Recent results from STAR

STAR 1APS Spring Meeting - April 2002 - malisa

Recent results from STARM.A. Lisa, for the STAR Collaboration


OutlineYear-1 data (Au+Au s=130 GeV)hadro-chemistry• driving dynamical physics and consistent picture @ low pT?

• central collisionsradial flow• two-particle correlations HBTK- correlations

balance functions• non-central collisionselliptical flowHBT vs reaction-plane

• low-pT summary• driving physics @ “high” pT?spectra compared to pp collisionselliptical flowtwo-particle correlations

• Summary


Particle ID in STAR

pion

s

kaons

pro

tons

deute

rons

electrons

STAR

dE/dx

dE/dx PID range: (dE/dx) = .08]

p ~ 0.7 GeV/c for K/

~ 1.0 GeV/c for p/p

RICH PID range:

1 - 3 GeV/c for K/

1.5 - 5 GeV/c for p/p

RICH

“kinks”:

K +

Vo

Decay vertices

Ks + + - p + -

p + + - + -

+ + + + K -

Topology CombinatoricsKs + + - K + + K -

p + - p + +

+ + - p + -

from K+ K- pairs

K+ K- pairs

m inv

m inv

same event dist.mixed event dist.

background subtracted

dn/dm

dn/dm


Vector meson production in Ultra-peripheral collisions

Signal region:

pT<0.15 GeV

0 PT

0

Au

Au

qq

• b > 2R electromagnetic interactions• d/dpT consistent with predictions for

coherent 0 production


Kaon Spectra at Mid-rapidity vs Centrality

Exponential fits to mT spectra: ⎟⎠

⎞⎜⎝

⎛−∝T

mA

dm

dN

mT

TT

exp1

K+ K- (K++K-)/2

Ks

STAR preliminary STAR preliminary STAR preliminary

0-6%

11-18%

26-34%

45-58%58-85%

Centralitycuts

0-6%

11-18%

26-34%

45-58%58-85%

Centralitycuts

0-6%

11-18%

26-34%

45-58%58-85%

Centralitycuts

Good agreement betweendifferent PID methods


Statistical Thermal Model: Fit Results

• b driven by p/p, K-/K+

• T driven by p/


Something different vs pT?Particle/Antiparticle Ratios

STAR Preliminary

Within the errors no or very small pT dependence(as one might expect from simply flow)

see talk by B. Norman


pT spectra: Flavor Dependence

Enhancement at ~2 GeV is not specific to baryons mass effectsimplest explanation: radial flow)


Thermal motion superimposed on radial flow

Fits by M. Kaneta

Hydro-inspired “blast-wave” thermal freeze-out fits to , K, p,

Tth = 107 ± 8 MeVhydro predictions reproduce early

pT spectra

preliminary


Hydro attempts to reproduce data

Rout

Rside

Rlong: model waits too longbefore emitting

• KT dependence approximately reproduced correct amount of collective flow

• Right dynamic effect / wrong space-time evolution??? the “RHIC HBT Puzzle”

generichydro

model emission timescale too long


Blastwave: radii vs pT

STAR data

blastwave: R=13.5 fm, freezeout=1.5 fm/c

Magnitude of flow and temperature from spectra can account for observed drop in HBT radii via x-p correlations, and Ro<Rs

…but emission duration must be small

Four parameters affect HBT radii

pT=0.4

pT=0.2

K

K

222s

2o RR β+=


From Rlong: tkinetic = 8-10 fm/c

Simple Sinyukov formula (S. Johnson)

– RL2 = tkinetic2 T/mT

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

B. Tomasik (~3D blast wave) tkinetic = 8-9 fm/c


Kaon – pion correlation:dominated by Coulomb interaction

Smaller source stronger (anti)correlation

K-p correlation well-described by:

• Blast wave with same parameters as spectra, HBT

But with non-identical particles, we can access more information…

STAR preliminary


Initial idea: probing emission-time ordering• Catching up: cos0

• long interaction time• strong correlation

• Ratio of both scenarios allow quantitative study of the emission asymmetry

• Moving away: cos0• short interaction time• weak correlation

Crucial point:kaon begins farther in “out” direction(in this case due to time-ordering)

purple K emitted firstgreen is faster

purple K emitted firstgreen is slower


measured K- correlations - natural consequence of space-momentum correlations

• clear space-time asymmetry observed

• C+/C- ratio described by:– “standard” blastwave w/ no time shift

• Direct proof of radial flow-induced space-momentum correlations

Kaon <pt> = 0.42 GeV/c

Pion <pt> = 0.12 GeV/c

STAR preliminary


Balance functions: How they work

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

Charges: electric, strangeness, baryon numberBass, Danielewicz, Pratt (2000)


Balance functions - clocking the evolution

Model predictions Wide early creation of charges

nn, e+e- collisions Narrow late hadronization / (Q)GP

central collisions @ RHIC?

Pythia (wide)

Bjorken (narrow)

Bass, Danielewicz, Pratt (2000)


Balance Functions in STAR

STAR Preliminary

0.550.60.650.7

Data0 0.20.40.60.81

<>y

/b bmax-HIJING GEANT

STAR Preliminary

Pairs

• Peripheral collisions approach Hijing (NN)• Clear narrowing for central collisions

• In Bass/Danielewicz/Pratt model, central data consistent with:Tchem ~ 175 MeV Tkinetic ~ 110 MeV

tchem = 10 fm/c tkinetic = 13 fm/c

STAR 19APS Spring Meeting - April 2002 - malisapT (GeV/c)

0.2

0.1

0

0 1 2 3

Noncentral collision dynamicshydro evolution

• hydro reproduces v2(pT,m) @ RHIC for pT < ~1.5 GeV/c• system response (pressure):

x-space p-space anisotropy

• again: correct p-space dynamical effect

• freezeout shape evolution duration?STAR preliminarysee talk of J. Fu

v2

flow of neutral strange particlesPID beyond pT=1 GeV/c


Blast-wave fit to low-pT v2(pT,m)STAR, PRL 87 182301 (2001)

• spatial anisotropy indicated

• consistent with out-of-plane extended source(but ambiguity exists)

p=0°

p=90°

Rside (large)

Rside (small)

• possible to “see” via HBT relative to reaction plane?

• expect• large Rside at 0• small Rside at 90

2nd-orderoscillation


Out-of-plane extended source~ short system evolution time

STAR preliminary

• Same blastwave parameters as required to describe v2(pT,m), plus two more:

– Ry = 10 fm = 2 fm/c

• Both p-space and x-space anisotropies contribute to R()

– mostly x-space: definitely out-of-plane

• calibrating with hydro, freezeout ~ 7 fm/c

Ros2 - new “radius” important for

azimuthally asymmetric sources


RHIC 130 GeV Au+Au

Disclaimer: all numbers (especially time) are approximate

Low-pT dynamics — one (naïve?) interpretation:rapid evolution and a “flash”

K-

K* yield


Physics at “high” pT (~6 GeV/c)

hadrons

q

q

hadrons

leadingparticle suppressed

leading particle suppressed

hadrons

q

q

hadrons

leadingparticle

leading particle

Jets modified in heavy ion collisions

-Parton Energy loss in dense nuclear medium

-Modification of fragmentation function

1) high-pT suppression relative to NN(especially in central collisions)

2) finite, non-hydro v2 due to energy loss(non-central collisions)

see talk of J. Klay

y

Jet 1

Jet 2x


Inclusive spectra

preliminary

Statistical errors only


Power law fits

• Power Law: “pQCD inspired”• Fits wide range of hadronic spectra: ISR Tevatron

• Good fits at all centralities (2/ndf~1) • Smooth dependence on centrality

• most peripheral converges to Nucleon-Nucleon reference (UA1)

n

TT p

pA

dp

dN

p−+= )1(

1

0

(p0, n highly correlated)

STAR preliminary


• Central collisions: suppression of factor 3 (confirms PHENIX)• Peripheral collisions: “enhancement” consistent with zero

