TJH Warsaw University, Nov 28, 2003 1 Recent Results from STAR Tim Hallman Warsaw University November 28, 2003

TJH Warsaw University, Nov 28, 2003 TJH Warsaw University, Nov 28, 2003

1

Recent Results from STAR

Tim Hallman

Warsaw UniversityNovember 28, 2003


2

RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

Relativistic Heavy Ion Collider (RHIC)

2:00 o’clock

4:00 o’clock6:00 o’clock

8:00 o’clock

10:00 o’clock

STARPHENIX

RHIC

AGS

LINACBOOSTER

TANDEMS

9 GeV/uQ = +79

1 MeV/uQ = +32

HEP/NP

g-2

U-lineBAF (NASA)

PHOBOS12:00 o’clock BRAHMS

• 2 concentric rings of 1740 superconducting magnets• 3.8 km circumference• counter-rotating beams of ions from p to Au• max center-of-mass energy: AuAu 200 GeV, pp 500 GeV

RHIC RunsRun I: Au+Au at s = 130 GeVRun II: Au+Au and pp at s = 200 GeV


3

ZCal

Central Trigger Barrel+ TOF patch+ TOFr

FTPCs (1 + 1)

Time Projection Chamber

Barrel EM Calorimeter

Vertex Position Detectors

Magnet

Coils

TPC Endcap & MWPC

Endcap Calorimeter

ZCal ZCal

Silicon Vertex Tracker *

The STAR Detector

BBCs


4

The STAR Collaboration: 49 Institutions, ~ 500 People

England: University of Birmingham

France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes

Germany: Max Planck Institute – Munich University of Frankfurt

India:Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC

Netherlands:

NIKHEFPoland:

Warsaw University of TechnologyRussia:

MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP - Protvino

U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs

U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale

Brazil: Universidade de Sao Paolo

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

Croatia: Zagreb University

Czech Republic: Nuclear Physics Institute


5

The Phase Diagram of QCDT

em

per

atu

re

baryon density

Neutron stars

Early universe

nucleinucleon gas

hadron gascolour

superconductor

quark-gluon plasmaTc

0

critical point ?

vacuum

CFL


6

• New opportunity using Heavy Ions at RHIC Hard Parton Scattering sNN = 200 GeV at RHIC

– 17 GeV at CERN SPS• Jets and mini-jets

– 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

Hard Probes in Heavy-Ion Collisions

hadrons

q

q

hadronsleadingparticle

leading particle

schematic view of jet production

QGP

Vacuum


7

Partonic energy loss in dense matter

Thick plasma (Baier et al.):

glueSglue

Debye

sRBDMS

q

vLqC

E

2

2

ˆ

~ˆ4

L

ELogrdCE jet

glueSRGLV 23 2

,

Linear dependence on gluon density glue: • measure E gluon density at early hot, dense phase

High gluon density requires deconfined matter (“indirect” QGP signature !)

Gluon bremsstrahlung

Thin plasma (Gyulassy et al.):


8

What is a jet?

hadrons

hadrons

leading particle

Jet: A localized collection of hadrons which come from a fragmenting parton

c

chbbaa

abcdba

T

hpp

z

Dcdab

td

dQxfQxfdxdxK

pdyd

d

0

/222

)(ˆ

),(),(

Parton distribution Functions

Hard-scattering cross-section

Fragmentation Function

a

b

c

d

High pT (> ~2.0 GeV/c) hadron production in pp collisions:


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High pT Particle Production in A+A

Intrinsic kT , Cronin Effect

Parton Distribution Functions

Shadowing, EMC Effect

Fragmentation Function leading

particle suppressed

Partonic Energy Loss

c

d

hadrons

a

b

Hard-scattering cross-section

(According to pQCD…)

c

ccch

c

c

bbBaaA

ba

bBbaAa

baabcd

baT

hAB

z

QzD

z

zPd

cdabtd

d

QxSQxS

gg

QxfQxf

dddxdxKpdyd

dN

),(

)(

)(ˆ

),(),(

)()(

),(),(

2*0/

1

0

*

22

2/

2/

222

kk

kk


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ddpdT

ddpNdpR

TNN

AA

TAA

TAA /

/)(

2

2

<Nbinary>/inelp+p

Nucleus-nucleus yield

Nuclear Modification Factor:

AA

If R = 1 here, nothing “new”going on

A key probe, new at RHIC: hard scattering of quarks and gluons

peripheralbinperipheral

centralbincentral

TCPNYield

NYieldpR

/

/)(

Another way to test:


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Jets in Heavy Ion Collisions at RHIC

Jet event in eecollision STAR Au+Au collision


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• The overlap region in peripheral collisions 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

– Spatial anisotropy Momentum anisotropy• Interactions among constituents generates

a pressure gradient 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

• v2 is the 2nd harmonic Fourier coefficient of

the distribution of particles with respect to the reaction plane

Anisotropic Flow

x

yz

px

py

Anisotropic (Elliptic) Transverse Flow

Elliptic Flow at RHIC

Peripheral Collisions


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px

py

Anisotropic (Elliptic) Flow at RHIC

2cos2 vx

y

p

patan

Non-central Collisions

Anisotropic Flow

x

yz


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STAR Preliminary Au+Au @ 200 GeV/c0-5% most central

4 < pT(trig) < 6 GeV/c2 < pT(assoc.) < pT(trig)

• Identify jets on a statistical basis in Au-Au• Given a trigger particle with pT > pT (trigger),

associate particles with pT > pT (associated)

),(11

),(2 NEfficiencyN

CTRIGGER

You can see the jets in p-p data at RHIC

Statistical Identification of jets in AA Collisions


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In Detail: High-pT Spectra from STAR

Basic Idea:peripheral collisionsare p+p like no suppression

central collisionshot and dense matter suppression


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Comparison Au+Au/p+p at RHIC (STAR)


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Central/Peripheral Normalized by Nbin

suppressionsuppression


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Binary 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


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Peripheral Au+Au data vs. pp+flow

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

Ansatz: A high pTtriggered 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 innon-jet region (0.75 < || < 2.24)

Back-to-back Jet Correlation Results


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Central Au+Au data vs. pp+Flow

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

Back-to-Back Jet Correlation Results


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

• Indication of opacity of the source?

Away-side correlations disappear as collision becomes more central

Trigger: pT>4 GeV/cCorrelate: pT>2 GeV/c

Supression of the Back-to-Back Correlation


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A d+Au“control” experiment was been performed!

Results show:Observed suppressiondue to nature of (new)

produced matter !

not initial state effectsPedestal&flow subtracted

Run II AuAu results at full energy show strong suppression !

d+Au “control”data needed to distinguish between different interpretations

0 90 180 Degrees

d+Au

CentralAuAu


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Jet Quenching Result

PRL Cover Article

Special ColloquiumJune 17, 2003


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v2 vs. Centrality

• 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

Phys.Rev.Lett. 86, (2001) 402

more central

Hydro predictions


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v2 vs. pT and Particle Mass

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

Hydro does a surprisingly good job!

Preliminary

• The mass dependence is reproduced by hydrodynamic models

– Hydro assumes local thermal equilibrium

– At early times– Followed by

hydrodynamic expansion


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v2 for High pt Particles

v2 is large … but at pt > 2 GeV/c the data

starts to deviate from hydrodynamics

Phys.Rev.Lett. 90, 032301 (2003)


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v2 predictions at high pT

M. Gyulassy, I. Vitev and X.N. Wang

PRL 86 (2001) 2537

The 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

pQCD inelastic energy loss + parameterized hydro component

y

x

distance of fast parton propogation

Jet 1

Jet 2


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Elliptic flow as a function of transverse momentum

?

Could this effect be dueto Surface emission?

Significant v2 up to ~7 GeV/c in pt, the region where hard scattering begins to dominate.

The data support the conclusion that we have produced a medium that is dense, dissipative, and exhibits strong collective behavior

V2(4)V2(2)V2(RP)

V 2(%)

STAR Preliminary


29

Λ˚, K°s v2 versus pT: mass dependence or particle type?

Results suggest a scaling of v2 versus particle type (meson/baryon) rather than particle mass flow is built up at the partonic stage (?)


