kai schweda lawrence berkeley national laboratory for the star collaboration

1 DPG spring meeting, Tübingen, March 2003

Kai Schweda

Lawrence Berkeley National Laboratory

for the STAR collaboration

Recent results from STAR at RHIC

Ultra-relativistic Heavy Ion Collisions, A+A

Spin structure of the nucleon, p+p

Ultra-peripheral Heavy Ion Collisions


Outline

Introduction

The STAR detector at RHIC

High-pt phenomena – probe the medium

Collective dynamics – bulk properties

Conclusions / Outlook


QCD on the Lattice

Lattice calculations predictTC ~ (170 15) MeV

1) Large increase in !

Large increase in Ndof:

Hadrons vs. partons

2) TC ~ 170 MeV robust!

Z. Fodor et al, JHEP 0203:014(02) C.R. Allton et al, hep-lat/0204010F. Karsch, Nucl. Phys. A698, 199c(02).


Heavy Ion CollisionsHeavy Ion Collisions

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

1) Initial condition: 2) System evolves: 3) Bulk freeze-out:

- baryon transfer - parton/hadron expansion - hadronic dof

- ET production - interaction cease

- Partonic dof Tth, <T>

Time

Plot: Steffen A. Bass, Duke University


The STAR Collaboration

400 Collaborators, 49 Institutions, 9 Countries


The STAR Detector

221 ),(tanh yxtz pppE

py


Au + Au Collisions at RHICAu + Au Collisions at RHIC

STARSTAR

Central Event

(real-time Level 3)


Centrality Definition

Au + Au @ 130 GeV

|| < 0.75

K.H. Ackermann et al. Phys. Rev. Lett. 86 (2001) 402

More central collisions

• No direct measure of

impact parameter

• Use track multiplicity

to define collision

centrality


Particle IdentificationParticle Identification

Reconstruct multi-strange resonances in 2 acceptance of STAR!


• Partons lose energy due to interactions with the mediumJ.D. Bjorken, FERMILAB-Pub-82/59-THY (1982).

• Energy loss is a measure of the gluon densityX.N. Wang and M. Gyulassy, Phys. Rev. Lett. 68, 1480 (1992).

Partonic Energy Loss

measure a) leading hadrons (inclusive) b) leading di-hadron correlations (back to back)

hadrons

leading particle suppressed

qq

Quenched dijets


RAA: binary-scaled Au+Au / p+p

1.0

1.0

1.0

Mor

e ce

ntra

l col

lisio

ns

p+p-reference: UA1, C. Albajar et al., NPB 335 (1990) 261.

RAA ~ unity for peripheral collisions, at pT > 2GeV/c

RAA < unity, decreasing with centrality ‘jet quenching’?

RA

A


RAA for Identified Particles

pT = 2-6GeV/c:

K0, show different behavior!

Meson / Baryon effect ?

Mass effect ?


Jets in High Energy CollisionsJets in High Energy Collisions

p+p dijet Central Au+Au Event

Find this …………………………………… in here


How to Find Jets

• Correlation with respect to leading particle (>4 GeV/c)

• Consider only particles above 2 GeV/c

• jet-cone at 0 ?

• back to back jet-cone

at ?

Px (GeV/c)

Py

(GeV

/c)

-4 -3 -2 -1 0 1 2 3 4

-4

-3

-2 -

1

0 1

2

3

4

Par

ton

Jet


Azimuthal Correlations

1) ‘jet cone’ at = 0

2) Strong back to back

correlations in

peripheral Au+Au

collisions

3) Suppression of back to

back correlations in

central collisions

‘jet-quenching’?C. Adler et al., Phys. Rev. Lett. 90, 082302 (2003).


High-pHigh-pTT Particle Production @ Particle Production @ RHICRHIC

Naïve Surface emission?

?

Suppression of inclusive particle

production (a)

Suppression of back-to-back

correlations in most central Au+Au

collision (b)

Consistent with jet quenching scenario:

• frequent interactions

• medium opaque to fast partons


Pressure, Flow, …Pressure, Flow, …

pdVdUd Thermodynamic identity

– entropy p – pressureU – energy V – volume= kBT, thermal energy per dof

In A+A collisions, interactions among constituentsand density distribution lead to: pressure gradient collective flow

number of degrees of freedom (dof) Equation of State (EOS) accumulative – partonic + hadronic


(anti-)Protons From RHIC(anti-)Protons From RHIC130 GeV Au + Au Collisions, STAR Preliminary

Mor

e ce

ntra

l col

lisio

ns

1) In central collisions, mt distributions become more convex

collective flow !

2) Within |y|<0.5, dN/dy and <pT> are flat boost invariant !

22 masspm TT


Transverse Collective Flow

At pT ~ 2-3 GeV/c, yields approach each other. Heavier mass particles show stronger collective flow effects !

At what stage does the collectivity develop at RHIC?


dN/dpdN/dptt Distributions Distributions

• Two-parameter fit describes yields of

, K, p,

• Tth = 90 10 MeV

• <t> = 0.55 0.08 c

][(

GeV

/

2

2

c)-1

dydp

Nd

T

][GeV/ cpT

K (dE/dx)

p

K (kink)

Tth=107±8 [MeV]

<t>=0.55±0.08 [c]

n=0.65±0.09

2/dof=106/90

STAR central data, preliminary

solid lines: fit range


Stronger transverse flow at RHIC:

T= 0.55(c)

More explosive expansion !

Kinetic Freeze-out SystematicKinetic Freeze-out Systematic

<t>

Tfo


T versus <t> Plane

1) In central collisions,

, K, p, (group-I)

are different from

multi-strange baryons and group-II.

2) In peripheral collisions, group-I moves

towards the local minimum of group-II.

Multi-strange particles seem to freeze-out

earlier than , K, p, !

Measure and to possibly access

partonic stage !


ConclusionsConclusions

Moderately high transverse momentum

- frequent interactions at RHIC

Low transverse momentum

- strong collective motion at RHIC

collectivity among quarks/gluons or hadrons?


OutlookOutlook

Discover partonic collectivity: spectra and v2 of

s D c

J/ ...

kai schweda lawrence berkeley national laboratory for the star collaboration

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