Study of Bulk Matter Properties through Strange Hadrons with the STAR experiment

1. Study of Bulk Matter Properties through Strange Hadrons with the STAR experiment Marcelo G. Munhoz Universidade de São Paulo - Brasil for the Collaboration

2. Outline • Present new results from the STAR Collaboration towards the understanding of relativistic heavy ion collisions dynamics • What are the observable signatures for the identification and characterization of the QGP, mainly related to strange hadrons ?

3. Outline “… a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes”, STAR Collaboration, Nucl. Phys. A757 (2005) QGP

4. Outline Hot and High Density Medium ? • Bulk Strangeness production • v2 • Baryon/meson ratio vs pT • v2 of strange hadrons Partonic degrees of freedom ? HIC • v2 and v4: Hints from ideal hydro comparison? Local Thermalization ? d+Au collisions: Tests on cold nuclear matter

5. The STARexperiment at RHIC • Large acceptance detector • Excellent particle identification capability • High resolution tracking device • All these points make STAR unique for strange and heavy flavored hadrons measurements STAR Experiment

6. Bulk Properties and Strangeness • Bulk strangeness production is favored in the QGP environment relative to a pure hadronic one • Gluon fusion • Faster equilibration • Lower energy threshold for strangeness production J. Rafelski, B. Müller, PRL 48 (1982), 1066

7. Bulk Properties and Strangeness • QGP ⇒ Strangeness enhancement in heavy ion collisions relative to p+p or p+A collisions • Can the “Strangeness Enhancement” be explained by a suppression in p+p collisions due to phase space limitations? J. Rafelski, B. Müller, PRL 48 (1982), 1066 K. Redlich, A. Tounsi, Eur. Phys. J. C 24, 589–594 (2002)

8. Systematic Studies of Strangeness Production • Energy and system size systematic measurements • Allows to investigate the mechanisms behind strangeness production in these collisions • What is the influence of the system geometry? • How does strangeness production change as a function of energy?

9. Systematic Studies of Bulk Strangeness Production STAR Collaboration, nucl-ex/0809.0823 • Strange hadrons production are enhanced relative to p+p • Relative enhancement seems to be slightly lower than in SPS: no clear energy dependence • Strangeness content “hierarchy” • Production volume not proportional to Npart

10. Systematic Studies of Bulk Strangeness Production STAR Collaboration, nucl-ex/0809.0823 • Strange hadrons production at Cu+Cu √sNN = 200 GeV does not follow the same Npart dependence as in Au+Au collisions • Multiple collision effect? Core-corona? • The meson f production shows equivalent enhancement, although it is not subject to “canonical suppression” ⇒ strangeness enhancement STAR Collaboration Phys. Lett. B673, p.183 - 191, 2009.

11. Systematic Studies of Strangeness Production as a function of pT • Baryons are more abundantly produced than mesons at intermediate pT as observed in Au+Au collisions at √sNN = 200 GeV • p/π, Λ/Ks0, Ω/Φ • This behavior can be qualitatively reproduced by models that assume the coalescence of partons R. J. Fries et al, Phys. Rev., C68:044902, 2003 R. C. Hwa and C. B. Yang, Phys. Rev., C67:034902, 2003 V. Greco et al, Phys. Rev. Lett., 90:202302,2003. STAR Collaboration, J. Phys. G34, S933-936, 2007

12. Systematic Studies of Strangeness Production as a function of pT • Same behavior of Λ/Ks0 ratio observed for Au+Au and Cu+Cu at √sNN = 62.4 GeV • What about Ω/Φ ratio for Au+Au and Cu+Cu at √sNN = 62.4 GeV? Au+Au, √sNN = 62.4 GeV Cu+Cu, √sNN = 62.4 GeV STAR Preliminary STAR Preliminary

13. Systematic Studies of Strangeness Production as a function of pT Au+Au, √sNN = 62.4 GeV Cu+Cu, √sNN = 62.4 GeV STAR Preliminary STAR Preliminary • Is there coalescence of partons at lower energy? • Is this the only approach to describe such behavior? • See G. Vasconcelos talk

14. Azimuthal Anisotropy: Elliptic Flow Almond shape overlap region in coordinate space Interactions/ Rescattering Anisotropy in momentum space • Very important tool to probe the early stages of the collision dynamics !

15. hadronic partonic Elliptic Flow and Strangeness • Investigate particle type dependence (Ks0, Λ, Ξ) • Low hadronic interaction (Ω, f): probe partonic collectivity , Ω, Ξ, Λ, KS0 J/Ψ, D , K, p

16. Elliptic Flow of Strange Hadrons Hydro: P. Huovinen and P. V. Ruuskanen, Annu. Rev. Nucl. Part. Sci. 56, 163 (2006) • Hydro approach reproduces mass ordering • v2 of strange hadrons shows baryon-meson difference: • nq scaling: hadronization of partons • Indications of a different behavior for higher pT STAR preliminary

17. Elliptic Flow of Ω and f • Ω and f: low hadronic interaction ⇒ partonic collectivity ! STAR preliminary PHENIX: nucl-ex/0604011v1

18. STAR preliminary Hydro limit STAR preliminary Elliptic Flow of Strange Hadrons • From this approach, even in central Au + Au collisions, fitting results indicate that the system is still away from ideal hydro limit where: H.-J. Drescher, A. Dumitru, C. Gombeaud and J.-Y Ollitraut, Phys. Rev. C76, 024905 (2007).

19. The fourth harmonic (v4) of Strange Hadrons STAR preliminary • v4(pT) has been measured for , KS0 and  • The nq scaling for v4 is observed at (mT - m)/nq < 1 GeV/c2, similar to that of v2 • v4/v22 : can probe the ideal hydro approach STAR preliminary STAR preliminary N. Borghini and J.-Y. Ollitraut, Phys. Lett. B 642 227 (2006)

20. Cold Nuclear Matter • Why d+Au collisions are interesting? • Important probe to distinguish initial effects from final state interactions in Au+Au collisions • Strangeness production in d+Au collisions • Add important information on the particle type dependence of these effects for wide range of pT • The  meson has a special role, since it is a meson with mass comparable to proton (baryon) and ithas lower hadronic interaction cross section

21. Cold Nuclear Matter and Strangeness statistical error only for d+Au data STAR Preliminary • KS0 and Λ yields fit the trend for the most peripheral Au+Au and Cu+Cu collisions • Ξ yields fit the trend for the most peripheral Cu+Cu collisions • The strangeness hierarchy is preserved in d+Au dN/dy / <Npart> relative to pp Number of Participants Npart

22. Cold Nuclear Matter and Strangeness • Most central d+Au data approaches peripheral Au+Au ratio values • Similar explanation as in Au+Au? • Au+Au: Enhanced rescattering effects STAR Preliminary

23. Cold Nuclear Matter and Strangeness • K0s agree with pions at low pT • Λ agrees with proton at intermediate pT (2 – 4 GeV/c) • Indications of particle type (baryon/meson) dependence of RdAu for pT from 2.0 to 4 GeV/c • More data are necessary for Φ-meson measurement

24. Summary Hot and High Density Medium ? • Strangeness enhancement and v2 • Hadronization through quark coalescence • Partonic collectivity Partonic degrees of freedom ? HIC • Under investigation • Future effort Local Thermalization ? d+Au collisions: final state effects in HIC

25. Thank you !