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TJH Warsaw University, Nov 28, 2003 TJH Warsaw University, Nov 28, 2003
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Recent Results from STAR
Tim Hallman
Warsaw UniversityNovember 28, 2003
TJH Warsaw University, Nov 28, 2003 TJH Warsaw University, Nov 28, 2003
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RHIC BRAHMSPHOBOS
PHENIXSTAR
AGS
TANDEMS
Relativistic Heavy Ion Collider (RHIC)
2:00 o’clock
4:00 o’clock6:00 o’clock
8:00 o’clock
10:00 o’clock
STARPHENIX
RHIC
AGS
LINACBOOSTER
TANDEMS
9 GeV/uQ = +79
1 MeV/uQ = +32
HEP/NP
g-2
U-lineBAF (NASA)
PHOBOS12:00 o’clock BRAHMS
• 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 RunsRun I: Au+Au at s = 130 GeVRun II: Au+Au and pp at s = 200 GeV
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ZCal
Central Trigger Barrel+ TOF patch+ TOFr
FTPCs (1 + 1)
Time Projection Chamber
Barrel EM Calorimeter
Vertex Position Detectors
Magnet
Coils
TPC Endcap & MWPC
Endcap Calorimeter
ZCal ZCal
Silicon Vertex Tracker *
The STAR Detector
BBCs
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The STAR Collaboration: 49 Institutions, ~ 500 People
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:
NIKHEFPoland:
Warsaw University of TechnologyRussia:
MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP - Protvino
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 A&M, 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
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The Phase Diagram of QCDT
em
per
atu
re
baryon density
Neutron stars
Early universe
nucleinucleon gas
hadron gascolour
superconductor
quark-gluon plasmaTc
0
critical point ?
vacuum
CFL
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• 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
Hard Probes in Heavy-Ion Collisions
hadrons
q
q
hadronsleadingparticle
leading particle
schematic view of jet production
QGP
Vacuum
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Partonic energy loss in dense matter
Thick plasma (Baier et al.):
glueSglue
Debye
sRBDMS
q
vLqC
E
2
2
ˆ
~ˆ4
L
ELogrdCE jet
glueSRGLV 23 2
,
Linear dependence on gluon density glue: • measure E gluon density at early hot, dense phase
High gluon density requires deconfined matter (“indirect” QGP signature !)
Gluon bremsstrahlung
Thin plasma (Gyulassy et al.):
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What is a jet?
hadrons
hadrons
leading particle
Jet: A localized collection of hadrons which come from a fragmenting parton
c
chbbaa
abcdba
T
hpp
z
Dcdab
td
dQxfQxfdxdxK
pdyd
d
0
/222
)(ˆ
),(),(
Parton distribution Functions
Hard-scattering cross-section
Fragmentation Function
a
b
c
d
High pT (> ~2.0 GeV/c) hadron production in pp collisions:
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High pT Particle Production in A+A
Intrinsic kT , Cronin Effect
Parton Distribution Functions
Shadowing, EMC Effect
Fragmentation Function leading
particle suppressed
Partonic Energy Loss
c
d
hadrons
a
b
Hard-scattering cross-section
(According to pQCD…)
c
ccch
c
c
bbBaaA
ba
bBbaAa
baabcd
baT
hAB
z
QzD
z
zPd
cdabtd
d
QxSQxS
gg
QxfQxf
dddxdxKpdyd
dN
),(
)(
)(ˆ
),(),(
)()(
),(),(
2*0/
1
0
*
22
2/
2/
222
kk
kk
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ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
<Nbinary>/inelp+p
Nucleus-nucleus yield
Nuclear Modification Factor:
AA
If R = 1 here, nothing “new”going on
A key probe, new at RHIC: hard scattering of quarks and gluons
peripheralbinperipheral
centralbincentral
TCPNYield
NYieldpR
/
/)(
Another way to test:
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Jets in Heavy Ion Collisions at RHIC
Jet event in eecollision STAR Au+Au collision
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• 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
Anisotropic Flow
x
yz
px
py
Anisotropic (Elliptic) Transverse Flow
Elliptic Flow at RHIC
Peripheral Collisions
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px
py
Anisotropic (Elliptic) Flow at RHIC
2cos2 vx
y
p
patan
Non-central Collisions
Anisotropic Flow
x
yz
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STAR Preliminary Au+Au @ 200 GeV/c0-5% most central
4 < pT(trig) < 6 GeV/c2 < pT(assoc.) < pT(trig)
• Identify jets on a statistical basis in Au-Au• Given a trigger particle with pT > pT (trigger),
