Elliptic Flow in High Energetic Nuclear Collisions

1. Elliptic Flow in High Energetic Nuclear Collisions Marcus Bleicher & Xianglei Zhu FIAS & Institut für Theoretische Physik Goethe Universität Frankfurt Germany Marcus Bleicher, Berkeley, Oct. 2005

2. Thanks to • Sascha Vogel • Stephane Haussler • Hannah Petersen • Diana Schumacher • Nu Xu Marcus Bleicher, Berkeley, Oct. 2005

3. The tool: UrQMDv2.2 • Non-equilibrium transport model • Hadrons and resonances • String excitation and fragmentation • Cross sections are parameterized via AQM or calculated by detailed balance • pQCD hard scattering at high energies • Generates full space-time dynamics of hadrons and strings Marcus Bleicher, Berkeley, Oct. 2005

4. Transverse Momentum Distributions: Proton-Proton • PP works well • pQCD needed at RHIC • PYTHIA included in • UrQMD 2.x and HSD Marcus Bleicher, Berkeley, Oct. 2005

5. Proton-Nucleus • pA is well under control • CC and SiSi are also under control • What about AA? Inv. slope System size Marcus Bleicher, Berkeley, Oct. 2005

6. Transverse mass spectra • Standard UrQMD and HSD underestimate the data • Additional resonances of 2-3 GeV mass may improve the description mt-m0 Marcus Bleicher, Berkeley, Oct. 2005

7. Inverse slope systematics • ‘Step’ claimed to be signature of QGP onset (Gazdzicki) • High mass resonances improve • the description at low and high energies • How can we test those scenarios?use v2 to disentangle early and late stage E_CM (AGeV) Marcus Bleicher, Berkeley, Oct. 2005

8. Anisotropic flow Fourier expansion of the transverse angular distribution of the emitted particles: Reaction Plane v1– directed flow V2 -- elliptic flow Ollitrault, PRD 46 (1992)Poskanzer & Voloshin, PRC 58 (1998) Marcus Bleicher, Berkeley, Oct. 2005

9. Elliptic flow coordinate-space-anisotropy  momentum-space-anisotropy y py px x Taken from Nu Xu • V2 of low pt particles is the good measure the EOS of the fireball in the early stage. • V2 of high pt particles is the good measure of jet energy loss through the medium. Marcus Bleicher, Berkeley, Oct. 2005

10. Data for h- Hints from elliptic flow • High mass resonances can not explain scaled v2 above 40 AGeV • Data shows saturation of scaled v2 • Strong hint for large pressure • and short mean free paths in the • early stage of the reaction • already from 30 AGeV on ! Marcus Bleicher, Berkeley, Oct. 2005

11. ‘Partonic’ dof already atlow SPS energy • Breakdown of v2/<pt> scaling in model coincides with onset of ‘partonic’ matter signals onset of change of EoS in the early stage Marcus Bleicher, Berkeley, Oct. 2005

12. V2 at RHIC • Magnitude of v2 is large • Meson-baryon ordering • Constituent quark scaling • Decrease of v2 at high ptAre these unique QGP signatures? Zhu, Bleicher, Stoecker, nucl-th/0509081 Marcus Bleicher, Berkeley, Oct. 2005

13. Marcus Bleicher, Berkeley, Oct. 2005

14. Fluctuations are everywhere • Au+Au at RHIC • Strong fluctuations of initial state eccentricity Marcus Bleicher, Berkeley, Oct. 2005

15. Fluctuations are everywhere • Au+Au at RHIC • Strong fluctuations of final elliptic flow Marcus Bleicher, Berkeley, Oct. 2005

16. s2 v2 correlation • Only weak correlation between coordinate and momentum space in single events • Hydro yields strong correlation Marcus Bleicher, Berkeley, Oct. 2005

17. Elliptic flow: Centrality dependence • Integral flow STAR data is from nucl-ex/0409033 V2 from UrQMD is about 50% smaller than the data, Left space for parton rescattering? Marcus Bleicher, Berkeley, Oct. 2005

18. Cumulant method: Centrality In the most central bin: The fluctuations give larger v2{6} but smaller v2{4} In the very peripheral bins: The fluctuations give larger v2{6} and v2{4} Agree with the prediction of MCG model BUT: In the semi-central bins: the v2 fluctuations can be neglected. • Integral flow Cumulant method:Ollitrault, Borghini, Dinh, PRC 63, PRC 64, nucl-ex/0110016 Marcus Bleicher, Berkeley, Oct. 2005

19. Cumulant method results • Comparison to STAR data Good agreement of the ratios with STAR data. Decrease of g2 at peripheral bins are also reproduced. (the g2 decrease is possibly from the v2 fluctuations) (a.u.) Marcus Bleicher, Berkeley, Oct. 2005

20. Cumulant method: Rapidity • Even at large h non-flow effects are present • However, effects are small (<20% of the v2 value) Marcus Bleicher, Berkeley, Oct. 2005

21. Cumulant method: PT • Differential flow v2{2} is heavily affected by the non-flow effects especially at large pt. The non-flow effects have been eliminated in v2{4} and v2{6}. But v2{4} is still a little larger than the exact v2. Marcus Bleicher, Berkeley, Oct. 2005

22. Cross sections: AQM Marcus Bleicher, Berkeley, Oct. 2005

23. Nu Xu Plot • Multi-strange particles break flow scaling • Sign of early freeze-out no v2 from hadronic stage? Marcus Bleicher, Berkeley, Oct. 2005

24. V2(pt) from UrQMD Red--Mesons Blue-Baryons 1) Clear separation of meson and baryon v2 2) Low pt, v2(meson)>v2(baryon) 3) High pt, v2(m)<v2(b) 4) The v2’s of multi-strange baryons are comparable to light baryons Marcus Bleicher, Berkeley, Oct. 2005

25. NCQ-scaling Note:multi-strange hadrons follow the normal matter NCQ-scaling of v2 is roughly reproduced in UrQMD! Marcus Bleicher, Berkeley, Oct. 2005

26. Summary • At RHIC (transport models w/ strings and hadrons): • Part of v2 might also come from hadronic stage • Mass ordering is correct • Constituent quark scaling (w/o ReCo!) • non-flow correlations are correct • However, transport models w/o QGP produce to few pressure in the early stage above 30 GeV Marcus Bleicher, Berkeley, Oct. 2005