Roy A. LaceyRoy A. Lacey(SUNY Stony Brook(SUNY Stony Brook))

CCompressed ompressed BBaryonic aryonic Matter at the at the AGS: AGS:

A Review !! A Review !!

CCompressed ompressed BBaryonic aryonic Matter at the at the AGS: AGS:

A Review !! A Review !!

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The AGSThe AGS

                            

                     The Alternating Gradient Synchrotron (AGS) has been The Alternating Gradient Synchrotron (AGS) has been one of the world's premiere accelerators since 1960.one of the world's premiere accelerators since 1960.

The GSI Accelerator The GSI Accelerator facility has been one facility has been one

of the world'sof the world'spremier facilities for premier facilities for more than 25 years.more than 25 years.

Proposed

ExistingExisting

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A Diverse Range of Experimental Programs have been Carried out at the AGS

AGS Expts.AGS Expts.

E802/866E802/866

E810/891E810/891

E814/877E814/877

E864E864

E895E895

E917E917

DisclaimerDisclaimer

p+A, Si+A, Au+A 2 – 18 AGeV1986 - 14.6 AGeV/c Si1992 – 11.0 AGeV/c Au More thanMore than

200 pubs200 pubs

Only a Selection of the full range of Experimental Only a Selection of the full range of Experimental Results will be covered. Results will be covered.

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MotivationMotivation

Results & ImplicationsResults & Implications– Global ObservablesGlobal Observables

– Rapidity Distributions & StoppingRapidity Distributions & Stopping

– HBTHBT

– FlowFlow

– Particle ProductionParticle Production

Summary

OutlineOutline

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MotivationMotivation

Particular Particular FocusFocus

IdentificatioIdentification and Study n and Study of the of the LGPLGP and and QGPQGP

The Notion of a Phase Diagram for Nuclear Matter is PervasiveThe Notion of a Phase Diagram for Nuclear Matter is Pervasive

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F. WeberF. Weber s/

P ²e

Motivation – High Density Motivation – High Density Nuclear MatterNuclear Matter

Various competing forms of

matter are predicted at high

Baryon density

!! Crucial Information !!!! Crucial Information !!

•Property of Hadrons in Property of Hadrons in Dense nuclear MediumDense nuclear Medium

•Phase transition to Quark Phase transition to Quark Gluon Matter at high baryon Gluon Matter at high baryon densitydensity

•Nuclear Equation of State at Nuclear Equation of State at high baryon Densitieshigh baryon Densities

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Bao-an Li

Why Study Heavy Ion Reactions at the AGS ?Why Study Heavy Ion Reactions at the AGS ?Why Study Heavy Ion Reactions at the AGS ?Why Study Heavy Ion Reactions at the AGS ?

MotivationMotivation

Compressed Baryonic Matter is Produced at the AGS Compressed Baryonic Matter is Produced at the AGS

In an Interesting Region of the Phase Diagram ?In an Interesting Region of the Phase Diagram ?

Compressed Baryonic Matter is Produced at the AGS Compressed Baryonic Matter is Produced at the AGS

In an Interesting Region of the Phase Diagram ?In an Interesting Region of the Phase Diagram ?

Energy Density ~ 1 – 2 Gev/fmEnergy Density ~ 1 – 2 Gev/fm33

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Global Observables Barette et al., E877

Substantial Pseudorapidity Densities are achieved

Nc ~ 450 for central collisions

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time to thermalize the system (0 ~ 1 fm/c)~6.5 fm

dy

dE

RT

Bj0

2

11

Barette et al., E877

Bjorken~ 1.3 GeV/fm3

Critical Energy Density ~ 1-1.5 GeV/fm3

Energy Density

Large Energy Density pressure gradients & ExpansionLarge Energy Density pressure gradients & Expansion

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Significant Stopping is achieved in central collisions at the AGS

Rapidity Distributions and Baryon StoppingRapidity Distributions and Baryon Stopping

Holzmanet. alE917

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J. Klay et al. E895

Rapidity Distributions and Baryon StoppingRapidity Distributions and Baryon StoppingSi + Al Au + AuBraun-Munzinger et al.

2 cosh3

2 2

2 2

cosh cosh

my

TdN m mT e

dy T T y y

(T obtained from particle Spectra)

Maxwell-Boltzmann Distribution

Distributions are consistent with significant longitudinal Flow.

Longitudinal Flow Systematics

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Particle Spectra are compatible with

significant radial Flow.

