Multistrange Hadron v2 and Partonic Collectivity

1
Multi-strange Hadron v2 and Partonic
Collectivity

• Markus Oldenburg
• Lawrence Berkeley National Laboratory
• STAR Heavy Flavor Workshop
• October 13-15, 2005

2
Overview

• Motivation on why to measure
• v2 of multi-strange hadrons
• Analysis details and technique
• Data and results
• Discussion
• Conclusion
• Outlook
• from multi-strange to heavy flavor

3
Timeline of a heavy-ion collision
by S. Bass
4
Flow of strange hadrons

• freeze-out of multi-strange hadrons
• - at higher
• temperature Tfo
• - with lower
• collective
• velocity ??T?
• small cross section 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)
5
Importance of ? v2
STAR Phys. Rev. C65, 041901(R) (02) Phys.
Lett. B612, 181 (2005)
Kaon coalescence effectively ruled out as a
dominant channel for ? production at these
energies.

• ? is a true signal from the early stage of the
  collision!
• anisotropic flow measurement of ? will conclude
• type of the system at an early stage
• partonic vs. hadronic
• origin of observed scaling at intermediate pT
• mass vs. particle type

6
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

7
Dataset

• system AuAu collisions
• energy ?sNN 200 GeV
• event sample 11 M events
• centrality 080
• event plane
• resolution 75
• correction

8
Particle identification and mass spectra

• ?
• identified via decay topology
• ? K K-
• background estimation by event mixing
• gt 10,000,000 particles identified

O- and (anti-O) identified via decay
topology ? ? ? K and ? ? p ? background
estimated by rotating the ? by 180 in the
transverse plane gt 13,000 particles identified
?- and (anti- ?) identified via decay
topology ? ? ? ? and ? ? p ? background
estimated by rotating the ? by 180 in the
transverse plane gt 450,000 particles identified
? results by Sarah Blyth
9
New 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
• new method used for K0S, ?, ?, ?, and ? analysis
• standard method and v2 vs. minv method give
  consistent results

SIG BG
BG
BG (SIGBG)
SIG (SIGBG)
v2TOT(minv)
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v2 of multi-strange hadrons
_

• common fit to K and ?
• n number of constituent quarks
• X. Dong et al.,
• Phys. Lett. B597 (2004)

v2
?? OO ?
_
baryons
mesons
_
200 GeV AuAu
_
? results by Sarah Blyth
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Discussion of strange hadron v2 results
K0S and ? results by Yan Lu
STAR preliminary
? results by Sarah Blyth
Hydro P. Huovinen, priv. comm. (2004)

• ? flows as strongly as other mesons.
• Collective flow is generated during the partonic
  stage already.

• The strange baryons ? and O show strong elliptic
  flow.
• The ? v2 clearly follows the baryon v2(pT).

12
Conclusions from the measurements

• v2 of multi-strange hadrons
• ?, ?, and ? show strong elliptic flow.
• Their behavior is similar to the other mesons and
  baryons.
• They flow as strongly as the other particles.
• NCQ scaling of v2
• observed scaling is a meson?baryon, not a mass
  effect!

• Collectivity develops early among partons!
• Partonic Collectivity at RHIC

Thermalization?
13
Timeline of a heavy-ion collision
by S. Bass
14
Heavy-Flavor Quarks
B. Mueller, nucl-th/0404015.

• Even in a QGP with chiral restoration, the c, b
  (and t) quarks stay heavy.

• If charm quarks show collective behavior ( flow)
  the must have suffered frequent interactions with
  the light quarks u, d, s.
• The light quarks u, d, s must be thermalized.