Helen CainesYale University

ICPAQGP-Jaipur

Nov 2001

STAR

First Results from the STAR Detector at

RHIC(Au-Au at sNN=130

GeV)

If we knew what we were doing it would not be called research, would it? - A. Einstein

Helen Caines

ICPAQGP - 2001STAR

2

What are we looking for?

• What is the initial environment like for particle production?– Energy density– Net baryon density– Early equilibration

• What happens during the initial particle production?– Jet production/quenching– Chemistry

– Volume, expansion, emission duration

• Are re-interactions significant?– Rescattering of hadrons– Equilibration of strangeness– Radial flow

Baryon / antibaryon ratios

Ratios and yields2 particle

correlations

Strange baryon ratios

Hadron ratios vs. pT

mT slopes

Anisotropic flow

High pt measurements

Charged particle mult., <pT>

Helen Caines

ICPAQGP - 2001STAR

3 installation in 2003

Endcap Calorimeter

Year 2000,

The STAR Detector (Year-by-Year)

ZCal

Time Projection Chamber

Magnet

Coils

RICH * yr.1 SVT ladder

TPC Endcap & MWPC

ZCal

Central Trigger Barrel

FTPCs

Silicon Vertex Tracker *

Vertex Position Detectors

year 2001,

+ TOF patch

Barrel EM Calorimeter

year-by-year until 2003,

Helen Caines

ICPAQGP - 2001STAR

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Event (Centrality) Selection

PRL 86, (2001) 402

nch = primary tracks in || < 0.75

ZDC ZDC Au Au

Central Multiplicity Detectors

5% Central

central collisions

Data 2000 2.0 M total trigger events taken 844 K central (top 15%) 331 K good (top 5%) central for physics analysis 458 K good min bias events for physics analysis

Helen Caines

ICPAQGP - 2001STAR

5

Particle identification

Approx. 10% of a central event

V0

K0

p

p

and by extension

K

Kink

K

a) dE/dx

b) RICH

c) Topology

K p d

e

Helen Caines

ICPAQGP - 2001STAR

6

Anti-Baryon/Baryon Ratios

2Tr

pair

Y

Y65.0

Trpair

pair

p

pbar

YY

Y

Y

YPair product is larger than baryon transport:

2/3 of protons from pair production

1/3 from initial baryon number transported over 5 units of rapidity

central events mid-yaveraged over experimental pT

Measured in STAR acceptanceExtrapolated yields

BRAHMS preliminary

STAR data : submitted to PRLBRAHMS data : Quark Matter 2001

• Mid-rapidity region not yet baryon-free!

• Baryon-pair production increases with s

• Weak Centrality dependence of net p

Helen Caines

ICPAQGP - 2001STAR

7

Particle Multiplicity

PRL 87, 112303 (2001)

1cosh)/(

cosh)/(),(

22

mp

mpp

yJacobian:

h- : 5% most central

• h- spectra for –1 < < 1 in accordance with boost-invariant system

• better: dN/dy from also flat

• dN/dy looks boost-invariant BUT

• change in pT (mT) slopes for rapidity 0 1

STAR Preliminary

STAR Preliminary

Increase in particle production58% compared to Pb+Pb at √snn = 17.2 GeV

38% compared to (scaled) pbar+p

dNch /d= 567±1±38

Helen Caines

ICPAQGP - 2001STAR

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Models to Evaluate Tch and B

Assume: Hadron resonance ideal gas

Comparable particle ratios to experimental data

Qi : 1 for u and d, -1 for u and d

si : 1 for s, -1 for s

gi : spin-isospin freedom

mi : particle mass

Tch : Chemical freeze-out

temperatureq : light-quark chemical potential

s : strangeness chemical potential

s : strangeness saturation factor

Particle density of each particle:

J.Rafelski PLB(1991)333J.Sollfrank et al. PRC59(1999)1637

Statistical Thermal ModelF. BecattiniP. Braun-Munzinger et al. PLB(1999)

Assume: • thermally and chemically equilibrated fireball at hadro-chemical freeze-out • law of mass action is applicable !!!

