Recent Results from STAR Tim Hallman Warsaw University November 28, 2003

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Recent Results from STAR Tim
HallmanWarsaw UniversityNovember 28, 2003
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Relativistic Heavy Ion Collider (RHIC)

• 2 concentric rings of 1740 superconducting
  magnets
• 3.8 km circumference
• counter-rotating beams of ions from p to Au
• max center-of-mass energy AuAu 200 GeV, pp 500
  GeV

RHIC Runs Run I AuAu at ?s 130 GeV Run II
AuAu and pp at ?s 200 GeV
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The STAR Detector
Magnet
Silicon Vertex Tracker
Coils
TPC Endcap MWPC
ZCal
ZCal
ZCal
BBCs
Endcap Calorimeter
Central Trigger Barrel TOF patch TOFr
Barrel EM Calorimeter
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The STAR Collaboration 49 Institutions, 500
People

• U.S. Labs
• Argonne, Lawrence Berkeley, and Brookhaven
  National Labs
• U.S. Universities
• UC Berkeley, UC Davis, UCLA, Caltech, Carnegie
  Mellon, Creighton, Indiana, Kent State, MIT,
  MSU, CCNY, Ohio State, Penn State, Purdue,
  Rice, Texas AM, UT Austin, Washington, Wayne
  State, Valparaiso, Yale
• Brazil
• Universidade de Sao Paolo
• China
• IHEP - Beijing, IPP - Wuhan, USTC,
• Tsinghua, SINR, IMP Lanzhou
• Croatia
• Zagreb University
• Czech Republic
• Nuclear Physics Institute

England University of Birmingham France
Institut de Recherches Subatomiques Strasbourg,
SUBATECH - Nantes Germany Max Planck
Institute Munich University of
Frankfurt India Bhubaneswar, Jammu, IIT-Mumbai,
Panjab, Rajasthan, VECC Netherlands NIKHEF Polan
d Warsaw University of Technology Russia
MEPHI Moscow, LPP/LHE JINR Dubna, IHEP -
Protvino
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The Phase Diagram of QCD
Early universe
quark-gluon plasma
critical point ?
Tc
Temperature
colour superconductor
hadron gas
nucleon gas
nuclei
CFL
Neutron stars
r0
vacuum
baryon density
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Hard Probes in Heavy-Ion Collisions

• New opportunity using Heavy Ions at RHIC ? Hard
  Parton Scattering
• ?sNN 200 GeV at RHIC
• 17 GeV at CERN SPS
• Jets and mini-jets
• High pt leading particles
• Azimuthal correlations
• Extend into perturbative regime
• Calculations reliable
• Scattered partons propagate through matter
• radiate energy (dE/dx x) in colored medium
• Interaction of parton with partonic matter
• Suppression of high pt particles jet quenching
• Suppression of angular correlations

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Partonic energy loss in dense matter
Thick plasma (Baier et al.)
Gluon bremsstrahlung
Thin plasma (Gyulassy et al.)

• Linear dependence on gluon density ?glue
• measure DE ? gluon density at early hot, dense
  phase
• High gluon density requires
  deconfined matter
• (indirect QGP
  signature !)

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What is a jet?
Jet A localized collection of hadrons which come
from a fragmenting parton
c
a
Parton distribution Functions Hard-scattering
cross-section Fragmentation Function
b
d
High pT (gt 2.0 GeV/c) hadron production in pp
collisions
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High pT Particle Production in AA


(According to pQCD)
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A key probe, new at RHIC hard scattering of
quarks and gluons
Nuclear Modification Factor
Nucleus-nucleus yield
ltNbinarygt/sinelpp
Another way to test
AA
If R 1 here, nothing new going on
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Jets in Heavy Ion Collisions at RHIC
Jet event in ee- collision
STAR AuAu collision
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Elliptic Flow at RHIC
Anisotropic (Elliptic) Transverse Flow

• The overlap region in peripheral collisions is
  not symmetric in coordinate space
• Almond shaped overlap region
• Easier for particles to emerge in the
• direction of x-z plane
• Larger area shines to the side
• Spatial anisotropy ? Momentum anisotropy
• Interactions among constituents generates
• a pressure gradient which transforms the initial
  spatial anisotropy into the observed momentum
  anisotropy
• Perform a Fourier decomposition of the momentum
  space particle distributions in the x-y plane
• v2 is the 2nd harmonic Fourier coefficient of the
  distribution of particles with respect to the
  reaction plane

