What can we learn from the spectator momenta

1
Idea
BUU calculations 124Sn 124Sn Tlab 800
MeV/u b 5 fm L. Shi, P. Danielewicz, R.
Lacey, PRC 64 (2001)
Observation
T.Enqvist et al. NPA658(1999)47
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2
Experiment at the Fragment Separator
Inverse kinematics
From ToF ??? /???? 400
(36m)
A/?A 400
Once mass and charge are identified (A, Z are
integer numbers) the velocity is calculated from
B? gt very precise determination!
??? /???? B?/?B? 2000
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3
Characteristics of the data

• unambiguous identification precise
  longitudinal momenta
• limited acceptance 15mrad, 1.5 in momentum

only one fragment in one reaction measured
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4
Information with limited acceptance (op.I)

• single, predominantly largest residue per
  reaction unambiguously identified
• mid-peripheral collisions investigated
• the largest fragment is correlated with impact
  parameter

238UCu 1AGeV - ALADIN
fission
fission excluded
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5
Information with limited acceptance (op.II)
Reconstruction of the velocity distribution

• limited momentum acceptance

Several magnetic field settings need to be
combined to get complete velocity distribution
136XePb at 1A GeV
21Ne
D. Henzlova PhD thesis (in preparation)
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Information with limited acceptance (op.III)
How to distinguish fragmentation and fission?
238U (1 A GeV) Pb
Fragmentation heaviest residues fully accepted
(Agt90) Fission Only forward and backward
component accepted
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7
Velocity correction for limited acceptance

• Influence of limited angular acceptance on mean
  residue velocities is negligible (A 60) or
  small and correctable (25 A 60)

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