LBNL
Recent results Recent results from the STAR experimentfrom the STAR experiment
at RHICat RHIC
for the STAR collaboration
Lawrence Berkeley National Laboratory
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OutlineOutline
• STAR experiment at RHIC
• Physics results from sNN=130 GeV Au+Au collisions
• Very preliminary results from
sNN=200 GeV Au+Au
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Physics MotivationPhysics Motivation
• Goal– Study bulk
properties of matter under extremely high energy and particle density
– Information of observable come from Parton / hadron level
space
tim
e
hadron
parton
inelasticinteraction
Chemicalfreeze-out
elasticinteraction
Kineticfreeze-out
A
A
Ultra relativistic heavy ion collision isonly the tool to study this issue on the earth
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RHICRHIC
• Relativistic Heavy Ion Colliderat Brookhaven National Laboratory
PHENIX
PHOBOSBRAHMS
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STAR ExperimentSTAR Experiment
• Solenoidal Tracker At RHIC– ~40 Institutes/Universities– ~300 Collaborators
•One of large experiments at RHIC
•2 acceptance in
•Excellent particle Identification
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STAR DetectorSTAR DetectorYear 1
Central Trigger Barrel
Magnet
Coils
TPC Endcap & MWPC
ZDC
ZDC
RICH
yr.1 SVT ladder
Time Projection Chamber
4m
Silicon Vertex Tracker
FTPCs
Barrel EMC (install over 4 years)
Vertex Position Detectors
+ TOF patch
Year 2
Endcap EMC (half in 2003)
Silicon Strip Detector
Next year or later
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STAR EventSTAR Event
Tracks are reconstructed byonline tracking
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Particle IdentificationParticle Identification• dE/dx by TPC : ,K,p,d,He,……• Kink method :K
• RICH : 1-3 GeV/c for /K, 1.5-5 GeV/c for p
• Topology : K0s
• Combinatrics : 0……
K
p
e
|p/Z| [GeV/c]
dE/d
x
• TOF (year 2)• EMC (year 2)
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StatisticsStatistics
• Year 1– Minimum bias
• w/o vertex cut 0.9M events– Central
• w/o vertex cut 0.7M events
• Year 2– Minimum bias
• w/ vertex cut 2.6M events• w/o vertex cut 3.4M events
– Central• w/ vertex cut 4.7M events
– DST production is started as official version
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PublicationsPublications
• Elliptic Flow in Au+Au Collisions at sqrt(snn) = 130 GeV
K.H. Ackermann et al. Phys. Rev. Lett. 86 pp. 402-407 (2001).
• Midrapidity Antiproton-to-Proton Ratio from Au+Au sqrt(snn) = 130 GeV
C. Adler et al. Phys. Rev. Lett. 86 pp. 4778-4782 (2001).
• Pion Interferometry of sqrt(snn) = 130 GeV Au+Au collisions at RHIC
C. Adler et al. Phys. Rev. Lett. 87 , 082301 (2001).• Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions
at sqrt(snn) = 130 GeV
C. Adler et al. Phys. Rev. Lett. 87, 112303 (2001).
• Identified Particle Elliptic Flow in Au+Au Collisions at sqrt(snn) = 130 GeV
C. Adler et al. Phys. Rev. Lett. 87, 182301 (2001).
• Antideuteron and Antihelium production in Au+Au collisions at sqrt(snn) = 130 GeV
C. Adler et al. Phys. Rev. Lett. 87, 262301-1 (2001).
• Measurement of inclusive antiprotons from Au+Au collisions at sqrt(snn) = 130 GeV