Peripheral Collisions
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Anisotropic (Elliptic) Flow at RHIC
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Statistical Identification of jets in AA
Collisions

• You can see the jets in
• p-p data at RHIC

• Identify jets on a statistical basis in Au-Au
• Given a trigger particle with pT gt pT (trigger),
  associate particles with pT gt pT (associated)

STAR Preliminary AuAu _at_ 200 GeV/c 0-5 most
central 4 lt pT(trig) lt 6 GeV/c 2 lt pT(assoc.) lt
pT(trig)
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In Detail High-pT Spectra from STAR
Basic Idea peripheral collisions are pp like ?
no suppression central collisions hot and dense
matter ? suppression

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Comparison AuAu/pp at RHIC (STAR)
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Central/Peripheral Normalized by ?Nbin?
suppression
suppression
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Scaling pp to AA including the Cronin Effect

• At SPS energies
• High pt spectra evolves systematically from pp
  ? pA ? AA
• Hard scattering processes scale with the number
  of binary collisions
• Soft scattering processes scale with the number
  of participants
• The ratio exhibits Cronin effect behavior at
  the SPS
• No need to invoke QCD energy loss

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Peripheral AuAu data vs. ppflow
Back-to-back Jet Correlation Results

• Ansatz
• A high pTtriggered
• AuAu event is a superposition of a high pT
  triggered
• pp event plus anisotropic transverse flow
• v2 from reaction plane analysis
• A is fit in
• non-jet region
• (0.75 lt ?? lt 2.24)

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Central AuAu data vs. ppFlow
Back-to-Back Jet Correlation Results
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Supression of the Back-to-Back Correlation
Trigger pTgt4 GeV/c Correlate pTgt2 GeV/c
Away-side correlations disappear as collision
becomes more central

• Indication of opacity of the source?

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A dAucontrol experiment was been performed!
dAu
Run II AuAu results at full energy show
strong suppression ! dAu
controldata needed to distinguish
between different
interpretations
Central AuAu
Results show Observed suppression due to nature
of (new) produced matter ! not initial state
effects
0
90
180


?? Degrees
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Jet Quenching Result

PRL Cover Article Special
Colloquium June 17, 2003
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v2 vs. Centrality

• v2 is large
• 6 in peripheral collisions
• Smaller for central collisions
• Hydro calculations are in reasonable agreement
  with the data
• In contrast to lower collision energies where
  hydro over-predicts anisotropic flow
• Anisotropic flow is developed by rescattering
• Data suggests early time history
• Quenched at later times

Anisotropic transverse flow is large at RHIC
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v2 vs. pT and Particle Mass

• The mass dependence is reproduced by hydrodynamic
  models
• Hydro assumes local thermal equilibrium
• At early times
• Followed by hydrodynamic expansion

D. Teaney et al., QM2001 Proc.P. Huovinen et
al., nucl-th/0104020
Hydro does a surprisingly good job!
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v2 for High pt Particles
Phys.Rev.Lett. 90, 032301 (2003)
v2 is large but at pt gt 2 GeV/c the data starts
to deviate from hydrodynamics
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v2 predictions at high pT
pQCD inelastic energy loss parameterized hydro
component
distance of fast parton propogation
M. Gyulassy, I. Vitev and X.N. Wang
PRL 86 (2001) 2537
Jet 2
x
Jet 1

• The value of v2 at high pt sensitive to the
  initial gluon density
• Saturation and decrease of v2 as a function of pt
  at higher pt

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Elliptic flow as a function of transverse momentum
Could this effect be due to Surface emission?
V2(RP)
V2(2)
V2()
V2(4)
STAR Preliminary
Significant v2 up to 7 GeV/c in pt, the region
where hard scattering begins to dominate.
The data support the conclusion that we have
produced a medium that is dense, dissipative,
and exhibits strong collective behavior
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?, Ks v2 versus pT mass dependence or
particle type?
Results suggest a scaling of v2 versus particle
type (meson/baryon) rather than particle mass
? flow is built up at the partonic stage (?)
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HBT Correlations relative to the reactions plane
qside
qout
qlong ?
Heinz, Hummel, Lisa, Wiedemann PRC 044903 (2002)
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Centrality Dependence of HBT for AuAu at 200 GeV

