ISiS: Research Highlights

• Nuclear Expansion -- Analysis of IMF spectra and multiplicity distributions as a function of collision violence provides strong evidence for multifragmentation from an expanded/dilute source. The breakup density appears to be less than one-third normal nuclear matter density, . Direct experimental evidence for expansion/dilution comes from the Coulomb-like peaks of the IMF spectra, which are strongly distorted toward low energies for the most violent events. In addition, the expanding, emitting source model of W.A. Friedman describes both the spectra and multiplicity distributions with an effective compressibility parameter K = 144 MeV, consistent with .



• Heating Curve for Finite Nuclei -- The excitation energy vs. temperature dependence has been determined for the 4.8 GeV ³He + ^natAg, ¹⁹⁷Au systems. Excitation energy distributions for the fragmenting nuclei were reconstructed event-by-event from the spectra, and temperatures were based on the double-isotope ratio method (^2,3H/^3,4He). The heating curve does not show a plateau, but instead a systematic increase approximately consistent with predictions of both the expanding, emitting source model (EES) model of W.A. Friedman and the statistical multifragmentation (SMM) model of A. Botvina.
  
  
• Collision Dynamics -- Multiplicity distributions for thermal-like LCPs and IMFs indicate that the average energy deposited in heavy target nuclei saturates in the vicinity of 5 GeV bombarding energy. This is explained in terms of a tradeoff between the increased projectile energy and increased transparency for fast cascade hadrons. In addition, and p beams are found to yield identical multiplicity results, stressing the independence of hadron type in initiating the sequence of collisions that deposits energy in the residual heavy nucleus.



• Source Properties -- One of the remarkable features of hadron-induced reactions is the deposition of energies up to 1.5 GeV in the residual nucleus while imparting little velocity, <v_source> 0.01 c. A rapidity analysis also indicates thermal-like behavior for the disintegrating source. These observations argue for the excitation of baryonic resonances (, N*, etc.) And subsequent reabsorption as a significant complement to N-N scattering in the energy deposition process.



• Pre-Fragmentation IMF Emission -- Large-angle IMF-IMF energy correlations show that prior to multifragmentation of the hot residues, some cooling occurs via the emission of light IMFs (Li, Be. B). This result supports a time-dependent scenario for multifragmentation in which fragment emission occurs during expansion, followed by multibody breakup of the residue.



• Time Scales -- The time scales for multifragmentation in light-ion-induced reactions has been shown to be 20-50 fm/c, as deduced from small-angle IMF-IMF velocity correlations.