Results from STARMarkus D. Oldenburg

MPI Colloquium October 22, 2002

Munich, Germany

For the STAR Collaboration

Markus D. Oldenburg

MPI Colloquium October 22, 2002 2

Outline

• Physics introduction

• STAR @ RHIC

• Analyses & Results– Particle spectra

– Anisotropic Flow

– Jets at RHIC

– Ultra-Peripheral Collisions

• Summary

• Outlook

Markus D. Oldenburg

MPI Colloquium October 22, 2002 3

Phase Diagram for Nuclear Matter

K. Rajagopol

• Study of nuclear matter under extreme conditions (high temperature and/or high pressure)

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MPI Colloquium October 22, 2002 4

The Relativistic Heavy Ion Collider

• Two independent accelerator rings• 3.83 km in circumference• Accelerates everything from p to Au

Running conditions: Au-Au 2001• 55-56 bunches per ring

(tested up to 110)• 7.5108 Au/bunch @ storage energy• Storage energy: 100 GeV/A• Peak luminosity: 51026 cm-2 s-1

Running conditions: pp 2001• 55 bunches per ring• 0.81011 p/bunch• Energy/beam: 100 GeV• Peak luminosity: 1.51030 cm-2 s-1

• Beam polarization ~ 25% ( AGS)Long IslandLong Island

STAR

The STAR experiment at RHIC

STAR uses the world’s largest Time Projection Chamber

One of the first Au on Au Events at CM Energy of 200 GeVA

STARSTAR

Markus D. Oldenburg

MPI Colloquium October 22, 2002 7

Spectra Measured vs. Centrality (impact parameter)

Peripheral Collision

x

yz

x

yz

(near) Central Collision

X

Y

X

Y

central collision

high multiplicity in CTB &

low multiplicity in ZDcal

Markus D. Oldenburg

MPI Colloquium October 22, 2002 8

STAR Preliminary

Bose-Einstein fits

STAR Preliminary

mTmAe

/mt exponential fits

K-

Identified Particle Spectra at 200 GeV

+, -, K+, K- spectra versus centrality

(130 GeV/N data in nucl-ex/0206008)

)1/( / effTmeA

+

Markus D. Oldenburg

MPI Colloquium October 22, 2002 9

130 GeV data

p

Preliminary 200 GeV data

22 2/ pAegaussian fits

Anti-Proton Spectra at 200/130 GeV/NAu + Au p + X

p

p and p-bar spectra versus centrality(130 GeV data in PRL 87 (2002))

Markus D. Oldenburg

MPI Colloquium October 22, 2002 10

Anti-Particle to Particle Ratios

Excellent agreement between experiments at y = 0, s = 130

STAR results on thep/p ratio• p-bar/p = 0.11 ± 0.01 @ 20 GeV

• p-bar/p = 0.71 ± 0.05 @ 130 GeV• Previously reported as 0.60 ± 0.06

• p-bar/p = 0.80 ± 0.05 @ 200 GeV

p-bar/p ratios

K+/K- ratios

Markus D. Oldenburg

MPI Colloquium October 22, 2002 11

Anti-Baryon/Baryon Ratios vs. sNN

p+p p/p ISR

• In the early universe

– p-bar/p ratio = 0.999999

• At RHIC, pair-production increases

with s

• Mid-rapidity region is not yet

baryon-free!

• Pair production is larger than baryon

transport

• 80% of protons from pair production

• 20% from initial baryon number

transported over 5 units of rapidity

4Tr

pair

Y

Y

8.0

Transpair

pair

p

pbar

YY

Y

Y

Y

______

STAR preliminary

_

In HI collisions at RHIC, more baryons are pair produced than are brought in by the initial state

Markus D. Oldenburg

MPI Colloquium October 22, 2002 12

Particle Ratios at RHIC

Good agreement between the 4 experiments STAR, PHOBOS, PHENIX, BRAHMS

p/p = 0.71 ± 0.02(stat) ± 0.05 (sys)= 0.60 ± 0.04(stat) ± 0.06 (sys) = 0.64 ± 0.01(stat) ± 0.07 (sys)= 0.64 ± 0.04(stat) ± 0.06 (sys)

/ = 0.73 ± 0.03(stat)

+/- = 0.83 ± 0.03(stat.)±0.05(sys.)