• 15 bins, 72 CF's total for 12 ? bins
  3 centrality bins 2 pion signs
• 0.15 lt kT lt 0.65
• Oscillations exist in transverse radii
• for all bins

Results show oscillations which indicate
out-of-plane extended source and
short lifetime!
STAR Preliminary
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Probing Thermalization The HBT Puzzle
Hydro RQMD

• HBT radii pose serious difficulties for
  hydro models

STAR PRL 87, 082301 (2001) PHENIX PRL 88 192302
(2002)
Blast wave parameterization (Sollfrank
model) can approximately describe
data (spectra HBT) but emission
duration must be small ????
0.6 (radial flow), T 110 MeV
R 13.5 ? 1fm (hard-sphere)
?emission 1.5 ? 1 fm/c (Gaussian)
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In-plane/out-of-plane back-to-back jet suppression
STAR preliminary
STAR preliminary
Back-to-back suppression is larger in the
out-of-plane direction
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Results on Soft Physics

• Particle production per participant is large
• Total Nch 5000 (AuAu ?s 200 GeV) ? 20 in
  pp
• Nch/Nparticipant-pair 4 (central region) ?
  2.5 in pp
• ? AA is not a simple superposition of pp
• Energy density is high 4-5 GeV/fm3 (model
  dependent)
• System exhibits collective behavior (flow)
• ? strong internal pressure
• The system appears to freezes-out very fast
• explosive expansion
• Large system at freeze-out ? 2 ? size of nuclei

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Conclusions About Matter Produced at RHIC

• We have produced matter which exhibits
  features
• qualitatively different than has been
  observed before !
• The evolution is fast
• Transverse expansion with an average velocity of
  0.55 c
• Large amounts of anisotropic flow (v2) suggest
  hydrodynamic expansion and high pressure at early
  times in the collision history
• The duration of hadronic particle emission
  appears to be very short
• The produced matter appears to be opaque
• Saturation of v2 at high pT
• Suppression of high pT particle yields relative
  to p-p
• Suppression of the away side jet
• Statistical models describe the final state well
• Excellent fits to particle ratio data with
  equilibrium thermal models
• Excellent fits to flow data with hydrodynamic
  models that assume equilibrated systems
• Chemical freeze-out at about 175 MeV thermal
  freeze-out at 100 MeV

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Conclusions About Matter at RHIC

• Is there a phase with bulk properties which are
  Partonic ?
• The data on high pt suppression and correlations
  support the conclusion that we have produced a
  medium that
• is dense (pQCD theory ? many times cold nuclear
  matter density)
• is dissipative ( very strongly interacting)
• We need to show that
• dissipation and collective behavior occur at the
  partonic stage
• the system is deconfined and thermalized
• a transition occurs can we turn the effects off
  ?
• We need
• extended AuAu run needed to address several
  important probes
• that need large data sets ( e.g., pT
  dependence of suppression J/?, ?, open charm,
  heavy baryon / meson flow) also, species and
  energy scans to map the evolution of key
  observables.
• more guidance from theory (!) particularly on
  what to expect from hadronic
• scenarios

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Pressing the search with heavy flavor first
direct observation at RHIC of open charm in
dAu and min-bias AuAu collisions

Open charm a probe of initial conditions, and
possible equilibration at early times
D ? K??, dAu
D0 ? K?, dAu
A.Andronic, P.Braun-Munzinger,
K.Redlich, J.Stachel (nucl-th/0209035)
Star Preliminary
STAR Preliminary
y lt 0.25, 7 ltpt lt10 GeV/c
y lt 1, pt lt 4 GeV/c
Do c quarks thermalize? If yes, ratio of
charm hadrons yield changes from p-p to Au-Au
Ds most sensitive.
D ? K??, AuAu
STAR Preliminary
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The STAR Forward Pion Detector