C. Adler et al. Phys. Rev. Lett. 87, 262302-1 (2001).
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Ultra Relativistic Heavy Ion Ultra Relativistic Heavy Ion CollisionCollision
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1) Initial Condition - Baryon number transfer - ET production - partons dof
2) System Evolve - parton/hadron expansion
3) Bulk Freeze-out - hadrons dof - interactions stop
Momentum distribution
Particle ratio/yield
hadronization
Event anisotropy
Particle correlation (HBT)
Coalescence
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Particle Ratio / Chemical Freeze-Particle Ratio / Chemical Freeze-outout
• Chemical freeze-out– End of inelastic interactions– Information of number of particle is frozen
• The particle ratios are described statistical model– Hadron resonance ideal gas + decay effect– The data are described in SIS over SPS
energy (AA), and LEP (e+e-) and SppS (pp)
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Model of Chemical Freeze-outModel of Chemical Freeze-out
• Hadron resonance ideal gas– density of hadron i is
ch : Chemical freeze-out temperatureq : light-quark chemical potentials : strangeness chemical potentials : strangeness saturation factor Relation to quantum number
Baryon number B = 3qStrangeness S = q-s
Comparable particle ratios to experimental data
All resonances and unstable particles are decayed
Refs. J.Rafelski PLB(1991)333J.Sollfrank et al. PRC59(1999)1637
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Data vs. ModelData vs. Model
BRAHMS PHENIXPHOBOS STAR
Chemical freeze-out parametersTch = 170±4 MeVB =3q= 40±4 MeV
s = 1.1±2.0 MeVs = 1.09 ±0.06 2/dof = 16.7/9
2/dof = 12.2/8 w/o -/h-)
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Phase DiagramPhase Diagram
• Beam energy dependence– Temperature increases– Baryon chemical
potential decreases
• At RHIC– Being close to phase
boundary– Fully strangeness
equilibration (s~1)
at central collisions
parton-hadron phase boundary
<E>/<N>~1GeV, J.Cleymans and K.Redlich, PRC60 (1999) 054908
SPS
Lattice QCD predictions
Baryon Chemical Potential B [GeV]Neutron star
central collisions
RHIC130GeV
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ppTT Distribution / Kinetic Freeze-out Distribution / Kinetic Freeze-out
• Kinetic freeze-out– End of elastic interactions– Information of momentum is frozen
• Boltzmann distribution + flow effect
tanh 1r
nRrpxf ssr /),(
)0 ,sinh ,(cosh )0,,( rezrtu
No Boost
Boosted
Blast wave model;E. Schnedermann et al., PRC48(1993)2462
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ppTT Distribution from STAR Distribution from STAR
pT [GeV/c]
]G
eV/c
)[(
2
2-2
TT
dpdy
pn
d
K
(dE/dx)p
K
(dE/dx)K
(kink)
K (kink) p
STAR Preliminary
K0s
0.2 < pT < 2.4
STAR Preliminary
MT-M0 (GeV/c2)
Statistical error only
Central events
(top 14%)
K*0
0.4 < pT < 3.6
STAR Preliminary
STAR Preliminary
• Inverse slope parameter– Increasing
• with centrality• with particle mass
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ppTT Distribution vs. Centrality Distribution vs. Centrality
pT [GeV/c]
]G
eV/c
)[(
2
2-2
TT
dpdy
pn
d
K
(dE/dx) pK
(dE/dx)K
(kink)K (kink) p
STAR Preliminary
<Npart> for K, p345728092358180913581004 704 253
<Npart> for 34572899221415291024 634 353 202 94-------
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Centrality dependence of Centrality dependence of T T thth and and <<rr>>
• As a function of centrality– Tth ~ 100 MeV– <r> goes up then saturated– Flow profile changed?
• Selected similar centrality region in and K,p
K
pK
p
pT [GeV/c]
]G
eV/c
)[(
2
2-2
TT
dpdy
pn
d
38 115 224 347 <Npart>
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How about Strange Baryons?How about Strange Baryons?
• Comparison of fit result to and
• Model has large discrepancy with data in low pT– does not have
common Tth and r
with ,K,p,
Note: Vertical axis is not same with previous plot
STAR preliminaryCentral data
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Mass Dependence of <pMass Dependence of <pTT>>
• shows a deviation from common thermal freeze-out
Kinetic freeze-outmodel prediction
<>=0
- KRSX plot -
D
?
• Heavy particle is important!
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Bombarding Energy Bombarding Energy DependenceDependence
•From SPS to RHIC– Increasing flow–Decreasing temperature
–Longer time for cooling at RHIC?
Tth
[GeV
]< r
> [
c]
STA
R
PHE
NIX
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•Kinetic Freeze-out• Tth ~ 100 MeV, r ~0.55c in central collisions
• Strong transverse flow• Somehow long time for cooling
•Chemical Freeze-out• Tch ~ 170MeV, B ~ 40MeV• Fully strangeness equilibration in
central collisions
Summary of Chemical and Kinetic Freeze-Summary of Chemical and Kinetic Freeze-outout
data address early freeze-outof multi strangeness baryon!
