 up to 12 GeV/c v 2 seems to remain saturated

25. Markus D. OldenburgMPI Colloquium October 22, 200225 Hard Probes in Heavy-Ion Collisions New opportunity using Heavy Ions at RHIC Hard Parton Scattering – s NN = 200 GeV at RHIC –17 GeV at CERN SPS Jets and mini-jets –30-50 % of particle production –High p t leading particles –Azimuthal correlations Extend into perturbative regime –Calculations reliable (?) Scattered partons propagate through matter & radiate energy (dE/dx ~ x) in colored medium –Interaction of parton with partonic matter –Suppression of high p t particles: jet quenching –Suppression of angular correlations hadrons q q leading particle leading particle schematic view of jet production QGP Vacuum

26. Markus D. OldenburgMPI Colloquium October 22, 200226 Preliminary Inclusive p t Distribution of Hadrons Scale Au-Au data by the number of binary collisions Compare to UA1 pp reference data measured at 200 GeV

27. Markus D. OldenburgMPI Colloquium October 22, 200227 Comparison: Au+Au / p+p at 130 GeV

28. Markus D. OldenburgMPI Colloquium October 22, 200228 Evidence for hadron suppression at high p t Partonic interaction with matter? dE/dx? Flow vs. Inclusive Hadron Spectra Different views of same physics?

29. Markus D. OldenburgMPI Colloquium October 22, 200229 Jets in Hadronic Collisions p+p jet+jet (STAR@RHIC) Au+Au ??? (STAR@RHIC)

30. Markus D. OldenburgMPI Colloquium October 22, 200230 Identifying jets on a statistical basis in Au-Au Given a trigger particle with p t > p t (trigger), associate particles with p t > p t (associated) Au+Au –flow p+p and Au+Au collisions: –dijets –momentum conservation –jets –resonances STAR Preliminary Au+Au @ 200 GeV/c, 0-5% most central 4 < p t (trig) < 6 GeV/c, 2 < p t (assoc.) < p t (trig) Small All

31. Markus D. OldenburgMPI Colloquium October 22, 200231 Peripheral Au+Au data vs. pp+flow Ansatz: A high p t triggered Au+Au event is a superposition of a high p t triggered p+p event plus anisotropic transverse flow v 2 from reaction plane analysis A is fit in non- jet region (0.75 < | | < 2.24)

32. Markus D. OldenburgMPI Colloquium October 22, 200232 Central Au+Au data vs. pp+flow

33. Markus D. OldenburgMPI Colloquium October 22, 200233 Jets at RHIC The backward going jet is missing in central Au-Au collisions when compared to p-p data + flow Other features of the data –High p t charged hadrons dominated by jet fragments Relative charge Azimuthal correlation width Evolution of jet cone azimuthal correlation strength with centrality ? Surface emission? Suppression of back-to-back correlations in central Au+Au collisions Other explanations for the disappearance of back-to-back correlations in central Au-Au? –Investigate nuclear k T effects Experiment: p+Au or d+Au Theory: Add realistic nuclear k T to the models

34. Markus D. OldenburgMPI Colloquium October 22, 200234 Ultra-Peripheral Collisions b > 2R A; –no hadronic interactions – ~ 20-60 fermi at RHIC Ions are sources of fields –Fields couple coherently to ions p t < h/R A, ~30 MeV/c for heavy ions p || < h/R A ~ 3 GeV/c at RHIC Photonuclear (Photon-Pomeron) Interactions A,,, J/,… A –Vector Meson Dominance A qqA (elastic scattering) VA – ~ 350 mb at 130 GeV/nucleon 5% of AuAu (had.) Electromagnetic particle production leptons, mesons –Strong Field (nonperturbative?) QED Au Coupling ~ nuclear form factor, P, or meson -

