Spectator response to participants blast -experimental evidence and possible

implications

New tool for investigating the momentum- dependent properties of nuclear matter.

Vladimir Henzl

GSI-Darmstadt, Germany

Outline

Introduction & motivation:• properties of nuclear matter: and relevance for astrophysics• static vs. dynamic properties: peculiarities of investigated systems• standard tools of investigation: collective flows, kaon production, ...

Spectator response:• original idea and theoretical predictions:• first observation: reacceleration of fragmentation residues

Results of dedicated experiments:

Summary & Outlook

• spectator response in Au+Au @ 1 A GeV• spectator response in Au+Au,Al @ 500 A MeV:• comparison with BUU calculations

Experimental approach: possibilities of FRS

Astrophysical interest:

• evolution of the early universe • supernovae explosions • formation and stability of neutron stars

influenced by properties of the nuclear matter (NM)under extreme conditions (high T, P, ρ, …)

Properties of the NM:

• static – (in)compressibility, phase transitions, excitation…• dynamic – viscosity, momentum dependence of the mean field …

General motivation

Static vs. dynamic properties

Problem: most of the experimental observables are not selective;

Static properties are studied in dynamical processes !!!

Aichelin et al. PRL 58(1987)1926

=> the interpretation is influenced by competing phenomena,

!!! The results are very often ambiguous !!!

Present knowledge

Recent analysis:(Danielewicz et al.)

Sci

ence

298

(20

02)

1592

Attempt to constrain nuclear matter equation of state by results of performed experiments.

Only the most extreme models could be excluded by the experiment

Tools to investigate the nuclear matter

BUU calculations : 124Sn +124Sn Tlab= 800 MeV/u b = 5 fm

L. Shi, P. Danielewicz, R. Lacey, PRC 64 (2001)

the spectator is not a passive witness, but rather a victim of violent participants !

Standard tools:

Spectator response:

eliptic flow, radial flow, transverse momentum, (anti)kaon production, …

• L. Shi, P. Danielewicz, R. Lacey, PRC 64 (2001)

• M.V.Ricciardi et al. PRL 90(2003)212302

! New !

Spectator response to the participant blast

Spectator response or „what can we learn from victims“

Theoretical prediction: (Shi, Danielewicz, Lacey)

1) Net momentum change depends on nonlocality of nuclear mean field. 2) Net momentum change is almost insensitive to the stiffness of the EoS.

Spectator response is selectively sensitive to nonlocal properties of nuclear mean field !!!

PCMS/A = 682 MeV/c

Observatio

n3) to study possible dependence of spectator response on incident energy and/or size of the colliding system

2) to establish correlation of Ares and impact parameter b1) to improve experimental signature of spec. response

Idea

BUU calculations : 124Sn +124Sn Tlab= 800 MeV/u b = 5 fm

L. Shi, P. Danielewicz, R. Lacey, PRC 64 (2001)

T.Enqvist et al. NPA658(1999)47 BUU by V.H.

Motivation for new experiments:

Proposal of new experimental program:

197Au+197Au @ 0.5 and 1.0 A GeV

... aproved and carried out in 2004

Experimental approach

The Fragment Separator at GSI-Darmstadt

Once mass and charge are identified (A, Z are integer numbers) the velocity is calculated from B:

A/∆A ≈ 400

Inverse kinematics:

From ToF: /∆ ≈ 400

/∆ = B/∆B ≈ 2000

(36m)

=> very precise determination!

Characteristics of the data

• unambiguous identification & precise longitudinal momenta

only one fragment in one reaction measured

Au+Au@1 A GeV Pb+p@1 A GeV

• limited acceptance: ±15mrad, ±1.5% in momentum

Velocity distributions with limited acceptance136Xe+natPb @ 1 A GeV (D.Henzlova)

• limited momentum acceptance:

Several magnetic field settings need to be combined to get complete velocity distribution (each color = 1 magnetic setting)

fission

Information from full acceptance experimentsInformation from full acceptance experiments

fission

197Au+197Au @ 1 A GeV - ALADIN

238U+Cu @ 1 A GeV - ALADIN

single, unambiguously identified fragment at FRSsingle, unambiguously identified fragment at FRS is predominantly largest residue per collisionpredominantly largest residue per collision

fragmentation

fragmentation

the largest fragment is well correlated with the largest fragment is well correlated with ZZboundbound (for Z (for Zmaxmax>30 >30 ~ A~ Amaxmax>65)>65)

