Centrality Dependence of Azimuthal Anisotropy of Strange Hadrons in 200 GeV Au Au Collisions

1
Centrality Dependence ofAzimuthal Anisotropyof
Strange Hadrons in 200 GeV AuAu 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 2631, University of California, Los
  Angeles, USA

2
Overview

• Motivation
• Analysis details and technique
• Data and results for v2 and v4
• Discussion
• Conclusions

3
Elliptic flow v2

• non-central collisions azimuthal anisotropy in
  coordinate-space
• interactions ? asymmetry in momentum-space
• sensitive to early time in the systems evolution
• Measurement Fourier expansion of the azimuthal
  pT distribution

4
Flow of strange hadrons

• 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 stage

STAR
Nucl. Phys. A715, 458c (2003) Phys. Rev. Lett.
92, 112301 (2004) Phys. Rev. Lett. 92, 182301
(2004)
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Dataset and analysis method

• system AuAu collisions
• energy ?sNN 200 GeV
• event sample
• 13.3 M events 080
• 6.6 M events 4080
• 5.0 M events 1040
• 19 M events 010
• event plane resolution
• 76 for 080
• 66 for 4080
• 82 for 1040
• 69 for 010

• analysis method v2 vs. minv
• motivated by Borghini et al. nucl-th/0407041
• detailed studies regarding systematic
  uncertainties still underway
• for K0S and ??
• 5 error on v2 for pTlt4 GeV/c
• rising up to 2530 at 4ltpTlt6 GeV/c
• possible significant non-flow contribution for
  pTgt5 GeV/c
• Only statistical errors shown in this
  presentation!

_
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Min. bias v2(pT) for strange hadrons
K0S and ? data provided by Yan Lu ? poster on
Thursday

• mass ordering at low pT
• standard Hydro calculation Tch165 MeV,
  Tkin130 MeV
• P. Huovinen, private communication
• model works reasonably well for min. bias at low
  pT

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Centrality dependence of v2(pT)
Hydro model results by P. Huovinen, private
communication

• available high statistics allows for measurement
  of centrality dependence of v2(pT)
• comparison to Hydro model calculations shows
  deviations even at low pT

K0S and ? data provided by Yan Lu ? poster on
Thursday
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NCQ scaling of v2(pT) for min. bias

• scaled meson and baryon v2 agrees at intermediate
  pT
• high statistics measurements show deviation from
  ideal scaling

PHENIX (open symbols) Phys. Rev. Lett. 91,
182301 (2003)
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Centrality dependence of NCQ scaling

• polynomial fit through K0S, ?, and ? data
• NCQ scaling seems to work for different
  centralities as well

See Yan Lus poster on Thursday!
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v4 for ?- and ?
_
v4
_
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
0.5 v22
200 GeV AuAu
min. bias (080)

• 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?
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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 ?-?
• shows same scaling (1.2 v22) as other particle
  species
• Hint for incomplete thermalisation?

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

SIG BG
BG
BG (SIGBG)
SIG (SIGBG)
v2TOT(minv)
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Systematic error estimations for K0S and ?