Roy A. Lacey (SUNY Stony Brook ) C ompressed B aryonic at the AGS: A Review !! C ompressed B aryonic M atter at the AGS: A Review !!

Stony Brook The AGS The Alternating Gradient Synchrotron (AGS) has been one of the world's premiere accelerators since The GSI Accelerator facility has been one of the world's premier facilities for more than 25 years. Proposed Existing

Stony Brook A Diverse Range of Experimental Programs have been Carried out at the AGS AGS Expts. E802/866E810/891E814/877E864E895E917 Disclaimer p+A, Si+A, Au+A 2 – 18 AGeV AGeV/c Si 1992 – 11.0 AGeV/c Au More than 200 pubs Only a Selection of the full range of Experimental Results will be covered.

Stony Brook Motivation Results & Implications –Global Observables –Rapidity Distributions & Stopping –HBT –Flow –Particle Production Summary Outline

Stony Brook Motivation Particular Focus Identification and Study of the LGP and QGP The Notion of a Phase Diagram for Nuclear Matter is Pervasive

Stony Brook F. Weber Motivation – High Density Nuclear Matter Various competing forms of matter are predicted at high Baryon density !! Crucial Information !! Property of Hadrons in Dense nuclear MediumProperty of Hadrons in Dense nuclear Medium Phase transition to Quark Gluon Matter at high baryon densityPhase transition to Quark Gluon Matter at high baryon density Nuclear Equation of State at high baryon DensitiesNuclear Equation of State at high baryon Densities

Stony Brook Bao-an Li Why Study Heavy Ion Reactions at the AGS ? Motivation Compressed Baryonic Matter is Produced at the AGS In an Interesting Region of the Phase Diagram ? Compressed Baryonic Matter is Produced at the AGS In an Interesting Region of the Phase Diagram ? Energy Density ~ 1 – 2 Gev/fm 3

Stony Brook Global Observables Barette et al., E877 Substantial Pseudorapidity Densities are achieved N c ~ 450 for central collisions

Stony Brook time to thermalize the system (  0 ~ 1 fm/c) ~6.5 fm Barette et al., E877   Bjorken  ~ 1.3 GeV/fm 3 Critical Energy Density ~ GeV/fm 3 Energy Density Large Energy Density pressure gradients & Expansion

Stony Brook Significant Stopping is achieved in central collisions at the AGS Rapidity Distributions and Baryon Stopping Holzman et. al E917

Stony Brook J. Klay et al. E895 Rapidity Distributions and Baryon Stopping Si + Al Au + Au Braun-Munzinger et al. (T obtained from particle Spectra) Maxwell-Boltzmann Distribution Distributions are consistent with significant longitudinal Flow. Longitudinal Flow Systematics

Stony Brook Particle Spectra are compatible with significant radial Flow. Radial Flow Au + Au (-0.05 < y < 0.05 Significant Transverse Expansion

Stony Brook HBT In the Longitudinal CMS, where (p 1 +p 2 ) beam = 0, C 2 is measured as, Observables 3 radii: duration time: chaoticity: Q TS Q TO QLQL Probability to detect 2 particles at p 1 and p 2,

Stony Brook HBT Stachel et al.

Stony Brook HBT – Reaction plane Dependence Rout < Rside Initial Overlap => Shape at freeze-out

Stony Brook Flow Low Energy: Squeeze-out Pressure Gradients Drive Transverse and Elliptic flow High Energy In-plane

Stony Brook V 2 is sensitive to the EOS Danielewicz et al.

Stony Brook V 2 is sensitive to the Phase Transition Danielewicz et al.

Stony Brook Flow (E895) E877

Stony Brook Good Agreement with theory, Softening of EOS

Stony Brook Differential Flow DifferentialMeasurements(E895)

Stony Brook Differential Elliptic Flow Studies Provide Important Additional Insights on the EOS Differential Elliptic Flow Studies Provide Important Additional Insights on the EOS d1d1 d2d2

Stony Brook Good Agreement with calculation which assumes p dependent meanfield H. Liu E895 Sahu et al.

Stony Brook New constraints for the EOS achieved Danielewicz et al. Flow

Stony Brook Flow of Produced Particles Clear Evidence for in-medium potential

Stony Brook Particle Production OF Particular Interest Enhancement in Strangeness Production Enhancement in the ratio Antihyperon/Antibaryon  Probes for the QGP

Stony Brook Particle Production Yields Increase from Peripheral to Central Collisions -- Consistent With Multiple Collisions per participant F. Wang

Stony Brook Particle Production Ratio increases with beam energy… possible maximum p+p Smooth Decrease in enhancement

Stony Brook Particle Production Ratio Increase from Peripheral to Central Collisions -- Reasonable agreement with model calculations

Stony Brook Particle Production Remarkable Agreement with Predictions of Thermal model Braun-Munzinger et al.

Stony Brook Stachel et al.

Stony Brook Compressed Baryonic Matter is Produced With Significant Energy Density at the AGS.  The study of this matter has provided a wealth of insights  Further Studies are Required for a more complete understanding as well as further mapping of the phase diagram.

Stony Brook New constraints for the EOS achieved

Stony Brook Motivation – Strange Particles K - & K 0  attractive Interaction K + & K 0  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 constitutes an Important Probe