1. Dynamical fragment production in non-central heavy-ion collisions E *, J PLF* TLF* Sylvie Hudan, Indiana University EvaporationBinary breakupfragmentation See R.T. de Souza on Friday

2. Binary breakup : dynamical effect 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) U+C at 24 MeV/n :  aligned /  binary  3% U+U at 24 MeV/n :  aligned /  binary  20% Xe+Sn at E beam > 40 MeV/n :  aligned /  binary  70%  Large cross-section See J. Colin in this session  Large asymmetries 1 0.5 Normalized scale

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

4. Characteristics of the selected events  Correlation between Z PLF* and the total multiplicity Selection of peripheral events

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

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

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

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

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

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 v PLF*  E*

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

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

13. 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 Dynamical Statistical

14. Deviation from the Viola systematic  Deviation of the statistical case from Viola (E*  0)  Offset of the dynamical case  Offset independent of velocity damping (  E*) Dynamical Statistical Dynamical Statistical Offset(v PLF* =9.3) = 0

15. 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*

16. 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 114 Cd+ 92 Mo @ 50 MeV/n : b = 0 - 9.2 fm Dynamical calculation At t = 300 fm/c : Clusterization (dR<5fm) Statistical decay 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)

17. AMD : global features 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)

18. AMD : hot and cold fragments Characteristics before decay Before decay After decay

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

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

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

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

23. 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.”

24. Acknowledgments 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 the LASSA collaboration : To A. Ono for the AMD calculations To J. Colin for providing figures