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Dynamical fragment production in non-central heavy-ion collisions

TLF*. PLF*. fragmentation. Evaporation. Binary breakup. Dynamical fragment production in non-central heavy-ion collisions. Sylvie Hudan, Indiana University. E * , J. See R.T. de Souza on Friday. 1. Normalized scale. Large asymmetries. 0.5. Binary breakup : dynamical effect.

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Dynamical fragment production in non-central heavy-ion collisions

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  1. TLF* PLF* fragmentation Evaporation Binary breakup Dynamical fragment productionin non-central heavy-ion collisions Sylvie Hudan, Indiana University E*, J See R.T. de Souza on Friday

  2. 1 Normalized scale • Large asymmetries 0.5 Binary breakup : dynamical effect • U+C at 24 MeV/n :aligned/binary  3% • U+U at 24 MeV/n :aligned/binary  20% • Xe+Sn at Ebeam > 40 MeV/n :aligned/binary  70% • Large cross-section F. Bocage et al., NP A676, 391 (2000) J. Normand, PhD Thesis, université de Caen (2001) S. Piantelli et al., PRL 88, 052701 (2002) B. Davin et al., PRC 65, 064614 (2002) See J. Colin in this session

  3. Experimental setup 114Cd + 92Mo at 50 A.MeV LASSA : Mass resolution up to Z=9 7  lab  58 Ring Counter : Annular Si (300 m) – CsI(Tl) (2cm) 2.1  lab  4.2 1 unit Z resolution Mass deduced† Beam † : Modified EPAX K. Sümmerer et al., PRC 42, 2546 (1990)  Detection of charged particles in 4p Selected events : 2 fragments (Z4) detected in the Ring Counter Reconstruction of the PLF* : PLF*  Heavy + Light  ZPLF*, APLF*, vPLF*

  4. Selection of peripheral events Characteristics of the selected events • Correlation between ZPLF* and the total multiplicity

  5. Heavy emitted backward to the PLF* Heavy emitted forward to the PLF* Asymmetry of the angular distributions 6  Nc 10 PLF* frame Heavy • Heavy more forward focused Distinction of 2 cases : forward and backward

  6. backward forward § : Consistent with Montoya et al., PRL73, 3070 (1994) Peak at Z=6 § Deviation from standard statistical fission B. Davin et al., PRC 65, 064614 (2002) 6  Nc 10 • Different asymmetry forward backward • Different charge correlation • In both cases ZPLF* 41

  7. forward backward Deviation from standard statistical fission 6  Nc 10 B. Davin et al., PRC 65, 064614 (2002) Viola systematics • Different relative velocities • Large effect ( 50%)

  8. Z=6 vPLF* backward forward E*, J 6  Nc 10 Velocity dissipation B. Davin et al., PRC 65, 064614 (2002) • Similar vPLF* distribution forward backward • When selected on vPLF* : • Different charge asymmetries • forward : • Strong asymmetry for all vPLF* backward : compatible with standard statistical fission forward: dynamical features

  9. Statistical Dynamical Velocity damping and excitation energy • Same trend for both cases • More dissipation and fluctuations as ZPLF* decreases • For a given size, less dissipation in the dynamical case Dynamical Statistical • Anti-correlation •  expected if vPLF*and (vPLF*) correlated to a common quantity • Same correlation •  correlated to E*

  10. Damping and excitation : fission case • Deviation from the Viola systematics (predominantly Coulomb) as damping increases • More fluctuations on the kinetic energy released in the fragments As velocity damping increases, E* increases vPLF* E*

  11. Process probability : opening channel 1 fragment case (x 0.1) Dynamical Statistical • Dynamical process appear at lower velocity damping • Up to 10% of the cross-section in binary breakup

  12. Charge split and Coulomb cost Statistical Dynamical • Higher asymmetry for the dynamical case Statistical Dynamical • Different Coulomb cost Less damping required for the dynamical case

  13. Dynamical Statistical Kinetic energy transferred • More kinetic energy in the fragments for the dynamical case • For a given velocity damping, difference of  20-30 MeV • Constant offset with velocity damping when Coulomb subtracted

  14. Observation of a dynamical component • Process with a large cross-section • As compared to standard fission, the dynamical process has: •  Lower E* threshold •  Large asymmetry (dependent on E*) •  Strong alignment •  Large kinetic energy in the 2 fragments, for all E* •  Constant (TKE-Coulomb) for all E*

  15. AMD : description • Antisymmetrized Molecular Dynamics : • Microscopic approach to nuclear collision dynamics • Slater determinant of Gaussian packets • TDVP Equation of Motion for centroids • Quantum branching processes • NN collisions • Wave packet diffusion/shrinking 114Cd+92Mo @ 50 MeV/n : b = 0 - 9.2 fm Dynamical calculation At t = 300 fm/c : Clusterization (dR<5fm) Statistical decay AMD A. Ono et al., Prog. Theor. Phys. 87, 1185 (1992) A. Ono and H. Horiuchi, Phys. Rev. C59, 853 (1999) A. Ono, S. Hudan, A. Chbihi and J.D. Frankland, Phys. Rev. C66, 014603 (2002)

  16. AMD : global features AMD + decay For all impact parameters • PLF and TLF branches • Fragment production at mid-rapidity • Large production of Z=5-6 at all v// (already before decay)

  17. INDRA data, Gd+U @ 36 MeV/u F. Bocage et al., NP A676, 391 (2000) PLF* frame AMD + decay Heavy AMD : alignment We select events with 2 fragments (Z4) emitted forward to the CM • Heavy mostly forward peaked in the PLF* frame • High cross section : • forward : /TOT  0.23 • backward : /TOT  0.10

  18. AMD + decay forward backward AMD : charge asymmetry Cd+Mo @ 50 MeV/n B. Davin et al., PRC 65, 064614 (2002) DATA forward backward • forward: • peaked at large asymmetry • backward: •  flat distribution

  19. AMD + decay forward backward AMD : relative velocity DATA Cd+Mo @ 50 MeV/n B. Davin et al., PRC 65, 064614 (2002) forward backward • forward case is characterized by a higher relative velocity as compared to the backward case • 10% effect (25% in the data)

  20. AMD : Influence of the target 114Cd+12C @ 50 MeV/n • Few fragments produced at mid-rapidity • binary/tot < 2%

  21. Conclusions • The AMD calculations show the trends observed in the experimental data : • alignment • asymmetry • relative velocity with a lower magnitude • influence of the target • A total of 8000 events have been calculated, representing 160000 cpuhours ( 18 years). • Thanks to the UITS and RATS group at IU. • “This work was supported in part by Shared University Research grants from IBM, Inc. to Indiana University.”

  22. Acknowledgments To the LASSA collaboration : S. Hudan , B. Davin, R. Alfaro, R. T. de Souza, H. Xu, L. Beaulieu, Y. Larochelle, T. Lefort, R. Yanez and V. Viola Department of Chemistry and Indiana University Cyclotron Facility, Indiana University, Bloomington, Indiana 47405 R. J. Charity and L. G. Sobotka Department of Chemistry, Washington University, St. Louis, Missouri 63130 T.X. Liu, X.D. Liu, W.G. Lynch, R. Shomin, W.P. Tan, M.B. Tsang, A. Vander Molen, A. Wagner, H.F. Xi, and C.K. Gelbke National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 To A. Ono for the AMD calculations To J. Colin for providing figures

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