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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
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Outline
Introduction
The STAR detector at RHIC
High-pt phenomena – probe the medium
Collective dynamics – bulk properties
Conclusions / Outlook
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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).
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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
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The STAR Collaboration
400 Collaborators, 49 Institutions, 9 Countries
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The STAR Detector
221 ),(tanh yxtz pppE
py
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Au + Au Collisions at RHICAu + Au Collisions at RHIC
STARSTAR
Central Event
(real-time Level 3)
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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
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Particle IdentificationParticle Identification
Reconstruct multi-strange resonances in 2 acceptance of STAR!
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• 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
Quenched dijets
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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
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RAA for Identified Particles
pT = 2-6GeV/c:
K0, show different behavior!
Meson / Baryon effect ?
Mass effect ?
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Jets in High Energy CollisionsJets in High Energy Collisions
p+p dijet Central Au+Au Event
Find this …………………………………… in here
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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
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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).
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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
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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
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(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
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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?
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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
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Stronger transverse flow at RHIC:
T= 0.55(c)
More explosive expansion !
Kinetic Freeze-out SystematicKinetic Freeze-out Systematic
<t>
Tfo
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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 !
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ConclusionsConclusions
Moderately high transverse momentum
- frequent interactions at RHIC
Low transverse momentum
- strong collective motion at RHIC
collectivity among quarks/gluons or hadrons?
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OutlookOutlook
Discover partonic collectivity: spectra and v2 of
s D c
J/ ...
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