Radial FlowRadial FlowAu + Au (-0.05 < y < 0.05

/2

1/ 22

1 sinhcosh

/ 1

tm T

t t t t

dN T Te

m dm m m

p T

and T

Sign

ifica

nt T

rans

vers

e

Sign

ifica

nt T

rans

vers

e

Expan

sion

Expan

sion

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HBTHBT

21

2

1224

14

2 xxxdxdC

In the Longitudinal CMS, where (p1+p2)beam = 0,

222TO

2TO

2TS

2TS

2L

2L2

2

2

2TO

2TO

2TS

2TS

2L

2L

ERqRqRqexp1C

2

t

R2

r

R2

r

R2

rexp,tr

21

21

2

exp2

dpd

dpd

dpdpd

C

expTOR

2

2expTS

2expTO2

222TO

2TO

2TS

2TS

2L

2L2

RR

RqRqRqexp1C

C2 is measured as,

Observables3 radii: duration time:

chaoticity:

222TO

expTOTSL RR,R,R

QTS QTO QL

Probability to detect 2 particles at p1 and p2,

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HBTHBT

expTOR

2

2expTS

2expTO2

222TO

2TO

2TS

2TS

2L

2L2

RR

RqRqRqexp1C

3

3

V ~ 2600 fm (2X Au)

~ 0.12/fm

Stachel et al.

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HBT – Reaction plane HBT – Reaction plane DependenceDependence

Rout < RsideInitial Overlap => Shape at freeze-out

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Flow

pass0 0

expant

2t

~

~

S

R

R

c

Low Energy:Low Energy:Squeeze-out

Pressure Gradients Drive Pressure Gradients Drive Transverse and Elliptic flowTransverse and Elliptic flow

High EnergyHigh Energy In-plane

1 2~ 1 2 cos( ) 2 cos(2 )dN

v vd

1 2~ 1 2 cos( ) 2 cos(2 )dN

v vd

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1 2

2

~ 1 2 cos( ) 2 cos(2 )

cos(2 )

dNv v

d

v

1 2

2

~ 1 2 cos( ) 2 cos(2 )

cos(2 )

dNv v

d

v

/

9s

dpK

d

VV22 is sensitive to the EOS is sensitive to the EOS

Danielewicz et al.

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VV22 is sensitive to the Phase Transition is sensitive to the Phase Transition

Danielewicz et al.

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FlowFlow

(E895)(E895)E877

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Good Agreement with theory, Softening of EOSGood Agreement with theory, Softening of EOS

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Differential Flow

Differential Differential MeasurementsMeasurements

(E895)(E895)

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•Differential Elliptic Flow Studies Provide Differential Elliptic Flow Studies Provide Important Additional Insights on the EOSImportant Additional Insights on the EOS•Differential Elliptic Flow Studies Provide Differential Elliptic Flow Studies Provide Important Additional Insights on the EOSImportant Additional Insights on the EOS

pass0 0

2t ~

R

pass

0 0

2t ~

R

1expant ~

S

d

c

1expant ~

S

d

c

2expant ~

S

d

c

2expant ~

S

d

c

d1

d2

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Good Agreement with Good Agreement with calculation which assumes calculation which assumes

p dependent meanfield p dependent meanfield

H. Liu E895 Sahu et al.

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New constraints for the EOS achievedNew constraints for the EOS achieved

Danielewicz et al.

FlowFlow

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Flow of Produced ParticlesFlow of Produced Particles

Clear Evidence for in-medium potentialClear Evidence for in-medium potential

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Particle ProductionParticle Production

OF Particular InterestOF Particular Interest• Enhancement in Strangeness Production

• Enhancement in the ratio Antihyperon/Antibaryon

Probes for the QGP

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Particle ProductionParticle Production

Yields Increase from Peripheral to Central CollisionsYields Increase from Peripheral to Central Collisions-- Consistent With Multiple Collisions per participant -- Consistent With Multiple Collisions per participant

F. Wang

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Particle ProductionParticle Production

Ratio increases with beam Ratio increases with beam energy… possible maximumenergy… possible maximum

p+p

Smooth Decrease in enhancementSmooth Decrease in enhancement

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Particle ProductionParticle Production

Ratio Increase from Peripheral to Central CollisionsRatio Increase from Peripheral to Central Collisions-- Reasonable agreement with model calculations-- Reasonable agreement with model calculations

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Particle ProductionParticle Production

Remarkable Agreement with Predictions of Thermal modelRemarkable Agreement with Predictions of Thermal model

& TB

Braun-Munzinger et al.

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Stachel et al.

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Compressed Baryonic Matter is Produced With Compressed Baryonic Matter is Produced With Significant Energy Density at the AGS.Significant Energy Density at the AGS.

The study of this matter has provided a wealth of insightsThe study of this matter has provided a wealth of insights Further Studies are Required for a more complete Further Studies are Required for a more complete

understanding as well as further mapping of the phase understanding as well as further mapping of the phase diagramdiagram

..

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New constraints for the EOS achievedNew constraints for the EOS achieved

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Motivation – Strange ParticlesMotivation – Strange Particles

K- & K0 attractive Interaction

K+ & K0 Repulsive Interaction

- Consequences for Flow

In QGP

Production in hadronic gas pairs of strange hadrons with

increased threshold

Strangeness Enhancement

The Production and Propagation of Strange Hadrons The Production and Propagation of Strange Hadrons

constitutes an Important Probeconstitutes an Important Probe

gg ss