(uncertainties due to <Nbinary> and NN reference)

• Smooth transition central peripheral

preliminary

low pT scales as <Npart>

ηηddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

=


Azimuthal anisotropy - theory and data

Preliminary

• pT<2 GeV: good description by hydrodynamics• pT>4 GeV: hydro fails but finite v2

• finite energy loss finite v2 at high pT

• sensitive to gluon density

y

Jet 1

Jet 2 x

model: Gyulassy, Vitev and Wang, (2001)

Low pT: parameterized hydro High pT: pQCD with GLV radiative energy loss


V2 centrality dependence

Preliminary

all centralities: finite v2 at high pT


But are we looking at jets? - 2 Particle Correlations

• Trigger particle pT>4 GeV/c, |η0• azimuthal correlations for pT>2 GeV/c• short range η correlation: jets + elliptic flow • long range η correlation: elliptic flow

subtract correlation at |η1η0• NB: also eliminates the away-side jet correlations

• extracted v2 consistent with reaction-plane method

• what remains has jet-like structure first indication of jets at RHIC!

preliminary0-11%


STAR vs UA1

UA1: Phys. Lett. 118B, 173 (1982)(most events from high ET trigger data)

• UA1: very similar analysis (trigger pT>4 GeV/c)• But sqrt(s)=540 GeV, |η|<3.0

preliminary


Brief Summary• chemistry:

• wide range of particle yields well-described by thermal model• Tchem ~ 170 MeV b ~ 45 MeV

• pT dependence of yields (e.g. baryon dominance) consistent with radial flow

• dynamics at pT < 2 GeV/c• “real” model (hydro) reproduces flow systematics, but not HBT• finger-physics analysis of probes sensitive to time:

• short system evolution, then emission in a flash• Tchem ~ 170 MeV Tkin ~ 110 MeV

• tchem ~ 10 fm/c tkin ~ 13 fm/c

• naïve? unphysical? useful feedback to modelers?

• dynamics at pT > 2 GeV/c• hydro picture breaks down• preliminary jet signal observed• evidence for medium effects at high pT


THE END


Ratios driving the thermal fits

Plots from D. Magestro, SQM2001


Blast Wave Mach I - central collisions

)0 ,sinh ,(cosh )0,,( rezrtu ==

β= −tanh 1r )( rfst ββ =R

βs

Ref. : E.Schnedermann et al, PRC48 (1993) 2462

flow profile selected

(βt =βs (r/Rmax)n)

mt

1/m

t dN

/dm

t

TfoA

βt

2-parameter (Tfo, βt) fit to mT distributions


Blastwave Mach II - Including asymmetries

R

βt

( )

( )

( )22

psT

/t

y222

cossinhT

p

T1

e

R/xy1

e

coshT

mKp,xf

τΔ−

φ−φρ

×η+−θ

×

×⎟⎠⎞

⎜⎝⎛ ρ=

rr

– Flow

• Space-momentum correlations

• <> = 0.6 (average flow rapidity)

• Assymetry (periph) : a = 0.05

– Temperature

• T = 110 MeV

– System geometry

• R = 13 fm (central events)

• Assymetry (periph event) s2 = 0.05

– Time: emission duration

• = emission duration

}}}

analytic description of freezeout distribution: exploding thermal source


Comparison to Hijing

Ratio of integrals over correlation peak: 1.3

Hijing fragmentation is independent of quenching


High-pT highlights

Qualitative change at 2 GeV

Jet-like structure


measured K- correlations - natural consequence of space-momentum correlations

• clear space-time asymmetry observed

• C+/C- ratio described by:– static (no-flow) source w/ tK- t=4 fm/c

– “standard” blastwave w/ no time shift

• We “know” there is radial flow further evidence of very rapid freezeout

• Direct proof of radial flow-induced space-momentum correlations

Kaon <pt> = 0.42 GeV/c

Pion <pt> = 0.12 GeV/c

STAR preliminary

Recent results from STAR

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