K-/ - = 0.15 ± 0.01 (stat) ± 0.02 (sys)

K+/ + = 0.16 ± 0.01 (stat) ± 0.02 (sys)

/ = 1.00 ± 0.01(stat) ± 0.02 (sys) = 0.95 ± 0.03(stat) ± 0.05 (sys)

/h- = 0.021 ± 0.001 (stat) ± 0.005 (sys)

/h- = 0.060 ± 0.001 (stat) ± 0.006 (sys)

/ h- = 0.043 ± 0.001 (stat) ± 0.004(sys)

K0s / h

- = 0.124 ± 0.001 (stat)

(K*+K* ) / 2 h- = 0.032 ± 0.003(stat.) ± 0.008 (sys.)

2 /(K*+K* ) = 0.64 ± 0.06 (stat) ± 0.16 (sys)

K-/K+ = 0.89 ± 0.008(stat) ± 0.05 (sys) = 0.91 ± 0.07(stat) ± 0.06 (sys) = 0.89 ± 0.07(stat) ± 0.05 (sys) K+/K- = 1.08 ± 0.03(stat) ± 0.22(sys) min. bias K-/ - = 0.15 ± 0.01 (stat) ± 0.02 (sys) K+/ + = 0.16 ± 0.01 (stat) ± 0.02 (sys)K*/K* = 0.92 ± 0.14(stat.)

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MPI Colloquium October 22, 2002 13

Chemical Freeze-out (thermal model)

(P. Braun-Munzinger et al.: hep-ph/105229)

Thermal model fits

Compare to QCD on Lattice:

Tc = 154 ± 8 MeV (Nf=3)

Tc = 173 ± 8 MeV (Nf=2)(ref. Karsch QM01)

MeV 651(RHIC)μ

MeV 7175(RHIC)T

B

ch

MeV 270(SPS)μ

MeV 170160(SPS)T

B

ch

Assume: - Thermally and chemically equilibrated fireball at hadro-chemical freeze-out

Recipe: - Grand canonical ensemble to describe partition function density of particles

of species i

- Fixed by constraints: Volume V, strangeness chemical potential S, and isospin

input: measured particle ratios output: temperature T and baryo-chemical potential B

Markus D. Oldenburg

MPI Colloquium October 22, 2002 14

Putting STAR on the Phase Diagram• Final-state analysis

suggests RHIC reaches the phase boundary

• Hadron yields cannot probe higher temperatures

• <E>/N ~ 1 GeV(J. Cleymans and K. Redlich, Phys. Rev. Lett., 81, 5284, 1998)

Lattice results

Neutron STAR

We know where we are on the phase diagram but now we want to know what other features are

on the diagram

Markus D. Oldenburg

MPI Colloquium October 22, 2002 15

Chemical and Kinetic Freeze-out

• Chemical freeze-out (first)– End of inelastic interactions– Number of each particle species

is frozen

• Useful data– Particle yields

• Kinetic freeze-out (later)– End of elastic interactions

– Particle momenta are frozen

• Useful data– Transverse momentum distributions

– and Effective temperatures

space

tim

e

inelasticinteractions

Chemicalfreeze-out

elasticinteractions

Kineticfreeze-out

blue beam yellow beam

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MPI Colloquium October 22, 2002 16

Transverse Flow

The transverse radial expansion of the source (flow) adds kinetic energy to the particle distribution. So the classical expression for ETot

suggests a linear relationship

-

K -

p

Au+Au at 200 GeV

STAR Preliminary

2KFOObs massTT

Slopes decrease with mass. <pT> and the effective temperature increase with mass.

T ≈ 575 MeV

T ≈ 310 MeV

T ≈ 215 MeV

Markus D. Oldenburg

MPI Colloquium October 22, 2002 17

Kinetic Freezeout from Transv. Flow

<ßr> (RHIC) = 0.55 ± 0.1 cTKFO (RHIC) = 100 ± 10 MeV

Explosive Transverse Expansion at RHIC High Pressure

Tth

[GeV

]<

r>

[c]

STA

RPH

EN

IX

Markus D. Oldenburg

MPI Colloquium October 22, 2002 18

Anisotropic Flow• Look at peripheral collisions

• Overlap region 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

x

yz

px

py

y

x

nvn cosx

y

p

patan

• Spatial anisotropy Momemtum anisotropy– Interactions among constituents generate a pressure

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

– vn is the n-th harmonic Fourier coefficient of the distribution of particles with repsect to the reaction plane

• v1: “directed flow”

• v2: “elliptic flow”

Markus D. Oldenburg

MPI Colloquium October 22, 2002 19

PRL 86, (2001) 402

more central

v2 vs. Centrality (130 GeV)

• 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

Hydro predictions

Markus D. Oldenburg

MPI Colloquium October 22, 2002 20

v2 vs. pt and Particle Mass (130 GeV)