Recipe:• grand canonical ensemble to describe partition function density of particles of species i

• fixed by constraints: Volume V, ,

strangeness chemical potential S,

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

Chemical Freeze-Out Model

Helen Caines

ICPAQGP - 2001STAR

9

Models to Evaluate Tch and B

Central

Chemical freeze-out parameters:

Tch = 179±4 MeV, s= -0.8±2.0 MeVB = 51±4 MeV, s= 0.99 ±0.03

M. Kaneta, N. Xu

MeV 270(SPS)μ 46(RHIC)μ

MeV 170160(SPS)T174(RHIC)T

BB

chch

P. Braun-Munzinger et al. SQM 2001

Simple pictures seem to work and give similar answers All results preliminary, central and at mid-y

Helen Caines

ICPAQGP - 2001STAR

10

The flies in the thermal ointment.

/h- = 0.0122+/-0.0006

/K- =0.084+/-0.006

T (MeV)

Rat

ios

Braun-Munzinger et al.hep-ph/0105229

Thermal fit resultsin T ~ 175 MeV

Model gets simple ratios correct,but miss multi-strange ratios significantly!!!

Statistical errors only

+/

Preliminary STAR 10% central data

-/K-

Helen Caines

ICPAQGP - 2001STAR

11

New Point in Phase-Diagram

All models so far (despite small differences in the details) give similar results: RHIC Tch ~ 175 MeV , B = 50 MeV

Compare to QCD on Lattice:Tc = 154±8 MeV (Nf=3)Tc = 173±8 MeV (Nf=2)

(ref. Karsch QM01)

neutron stars

Baryonic Potential B [MeV]

early universe

Chem

ical Tem

pera

ture

Tch

[M

eV

]

0

200

250

150

100

50

0 200 400 600 800 1000 1200

AGS

SIS

SPS

RHIC quark-gluon plasma

hadron gas

thermal freeze-out

deconfinementchiral restauration

Lattice QCD

atomic nuclei

?!

Beam energy dependence

Temperature increases

Baryon chemical potential decreases

At RHIC

Fully strangeness equilibration (s~1)

Being close to phase boundary

Helen Caines

ICPAQGP - 2001STAR

12

mT slopes vs. Centrality

Increase in slope with collision centrality consistent with radial flow.

Helen Caines

ICPAQGP - 2001STAR

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Mass dependence of mT slopes

Indication of strong radial flow at RHIC

Situation appears to be more complicated at RHIC than at the SPS

Note: inverse slope depends on the measured pT range(dE/dx p < 1 GeV/c)

1/m

T d

N/d

mT

(a.u

.)mT-m

STAR Preliminary

Helen Caines

ICPAQGP - 2001STAR

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Hydrodynamics motivated mT fit

mT - m0 (GeV)

1/m

T d

N/d

mT

(a

.u.)

STAR Preliminary

tanh 1 r r (r) s f (r)

R

s

E.Schnedermann et al, PRC48 (1993) 2462

Flow profile used

r =s (r/R)0.5

-

K-

p

solid : used in fit

dn

mT dmT r dr mT K1

mT coshT

0

R

I0pT sinh

T

Shape of the mT spectrum depends on particle mass

Inverse-slope depends on mT-range

where and

Helen Caines

ICPAQGP - 2001STAR

15

K-p

-

<r > [c]

Tth [

GeV

]

0 0.40 0.4<r > [c]

Tth [

GeV

]

Fits to the hydro. modelSTAR Preliminary

STA

R

PHE

NIX

Tth

[GeV

]< r

> [

c]

explosive radial expansion at RHIC high pressure

r (RHIC) = 0.52c Tfo (RHIC) = 0.13 GeV

Helen Caines

ICPAQGP - 2001STAR

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Comparison of h- and , pT dist.

STAR Preliminary

Suggestive that the ratio baryons/mesons > 1 at high pT

Consequence of radial flow ?

or novel baryon dynamics ?Vitev and Gyulassy nucl-th/0104066

Helen Caines

ICPAQGP - 2001STAR

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Event anisotropy

• The pressure gradient generates collective motion (aka flow) Central collisions

