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Collective Dynamics at RHIC

Collective Dynamics at RHIC. Nu Xu LBNL, Berkeley, USA. 1) Introduction: QGP  partonic collectivity 2) Some results from SPS and RHIC 3) Summary and outlook. J. Fu, H. Huang, M. Kaneta, F. Liu, H.G. Ritter, K. Schweda, R. Snellings, Z. Xu, E. Yamamoto …. 1) Initial Condition

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Collective Dynamics at RHIC

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  1. Collective Dynamics at RHIC Nu Xu LBNL, Berkeley, USA 1) Introduction: QGP  partonic collectivity 2)Some results from SPS and RHIC 3)Summary and outlook J. Fu, H. Huang, M. Kaneta, F. Liu, H.G. Ritter, K. Schweda, R. Snellings, Z. Xu, E. Yamamoto…

  2. 1) Initial Condition - baryon transfer - ET production - parton dof 2) System Evolves - parton/hadron expansion 3) Bulk Freeze-out - hadron dof - interactions stop Introduction J/y, D W K* X F,L p, K D, p d, HBT Q2 ? v2 saturates ? ? ? ? ? bT saturates time

  3. Pressure, Flow, … • Thermodynamic identity • – entropy p – pressure U – energy V – volume t = kBT, thermal energy per dof • In nuclear collisions, interactions among constituents • and density distribution lead to: pressure gradient  collective flow • number of degrees of freedom (dof) • Equation of State (EOS) • time integral – partonic + hadronic effects

  4. Transverse flow observables • As a function of particle mass: • Directed flow (v1) – early • Elliptic flow (v2) – early • Radial flow – integrated over whole evolution • Note: • 1) Effect of collectivity is additive – final effect is the sum of all • processes as long as interactions are there. • 2) No thermalization is needed – pressure gradient only depends • on the density gradient and interactions.

  5. At RHIC ~ constant vs. centrality • At AGS, ratios changes factor ~100 / SPS factor ~ 2 variation •  re-scatterings at hadronic stage reduced at RHIC • STAR: Phys. Rev. Lett. 86, 4778(01), 87, 262301(01), 89, 092301(02) Results from RHIC STAR preliminary

  6. Fiducial yields Total yields Systematic errors Proton flow at RHIC 197Au + 197Au at 130 GeV STAR Preliminary 1) <pt> increases with centrality  flow 2) RQMD describes transverse motion well  hadronic re-scattering 3) It underestimates pbar yield due to large annihilation x-section re-scattering at earlier stage?

  7. Transverse momentum distribution NA44, Phys. Rev. Lett. 78, 2080(97) SPS: Dependence on the particle mass and the size of the colliding system  collective flow !

  8. T vs. mass plot(SPS) H. van Hecke, H. Sorge, N. Xu, Phys. Rev. Lett. 81, 5764(98). • Interactions with hadronic gas: • Large x-section limit: pions, kaons, protons • Small x-section limit: , J/ sensitive to hadronization! At SPS, the observed collective transverse flow, b ~ 0.4c, develops mostly at the hadronic stage. W and J/ do not flow!

  9. Beam energy systematics 1) Smaller baryon chemical potential mB = 45 MeV with Tch = 170 MeV  Approaching net-baryon free ! 2) Stronger transverse flow, bT= 0.55(c)  More explosive expansion !

  10. v2 for K0 and  1) Integrated v2 increases with particle mass ; 2) Hydro model results are consistent with data. ‘QGP’ EoS used in calculations! Does v2 signal partonic flow? STAR Phys. Rev. Lett. 87, 182301(01) STAR, Phys. Rev. Lett. , accepted, (02)

  11. Transverse collective flow Heavier mass particles show stronger collective flow effects ! PHENIX: Phys. Rev. Lett. 88 242301(02) / STAR: f Phys. Rev. C65, 041901(02) / STAR: L Phys. Rev. Lett. 89, 092301(02)

  12. Slope parameters vs. mass ? At high energy, high gluon density and strong interactions  partonic flow , D, J/y...sensitive to partonic collectivity ? At RHIC, the observed collective transverse flow, b ~ 0.55c, sum of partonic and hadronic interactions ! W and J/ should flow!

  13. Partonic Flow at RHIC? ? YES NO We need: 1) Non-zero values of v2 for W 2) Increase of T for W, D, J/ …

  14. Summary 1) SPS: most of the collective flow develops at later hadronic stage 2) RHIC: Copious scattering needed, Not at the later hadronic stage, Evidence of early patonic flow?! 3) To ‘see’ the partonic flow directly, spectra and v2 for all hadrons, especially, Ks f L X W D J/ ...

  15. Outlook Discover partonic collectivity – ‘QGP’ New Form of Matter ! Diagnose bulk properties of ‘QGP’ Important: Scan collision geometry b Scan collision size A Scan collision energy E

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