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HBT Correlations relative to the reactions plane

What we measure?HBT radii as a function of emission angle

reactionplane

What we expect to see?2nd-order oscillations in HBT radii

Rside2

Why we're interested?The size and orientation of the source at freeze-out places tight constraints on expansion/evolution

What should be rememberedAt finite kT, we don't measure the entire source size. We measure "regions of homogeneity" and relating this to the full source size requires a model dependence.

qoutqside

qlong

Heinz, Hummel, Lisa, Wiedemann PRC 044903 (2002)


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Centrality Dependence of HBT for AuAu at 200 GeV

= 0°

90°

Rside (large)

Rside (small)

15° bins, 72 CF's total for 12 bins × 3 centrality bins ; × 2 pion signs

0.15 < kT < 0.65

Oscillations exist in transverse radii for all bins

Results show oscillations whichindicate out-of-plane extended source and short lifetime!

STAR Preliminary


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“Blast wave” parameterization (Sollfrank model) can approximately describe data (spectra + HBT)

…but emission duration must be small

= 0.6 (radial flow), T = 110 MeV

R = 13.5 1fm (hard-sphere)

emission= 1.5 1 fm/c (Gaussian)

STAR PRL 87, 082301 (2001)PHENIX PRL 88 192302 (2002)

STAR 130 GeV

PHENIX 130 GeV

Hydro + RQMD

Probing Thermalization: The HBT Puzzle

HBT radii pose serious difficulties for hydro models


33

In-plane/out-of-plane back-to-back jet suppression

STAR preliminarySTAR preliminary

Back-to-back suppression is larger in the out-of-plane direction


34

Results on “Soft” Physics

– Particle production per participant is large

• Total Nch ~ 5000 (Au+Au s = 200 GeV) ~ 20 in p+p

• Nch/Nparticipant-pair ~ 4 (central region) ~2.5 in p+p

A+A is not a simple superposition of p+p

– Energy density is high ~ 4-5 GeV/fm3 (model dependent)

– System exhibits collective behavior (flow) strong internal pressure

– The system appears to freezes-out very fast • explosive expansion

– Large system: at freeze-out 2 size of nuclei


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Conclusions About Matter Produced at RHIC:

We have produced matter which exhibits features qualitatively different than has been observed before !

• The evolution is fast– Transverse expansion with an average velocity of 0.55 c– Large amounts of anisotropic flow (v2) suggest hydrodynamic

expansion and high pressure at early times in the collision history– The duration of hadronic particle emission appears to be very short

• The produced matter appears to be opaque– Saturation of v2 at high pT

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

• Statistical models describe the final state well– Excellent fits to particle ratio data with equilibrium thermal models– Excellent fits to flow data with hydrodynamic models that assume

equilibrated systems– Chemical freeze-out at about 175 MeV; thermal freeze-out at 100 MeV


36

Conclusions About Matter at RHIC:

Is there a phase with bulk properties which are Partonic ?• The data on high pt suppression and correlations support the

conclusion that we have produced a medium that: is dense; (pQCD theory many times cold nuclear matter density) is dissipative ( very strongly interacting)

• We need to show that: dissipation and collective behavior occur at the partonic stage the system is deconfined and thermalized a transition occurs: can we turn the effects off ?

• We need: extended AuAu run needed to address several important probes that need large data sets ( e.g., pT dependence of suppression; J/, , open

charm, heavy baryon / meson flow); also, species and energy scans to map the evolution of key observables.

more guidance from theory (!) particularly on what to expect from hadronic scenarios


37

Open charm: a probe of initial conditions, and possible equilibration at early times

Pressing the search with heavy flavor: first direct observation at RHIC of open charm in d+Au and min-bias Au+Au collisions

D0 K, d+AuD± K, d+Au

|y| < 1, pt < 4 GeV/c | y |< 0.25, 7 <pt <10 GeV/c Star Preliminary

0.0130.0003J//D0

0.1730.14c+/ D0

0.3930.20Ds+/ D0

0.4550.33D+/ D0

Au-Au

Thermal*

Pythia

p-p 200 GeV

Do c quarks thermalize? If yes, ratio of charm hadrons yield changes from p-p to Au-Au ; Ds

+ most sensitive.