35. Markus D. OldenburgMPI Colloquium October 22, 200235 Exclusive 0 p t <0.15 GeV 0 p t Signal region: p t <0.15 GeV 200GeV Preliminary Trigger on low multiplicity events veto on cosmic rays 2 track vertex w/ charge 0 –reject (coplanar) cosmic rays peak for p t < 150 MeV/c and give background shape –scaled up by 2.1 - )

36. Markus D. OldenburgMPI Colloquium October 22, 200236 Minimum Bias Data 800,000 triggers neutron signals in ZDCs Nuclear excitation tags small b interactions –excitation and 0 are independent Analysis same as in peripheral Preliminary 200 GeV Signal region: p t <0.15 GeV d /dM mb/GeV 200 GeV Preliminary 0 p t - ) Normalized to 7.2 b hadronic cross section Systematic uncertainties: luminosity, overlapping events, vertex & tracking simulations, single neutron selection, etc.

37. Markus D. OldenburgMPI Colloquium October 22, 200237 Summary of Analyses shown: Particle yields / ratios / spectra Anisotropic Flow Jets at RHIC Ultra-Peripheral Collisions not shown: Interferometry (HBT) Fluctuations Gluon density saturation Spin physics program

38. Markus D. OldenburgMPI Colloquium October 22, 200238 Conclusions About Nucl. Matter @ RHIC Its hot –Chemical freeze out at 175 MeV –Thermal freeze out at 100 MeV –The universal freeze out temperatures are surprisingly flat as a function of s Its fast –Transverse expansion with an average velocity greater than 0.55 c –Large amounts of anisotropic flow (v 2 ) suggest hydrodynamic expansion and high pressure at early times in the collision history Its opaque –Saturation of v 2 at high p t –Suppression of high p t particle yields relative to p-p –Suppression of the away side jet And its not inconsistent with thermal equilibrium –Excellent fits to particle ratio data with equilibrium thermal models –Excellent fits to flow data with hydrodynamic models that assume equilibrated systems Looks like we are observing the QGP!

39. Markus D. OldenburgMPI Colloquium October 22, 200239 RHIC Performance Goals for 2003 29 weeks of d-Au (including cooldown) 8 weeks of p p (We wont have Si-Si nor Au-Au next year.) More interesting physics to come...

40. Markus D. OldenburgMPI Colloquium October 22, 200240 STAR Institutions U.S. Labs: Argonne, Brookhaven, and Lawrence Berkeley National Labs U.S. Universities: UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, Michigan State, CCNY, Ohio State, Penn State, Purdue, Rice, UT Austin, Texas A&M, Valparaiso, Washington, Wayne State, Yale Brazil: Universidade de Sao Paolo China: IPP - Wuhan, IMP - Lanzhou USTC, SINR, Tsinghua University, IHEP - Beijing England: University of Birmingham France: IReS - Strasbourg SUBATECH - Nantes Germany: Max Planck Institute - Munich University of Frankfurt India: Institute of Physics - Bhubaneswar IIT - Mumbai, VECC - Calcutta Jammu University, Panjab University University of Rajasthan The Netherlands: NIKHEF Poland: Warsaw University of Technology Russia: MEPHI - Moscow, IHEP - Protvino LPP & LHE JINR - Dubna

41. Markus D. OldenburgMPI Colloquium October 22, 200241

42. Markus D. OldenburgMPI Colloquium October 22, 200242 Binary scaling Participant scaling Scaling pp to AA … including the Cronin Effect At SPS energies: –High p t spectra evolves systematically from pp pA AA –Hard scattering processes scale with the number of binary collisions –Soft scattering processes scale with the number of participants –The ratio exhibits Cronin effect behavior at the SPS –No need to invoke QCD energy loss

43. Markus D. OldenburgMPI Colloquium October 22, 200243 R AA Comparison to p t = 6 GeV/c 130 GeV nucl-ex/0206011 Preliminary s NN = 200 GeV Similar Suppression at high p t in 130 and 200 GeV data Preliminary s NN = 200 GeV