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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.  . Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration. Outline. Introduction

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Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration

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  1. 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   Kai Schweda Lawrence Berkeley National Laboratory for the STAR collaboration

  2. Outline • Introduction • The STAR detector at RHIC • High-pt phenomena – probe the medium • Collective dynamics – bulk properties • Conclusions / Outlook

  3. QCD on the Lattice • 1) Large increase in  ! • Large increase in Ndof: Hadrons vs. partons 2) TC~ 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). Lattice calculations predict TC ~ (170  15) MeV

  4. Heavy Ion Collisions Time  1) Initial condition: 2) System evolves: 3) Bulk freeze-out: - baryon transfer - parton/hadron expansion - hadronic dof - ET production - interaction cease - Partonic dof Tth, <bT> Plot: Steffen A. Bass, Duke University

  5. The STAR Collaboration 400 Collaborators, 49 Institutions, 9 Countries

  6. The STAR Detector

  7. STAR Au + Au Collisions at RHIC Central Event (real-time Level 3)

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

  9. Particle Identification Reconstruct multi-strange resonances in 2p acceptance of STAR!

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

  11. 1.0 1.0 1.0 RAA ~ unity for peripheral collisions, at pT > 2GeV/cRAA < unity, decreasing with centrality  ‘jet quenching’? RAA: binary-scaled Au+Au / p+p RAA More central collisions p+p-reference: UA1, C. Albajar et al., NPB 335 (1990) 261.

  12. RAA for Identified Particles • pT = 2-6GeV/c:K0, L show different behavior! • Meson / Baryon effect ? • Mass effect ?

  13. Jets in High Energy Collisions Find this …………………………………… in here Central Au+Au Event p+p dijet

  14. Parton Jet Py (GeV/c) Df -4 -3 -2 -1 0 1 2 3 4 Px (GeV/c) -4 -3 -2 -1 0 1 2 3 4 How to Find Jets • Df - Correlation with respect to leading particle (>4 GeV/c) • Consider only particles above 2 GeV/c • jet-cone at Df 0 ? • back to back jet-coneat Df p ?

  15. Azimuthal Correlations • ‘jet cone’ at Df = 0 • Strong back to back correlations in peripheral Au+Au collisions • Suppression of back to back correlations in central collisions •  ‘jet-quenching’?  C. Adler et al., Phys. Rev. Lett. 90, 082302 (2003).

  16. ? High-pT Particle Production @ RHIC • 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 Naïve Surface emission?

  17. Pressure, Flow, … • Thermodynamic identity • – entropy p – pressure U – energy V – volume t = kBT, thermal energy per dof • In A+A collisions, interactions among constituentsand density distribution lead to: pressure gradient  collective flow • number of degrees of freedom (dof) • Equation of State (EOS) • accumulative – partonic + hadronic

  18. (anti-)Protons From RHIC 130 GeV Au + Au Collisions, STAR Preliminary More central collisions • In central collisions, mt distributions become more convex  collective flow ! • 2) Within |y|<0.5, dN/dy and <pT> are flat boost invariant !

  19. Transverse Collective Flow At pT ~ 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. dN/dpt Distributions STAR central data, preliminary p Tth=107±8 [MeV] <bt>=0.55±0.08 [c] n=0.65±0.09 2/dof=106/90 • Two-parameter fit describes yields ofp, K, p, L • Tth = 90  10 MeV • <bt> = 0.55  0.08 c ] c)-1 K (dE/dx) K (kink) [(GeV/ solid lines: fit range p dy N T dp L 2 d p 2

  21. Kinetic Freeze-out Systematic • Stronger transverse flow at RHIC:bT= 0.55(c) More explosive expansion ! <bt> Tfo

  22. T versus <bt> Plane • In central collisions,p, K, p, L (group-I) are different from multi-strange baryons X and W (group-II). • In peripheral collisions, group-I moves towards the local minimum of group-II. •  Multi-strange particles seem to freeze-out earlier than p, K, p, L ! •  Measure X and W to possibly access partonic stage !

  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. Outlook • Discover partonic collectivity: spectra and v2 of • Ks f L X W DLc J/...

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