Recent Results from STAR

Rene Bellwied, Wayne State, for the STAR Collaboration

Thermalization & Timescales

High pt physics

Fluctuations 130 to 200 GeV comparison

STAR’s strength

• STAR can map out the time, space and kinematic evolution of the colliding system by reconstructing hadronic probes over a large range of momentum and over 2in space. The coverage potentially allows to measure variables on an event-by-event basis.

STAR’s Physics in the first two years(i.e. the topics of my talk)

• The Evolution of the System (i.e. Thermalization, Expansion, Kinetic Freeze-Out, Time Scales)

•hadron production (strange and non-strange)

•flow (radial and elliptic) and HBT, balance functions

•The Critical Point

•Fluctuations

•The Early Conditions

•High pt physics

•Jet Quenching/Partonic Energy Loss

T = 190 MeV

T = 300 MeV

Tp = 565 MeV

mid-rapidity

Spectra via dE/dx and V0 topology

Will reach out to 5 GeV/c with Year-2 stats

Measuring yields and mt spectra up the

baryon

Preliminary

dN(-++) /dy = 0.64±0.14

dN-/dy = 0.32±0.09

dN+/dy = 0.34±0.09

Do yields (ratios) agree with the statistical model picture ?

Thermal fit prediction using all ratio except

/h-, /h-, /Thermal statistical model

fits particle ratios

ch =170±10 MeVB=48±10 MeVS=2.3±5.1 MeVS=0.99±0.11

/ (fit) = 0.96 0.07

M.Kaneta (LBNL)

STAR Preliminary

/ h(fit) = 0.00113 0.0007

/ (exp) = 0.95 0.15

/ h(exp) = 0.00127 + 0.0004

Wroblewski factor evolution(Strangeness Excitation

Function)

Wroblewski factordependent on T and B

dominated by Kaons

Peaks at 30 A GeV in AA collisions due to strong B dependence

mesons

baryons

hidden strangeness mesons

PBM et al., hep-ph/0106066

total

Preliminary

?

Multi-strangeness Excitation function

Preliminary

Temperature and collective behavior

Stronger radial flow at RHIC than SPS

Strange baryons freeze-out earlier

(stat. errors only)STAR Preliminary

What is the inverse slope parameter ?

T = 411±46MeV(stat.)Additional systematic error ~ 10%

Radial Flow at 200 GeV

K p

5% Central Events

60-80% Peripheral Events

p+p DataSTAR preliminary

Strangeness high pt spectra(Year-1)

Interesting agreementwith PHENIX result ofpbar vs. pion spectra

Simple hydrodynamicexplanation or more fundamental ?

In year-2:Lambdas out to 5 GeV/cCharged Kaons out to10 GeV/c via kinks

Ratio Comparison to pQCD (Y-2)

Done with 5% of totalstatistics.

With factor 20 more datathe ratio will go out to5.5 GeV/c with an errorbar comparable to the 2 GeV/c error bar in thisplot

Almond shape overlap region in coordinate space

y2 x2 y2 x2

2cos2 vx

y

p

patan

v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane

Origin: spatial anisotropy of the system when created and rescattering of evolving system. spatial anisotropy momentum anisotropy

Anisotropic (Elliptic) Flow – What is it ?

V2 pt dependence

v2(pt) - STAR Collaboration, PRL 87 (2001) 182301

v2 - STAR Collaboration, PRL 86 (2001) 402

Centrality dependence of v2(pt) at large pt

Inclusive pt distribution for negative hadrons

Hadron suppression factor = 2 relative to scaled NN (UA1) or peripheral

hadrons

q

q

hadrons leadingparticle

leading particle

Year-1 data

Two-Particle Azimuthal Correlations

Can’t fully reconstruct jets in Au+Au events Identify jet candidates using trigger particle with 4<pT<6 GeV/c. Associate with other charged tracks with 2<pT<pT(trig).= UA1 method (PLB 118, 173 (1982), pp @ √s = 540 GeV, Jet

Cone: <30˚ |y| < 0.5 Azimuthal correlation function:

Efficiency for finding the trigger particle cancels in definition of C2

No need for mixed events due to full azimuthal coverage

C2 ()1

N trigger

1

efficiencyd()N ( ,)

Jet analysis @ 130 GeV

130 GeV:= 0.27+-0.09 radArea = 4.9+-1.7 %

Area in agreementwith pp data(no statement about jet suppression)

Area = % of charged particles with pt>4 GeV/c that have an association

Effects of jet quenching and charge dependence

Quenching has negligible effect on angular correlations near = 0.