A.Andronic, P.Braun-Munzinger, K.Redlich,J.Stachel (nucl-th/0209035)

STAR Preliminary

D± K, Au+Au

STAR Preliminary


38

The STAR Forward Pion Detector

Run 3 Objectives:

• Probe of Color Glass Condensate in d+Au pT dependence of large yield

• Improve understanding of dynamical origin of AN

in p+p 0 +X Collins effect sensitivity to transversity Sivers effect sensitivity to orbital motion twist-3 effect quark/gluon correlations

• Serve as local polarimeter at STAR IR

East of STAR

Top

Bottom

North South

BNL, Penn State, IHEP-Protvino, UC Berkeley/SSL, UCLA, ANL

d+Au +X, sNN = 200 GeV

• 10 < E < 80 GeV

• ~ 4 (relative to d)


39

STAR-Spin Results from Run 2

• Measured cross sections consistent with pQCD calculations• Large spin effects observed for s = 200 GeV pp collisions Status: final analysis complete / paper in final preparation

DIS2003

p + p + X , s = 200 GeV


40

OFF Pvert

ON Plong

STAR spin rotator:

Mistuned rotators

STAR Spin Rotator Magnet Tuning (Run III result)

L R

T

B*

BBC West

BBC East

InteractionVertex

3.3<||< 5.0

• Use inner tiles of BBC as a Local Polarimeter monitoring pp collisions.• Rotators OFF BBC L/R spin asymmetries comparable to RHIC polarimeter (CNI).• Rotators ON adjust rotator currents to minimize BBC L/R and T/B spin asymmetries.

RHIC polarimeter (CNI) establishes polarization magnitude; Local polarimeter (BBC) establishes polarization direction at STAR.

“Double-blind” intentional mis-tune check

Partial Snake Operation


41

Projections for Sensitivity to G for Run III and Run IV

Longitudinal spin asymmetry (ALL) for mid-rapidity jet production

may be first measurements directly sensitive to gluon polarization.

Jet reconstruction: cone algorithm (seed = 1 GeV, R = 0.7)

Polarization 0.4, Luminosity: 3 pb-1

Simulation based on Pythia + trigger and jet reconstruction efficiencyEMC Barrel Coverage includes 0 < Φ < 2π and 0 < η < 1Jet Trigger: ET > 5 GeV over one patch (Δη = 1) X (ΔΦ = 1)


42

Future STAR Spin Physics GoalsFuture STAR Spin Physics Goals

G (x) determination via ALL in p + p + jet + X

u , d determination via AL

PV in p + p W ± + X @ s = 500 GeV

– –

At design luminosity, a 10-week runs (with 50% RHICSTAR efficiency) apiece would yield:

s = 200 GeV, P = 0.7, L = 8 10 31 P 4L eff dt 60 pb –1

s = 500 GeV, P = 0.7, L = 2 10 32 P 4L eff dt 150 pb –1


43

The first 3 runs in STAR have been an outstanding success producing a wealth of results and new physics; even so, the most important achievements are still goals. The next 1-2 years will be extremely exciting.

The highest priority scientifically for the coming run is to go as far as possible to determine the properties of the qualitatively new, dissipative medium discovered in central Au+Au collisions at RHIC, and to study how these may change at a lower energy.

The STAR spin program is off to a great start. Continued progress in the near-term is critical.

STAR is now on a path to RHIC II. The strategy is to extend the scientific reach of the detector, maintaining the core capability of STAR to provide nearly complete event characterization over a wide range of central rapidity. Upgrades will be staged in such a way as to allow a vigorous physics program between now and 2010. All signs are positive for the MRPC TOF Barrel project becoming an approved construction project in the next few months as the first step to RHIC II in STAR.

Recent Results from STAR - Conclusions


44

Probing Chemical Equilibrium: Yield Ratios

STAR Preliminary

• No significant deviation seen from chemical thermal models

13 Ratios7 used

6 predicted

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

The STAR Experimental Program

Tch(RHIC) 175 ± 7 MeVB(RHIC) 51 ± 6 MeV

Lattice: (Karsch QM01)

Tch(RHIC) 173 ± 8 MeV, NF = 2Tch(RHIC) 154 ± 8 MeV, NF = 3


45

Resonance production: a tool for precision studies of the late stages of the collision at RHIC

STAR Preliminary

0.8 pT 0.9 GeV/c

|y| 0.5

pp Minimum Bias Au+Au 40% to 80%

1.2 pT 1.4 GeV/c

|y| 0.5

STAR Preliminary K*0

*(1520)

STAR preliminary p+p at 200 GeV

, , *(892), *(1385),*(1520), D*


46

The full spectrum of strange particles is available in STAR

K0s

STAR Preliminary

Documents

TJH Warsaw University, Nov 28, 2003 1 Recent Results from STAR Tim Hallman Warsaw University November 28, 2003