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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