Prezentace aplikace PowerPoint

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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
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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

Experimental approach possibilities of FRS
Results of dedicated experiments

• spectator response in AuAu _at_ 1 A GeV
• spectator response in AuAu,Al _at_ 500 A MeV
• comparison with BUU calculations

Summary Outlook
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General motivation
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, ?, )
Properties of the NM

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

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Static vs. dynamic properties
Aichelin et al. PRL 58(1987)1926
Static properties are studied in dynamical
processes !!!
Problem most of the experimental observables are
not selective
gt the interpretation is influenced by competing
phenomena,
!!! The results are very often ambiguous !!!
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Present knowledge
Recent analysis (Danielewicz et al.)
Science 298 (2002) 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
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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)
Standard tools
eliptic flow, radial flow, transverse momentum,
(anti)kaon production,
Spectator response
the spectator is not a passive witness, but
rather a victim of violent participants !
! New !

• L. Shi, P. Danielewicz, R. Lacey, PRC 64 (2001)
• M.V.Ricciardi et al. PRL 90(2003)212302

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Spectator response to the participant blast
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Spectator response or what can we learn from
victims
Theoretical prediction (Shi, Danielewicz, Lacey)
PCMS/A 682 MeV/c

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

Spectator response is selectively sensitive to
nonlocal properties of nuclear mean field !!!
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Idea
BUU calculations 124Sn 124Sn Tlab 800
MeV/u b 5 fm L. Shi, P. Danielewicz, R.
Lacey, PRC 64 (2001)
Motivation for new experiments
1) to improve experimental signature of spec.
response
2) to establish correlation of Ares and impact
parameter b
3) to study possible dependence of spectator
response on incident energy and/or size of the
colliding system
Observation
Proposal of new experimental program
197Au197Au _at_ 0.5 and 1.0 A GeV
T.Enqvist et al. NPA658(1999)47
BUU by V.H.
... aproved and carried out in 2004
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Experimental approach
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Experiment at the Fragment Separator
Inverse kinematics
From ToF ??? /???? 400
A/?A 400
(36m)
Once mass and charge are identified (A, Z are
integer numbers) the velocity is calculated from
B?
??? /???? B?/?B? 2000
gt very precise determination!
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Characteristics of the data
AuAu_at_1 A GeV
Pbp_at_1 A GeV

• unambiguous identification precise
  longitudinal momenta

• limited acceptance 15mrad, 1.5 in momentum

only one fragment in one reaction measured
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Velocity distributions with limited acceptance
136XenatPb _at_ 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)
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Information from full acceptance experiments
238UCu _at_ 1 A GeV - ALADIN
fission
fragmentation
197Au197Au _at_ 1 A GeV - ALADIN
fission

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

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Information from the Zmax
Aladin data AuAu _at_ 400, 600, 800, 1000 A MeV
Aladin data AuAu _at_ 600 A MeV

• Zbound is a measure of the impact parameter

• the largest fragment is well correlated with
  Zbound (for Zmaxgt30 Amaxgt65)

Zmax carries information on impact parameter

• fragments with Zgt20 are produced in reactions
  with b 9fm (in AuAu system)

• peripheral collisions investigated

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Different reaction processes
How to distinguish fragmentation and fission?
238U (1 A GeV) Pb
197Au197Au _at_ 1 A GeV (V.H.)
fission
Fragmentation heaviest residues fully accepted
(Agt90)
Fission Only forward and backward component
accepted
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Results of dedicated experiments
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First dedicated experiment
V.H. PhD thesis (in preparation)

• most peripheral collisions yield deceleration

mean velocities in agreement with Morrissey
systematics.

• with decreasing mass loss, velocities level off
  and increase

residues with Ares 85 on average faster than
the beam
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More dedicated experiments
V.H. PhD thesis (in preparation)

• 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
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New experimental data gt 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 !!!
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How to relate Ares and an impact parameter
Aladin

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

Region of mixing Zmax Zmax2 cant be used to
deduce b !
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New experimental data gt new simulations
Only data in blue area suitable for extraction of
impact parameter !!!
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 ...
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Summary outlook
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Summary Outlook
Summary

• longitudinal velocities of fragmentation
  residues measured in AuAu _at_ 0.5, 1 A GeV, AuAl
  _at_ 0.5 A MeV

• 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

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

Outlook

• AuAu/Al _at_ 1/0.5 A GeV data analysis finished,
  interpretation in progress

• More BUU calculations on the way, many more needed

• 112,124Sn112,124Sn _at_ 1 A GeV experiment in
  preparation - 2005/2006

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Comparison with ALADIN
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Information from full acceptance experiments
197Au197Au 1AGeV - ALADIN
fission
fragmentation

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