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.