Strangeness thermalization at RHIC – partonic or hadronic ?

1. Strangeness thermalization at RHIC – partonic or hadronic ? 1.) strangeness yields - enhancements chemical equilibration, saturation, equilibration how do we compare pp, dA, AA properly ? 2.) strangeness spectra - dynamics kinetic equilibration, flow, suppression, fragmentation, recombination how do we compare pp, dA, AA properly ? Rene Bellwied Wayne State University 20th Winter Workshop on Nuclear Dynamics Montego Bay, March 15th -20th , 2004

2. Directed flow Elliptic flow Elliptic(anisotropic)Flowfor a mid-peripheral collision– a strong indicator of collectivity Flow Y Out-of-plane In-plane Reaction plane Flow X Dashed lines: hard sphere radii of nuclei Re-interactions  FLOW Re-interactions among what? Hadrons, partons or both? In other words, what equation of state?

3. v2 (anisotropy, squeeze-out) measurements

4. Y Time X Time System deformation in HBT • Final state eccentricity from • v2 • HBT with respect to reaction plane • Conclusions: • System was still deformed at freezeout • System froze out EARLY

5. (nucl-th/0403032) Consequences of a strong v2 at RHIC 1.) v2 is strong and has to come from very early time after collision. Hadronic v2 is not sufficient in terms of magnitude and timescale 2.) v2 is very well described by hydrodynamics (fluid dynamics). 3.) if the phase producing the flow is partonic then we have partonic fluid (dissipative, strongly interacting, small correlation length) rather than a plasma (large correlation length, weakly interacting quasi-particle gas).

6. Shuryak, QM04 Cassing, 2004 parton fluid (pre-hadrons) deconfinement c restoration New phase diagrams for RHIC

7. A strongly interacting parton liquid Bulk properties seemingly well described by: - dynamical hydrodynamics - single freeze-out surface blast wave parametrization - thermal freeze-out models Are there other signatures of a bulk partonic liquid in strangeness production or strangeness kinematics ? Is this liquid thermalized ?

8. Strangeness chemistry: beautiful agreement with statistical chemical equilibration model for non-resonant particles

9. Lines of constant lS I. Increase instrange/non-strangeparticle ratios RHIC fixed target mode (internal gas target) PBM et al., hep-ph/0106066 K/p total II. Maximum isreached mesons III. Ratios decrease (Strange baryonsaffected more stronglythan strange mesons) K+/K- baryons hidden strangeness mesons <E>/<N> = 1 GeV [GeV] Peaks at 30 A GeV in AA collisions due to strong mB dependence Strangeness enhancement:Wroblewski factor evolution Wroblewski factor dependent on T and mB dominated by Kaons

10. Does the thermal model always work ? see talk by C.Markert Data – Fit (s) Ratio • Resonance ratios not well described  Reaction dynamics

11. The switch from canonical to grand-canonical(Tounsi,Redlich, hep-ph/0111159, hep-ph/0209284) The strangeness enhancement factors at the SPS (WA97) can be explained as a suppression in pp rather than an enhancement in AA. In pp the phase space for particle production is small. The small volume term will dominate the canonical ensemble (suppression) whereas in AA the volume and strangeness content is large (grand-canonical)

12. equilibration volume ? Tounsi et al. Plots of canonical suppression

13. Grandcanonical prediction Strangeness enhancement factors at RHIC No Npart-scaling in Au-Au at RHIC -> lack of Npart scaling = no thermalization ? Alternatives: no strangeness saturation in peripheral collisions (gs = 1) non-thermal jet contributions rise with centrality

14. Non –thermal jet contributions ? • jet contributions scale with Nbin • around 20% of the multistrange yield is above 2 GeV/c at RHIC (little centrality and baryon dependence) • from 2 GeV/c on all strange baryon spectra scale with Nbin

15. < 2 GeV/c Npart scaling >2 GeV/c Nbin scaling Corrected strangeness enhancement factors

