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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
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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
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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
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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
)
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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!
_
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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
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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]
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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%)
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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
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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
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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?
_
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M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 12
Backup
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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)
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M. Oldenburg Strange Quark Matter 2006 — March 26–31, Los Angeles, California 14
Systematic error estimations for K0S and Λ
STAR preliminary STAR preliminary