associate particles with pT > pT (associated)
),(11
),(2 NEfficiencyN
CTRIGGER
You can see the jets in p-p data at RHIC
Statistical Identification of jets in AA Collisions
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In Detail: High-pT Spectra from STAR
Basic Idea:peripheral collisionsare p+p like no suppression
central collisionshot and dense matter suppression
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Comparison Au+Au/p+p at RHIC (STAR)
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Central/Peripheral Normalized by Nbin
suppressionsuppression
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Binary scaling
Scaling pp to AA … including the Cronin Effect
1Yield
NYield
pp
centralbinarycentral /
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 Au+Au data vs. pp+flow
C2(Au Au) C2(p p) A *(1 2v22 cos(2))
Ansatz: A high pTtriggered Au+Au event is a superposition of a high pT triggered p+p event plus anisotropic transverse flow
v2 from reaction plane analysis
“A” is fit innon-jet region (0.75 < || < 2.24)
Back-to-back Jet Correlation Results
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Central Au+Au data vs. pp+Flow
C2(Au Au) C2(p p) A *(1 2v22 cos(2))
Back-to-Back Jet Correlation Results
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C2(Au Au) C2(p p) A *(1 2v22 cos(2))
• Indication of opacity of the source?
Away-side correlations disappear as collision becomes more central
Trigger: pT>4 GeV/cCorrelate: pT>2 GeV/c
Supression of the Back-to-Back Correlation
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A d+Au“control” experiment was been performed!
Results show:Observed suppressiondue to nature of (new)
produced matter !
not initial state effectsPedestal&flow subtracted
Run II AuAu results at full energy show strong suppression !
d+Au “control”data needed to distinguish between different interpretations
0 90 180 Degrees
d+Au
CentralAuAu
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Jet Quenching Result
PRL Cover Article
Special ColloquiumJune 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 timesAnisotropic transverse flow is large at RHIC
Phys.Rev.Lett. 86, (2001) 402
more central
Hydro predictions
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v2 vs. pT and Particle Mass
D. Teaney et al., QM2001 Proc.P. Huovinen et al., nucl-th/0104020
Hydro does a surprisingly good job!
Preliminary
• The mass dependence is reproduced by hydrodynamic models
– Hydro assumes local thermal equilibrium
– At early times– Followed by
hydrodynamic expansion
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v2 for High pt Particles
v2 is large … but at pt > 2 GeV/c the data
starts to deviate from hydrodynamics
Phys.Rev.Lett. 90, 032301 (2003)
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v2 predictions at high pT
M. Gyulassy, I. Vitev and X.N. Wang
PRL 86 (2001) 2537
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
pQCD inelastic energy loss + parameterized hydro component
y
x
distance of fast parton propogation
Jet 1
Jet 2
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Elliptic flow as a function of transverse momentum
?
Could this effect be dueto Surface emission?
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
V2(4)V2(2)V2(RP)
V 2(%)
STAR Preliminary
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Λ˚, K°s 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
What we measure?HBT radii as a function of emission angle
reactionplane
What we expect to see?2nd-order oscillations in HBT radii
Rside2
Why we're interested?The size and orientation of the source at freeze-out places tight constraints on expansion/evolution
What should be rememberedAt finite kT, we don't measure the entire source size. We measure "regions of homogeneity" and relating this to the full source size requires a model dependence.
qoutqside
qlong
Heinz, Hummel, Lisa, Wiedemann PRC 044903 (2002)
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Centrality Dependence of HBT for AuAu at 200 GeV
= 0°
90°
Rside (large)
Rside (small)
15° bins, 72 CF's total for 12 bins × 3 centrality bins ; × 2 pion signs
0.15 < kT < 0.65
Oscillations exist in transverse radii for all bins
Results show oscillations whichindicate out-of-plane extended source and short lifetime!
