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