Information from the ZInformation from the Zmaxmax

Aladin data: Au+Au @ 400, 600, 800, 1000 A MeV

peripheral collisions investigatedperipheral collisions investigated

Aladin data: Au+Au @ 600 A MeV

fragments with Z>20 are produced in fragments with Z>20 are produced in reactions with b reactions with b ≥ 9fm (in Au+Au system) ≥ 9fm (in Au+Au system)

ZZmaxmax carries information on impact parameter carries information on impact parameter

ZZboundbound is a measure of the impact parameter is a measure of the impact parameter

Different reaction processesDifferent reaction processes

fission

How to distinguish fragmentation and fission?238U (1 A GeV) + Pb

Fragmentation: heaviest residues fully accepted (A>90)Fission: Only forward and backward component accepted

197Au+197Au @ 1 A GeV (V.H.)

Results of dedicated experiments

First dedicated experiment

• most peripheral collisions yield deceleration

residues with Ares ≤ 85 on average faster than the beam

mean velocities in agreement with Morrissey systematics. • with decreasing mass loss, velocities level off and increase

V.H.: PhD thesis

(in preparation)

More dedicated experiments

• reacceleration smaller with smaller incident energy• reacceleration smaller in smaller reaction systems

all systems yield clearly visible net reacceleration

Reacceleration and its behavior is an experimental fact !Interpretation possible only with help of calculations

V.H.: PhD thesis

(in preparation)

New experimental data => new simulations

• BUU calculations with MD mean fields qualitatively agree with experiment (no sensitivity to stiffness of EoS)

• BUU calculations with static MI field are not able to describe trend of the data

BUT: Correlation of Ares with impact parameter b nontrivial !!!

How to relate Ares and an impact parameter

•Zmax2 has different (and worse) correlation with Zbound (impact par.)

Aladin:

Region of mixing Zmax & Zmax2 can‘t be used to deduce b !

Only data in blue area suitable for extraction of impact parameter !!!

New experimental data => new simulations

Calculations with MD MF induce gain of the momenta, but for too low impact parameters with respect to the experiment !!!

Open question: which parameters of BUU can influence the spectator response? ... one possible idea ...

Summary & outlook

Summary & Outlook

• More BUU calculations on the way, many more needed

Outlook:

• further experiments & simulations needed to constrain MD properties of nuclear mean field

Summary:

• reacceleration phenomena seen in all systems, its strength depends on incident energy and size of the colliding system

• only BUU with MD MF induce recovery of the fragment velocities with decreasing impact parameter, in qualitative agreement with the experiment

• longitudinal velocities of fragmentation residues measured in Au+Au @ 0.5, 1 A GeV, Au+Al @ 0.5 A MeV

• Au+Au/Al @ 1/0.5 A GeV: data analysis finished, interpretation in progress

• 112,124Sn+112,124Sn @ 1 A GeV: experiment in preparation - 2005/2006

CHARMS & re-acceleration(Collaboration for High-Accuracy Experiments on Nuclear Reaction Mechanisms with the FRS)

 

V. Henzl1, J. Benlliure2, P.Danielewicz4, T. Enqvist5, M. Fernandez2, A. Heinz6, D. Henzlova1, A. Junghans7, B. Jurado8, A. Kelic1, J. Pereira2, R. Pleskac1,

M. V. Ricciardi1, K.-H. Schmidt1, C. Schmitt1, L.Shi4, J. Taïeb3, A. Wagner7, O. Yordanov1

 1GSI, Planckstr. 1, 64291, Darmstadt, Germany

2Universidad de Santiago de Compostela, 15706 Santiago de Compostela, Spain3CEA/Saclay, 91191 Gif sur Yvette, France

4National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy,Michigan State University, East Lansing, MI 48824, USA

5Department of Physics, University of Jyväskylä, 40014, Finland6Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520, USA

7FZ Rossendorf, Bautzener Landstrasse 128, 01328, Dresden, Germany 8GANIL, 14076 Caen, France