• The mass dependence is reproduced by hydrodynamic models– Hydro assumes local

thermal equilibrium

– At early times

– Followed by hydrodynamic expansion

PRL 86, 402 (2001) & nucl-ex/0107003

Hydro does a very good job

D. Teaney et al., QM2001 Proc.P. Huovinen et al., nucl-th/0104020

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MPI Colloquium October 22, 2002 21

v2 for , K, K0, p and

PreliminaryPreliminary

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MPI Colloquium October 22, 2002 22

v2 for High pt Particles (130 GeV)

• pQCD inelastic energy loss + parameterized hydro component (M. Gyulassy, I. Vitev and X.N. Wang, PRL 86 (2001) 2537)

– 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

• data starts to deviate from hydrodynamics at pt > 2 GeV/c

Adler et al., nucl-ex/0206006

Data is in qualitative agreement

with ‘jet-quenching’ scenario

Markus D. Oldenburg

MPI Colloquium October 22, 2002 23

Centrality dependence of v2(pt)

• v2 is saturated at high pt and it does not come back down as rapidly as expected

• What does v2 do at very high pt ?

200 GeV (preliminary)

130 GeV

peripheral

central

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MPI Colloquium October 22, 2002 24

v2 up to 12 GeV/c

v2 seems to remain saturated

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MPI Colloquium October 22, 2002 25

Hard Probes in Heavy-Ion Collisions• New opportunity using Heavy Ions at RHIC Hard Parton Scattering

sNN = 200 GeV at RHIC – 17 GeV at CERN SPS

• Jets and mini-jets – 30-50 % of particle production– 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

hadrons

q

q

hadronsleadingparticle

leading particle

schematic view of jet production

QGP

Vacuum

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MPI Colloquium October 22, 2002 26

Preliminary

Inclusive pt Distribution of Hadrons

• Scale Au-Au data by the number of binary collisions

• Compare to UA1pp reference data measured at 200 GeV

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MPI Colloquium October 22, 2002 27

Comparison: Au+Au / p+p at 130 GeV

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MPI Colloquium October 22, 2002 28

Evidence for hadron suppression at high pt

Partonic interaction with matter? dE/dx?

Flow vs. Inclusive Hadron Spectra

Different views of same physics?

Markus D. Oldenburg

MPI Colloquium October 22, 2002 29

Jets in Hadronic Collisions

p+p jet+jet (STAR@RHIC)

Au+Au ??? (STAR@RHIC)

Markus D. Oldenburg

MPI Colloquium October 22, 2002 30

Identifying jets on a statistical basis in Au-Au

• Given a trigger particle with pt > pt (trigger), associate particles with pt > pt (associated)

• Au+Au– flow

• p+p and Au+Au collisions:– dijets– momentum

conservation– jets – resonances

STAR Preliminary Au+Au @ 200 GeV/c, 0-5% most central

4 < pt(trig) < 6 GeV/c, 2 < pt(assoc.) < pt(trig)

Small

All

),()(11

)(2 NdefficiencyN

Ctrigger

Markus D. Oldenburg

MPI Colloquium October 22, 2002 31

Peripheral Au+Au data vs. pp+flow

C2(Au Au) C2(p p) A *(1 2v22 cos(2))

Ansatz: A high pt triggered 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 in non-jet region (0.75 < || < 2.24)

Markus D. Oldenburg

MPI Colloquium October 22, 2002 32

Central Au+Au data vs. pp+flow

C2(Au Au) C2(p p) A *(1 2v22 cos(2))

Markus D. Oldenburg

MPI Colloquium October 22, 2002 33

Jets at RHIC

• The backward going jet is missing in central Au-Au collisions when compared to p-p data + flow

• Other features of the data– High pt charged hadrons dominated by jet

fragments• Relative charge• Azimuthal correlation width• Evolution of jet cone azimuthal correlation

strength with centrality?

Surface emission?

Suppression of back-to-back correlations in central Au+Au collisions

• Other explanations for the disappearance of back-to-back correlations in central Au-Au?

– Investigate nuclear kT effects

• Experiment: p+Au or d+Au

• Theory: Add realistic nuclear kT to the models

Markus D. Oldenburg

MPI Colloquium October 22, 2002 34

Ultra-Peripheral Collisions

• b > 2RA;

– no hadronic interactions– <b> ~ 20-60 fermi at RHIC

• Ions are sources of fields– Fields couple coherently to ions

• pt < h/RA, ~30 MeV/c for heavy ions

• p|| < h/RA ~ 3 GeV/c at RHIC

• Photonuclear (Photon-Pomeron) Interactions

A ’, , , J/,… A – Vector Meson Dominance

• A ’ qqA ’ (elastic scattering) ’ VA

– ~ 350 mb at 130 GeV/nucleon• 5% of AuAu(had.)