• radial flow Peripheral collisions

• radial flow and anisotropic flow

x

y

p

patan

2cos2 vAlmond shape overlap region in

y2 x2 y2 x2

x

z

y

Coordinate anisotropy Momentum anisotropy

py

px

Helen Caines

ICPAQGP - 2001STAR

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Low pT v2

midrapidity : |h| < 1.0

Peripheral Central

First time data is well represented by a hydrodynamical model

•Mass dependence

–Also typical hydrodynamic behavior

STAR PRL87 (2001)182301

STARModel

Helen Caines

ICPAQGP - 2001STAR

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M. Gyulassy, I. Vitev, X.N. Wang nucl-th/0012092

v2 at High pT

STAR Preliminary

Kp

Flattening at high pT not described by models

Appears for identified particles too

STAR Preliminary

Helen Caines

ICPAQGP - 2001STAR

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Inclusive pT dist. of negative hadrons

Preliminary QM01

Preliminary QM01

Hadron suppression by ~ factor 2 at high pT

Helen Caines

ICPAQGP - 2001STAR

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pbar/p ratio versus pT

X.N.Wang, Phys. Rev. C 58 (1998) 2321

pbar

/p r

atio

pb

ar/p

Preliminary

Ratio constant out to 2.5 GeV/c

Helen Caines

ICPAQGP - 2001STAR

22

Summary – First year of STAR

• What is the initial environment like for particle production?– Net baryon density– Early equilibration – Energy density

• What happens during the initial particle production?– Jet quenching – Strangeness production

– Volume,expansion, emission duration

• Are re-interactions significant?– Rescattering of hadrons– Equilibration of strangeness– Radial flow

Not yet baryon free

Unlike ratios similar to SPS

High flow creates new picture

Models don’t reproduce multi-s

Significant radial flow

Baryon>meson at high pT

Significant increase in multiplicity and mean pT relative to SPS

High flow agrees with hydro-dynamics

Suppression of particles at high pT

Ratios flat as function pT

Helen Caines

ICPAQGP - 2001STAR

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July 2001

GeV 200sNN

Outlook – 2001 and Beyond• Additional physics beyond Year 1

FTPCs

measurements of charged hadrons,

strange particles at forward rapidities

Year 2001

Increased coverage for event-by-event physicsYear 2002

Already have ~10X statistics of year 2000

Will take some p-p reference data (and of course polarization data)

EMC

o identification, yields, slopes

high pT triggering, transverse energy

Installation of PMD

Installation of SSD

SVTmultiply-strange baryons ( yields & slopes

Helen Caines

ICPAQGP - 2001STAR

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The STAR CollaborationRussia:MEPHI - MoscowLPP/LHE JINR - DubnaIHEP - Protvino

U.S. Labs:ArgonneBerkeleyBrookhaven

U.S. Universities: Arkansas UniversityUC BerkeleyUC DavisUC Los AngelesCarnegie Mellon UniversityCreighton UniversityIndiana UniversityKent State UniversityMichigan State UniversityCity College of New YorkOhio State UniversityPenn. State UniversityPurdue UniversityRice UniversityTexas A&MUT AustinWashington UniversityWayne State UniversityYale University

Brazil: Universidade de Sao Paolo

China: IHEP - BeijingIPP - Wuhan

England: University of Birmingham

France:IReS StrasbourgSUBATECH - Nantes

Germany: MPI – MunichUniversity of Frankfurt

India:IOP - BhubaneswarVECC - CalcuttaPanjab UniversityUniversity of RajasthanJammu UniversityIIT - Bombay

Poland:Warsaw University of Technology

Helen Caines

ICPAQGP - 2001STAR

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Different views of the same physics ?

Evidence of hadron suppression at high pT

Sensitive to partonic interaction with matter?

STAR Preliminary

Kp

Helen Caines

ICPAQGP - 2001STAR

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h- : pTDistributions and pT

NA49pp

h-

STAR Preliminary

Power Law:

A (1+pt /p0) - n

h-

<pt> increases with centralityFor central collisions higher than in min. bias pp collisions @ s = 1.8 TeV (CDF)

STAR

Helen Caines

ICPAQGP - 2001STAR

27

•Surprising: source sizes roughly same as at AGS/SPS ( < 10fm)

• radii increase with centrality (expected for ROut,RSide)

• Radii decrease with increasing kT

(flow)

• Unexpected: ROut/RSide ~ 1

The Rout/Rside Ratio

kT = pair pT

RsideRout

Hydrodynamical QGP + (URQMD or RQMD)

can not reproduce Ro< Rs

STAR data

model: R=13.5 fm, =1.5 fm/c Tth=0.11 GeV, r = 0.5 c

PHENIX Preliminary

Consistent Tth and r with those from spectra and v2