m. oldenburg star heavy flavor workshop october 13–15, 2005, lbnl 1 multi-strange hadron v 2 and...
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M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 1
Multi-strange Hadron v2
and Partonic Collectivity
Markus OldenburgLawrence Berkeley National Laboratory
STAR Heavy Flavor WorkshopOctober 13−15, 2005
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 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
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 3
Timeline of a heavy-ion collision
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
Time
partonic stage
thermal photons
hadr
oniz
atio
n
Ξ, ,
hadronic stage
, K, pdirect photons
initial collisions
hard scatterings,jet production
by S. Bass
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 4
Flow of strange hadrons
STAR:
• 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 stageNucl. Phys. A715, 458c (2003)
Phys. Rev. Lett. 92, 112301 (2004)Phys. Rev. Lett. 92, 182301 (2004)
(GeV
)
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 5
Importance of v2
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
Kaon coalescence effectively ruled out as a dominant channel for production at these energies.
STAR: Phys. Rev. C65, 041901(R) (‘02)Phys. Lett. B612, 181 (2005)
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 6
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 STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 7
Dataset
• system: Au+Au collisions
• energy: sNN = 200 GeV
• event sample: ~11 M events• centrality: 0–80 %• event plane
resolution ~75 %correction:
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 8
Particle identification and mass spectra
Ξ- and (anti- Ξ)+
identified via decay topology:Ξ Λ + and Λ p +
background estimated by rotating the Λ by 180° in the transverse plane
> 450,000 particles identified
Ω- and (anti-Ω)+
identified via decay topology: Λ + K and p +
background estimated by rotating the Λ by 180° in the transverse plane
> 13,000 particles identified
identified via decay topology: K+ + K-
background estimation by event mixing
> 10,000,000 particles identified
results by Sarah Blyth
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 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, Λ, Ξ, ,
and analysis
• standard method and v2 vs. minv method give consistent results
)()()(
)(2cos()(
22
2
invinvBG
invSIG
invTOT
mBGSIG
BGmvm
BGSIG
SIGv
mv
SIG + BG
BG
BG(SIG+BG)
SIG (SIG+BG)
v2TOT(minv)
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 10
v2 of multi-strange hadrons
_
_
baryons
mesons
Ξ+ΞΩ+Ω
200 GeVAu+Au
v 2
ndcbnp
nanf
Tv
)/)/(exp(1
)(2
• common fit to K and Λ
n = number of constituent quarks
[X. Dong et al.,
Phys. Lett. B597 (2004)]
pT/n > 0.75
GeV/c
2/ndf for NCQ=2
2/ndf for
NCQ=3
Ξ+Ξ 82.7/6 27.4/6
Ω+Ω 4.1/3 2.1/3
2.0/5 7.4/5
__
results by Sarah Blyth
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 11
Discussion of strange hadron v2 results
flows as strongly as other mesons.
•Collective flow is generated during the partonic stage already.
•The strange baryons Ξ and Ω show strong elliptic flow.
•The Ξ v2 clearly follows the baryon v2(pT).
STA
R p
relim
inary
Hydro: P. Huovinen,
priv. comm. (2004)
results by Sarah B
lyth
K0S and Λ
results by Yan Lu
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 12
Conclusions from the measurements
• v2 of multi-strange hadrons: , Ξ, 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?
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 13
Timeline of a heavy-ion collision
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
Time
partonic stage
thermal photons
hadr
oniz
atio
n
Ξ, ,
hadronic stage
, K, pdirect photons
initial collisions
hard scatterings,jet production
production of heavy quarks
by S. Bass
M. Oldenburg STAR Heavy Flavor Workshop — October 13–15, 2005, LBNL 14
Heavy-Flavor QuarksM
ass
(MeV
/c2 )
106
105
104
103
102
10
1
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.
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