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Collective Flow in Heavy-Ion Collisions

Collective Flow in Heavy-Ion Collisions. Kirill Filimonov (LBNL). What is Flow in Heavy-Ion Collisions?. Collective motion characterized by space-momentum correlation of dynamic origin. Concept from Hydrodynamics:

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Collective Flow in Heavy-Ion Collisions

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  1. Collective Flow in Heavy-Ion Collisions Kirill Filimonov (LBNL)

  2. What is Flow in Heavy-Ion Collisions? • Collective motion characterized by space-momentum correlation of dynamic origin • Concept from Hydrodynamics: • - hot and compressed matter behaves like a compressible fluid Types of Flow: • axially symmetric radial flow • azimuthally anisotropic transverse flow

  3. b – impact parameter Collective Behavior in non-central Heavy Ion Collisions Low energy heavy-ion collisions: E/A=25 MeV

  4. b – impact parameter “spectators” “participants” “spectators” Collective Behavior in non-central Heavy Ion Collisions Relativistic heavy-ion collisions: E/A~0.4-10 GeV

  5. “spectators” “participants” REACTION PLANE “spectators” Collective Behavior in non-central Heavy Ion Collisions Passage time: 2R/(βcmγcm) • 15 fm/c at 1 GeV/nucleon • 5.4 fm/c at 10 GeV/nucleon • 1.4 fm/c at 160 GeV/nucleon

  6. Azimuthal anisotropy in momentum space (directed flow) py Spectator blocking px TARGET PROJECTILE y x View in transverse plane

  7. Directed (sideward) Flow Example: E877 (AGS, 11 AGeV) py protons deuterons px <px> ≠0

  8. py px dN/d y  -/2 0 /2 x Out-of-plane squeeze-out (spectator blocking) Azimuthal anisotropy in momentum space (elliptic flow)

  9. py px dN/d y  -/2 0 /2 x In-plane elliptic flow (due to pressure gradient) Azimuthal anisotropy in momentum space (elliptic flow)

  10. Interplay of passage/expansion times Passage time: 2R/(βcmγcm) Expansion time:R/cs cs=c√dp/dε - speed of sound

  11. Sensitivity to nuclear EOS Science, Vol 298, Issue 5598, 1592-1596, 22 November 2002Determination of the Equation of State of Dense Matter Pawel Danielewicz, Roy Lacey, William G. Lynch Directed Flow: Elliptic flow:

  12. “spectators” b – impact parameter “spectators” Elliptic flow at RHIC Longitudinal and transverse expansion => no influence of spectator matter at midrapidity

  13. Elliptic flow at RHIC Flow Y Out-of-plane In-plane Reaction plane Flow X Re-interactions  FLOW Re-interactions among what? Hadrons, partons or both? In other words, what equation of state?

  14. Azimuthal distributions at RHIC STAR, PRL90 032301 (2003) b ≈ 6.5 fm b ≈ 4 fm “central” collisions midcentral collisions

  15. “v2” Azimuthal distributions at RHIC STAR, PRL90 032301 (2003) b ≈ 10 fm b ≈ 6.5 fm b ≈ 4 fm peripheral collisions

  16. v2 Excitation Function Rich structure Transition from in-plane to out-of-plane and back to in-plane emission Geometry effect in addition to (smooth?) change in pressure

  17. v2 vs Energy Density Steady increase with energy density Close to hydrodynamic limit for most central collisions at RHIC

  18. Elliptic flow => sensitivity to early system • “Elliptic flow” • evidence ofcollective motion • sensitive to early pressure • evidence for • early thermalization • QGP in early stage Hydrodynamic calculation of system evolution

  19. Quark-number scaling At intermediate pT v2 appears to depend on quark-number For pT/n > 0.6 GeV/c, v2 scales with the number of quarks n, as predicted for hadron formation by quark coalescence Pions deviate: perhaps because they are goldstone bosons but also because of resonance decay contributions.

  20. Conclusions and Outlook • Elliptic flow at RHIC => Evidence for early pressure • First time hydro works in heavy ion collisions! • Indications of re-interaction between constituent quarks • Will charm flow at RHIC?

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