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Elliptic Flow and Constituent Quark Scaling in High Energy Nuclear Collisions

Elliptic Flow and Constituent Quark Scaling in High Energy Nuclear Collisions. Marcus Bleicher 1 & Xianglei Zhu 2 1 Institut für Theoretische Physik 2 Frankfurt Institute for Advanced Studies Goethe Universität Frankfurt Germany. Thanks to. Sascha Vogel (  Talk on resonances )

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Elliptic Flow and Constituent Quark Scaling in High Energy Nuclear Collisions

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  1. Elliptic Flow and Constituent Quark Scalingin High Energy Nuclear Collisions Marcus Bleicher1 & Xianglei Zhu2 1Institut für Theoretische Physik 2Frankfurt Institute for Advanced Studies Goethe Universität Frankfurt Germany Marcus Bleicher, La Jolla 2006

  2. Thanks to • Sascha Vogel (Talk on resonances) • Stephane Haussler • Hannah Petersen • Diana Schumacher • Qingfeng Li • Horst Stoecker (Talk on mono-jets) • Xianglei Zhu • Paul Sorensen (Talk about STAR) • Nu Xu Marcus Bleicher, La Jolla 2006

  3. Parton Number Scaling of v2 • in leading order of v2, recombination predicts: Is this the only explanation? P. Soerensen, UCLA & STAR @ SQM2003 • smoking gun for recombination • measurement of partonic v2 ! Taken from: Bass, Nonaka, Mueller, Fries Marcus Bleicher, La Jolla 2006

  4. Content • Introduction • Different methods for v2 • Constituent quark scaling • Summary Marcus Bleicher, La Jolla 2006

  5. 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, La Jolla 2006

  6. Model check: Multiplicities • Rapidity distributions in line with data (Phobos) • Centrality dependence in line with data Marcus Bleicher, La Jolla 2006

  7. Model check: Expansion Transverse Expansion of the bulk is described Model uncertainties on level of 30-50% Bratkovskaya, M.B. et al., Phys.Rev.C69:054907,2004 Uncertainties depend on:PYTHIA implementation and properties of high mass resonances Marcus Bleicher, La Jolla 2006

  8. Model check: Correlations Q. Li, M.B., H. Stoecker, nucl-th/0602032; Data: STAR • Correlations are well described except for most central reactions Marcus Bleicher, La Jolla 2006

  9. Anisotropic flow Fourier expansion of the transverse angular distribution of the emitted particles: Reaction Plane v0 – radial flowv1 – directed flow v2 -- elliptic flow Marcus Bleicher, La Jolla 2006

  10. Elliptic flow coordinate-space-anisotropymomentum-space-anisotropy y py px x • Elliptic flow is a self-quenching effect  shuts itself off after the early stage of the reaction • Radial flow (<pT>) is an integral quantity  developed over the whole reaction time Marcus Bleicher, La Jolla 2006

  11. V2 at RHIC • Magnitude of v2 is large • Meson-baryon ordering • Constituent quark scaling • Decrease of v2 at high pT Are these unique QGP signatures? Marcus Bleicher, La Jolla 2006

  12. Cumulant: Rapidity • Differential flow At large eta, the non-flow effects are less obvious. If the v2 fluctuations are also negligible to the cumulant method, the v2{2}, v2{4} and v2{6} should all agree with the exact v2. X. Zhu, M.B., H. Stoecker, Phys.Rev.C72:064911,2005 Marcus Bleicher, La Jolla 2006

  13. Cumulants: 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 X. Zhu, M.B., H. Stoecker, Phys.Rev.C72:064911,2005 Marcus Bleicher, La Jolla 2006

  14. Elliptic flow: Magnitude • Integral flow • V2 from UrQMD is about 50% smaller than the data • Space for parton rescattering? X. Zhu, M.B., H. Stoecker, Phys.Rev.C72:064911,2005 STAR data is from nucl-ex/0409033 Marcus Bleicher, La Jolla 2006

  15. Initial ‘string matter’ • String matter dominates the early stages • lack of early pressure ‘string matter‘ = QGP? H. Petersen, X. Zhu, M.B. Marcus Bleicher, La Jolla 2006

  16. Energy dependence • Qualitative description OK • Importance of potentials at low energies • Lack of pressure shows up at lower SPS energies •  Color glas initial state might fix the initial pressure problem H. Petersen, X. Zhu, M.B. Marcus Bleicher, La Jolla 2006

  17. Back to the story line: Multi-strange hadrons have less radial flow • freeze-out early • all v2 should be from QGP • Thus, if W, X and f have v2 • Proof of parton coalescence (and QGP) Marcus Bleicher, La Jolla 2006

  18. Indications of early freeze-out • Two different groups: (a) p,K,p (b) f, W • Multi-strange particle freeze-out earlier than bulk K. Schweda, STAR  Sensitivity to early (partonic) stage Marcus Bleicher, La Jolla 2006

  19. Early freeze-out: models • Omega does not flow strong enough  early freeze-out UrQMD A. Dumitru, S. Bass, M.B., H. Stoecker, Phys.Lett.B460:411-416,1999 Marcus Bleicher, La Jolla 2006

  20. When is v2 created? • The earlier a particle is emitted the larger is the elliptic flow • The higher the pT of a particle the larger is the elliptic flow • High pT particles are more sensitive to the initial v2 Y. Lu, M.B., et al., nucl-th/0602009 Marcus Bleicher, La Jolla 2006

  21. Do multi-strange hadrons flow? • Data indicates approximate 3:2 scaling with constituent quarks • Baryons are generally below mesons • Decrease of v2 at high pTIs this rough scaling a signal for recombination? P. Sorensen, QM 2005 Marcus Bleicher, La Jolla 2006

  22. Compare apples to apples • 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. Use Lee-Yang zero method X. Zhu, M.B., H. Stoecker, Phys.Rev.C72:064911,2005 LYZ-method in UrQMD: nucl-th/0601049 Marcus Bleicher, La Jolla 2006

  23. V2(pT) for various hadrons min. bias Open – MesonsFull -- Baryons UrQMD Y. Lu, M.B., et al., nucl-th/0602009 1) Clear separation of meson and baryon v2 2) Low pT, v2(meson)>v2(baryon) 3) High pT, v2(m)<v2(b) 4) v2’s of multi-strange hadrons comparable to light hadrons Marcus Bleicher, La Jolla 2006

  24. NCQ-scaling • multi-strange baryons follow the normal matter • fdoes flow!(maybef only flows because of KK recombination) UrQMD Y. Lu, M.B., et al., nucl-th/0602009 NCQ-scaling of v2 is roughly reproduced in UrQMD! Marcus Bleicher, La Jolla 2006

  25. Summary • At RHIC (transport models w/ strings and hadrons): • Part of v2 might also come from hadronic stage • non-flow correlations are correct • Mass ordering is correct • Constituent quark scaling (w/o ReCo!) • However, transport models w/o QGP produce to few pressure in the early stage above 30 GeV Marcus Bleicher, La Jolla 2006

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