Effects of collective expansion on light cluster spectra in relativistic heavy ion collisions

We discuss the interplay between collective flow and density profiles, describing light cluster production in heavy ion collisions at very high energies. Calculations are performed within the coalescence model. We show how collective flow can explain some qualitative features of the measured deuteron spectra, provided a proper parametrization of the spatial dependence of the single particle phase space distribution is chosen.Comment: 11 pages Latex, 2 figures, to be published in Phys. Lett.

Nuclear multifragmentation induced by electromagnetic fields of ultrarelativistic heavy ions

We study the disintegration of nuclei by strong electromagnetic fields induced by ultrarelativistic heavy ions. The proposed multi-step model includes 1) the absorption of a virtual photon by a nucleus, 2) intranuclear cascades of produced hadrons and 3) statistical decay of the excited residual nucleus. The combined model describes well existing data on projectile fragmentation at energy 200 GeV per nucleon. Electromagnetic multifragmentation of nuclei is predicted to be an important reaction mechanism at RHIC and LHC energies.Comment: 18 LaTeX pages including 4 figures, uses epsf.sty. Submitted to Phys.Rev.

Simultaneous Heavy Ion Dissociation at Ultrarelativistic Energies

We study the simultaneous dissociation of heavy ultrarelativistic nuclei followed by the forward-backward neutron emission in peripheral collisions at colliders. The main contribution to this particular heavy-ion dissociation process, which can be used as a beam luminosity monitor, is expected to be due to the electromagnetic interaction. The Weizsacker-Williams method is extended to the case of simultaneous excitation of collision partners which is simulated by the RELDIS code. A contribution to the dissociation cross section due to grazing nuclear interactions is estimated within the abrasion model and found to be relatively small.Comment: Talk given at Bologna 2000 Conference - Structure of the Nucleus at the Dawn of the Century, May 29 - June 3, 2000, 4 pages, 2 figure

Isotopic and Microcanonical Temperatures in Nuclear Multifragmentation

A systematic comparison of different isotopic temperatures with the thermodynamical temperature of a multifragment system is made on the basis of the Statistical Multifragmentation Model. It is demonstrated that isotopic temperatures are strongly affected by the secondary decays of hot primary fragments and the population of particle-stable excited states in final fragments. The He-Li temperatures, measured recently by the ALADIN group, are reproduced fairly well both as a function of excitation energy and bound charge. Our analysis confirms the anomaly in the nuclear caloric curve.Comment: 10 pages in LaTeX, 3 ps figures, accepted for publication in Phys. Rev.

Multifragmentation of non-spherical nuclei

The shape influence of decaying thermalized source on various characteristics of multifragmentation as well as its interplay with effects of angular momentum and collective expansion are first studied and the most pertinent variables are proposed. The analysis is based on the extension of the statistical microcanonical multifragmentation model.Comment: 5 pages, 4 figure

Reconstruction of the Proton Source in Relativistic Heavy Ion Collisions

We describe a direct method to reconstruct the transverse proton source formed in a relativistic heavy ion collision, making use of experimentally measured proton and deuteron spectra and assuming that deuterons are formed via two-nucleon coalescence. We show that an ambiguity with respect to the source temperature still persists and we indicate a possible solution to the problem

Fragment size correlations in finite systems - application to nuclear multifragmentation

We present a new method for the calculation of fragment size correlations in a discrete finite system in which correlations explicitly due to the finite extent of the system are suppressed. To this end, we introduce a combinatorial model, which describes the fragmentation of a finite system as a sequence of independent random emissions of fragments. The sequence is accepted when the sum of the sizes is equal to the total size. The parameters of the model, which may be used to calculate all partition probabilities, are the intrinsic probabilities associated with the fragments. Any fragment size correlation function can be built by calculating the ratio between the partition probabilities in the data sample (resulting from an experiment or from a Monte Carlo simulation) and the 'independent emission' model partition probabilities. This technique is applied to charge correlations introduced by Moretto and collaborators. It is shown that the percolation and the nuclear statistical multifragmentaion model ({\sc smm}) are almost independent emission models whereas the nuclear spinodal decomposition model ({\sc bob}) shows strong correlations corresponding to the break-up of the hot dilute nucleus into nearly equal size fragments

An investigation of standard thermodynamic quantities as determined via models of nuclear multifragmentation

Both simple and sophisticated models are frequently used in an attempt to understand how real nuclei breakup when subjected to large excitation energies, a process known as nuclear multifragmentation. Many of these models assume equilibriumthermodynamics and produce results often interpreted as evidence of a phase transition. This work examines one class of models and employs standard thermodynamical procedure to explore the possible existence and nature of a phase transition. The role of various terms, e.g. Coulomb and surface energy, is discussed.Comment: 19 two-column format pages with 24 figure

Mass Parameterizations and Predictions of Isotopic Observables

We discuss the accuracy of mass models for extrapolating to very asymmetric nuclei and the impact of such extrapolations on the predictions of isotopic observables in multifragmentation. We obtain improved mass predictions by incorporating measured masses and extrapolating to unmeasured masses with a mass formula that includes surface symmetry and Coulomb terms. We find that using accurate masses has a significant impact on the predicted isotopic observables.Comment: 12 pages, 4 figure

Classification of the Nuclear Multifragmentation Phase Transition

Using a recently proposed classification scheme for phase transitions in finite systems [Phys.Rev.Lett.{\bf 84},3511 (2000)] we show that within the statistical standard model of nuclear multifragmentation the predicted phase transition is of first order.Comment: 5 pages, 4 eps figures, accepted for publication in Phys.Rev.C (in press