• 10 lt Ep lt 80 GeV
• hp 4 (relative to d)

BNL, Penn State, IHEP-Protvino, UC
Berkeley/SSL, UCLA, ANL

• Run 3 Objectives
• Probe of Color Glass Condensate in dAu
• ? pT dependence of large h yield
• Improve understanding of dynamical origin of AN
• in p?p ? p0 X ?
• Collins effect ? sensitivity to transversity
• Sivers effect ? sensitivity to orbital motion
• twist-3 effect ? quark/gluon correlations
• Serve as local polarimeter at STAR IR

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STAR-Spin Results from Run 2
p? p ? p0 X , ?s 200 GeV
DIS2003

• Measured cross sections consistent with pQCD
  calculations
• Large spin effects observed for ?s 200 GeV
  pp collisions
• Status final analysis complete / paper in
  final preparation

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STAR Spin Rotator Magnet Tuning (Run III result)
RHIC polarimeter (CNI) establishes polarization
magnitude Local polarimeter (BBC) establishes
polarization direction at STAR.
Partial Snake Operation

• Use inner tiles of BBC as a Local
• Polarimeter monitoring pp collisions.
• Rotators OFF ? BBC L/R spin asymmetries
• comparable to RHIC polarimeter (CNI).
• Rotators ON ? adjust rotator currents to
• minimize BBC L/R and T/B spin
• asymmetries.

Double-blind intentional mis-tune check
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Projections for Sensitivity to DG for Run III and
Run IV
Longitudinal spin asymmetry (ALL) for
mid-rapidity jet production ? may be first
measurements directly sensitive to gluon
polarization.
Simulation based on Pythia trigger and jet
reconstruction efficiency EMC Barrel Coverage
includes 0 lt F lt 2p and 0 lt ? lt 1 Jet Trigger ET
gt 5 GeV over one patch (?? 1) X (?F 1)
Jet reconstruction cone algorithm (seed 1
GeV, R 0.7) Polarization 0.4, Luminosity 3
pb-1
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? ?
?u , ?d determination via ALPV in p p ? W
X _at_ ? s 500 GeV
At design luminosity, a 10-week runs (with ? 50
RHIC?STAR efficiency) apiece would yield

• ? s 200 GeV, P 0.7, L 8 ? 10 31 ? P 4?L
  ? eff dt ? 60 pb 1
• ? s 500 GeV, P 0.7, L 2 ? 10 32 ? P 4?L
  ? eff dt ? 150 pb 1

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Recent Results from STAR - Conclusions

• The first 3 runs in STAR have been an
  outstanding success producing a wealth of
• results and new physics even so, the
  most important achievements are still goals.
• The next 1-2 years will be extremely
  exciting.
• The highest priority scientifically for
  the coming run is to go as far as possible to
• determine the properties of the
  qualitatively new, dissipative medium discovered
  in
• central AuAu collisions at RHIC, and
  to study how these may change at a lower energy.
• The STAR spin program is off to a great
  start. Continued progress in the near-term is
  critical.
• STAR is now on a path to RHIC II. The
  strategy is to extend the scientific reach of the
  detector,
• maintaining the core capability of STAR
  to provide nearly complete event characterization
  
• over a wide range of central rapidity.
  Upgrades will be staged in such a way as to allow
  a
• vigorous physics program between now and
  2010. All signs are positive for the MRPC TOF
• Barrel project becoming an approved
  construction project in the next few months as
  the
• first step to RHIC II in STAR.

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Probing Chemical Equilibrium Yield Ratios
The STAR Experimental Program
Tch(RHIC) 175 7 MeV ?B(RHIC) 51 6
MeV Lattice (Karsch QM01) Tch(RHIC) 173 8
MeV, NF 2 Tch(RHIC) 154 8 MeV, NF 3
STAR Preliminary
13 Ratios 7 used 6 predicted
( P. Braun-Munzinger et al hep-ph/105229)

• No significant deviation seen from chemical
  thermal models

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Resonance production a tool for precision
studies of the late stages of the collision at
RHIC
?, ?, ?(892), ?(1385), ?(1520) ?, D
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The full spectrum of strange particles is
available in STAR
W
??
f
K0s
STAR Preliminary
L
X-
X
K