STAR Preliminary
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“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)
STAR PRL 87, 082301 (2001)PHENIX PRL 88 192302 (2002)
STAR 130 GeV
PHENIX 130 GeV
Hydro + RQMD
Probing Thermalization: The HBT Puzzle
HBT radii pose serious difficulties for hydro models
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In-plane/out-of-plane back-to-back jet suppression
STAR preliminarySTAR 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 (Au+Au s = 200 GeV) ~ 20 in p+p
• Nch/Nparticipant-pair ~ 4 (central region) ~2.5 in p+p
A+A is not a simple superposition of p+p
– 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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Open charm: a probe of initial conditions, and possible equilibration at early times
Pressing the search with heavy flavor: first direct observation at RHIC of open charm in d+Au and min-bias Au+Au collisions
D0 K, d+AuD± K, d+Au
|y| < 1, pt < 4 GeV/c | y |< 0.25, 7 <pt <10 GeV/c Star Preliminary
0.0130.0003J//D0
0.1730.14c+/ D0
0.3930.20Ds+/ D0
0.4550.33D+/ D0
Au-Au
Thermal*
Pythia
p-p 200 GeV
Do c quarks thermalize? If yes, ratio of charm hadrons yield changes from p-p to Au-Au ; Ds
+ most sensitive.
A.Andronic, P.Braun-Munzinger, K.Redlich,J.Stachel (nucl-th/0209035)
STAR Preliminary
D± K, Au+Au
STAR Preliminary
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The STAR Forward Pion Detector
Run 3 Objectives:
• Probe of Color Glass Condensate in d+Au pT dependence of large yield
• Improve understanding of dynamical origin of AN
in p+p 0 +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
East of STAR
Top
Bottom
North South
BNL, Penn State, IHEP-Protvino, UC Berkeley/SSL, UCLA, ANL
d+Au +X, sNN = 200 GeV
• 10 < E < 80 GeV
• ~ 4 (relative to d)
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STAR-Spin Results from Run 2
• 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
DIS2003
p + p + X , s = 200 GeV
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OFF Pvert
ON Plong
STAR spin rotator:
Mistuned rotators
STAR Spin Rotator Magnet Tuning (Run III result)
L R
T
B*
BBC West
BBC East
InteractionVertex
3.3<||< 5.0
• 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.
RHIC polarimeter (CNI) establishes polarization magnitude; Local polarimeter (BBC) establishes polarization direction at STAR.
“Double-blind” intentional mis-tune check
Partial Snake Operation
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Projections for Sensitivity to G for Run III and Run IV
Longitudinal spin asymmetry (ALL) for mid-rapidity jet production
may be first measurements directly sensitive to gluon polarization.
Jet reconstruction: cone algorithm (seed = 1 GeV, R = 0.7)
Polarization 0.4, Luminosity: 3 pb-1
Simulation based on Pythia + trigger and jet reconstruction efficiencyEMC Barrel Coverage includes 0 < Φ < 2π and 0 < η < 1Jet Trigger: ET > 5 GeV over one patch (Δη = 1) X (ΔΦ = 1)
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Future STAR Spin Physics GoalsFuture STAR Spin Physics Goals
G (x) determination via ALL in p + p + jet + X
u , d determination via AL
PV in p + p W ± + X @ s = 500 GeV
– –
At design luminosity, a 10-week runs (with 50% RHICSTAR efficiency) apiece would yield:
s = 200 GeV, P = 0.7, L = 8 10 31 P 4L eff dt 60 pb –1
s = 500 GeV, P = 0.7, L = 2 10 32 P 4L eff dt 150 pb –1
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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 Au+Au 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.
Recent Results from STAR - Conclusions
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Probing Chemical Equilibrium: Yield Ratios
STAR Preliminary
• No significant deviation seen from chemical thermal models
13 Ratios7 used
6 predicted
( P. Braun-Munzinger et al: hep-ph/105229)
The STAR Experimental Program
Tch(RHIC) 175 ± 7 MeVB(RHIC) 51 ± 6 MeV
Lattice: (Karsch QM01)
Tch(RHIC) 173 ± 8 MeV, NF = 2Tch(RHIC) 154 ± 8 MeV, NF = 3
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Resonance production: a tool for precision studies of the late stages of the collision at RHIC
STAR Preliminary
0.8 pT 0.9 GeV/c
|y| 0.5
pp Minimum Bias Au+Au 40% to 80%
1.2 pT 1.4 GeV/c
|y| 0.5
STAR Preliminary K*0
*(1520)
STAR preliminary p+p at 200 GeV
, , *(892), *(1385),*(1520), D*
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The full spectrum of strange particles is available in STAR
K0s
STAR Preliminary