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Ultra Relativistic Heavy Ion Ultra Relativistic Heavy Ion CollisionCollision
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1) Initial Condition - Baryon number transfer - ET production - partons dof
2) System Evolve - parton/hadron expansion
3) Bulk Freeze-out - hadrons dof - interactions stop
Momentum distribution
Particle ratio/yield
hadronization
Event anisotropy
Particle correlation (HBT)
Coalescence
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Event AnisotropyEvent Anisotropy
• The pressure gradient generates collective motion (aka flow) radial flow and anisotropic flow
• Hard process may dominant in high pT
x
y
p
patan
2cos2 v
Momentum spaceAlmond shape overlap region in coordinate space
y2 x2 y2 x2
x
z
y
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vv22 vs. Centrality vs. Centrality
• Central region follows Hydrodynamical model
Charged hadron mid-rapidity: ||<1.0
(PHOBOS : Normalized Paddle Signal)
Hydrodynamic limit
STAR: PRL86 (2001) 402
PHOBOS preliminary
Hydrodynamic limit
STAR: PRL86 (2001) 402
PHOBOS preliminary
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RQMD(v2.4)
Energy Dependence of vEnergy Dependence of v22
• Larger v2 at RHIC than at lower energy collisions
min-biascharged hadron
STARData
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Identified Particle vIdentified Particle v22
• Particle mass dependence– Typical Hydrodynamical type behavior
– Deviation in high pT region Hydrodynamical prediction
dashed solid
Tth [MeV] 135 20 100 24
<br> [c] 0.52 0.02 0.54 0.03
STAR PRL87, 182301 (2001)
pT [GeV/c]
Eve
nt
anis
otr
op
y v
2
STAR Preliminary
STAR preliminary
Hydrodynamical model results
J. Fu, LBNLP. Sorenson, UCLA
Kp
pT [GeV/c]1 2 3
Eve
nt
anis
otr
op
y v
2
0.2
0.1
0
0
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vv22 vs. p vs. pTT
Au+Au at 130 GeV
1) At pt >2 GeV/c, v2 saturates;
2) The saturation values increases with impact parameters;
STAR preliminary
K. Filimonov, LBNL
STAR preliminary
3) Clearly different from hydrodynamical
model(simply increasing with
pT
and no saturation) predictions.
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Particle CorrelationParticle Correlation
• Probe of the space time extent of heavy ion collisions
• Radius parameters– space-time geometry of
the emitting source– dynamical information
(e.g. collective flow)R
1
Hanbury-Brown Twisscorrelation
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Radius ParametersRadius Parameters
• Similar radius with SPS!• Strong space-momentum
correlation?
STAR data : PRL87(2001) 082301
cpT MeV/ 170correlation
RsideRout
Kt = pair Pt
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Radii vs. Radii vs. ppTT
• Blast wave model describes pT dependence– Consistent Tth and r
with them from spectra and v2
STAR PRL87(2001) 082301
Blast wave model : Mike Lisa, ACS Chicago, 2001
pT [GeV/c]
model:R=13.5 fm, =1.5 fm/cTth=0.11 GeV, r = 0.5 c• However……
– PHENIX data shows Ro/Rs is a constant
PHENIX: nucl-ex 0201008
line: kT dependence oftransverse flow
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CoalescenceCoalescence
• Production through final-state coalescence of antinucleons:
– BA • Small systems:
– Sensitive to size of produced (anti)nucleus• Large systems:
– Sensitive to geometry of system
• Antinucleus production– Direct pair production negligible– No background
where p = momentum / A
p
n
d
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Beam Energy Dependence of BBeam Energy Dependence of B22 and B and B33
B2 (SPS)
B2 (RHIC)1.10.1
B2 1
Veff
No DramaticIncrease in Volume!
B3(SPS)
B3 (RHIC)3.4 1.5
B3 1
Veff2
V(RHIC)
V(SPS)1.80.4
2
27
3
3
GeV10.)( 3.1.)( 3.24.8
csysstat
pd
NdE
3He (1.0<pT<5.0 GeV/c, |y|<0.8)
(0.5<pT<0.8 GeV/c, |y|<0.3)
2
23
3
3
GeV10.)( 3.0.)( 1.00.2
csysstat
pd
NdE
d
~50 times (SPS)~6×104 times (AGS)
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Coalescence Geometry Coalescence Geometry
• Thermal Coalescence Model– Thermal and chemical
equilibrium of coalescence source
• Hydro motivated density matrix formulation of coalescence – Calculate “homogeneity
volume” aka HBT
Model:A. Z. Mekjian, PRC 17, 1051 (1978)S. Das Gupta and A. Z. Mekjian, Phys. Rep. 72, 131 (1981).
Model:H. Sato and K. Yazaki, PL 98B, 153 (1981).
3.08.1/ 3 Hed
VV
3.02.2/ 3 Hed
VV
Model:R. Scheibl and U. Heinz, Phys. Rev. C 59, 1585 (1999).
3
fm 40600effd
V3
fm 503403
effHeV
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•Particle correlation (HBT)•Strong space-momentum correlation•No perfect model to describe the data
•Antinucleus / Coalescence•Large enhancement in yield over lower energies•No large volume increase over SPS•3He freeze out from smaller volume than d
SummarySummary
•Kinetic Freeze-out•Tth ~ 100 MeV r ~0.55c
•Strong transverse flow•long time for cooling?
•Chemical Freeze-out•Tch ~ 170MeV, B ~ 40MeV•Fully strangeness equilibration
•Event anisotropy•Strong anisotropic flow effect at RHIC!•Saturation of v2 at high pT
•Hydrodynamical picture works at low pT