16. preliminary preliminary Let’s fit spectra: kinetic equilibration Mass dependence of the transverse expansion, which is well described by thermal and hydrodynamics models

17. Blastwave: a hydrodynamic inspired description of spectra Spectrum of longitudinal and transverse boosted thermal source: bs R Ref. : Schnedermann, Sollfrank & Heinz, PRC48 (1993) 2462 Static Freeze-out picture, No dynamical evolution to freezeout

18. Tdec = 100 MeV Kolb and Rapp,PRC 67 (2003) 044903. , STAR preliminary ,K,P, Blastwave vs. Hydrodynamics Mike Lisa (QM04): Use it don’t abuse it ! Only use a static freeze-out parametrization when the dynamic model doesn’t work !!

19. STAR preliminary Radial flow & thermalization from <pt>? <pt> in pp = <pt> in AA for X and heavier particles. No partonic flow necessary to explain <pt> in AA ? What is the origin of <pt> in pp ? Same production mechanisms than in AA ?

20. STAR <pt> for Nch in pp, dA, AA Energy density in high mult. pp above critical density ?? Can one even speak about energy density in pp ? Is pp governed by a different mechanism, e.g. jet fragmentation ? Is there a <pt> saturation value or is this just an accident because we have no stats for high mult pp ?

21. How big an effect ??

22. High multiplicity bias in strange particles ?

23. Contributions to the effective temperature 1.) basic thermal slope (similar to pp ?) (might be very jet fragmentation dependent) heavier primary particles and decaying particles come from more energetic jet fragmentation ? 2.) hadron gas expansion 3.) parton fluid expansion 4.) Cronin effect: Initial state rescattering pushes spectrum to higher pt in pA collisions ?

24. Let’s look at Cronin at RHIC Cronin = initial state effect (but now measured by HERMES in eA ??)

25. PRL 68, 452 (1992) Straub et al. Lower Energy Cronin data • Ratio of per nucleon cross sections for p+W and p+Be collisions at √s=38.8 GeV • Enhancement varies with pT and with particle species • Cronin increases slope mimics expansion ? • Is there a sum rule ? Depletion at low momentum equals enhancement at higher momentum ? pT GeV/c

26. PRL 68, 452 (1992) Straub et al. Energy dependence of Cronin (data) RW/Be • Cronin enhancement decreasing with increasing √s • Certainly for p, K • Trend less clear for proton? √s

27. Energy dependence of Cronin (theory)(Cassing, Gallmeister, Greiner (hep-ph/0311358)) • Cronin enhancement decreasing with increasing √s but still sizeable at RHIC • bigger effect for baryons than for mesons because ‘more’ partons • can rescatter in the initial phase (3 instead of 2) – recombination ?

28. Only statistical errors shown for L Cronin in STAR and PHENIX(Spiros and Julia’s talks) RdAu STAR Preliminary h±  K0s  proton   K±

29. STAR anti-proton spectra in pp, dA, AA L.Molnar Cronin effect seems small ! √s

30. Whatever you believe, don’t trust this man !!!! Because it’s really a fluid, Baby !! The national flower of Jamaica, Maaan Physics Conclusions • We have a strongly collective, likely partonic, phase based on the multistrange baryon elliptic flow measurements (parton liquid ?). • It is likely that global (chemical and kinetic) thermalization is reached at all centralities, but simple enhancement plots show effects of non-thermal jet contributions. • pp and dA are not good reference systems for kinematic quantities such as <pt> and radial flow, because non-thermal contributions such as jets and Cronin effect mimic global expansion patterns. A kinematic ‘minimum bias’ pp measurement has to be evaluated differently for each particle species. In that sense Npart is an inappropriate scaling variable, also because any non-thermal contributions do not scale with Npart • Yields and ratios as well as the kinematics of the multi-strange baryons seem to indicate a thermalization of the early phase of the reaction.