Data

HIJING

opposite sign/same sign ≈ 2.6+-0.7property of LUND fragmentation picture

Time scales of the collision

hadronization

initial state

pre-equilibrium

QGP andhydrodynamic expansion

hadronic phaseand freeze-out

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM1 fm/c 5 fm/c 10 fm/c 50 fm/c time

dN/dt

Chemical freeze outKinetic freeze out

Measurements:HBTBalance functionResonances

Year-1 pion HBT

Published STAR HBT data Hydro does not describe

the data Blast wave with “default”

parameters does Pt dependence of radii well

reproduced Thanks to space-momentum

correlations

Striking feature: short emission duration = 1.5 fm/c

STAR data

Blast wave

Year 1 -K correlation functions Fitting in pair rest frame

Pionsource

KaonSource

Separation between and K andBoost to pairRest frame

Pion <pt> = 0.12 GeV/c

Kaon <pt> = 0.42 GeV/c

Out ratio 1 and K

source are shifted

Side and Long ratio ~1 as they must be

r* = (r - t) tpion-tkaon < 5.6 fm/c rkaon-rpion < 4.2 fm

<r*pion-r*kaon> = -6.3 fm (in pair rest frame )

Data agree with blast wave

RQMD overestimates the shift

From Rlong: Kinetic = 8-10 fm/c

Simple Sinyukov formula (Steve Johnson) Rlong2 = 2 T/mT

= 10 fm/c (when T=110 MeV)

B. Tomasik fit (~3D blast wave = 8 fm/c (++) = 9.2 fm/c (--)

Balance function principle

For each charge +Q, there is one extra balancing charge –Q.

Charges: electric, strangeness, baryon number

Hadronization

Early =Large Delayed =Small

Preliminary data on +- pairs

Bjorken + thermal model to reproduce data f = 15 fm/c > from Rlong (8-

10) Extremely low Tf (Tf = 45

MeV)Poor agreement with other measured parameters Ti = 175 MeV

From particle ratios i = 9-10 fm/c Tf = 100-110 MeV

From spectra f-i = = 2-4 fm/c

Resonance survival rate

UrQMD: signal loss in invariant mass reconstruction

K*(892) (1520)

SPS (17 GeV) [1] 66% 50% 26%

RHIC (200GeV) [2] 55% 30% 23%

Strange resonances studied with STAR K*(892)

Lifetime = 3.9 fm/c (1520)

Lifetime = 12.8 fm/c Rescattering

between chemical and kinetic freeze-out may wash out the resonance signal Sensitive to = Kinetic - Chemical

K*0 K+ + -

multiplicity for |y| <0.5 K*0 |y|<0.5 = 10.0 0.8 25%

Upper limit estimation: dN/dy preliminary

(1520) |y|<1 < 1.2 at 95% C. L.

(1520) p + K-

Survival rate interpretation according to

Rafelski

Upper limit

Combining both K* and (1520) results ~ 0-3 fm/c

Caveats: thermal fits

reproduce K* yield with T ~ 175 MeV (not Tchem~100 MeV!)

No need to destroy K* Possible K*

regeneration

Time scales according to STAR data

1 fm/c 5 fm/c 10 fm/c 20 fm/ctime

dN/dt

Chemical freeze outKinetic freeze out

Balance function (require flow)

Resonance survival

Rlong (and HBT wrt reaction plane)Rout, Rside

Comparison of <pt> fluctuations in two acceptance bins

Fluctuations are multiplicity dependent. Construct variable pt that allows to fold out the N dependence

pt = ptpt

Inclusive varianceDeviation of event Pt from event average

Conclusions

Yields, slope parameters, and ratios for all measured hadrons are well described by statistical models

Time scale for emission seems short. Two particle correlations are best described by blast wave parametrization.

Non statistical fluctuations are small but not zero. Flow and particle production at high pt seems to indicate a

new regime and potentially partonic energy loss. Future: year-2 will determine negative hadron spectra out

to 10 GeV/c, strange baryon spectra out to 5 GeV/c. The interesting physics might lie at high pt and in rare

probes (, D-meson, J/)