M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 1 Centrality Dependence of Azimuthal Anisotropy of Strange Hadrons in 200 GeV Au+Au Collisions Markus Oldenburg European Organisation for Nuclear Research CERN for the STAR Collaboration Strange Quark Matter 2006 International Conference on Strangeness in Quark Matter March 26–31, University of California, Los Angeles, USA

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 2 Overview Motivation Analysis details and technique Data and results for v 2 and v 4 Discussion Conclusions Time

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 3 x z y pxpx pypy y x ● non-central collisions: azimuthal anisotropy in coordinate-space ● interactions  asymmetry in momentum-space ● sensitive to early time in the system’s evolution ● Measurement: Fourier expansion of the azimuthal p T distribution Elliptic flow v 2

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 4 Flow of strange hadrons STAR: freeze-out of multi-strange hadrons - at higher temperature T fo - with lower collective velocity  T  → less interaction of strange hadrons with non-strange hadrons sensitivity to the early, partonic stage Nucl. Phys. A715, 458c (2003) Phys. Rev. Lett. 92, (2004) Phys. Rev. Lett. 92, (2004) (GeV)

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 5 Dataset and analysis method system: Au+Au collisions energy: s NN = 200 GeV event sample: –13.3 M events 0–80% –6.6 M events 40–80% –5.0 M events 10–40% –~19 M events 0–10% event plane resolution: –76% for 0–80% –66% for 40–80% –82% for 10–40% –69% for 0–10% analysis method: v 2 vs. m inv motivated by Borghini et al. [nucl-th/ ] detailed studies regarding systematic uncertainties still underway for K 0 S and Λ+Λ –~5% error on v 2 for p T <4 GeV/c –rising up to ~25 – 30% at 4<p T <6 GeV/c –possible significant non-flow contribution for p T >5 GeV/c Only statistical errors shown in this presentation! _

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California GeV Au+Au STAR preliminary mass ordering at low p T ‘standard’ Hydro calculation: T ch =165 MeV, T kin =130 MeV [P. Huovinen, private communication] model works reasonably well for min. bias at low p T Min. bias v 2 (p T ) for strange hadrons K 0 S and Λ data provided by Yan Lu → poster on Thursday

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 7 Centrality dependence of v 2 (p T ) available high statistics allows for measurement of centrality dependence of v 2 (p T ) comparison to Hydro model calculations shows deviations even at low p T 40-80% 10-40% 10-80% 0-10% 200 GeV Au+Au STAR preliminary K 0 S and Λ data provided by Yan Lu → poster on Thursday [Hydro model results by P. Huovinen, private communication]

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 8 NCQ scaling of v 2 (p T ) for min. bias PHENIX (open symbols): Phys. Rev. Lett. 91, (2003) scaled meson and baryon v 2 agrees at intermediate p T high statistics measurements show deviation from ideal scaling STAR preliminary 200 GeV Au+Au min. bias (0 – 80%)

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 9 Centrality dependence of NCQ scaling polynomial fit through K 0 S, Λ, and Ξ data NCQ scaling seems to work for different centralities as well See Yan Lu’s poster on Thursday! 200 GeV Au+Au STAR preliminary

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 10 v 4 for Ξ - and Ξ + _ ideal fluid dynamics would lead to v 4 /v 2 2 = 0.5 [Borghini and Ollitrault, nucl-th/ ; Kolb, Phys. Rev. C 68, (R)] Incomplete thermalisation? [Borghini et al., Phys. Lett. B 627, 49 (2005)] Will v 4 /v 2 2 be closer to 0.5 at LHC? Ξ+ Ξ v 4 _ 1.2 v v GeV Au+Au min. bias (0 – 80%) STAR preliminary Observation of sizable v 4 with strong p T dependence v 4 scales with ~1.2 v 2 2 (as it for charged hadrons) [STAR: Phys. Rev. C (2005)] v4v4

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 11 Conclusions The strong flow of strange and multi-strange hadrons indicates collectivity among partons! strange hadron v 2 at low p T : –show mass ordering –follow hydro model for minimum bias –deviate from hydro model predictions for different centralities NCQ scaling of v 2 at intermediate p T : –deviations from ideal NCQ scaling become visible for minimum bias –indication for NCQ scaling even for different centralities v 4 of Ξ - +Ξ + : –shows same scaling (1.2 v 2 2 ) as other particle species –Hint for incomplete thermalisation? _

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 12 Backup

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 13 Analysis technique analysis method: v 2 vs. m inv motivated by Borghini et al. [nucl-th/ ] advantages over standard method: –only one fit per p T bin  smaller systematic uncertainties method used for K 0 S, Λ, Ξ, , standard method and v 2 vs. m inv method give consistent results and provide means for estimating systematic errors SIG + BG BG (SIG+BG) SIG (SIG+BG) v 2 TOT (m inv )

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 14 Systematic error estimations for K 0 S and Λ STAR preliminary