• Electromagnetic particle production

’leptons, mesons– Strong Field (nonperturbative?) QED

Au

Au

Coupling ~ nuclear form factor

, P, or meson

-

Markus D. Oldenburg

MPI Colloquium October 22, 2002 35

Exclusive 0

pt<0.15 GeV

0 pt

Signal region:

pt<0.15 GeV

200GeV

Preliminary

• Trigger on low multiplicity events• veto on cosmic rays

• 2 track vertex w/ charge 0– reject (coplanar) cosmic rays

• peak for pt < 150 MeV/c

• and give background shape– scaled up by 2.1

-)

Markus D. Oldenburg

MPI Colloquium October 22, 2002 36

Minimum Bias Data

• 800,000 triggers neutron signals in ZDCs

• Nuclear excitation ‘tag’s small b interactions– excitation and 0 are independent

• Analysis same as in peripheral Preliminary

200 GeV

Signal region:

pt<0.15 GeV

d/

dM

m

b/G

eV

200 GeV

Preliminary

0 pt

-)

130 GeV STAR Theory0 with XnXn 36.6 2.4 8.9 mb 27 mb0 with 1n1n 2.50.40.6 mb 2.6 mbExclusive 0 410190100 mb 350 mb

• Normalized to 7.2 b hadronic cross section

• Systematic uncertainties: luminosity, overlapping events, vertex & tracking simulations, single neutron selection, etc.

Markus D. Oldenburg

MPI Colloquium October 22, 2002 37

Summary of Analyses

shown:• Particle yields / ratios / spectra

• Anisotropic Flow

• Jets at RHIC

• Ultra-Peripheral Collisions

not shown:• Interferometry (HBT)

• Fluctuations

• Gluon density saturation

• Spin physics program

Markus D. Oldenburg

MPI Colloquium October 22, 2002 38

Conclusions About Nucl. Matter @ RHIC

• It’s hot– Chemical freeze out at 175 MeV– Thermal freeze out at 100 MeV– The universal freeze out temperatures are surprisingly flat as a function of s

• It’s fast– Transverse expansion with an average velocity greater than 0.55 c– Large amounts of anisotropic flow (v2) suggest hydrodynamic expansion

and high pressure at early times in the collision history

• It’s opaque– Saturation of v2 at high pt

– Suppression of high pt particle yields relative to p-p– Suppression of the away side jet

• And it’s not inconsistent with thermal equilibrium– Excellent fits to particle ratio data with equilibrium thermal models– Excellent fits to flow data with hydrodynamic models that assume

equilibrated systems

Looks like we are

observing the QGP!

Markus D. Oldenburg

MPI Colloquium October 22, 2002 39

RHIC Performance Goals for 2003

• 29 weeks of d-Au (including cooldown)

• 8 weeks of pp• (We won’t have Si-Si nor Au-Au next year.)

More interesting physics to come ...

Markus D. Oldenburg

MPI Colloquium October 22, 2002 40

STAR InstitutionsU.S. Labs:

Argonne, Brookhaven, and Lawrence Berkeley National Labs

U.S. Universities:

UC Berkeley, UC Davis, UCLA, Carnegie Mellon, Creighton, Indiana, Kent State, Michigan State, CCNY, Ohio State, Penn State, Purdue, Rice, UT Austin, Texas A&M, Valparaiso, Washington, Wayne State, Yale

Brazil: Universidade de Sao Paolo

China:IPP - Wuhan, IMP - Lanzhou USTC, SINR, Tsinghua University, IHEP - Beijing

England: University of Birmingham

France: IReS - Strasbourg SUBATECH - Nantes

Germany: Max Planck Institute - Munich University of Frankfurt

India:Institute of Physics - BhubaneswarIIT - Mumbai, VECC - Calcutta Jammu University, Panjab UniversityUniversity of Rajasthan

The Netherlands:NIKHEF

Poland: Warsaw University of TechnologyRussia:

MEPHI - Moscow, IHEP - ProtvinoLPP & LHE JINR - Dubna

Markus D. Oldenburg

MPI Colloquium October 22, 2002 41

Markus D. Oldenburg

MPI Colloquium October 22, 2002 42

Binary scaling

Participant 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

Markus D. Oldenburg

MPI Colloquium October 22, 2002 43

RAA Comparison to pt = 6 GeV/c

130 GeV nucl-ex/0206011

Preliminary sNN = 200 GeV

Similar Suppression at high pt in 130 and 200 GeV data

Preliminary sNN = 200 GeV