Fragment-fragment correlations Access to time-scales of fragment emission and densities at freeze-out Mechanisms of fragment emission Phase transition and low freeze-out density? Simultaneous multifragment emission short t < 100 fm/c ~ growth of density fluctuations (bulk instabilities) Sequential evolutionary emission? Evolutionary emission? EES predictions larger t values. t ≥ 300 fm/c

Qrel correlations Nautilus Kr+Au: MIMF>2: t ≈ 1000 fm/c @ 30 A.MeV – t ≈ 200 fm/c @ 60 A.MeV Louvel et al., PLB 320 (1994) 221 Central: «prompt and simultaneous fragment emission»  Lopez et al., PLB 315 (1993) 34 FASA p+Au @ 8.1 GeV: t ≤ 70 fm/c - VFO = (5  1) Vo V.K. Rodionov et al., NPA 700 (2002) 457 V.A.Karnaukhov et al.

IMF-HR vs IMF-IMF correlation functions F-F and HR-IMF events vs Multigramentation events IMF-HR correlations: tIMF-HR ≈ 200-300 fm/c rotating binary decay IMF-IMF correlations: time scales for multifragment emission tIMF-IMF ≈ 200-1000 fm/c No significant change in time scales: sequential IMF emission Mfrag>1 => not enough to select multifragmentation events R. Trockel et al., PRL59, 2844 (1987)

IMF timescales Miniball data vs 2-Body Coulomb FSI, Y.D. Kim et al., PRL 67 (1991) 14 all 3-Body Coulomb trajectories slightly modify extracted times, and are important to investigate emitter sizes Y.D. Kim et al., PRC45 (1992) 387 T. Glassmacher et al., PRC50 (1994) 952 t ≈ 100-200 fm/c: Shorter than seq. evaporation

Apparent evolutionary multifragmentation Central Kr + Au @ 35-75 A.MeV (b < 0.2 bmax) Apparent emission times tIMF depend on fragment velocities Apparent evolutionary fragment emission mechanisms (EES predictions) C-Be time ordering measurement relative velocity Simultaneous emission + thermal/radial flow can explain this effect Miniball data, E. Cornell et al., PRL75 (1995) 1475 E. Cornell et al., PRL77 (1996) 4508 Similar conclusions in G. Wang et al., PRC 60 (1999) 014603 for central 3He+Ag,Au@1.8-4.8 A.MeV (Isis): r/r0 = 1/4-1/3 – t  50 fm/c

tIMF vs incident energy: onset of simultaneous multifragmentation Central Kr+Nb (b < 0.3 bmax) 35 AMeV 45 AMeV 55 AMeV 65 AMeV 75 AMeV Onset of simultaneous multifragmentation (bulk instabilities) Beam Energy (A MeV) 30 40 50 60 70 80 500 400 300 200 100 tIMF (fm/c) r0   tapp  flow   tapp  MSU 4p data, E. Bauge et al., PRL70 (1993) 3705

tIMF vs excitation energy: from surface to bulk emission in thermal multifragmentation p-, p + A 8.0, 8.2, 9.2, 10.2 GeV/c ISiS data, L. Beaulieu et al., PRL84 (2000) 5971 Thermally expanding and decaying source: tIMF decreases with increasing E*/A (assuming constant r=r0/3) Transition from surface emission to bulk emission around E*/A≈4-5 MeV ? Analysis: N-Body Coulomb trajectories T. Glassmacher et al., PRC50 (1994) 952 R. Popescu et al., PRC58 (1998) 270

About the space-time ambiguity Ar+Au @ 35-110 A.MeV – Miniball data – b/bmax ≤ 0.2 D. Fox et al., PRC50 (1994) 2424 Koonin-Pratt and 3-body Coulomb trajectory calculations The space-time extension of the composite system at freeze-out decreases with increasing beam energy Zres dependance

Summary What have we learnt from fragment-fragment Vred and Qrel correlations? With increasing beam or excitation energy, apparent IMF emission times decrease down to “simultaneous” emission fission “simultaneous” bulk emission (multifragmentation) ≈1000 fm/c ≤100 fm/c => for multifragmentation : evolutionnary type of descriptions (EES) can hardly account for apparent timescales The space-time extension of the emitting sources diminishies. As the radial and thermal flows develops… New correlation methods are needed to solve the space-time ambiguity, where flow should be taken into account when simulating N-body Coulomb trajectory in volume emissions. E* t 2 A.MeV 4 A.MeV sequential surface emission

Time sequence and time scale of neck fragmentation 124Sn + 64Ni reaction @ 35 A MeV (ternary events PLF-IMF-TLF, Chimera data) Prompt 1 2 3 1 40 fm/c 2 80 fm/c 3 120 fm/c Results of BNV transport model for IMFs emission probability from neck region for different impact parameters (V. Baran et al. Nucl. Phys. A730 329, 2004). Ternary Sequential binary