1. DPG spring meeting, Tübingen, March 2003 1 Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration Recent results from STAR at RHIC  Ultra-relativistic Heavy Ion Collisions, A+A  Spin structure of the nucleon, p+p  Ultra-peripheral Heavy Ion Collisions 

2. DPG spring meeting, Tübingen, March 2003 2 Outline  Introduction  The STAR detector at RHIC  High-p t phenomena – probe the medium  Collective dynamics – bulk properties  Conclusions / Outlook

3. DPG spring meeting, Tübingen, March 2003 3 QCD on the Lattice Lattice calculations predict T C ~ (170  15) MeV 1) Large increase in  !  Large increase in Ndof: Hadrons vs. partons 2) T C ~ 170 MeV robust! Z. Fodor et al, JHEP 0203:014(02) C.R. Allton et al, hep-lat/0204010 F. Karsch, Nucl. Phys. A698, 199c(02).

4. DPG spring meeting, Tübingen, March 2003 4 Heavy Ion Collisions 1) Initial condition:2) System evolves:3) Bulk freeze-out: - baryon transfer- parton/hadron expansion- hadronic dof - E T production- interaction cease - Partonic dof T th, Time  Plot: Steffen A. Bass, Duke University

5. DPG spring meeting, Tübingen, March 2003 5 The STAR Collaboration  400 Collaborators, 49 Institutions, 9 Countries

6. DPG spring meeting, Tübingen, March 2003 6 The STAR Detector

7. DPG spring meeting, Tübingen, March 2003 7 Au + Au Collisions at RHIC STAR Central Event (real-time Level 3)

8. DPG spring meeting, Tübingen, March 2003 8 Centrality Definition Au + Au @ 130 GeV |  | < 0.75 K.H. Ackermann et al. Phys. Rev. Lett. 86 (2001) 402 More central collisions No direct measure of impact parameter Use track multiplicity to define collision centrality

9. DPG spring meeting, Tübingen, March 2003 9 Particle Identification Reconstruct multi-strange resonances in 2  acceptance of STAR!

10. DPG spring meeting, Tübingen, March 2003 10 Partons lose energy due to interactions with the medium J.D. Bjorken, FERMILAB-Pub-82/59-THY (1982). Energy loss is a measure of the gluon density X.N. Wang and M. Gyulassy, Phys. Rev. Lett. 68, 1480 (1992). Partonic Energy Loss  measure a) leading hadrons (inclusive) b) leading di-hadron correlations (back to back) hadrons leading particle suppressed q q Quenched dijets

11. DPG spring meeting, Tübingen, March 2003 11 R AA : binary-scaled Au+Au / p+p 1.0 More central collisions p+p-reference: UA1, C. Albajar et al., NPB 335 (1990) 261. R AA ~ unity for peripheral collisions, at p T > 2GeV/c R AA < unity, decreasing with centrality  ‘jet quenching’? R AA

12. DPG spring meeting, Tübingen, March 2003 12 R AA for Identified Particles  p T = 2-6GeV/c: K 0,  show different behavior!  Meson / Baryon effect ?  Mass effect ?

13. DPG spring meeting, Tübingen, March 2003 13 Jets in High Energy Collisions p+p  dijet Central Au+Au Event Find this …………………………………… in here

14. DPG spring meeting, Tübingen, March 2003 14  How to Find Jets    Correlation with respect to leading particle (>4 GeV/c) Consider only particles above 2 GeV/c jet-cone at    0 ? back to back jet-cone at     ? Px (GeV/c) Py (GeV/c) -4 -3 -2 -1 0 1 2 3 4 Parton Jet

15. DPG spring meeting, Tübingen, March 2003 15 Azimuthal Correlations 1)‘jet cone’ at   = 0 2)Strong back to back correlations in peripheral Au+Au collisions 3)Suppression of back to back correlations in central collisions  ‘jet-quenching’? C. Adler et al., Phys. Rev. Lett. 90, 082302 (2003). 

16. DPG spring meeting, Tübingen, March 2003 16 High-p T Particle Production @ RHIC Naïve Surface emission? ?  Suppression of inclusive particle production (a)  Suppression of back-to-back correlations in most central Au+Au collision (b) Consistent with jet quenching scenario: frequent interactions medium opaque to fast partons

17. DPG spring meeting, Tübingen, March 2003 17 Pressure, Flow, … Thermodynamic identity  – entropy p – pressure U – energy V – volume  = k B T, thermal energy per dof In A+A collisions, interactions among constituents and density distribution lead to: pressure gradient  collective flow  number of degrees of freedom (dof)  Equation of State (EOS)  accumulative – partonic + hadronic

18. DPG spring meeting, Tübingen, March 2003 18 (anti-)Protons From RHIC (anti-)Protons From RHIC 130 GeV Au + Au Collisions, STAR Preliminary More central collisions 1)In central collisions, m t distributions become more convex  collective flow ! 2) Within |y| are flat  boost invariant !

19. DPG spring meeting, Tübingen, March 2003 19 Transverse Collective Flow At p T ~ 2-3 GeV/c, yields approach each other. Heavier mass particles show stronger collective flow effects ! At what stage does the collectivity develop at RHIC?

20. DPG spring meeting, Tübingen, March 2003 20 dN/dp t Distributions Two-parameter fit describes yields of , K, p,  T th = 90  10 MeV = 0.55  0.08 c ] [(GeV/ 2 2 c) -1 dy dp N d T   K (dE/dx) p  K (kink) T th =107±8 [MeV] =0.55±0.08 [c] n=0.65±0.09  2 /dof=106/90 STAR central data, preliminary solid lines: fit range

21. DPG spring meeting, Tübingen, March 2003 21  Stronger transverse flow at RHIC:  T = 0.55(c)  More explosive expansion ! Kinetic Freeze-out Systematic T fo

22. DPG spring meeting, Tübingen, March 2003 22 T versus Plane 1)In central collisions, , K, p,  (group-I) are different from multi-strange baryons  and  group-II . 2)In peripheral collisions, group-I moves towards the local minimum of group-II.  Multi-strange particles seem to freeze-out earlier than , K, p,  !  Measure  and  to possibly access partonic stage !

23. DPG spring meeting, Tübingen, March 2003 23 Conclusions  Moderately high transverse momentum - frequent interactions at RHIC  Low transverse momentum - strong collective motion at RHIC  collectivity among quarks/gluons or hadrons?

24. DPG spring meeting, Tübingen, March 2003 24 Outlook  Discover partonic collectivity: spectra and v 2 of  s  D  c J / ...

25. DPG spring meeting, Tübingen, March 2003 25