I. N. Mishustin

Statistical Multifragmentation of Nuclei

After an introduction to the main subject: break-up of nuclear matter, some elementary concepts from heavy ion dynamics are introduced. We discuss the collision process within a three step scenario, including fragmentation into many pieces of the interacting nuclei. The partition of the multiparticle system into clusters is discussed. The various components of the energy of a fragment assembly at the break up stage are introduced. They are generalizations of the Weissacker-energies. We consider the thermodynamics of a gaseous mixture of fragments in equilibrium. The thermodynamic probability determining the weight of a given partition is calculated. Some results of calculations are discussed.

In-medium kaon production at the mean-field level

Abstract The in-medium mass and energy of kaons and antikaons are studied within the relativistic mean-field approach compatible with kaon-nucleon scattering data and are compared with predictions from chiral models. Implications for the subthreshold production of kaons and antikaons in heavy-ion collisions are discussed. On the mean-field level we find only small in-medium corrections for the relevant kaon production processes. The production of kaons is even less favourable at high density due to repulsive vector interactions. We conclude that one has to go beyond the mean-field level and take fluctuations and secondary production processes via resonances into account to explain the recently observed enhancement of kaon production at subthreshold energies. The situation is different for antikaons where in-medium effects strongly enhance their production rates. We also see strong in-medium modifications of the absorption processes for antikaons and Λs which might be visible in flow measurements. We predict that at high density the threshold energy for antikaon and Λ production as well as for the annihilation become equal leading to similar numbers of antikaons and Λs in the dense zone of a relativistic heavy-ion collision.

Thermodynamical features of multifragmentation in peripheral Au + Au Collisions at 35 A.MeV

Abstract The distribution of fragments produced in events involving the multifragmentation of excited sources is studied for peripheral Au + Au reactions at 35 A MeV. The Quasi-Projectile has been reconstructed from its de-excitation products. An isotropic emission in its rest frame has been observed, indicating that an equilibrated system has been formed. The excitation energy of the Quasi-Projectile has been determined via calorimetry. A new event by event effective thermometer is proposed based on the energy balance. A peak in the energy fluctuations is observed related to the heat capacity suggesting that the system undergoes a liquid-gas type phase transition at an excitation energy ∼ 5 A MeV and a temperature 4–6 MeV, dependent on the freeze-out hypothesis. By analyzing different regions of the Campiplot, the events associated with the liquid and gas phases as well as the critical region are thermodynamically characterized. The critical exponents, τ, β, γ, extracted from the high moments of the charge distribution are consistent with a liquid-gas type phase transition.

Statistical multifragmentation of nuclei: (III). Decay of the fragments

Abstract The process of nuclear fragmentation is described through a two-step statistical model. The primordial partition of a hot nuclear system is calculated with the help of the Monte Carlo technique developed in parts (I) and (II) of the present work, whereas the subsequent decay of the highly-excited primary fragments is treated by a simplified evaporation approach. This model describes the main features of the inclusive experimental mass spectra of high-energy protoninduced reactions.

Statistical Multifragmentation in Central Au+Au Collisions at 35 MeV/u

Abstract Multifragment disintegrations, measured for central Au + Au collisions at E A = 35 MeV , are analyzed with the Statistical Multifragmentation Model. Charge distributions, mean fragment energies, and two-fragment correlation functions are well reproduced by the statistical breakup of a large, diluted and thermalized system slightly above the multifragmentation threshold.

Nonequilibrium Phase Transition in Rapidly Expanding Matter

Non-equilibrium features of a first order phase transition from the quark-gluon plasma to a hadronic gas in relativistic heavy-ion collisions are discussed. It is demonstrated that strong collective expansion may lead to the fragmentation of the plasma phase into droplets surrounded by undersaturated hadronic gas. Subsequent hadronization of droplets will generate strong non-statistical fluctuations in the hadron rapidity distribution in individual events. The strongest fluctuations are expected in the vicinity of the phase transition threshold.

Statistical evolution of isotope composition of nuclear fragments

Calculations within the statistical multifragmentation model show that the neutron content of intermediate mass fragments can increase in the region of the liquid-gas phase transition in finite nuclei. The model predicts also inhomogeneous distributions of fragments and of their isospin in the freeze-out volume caused by angular momentum and an external long-range Coulomb field. These effects can take place in peripheral nucleus-nucleus collisions at intermediate energies and lead to neutron-rich isotopes produced in the midrapidity kinematic region.

Sampling in statistical multifragmentation of nuclei

Abstract The multifragmentation of finite excited nuclei is discussed in a statistical model. Criteria for the representation of the partition space in a Monte Carlo calculation are discussed, and it is shown that the most probable partitions are not necessarily the most dominant experimental ones.

CHIRAL FLUID DYNAMICS AND COLLAPSE OF VACUUM BUBBLES

We study the expansion dynamics of a quark-antiquark plasma droplet from an initial state with restored chiral symmetry. The calculations are made within the linear

Nuclear multifragmentation induced by electromagnetic fields of ultrarelativistic heavy ions

\sigma