M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 1

Centrality Dependence ofAzimuthal Anisotropyof Strange Hadrons in

200 GeV Au+Au Collisions

Markus OldenburgEuropean Organisation for Nuclear Research CERN

for the STAR Collaboration

Strange Quark Matter 2006International Conference on Strangeness in Quark MatterMarch 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 v2 and v4

• Discussion• Conclusions

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

Time

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 3

x

zy

px

py

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 pT distribution

...])φ[2(2φcos211

2122

3

3

RRT

vvdydp

Nd

pd

NdE

])φ[2cos(2 Rv

Elliptic flow v2

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 Tfo

- with lower collective velocity T

→ less interaction of strange hadrons with non-strange hadrons

• sensitivity to the early, partonic stageNucl. Phys. A715, 458c (2003)

Phys. Rev. Lett. 92, 112301 (2004)Phys. Rev. Lett. 92, 182301 (2004)

(GeV

)

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 5

Dataset and analysis method• system: Au+Au collisions

• energy: sNN = 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: v2 vs. minv

• motivated by Borghini et al. [nucl-th/0407041]

• detailed studies regarding systematic uncertainties still underway

• for K0S and Λ+Λ

– ~5% error on v2 for pT<4 GeV/c

– rising up to ~25–30% at 4<pT<6 GeV/c

– possible significant non-flow contribution for pT>5 GeV/c

• Only statistical errors shown in this presentation!

_

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 6

200 GeV Au+AuSTAR preliminary

• mass ordering at low pT

• ‘standard’ Hydro calculation: Tch=165 MeV, Tkin=130 MeV

[P. Huovinen, private communication]

• model works reasonably well for min. bias at low pT

Min. bias v2(pT) for strange hadronsK

0S and Λ data provided by Y

an Lu →

poste

ron

Thu

rsday

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 7

Centrality dependence of v2(pT)

• available high statistics allows for measurement of centrality dependence of v2(pT)

• comparison to Hydro model calculations shows deviations even at low pT

40-80%

10-40%

10-80%

0-10%0-10%

200 GeV Au+AuSTAR preliminary

K0S 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 v2(pT) for min. bias

PHENIX (open symbols): Phys. Rev. Lett. 91, 182301 (2003)

• scaled meson and baryon v2 agrees at intermediate pT

• high statistics measurements show deviation from ideal scaling

STAR preliminary200 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 K0S, Λ, and Ξ data

• NCQ scaling seems to work for different centralities as wellSee 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

v4 for Ξ- and Ξ+_

• ideal fluid dynamics would lead to v4/v22 = 0.5

[Borghini and Ollitrault, nucl-th/0506045; Kolb, Phys. Rev. C 68, 031902(R)]• Incomplete thermalisation? [Borghini et al., Phys. Lett. B 627, 49 (2005)]

Will v4/v22 be closer to 0.5 at LHC?

Ξ+Ξ v4

_

1.2 v22

0.5 v22

200 GeV Au+Au

min. bias (0–80%)

STAR preliminary• Observation of sizable

v4 with strong pT dependence

• v4 scales with ~1.2 v22

(as it for charged hadrons) [STAR: Phys. Rev. C 72 014904 (2005)]

v4

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 v2 at low pT:– show mass ordering– follow hydro model for minimum bias– deviate from hydro model predictions

for different centralities

• NCQ scaling of v2 at intermediate pT:– deviations from ideal NCQ scaling become

visible for minimum bias– indication for NCQ scaling even for different centralities

• v4 of Ξ-+Ξ+:– shows same scaling (1.2 v2

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: v2 vs. minv

• motivated by Borghini et al. [nucl-th/0407041]

• advantages over standard method:– only one fit per pT bin smaller systematic uncertainties

• method used for K0S, Λ, Ξ, ,

• standard method and v2 vs. minv method give consistent results and provide means for estimating systematic errors

)()()(

)(2cos()(

22

2

invinvBG

invSIG

invTOT

mBGSIG

BGmvm

BGSIG

SIGv

mv

SIG + BG

BG

BG(SIG+BG)

SIG (SIG+BG)

v2TOT(minv)

M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 14

Systematic error estimations for K0S and Λ

STAR preliminary STAR preliminary