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High-energy nuclear reactions enable us to produce a large variety of hypernuclei through the capture of hyperons by nuclear residues. We explore the statistical disintegration of such hypernuclear systems and the connection of fragment production to the binding energies of hyperons. It has been demonstrated that the hyperon binding energies can be effectively evaluated from the yields of different isotopes of hypernuclei by using the double ratio method. The advantages of this procedure are its universality and the possibility to involve many different isotopes. This method can also be applied for multistrange nuclei, for which binding energies were very difficult to measure in previous hypernuclear experiments. Corrections caused by secondary deexcitation processes are also discussed.

Recent experiments at RHIC and LHC have demonstrated that there are excellent opportunities to produce light baryonic clusters of exotic matter (strange and anti-matter) in ultra-relativistic ion collisions. Within the hybrid-transport model UrQMD we show that the coalescence mechanism can naturally explain the production of these clusters in the ALICE experiment at LHC. As a consequence of this mechanism we predict the rapidity domains where the yields of such clusters are much larger than the observed one at midrapidity. This new phenomenon can lead to unique methods for producing exotic nuclei., Comment: 15 pages, 4 figures, to be published in Phys. Rev. C

We investigate the possibilities of producing neutron-rich nuclides in projectile fission of heavy beams in the energy range of 20 MeV/nucleon expected from low-energy facilities. We report our efforts to theoretically describe the reaction mechanism of projectile fission following a multinucleon transfer collision at this energy range. Our calculations are mainly based on a two-step approach: the dynamical stage of the collision is described with either the phenomenological Deep-Inelastic Transfer model (DIT), or with the microscopic Constrained Molecular Dynamics model (CoMD). The deexcitation/fission of the hot heavy projectile fragments is performed with the Statistical Mul- tifragmentation Model (SMM). We compared our model calculations with our previous experimental projectile-fission data of 238U (20 MeV/nucleon)+208Pb and 197Au (20 MeV/nucleon)+197Au and found an overall reasonable agreement. Our study suggests that projectile fission following periph- eral heavy-ion collisions at this energy range offers an effective route to access very neutron-rich rare isotopes toward and beyond the astrophysical r-process path.

We analyze the production cross sections and isotopic distributions of projectilelike residues in the reactions $^{112}\mathrm{Sn}+^{112}\mathrm{Sn}$ and $^{124}\mathrm{Sn}+^{124}\mathrm{Sn}$ at an incident beam energy of 1 GeV/nucleon measured with the fragment separator at the GSI laboratory. Calculations within the statistical multifragmentation model for an ensemble of excited sources were performed with ensemble parameters determined previously for similar reactions at 600 MeV/nucleon. The obtained good agreement with the experiment establishes the universal properties of the excited spectator systems produced during the dynamical stage of the reaction. It is furthermore confirmed that a significant reduction of the symmetry-energy term at the freeze-out stage of reduced density and high temperature is necessary to reproduce the experimental isotope distributions. A trend of decreasing symmetry energy for large neutron-rich fragments of low excitation energy is interpreted as a nuclear-structure effect.

Exclusive studies of sideways-peaked angular distributions for intermediate-mass fragments (IMFs) produced in hadron-induced reactions have been performed with the Indiana silicon sphere (ISiS) detector array. The effect becomes prominent for beam momenta above about 10thinspGeV/c. Both the magnitude of the effect and the peak angle increase as a function of fragment multiplicity and charge. When gated on IMF kinetic energy, the angular distributions evolve from forward peaked to nearly isotropic as the fragment energy decreases. Fragment-fragment correlation studies show no evidence for a preferred angle that might signal a fast dynamic breakup mechanism. Moving-source and intranuclear cascade simulations suggest a possible kinematic origin arising from significant transverse momentum imparted to the recoil nucleus during the fast cascade. A two-step cascade and statistical multifragmentation calculation is consistent with the data. {copyright} {ital 1998} {ital The American Physical Society}

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.

Charge and transverse energy distributions for intermediate mass fragments have been extracted for central Kr1Au collisions at E/A5352400 MeV. The slopes of the measured fragment charge distributions decrease monotonically with incident energy, consistent with the expectations for highly charged systems, but not with recent critical exponent analyses. Statistical model calculations, which reproduce the experimental trends, suggest that post-breakup fragment secondary decays alter significantly the observed charge distributions. Radial expansion velocities extracted from these calculations follow the systematics of Au1Au collisions. @S0556-2813~97!50205-6#

We analyze hypernuclei coming from fragmentation and multifragmentation of spectator residues obtained in relativistic ion collisions. These hypernuclei have a broad distribution in masses and isospin. They reach beyond the neutron and proton drip lines, and they are expected to be stable with respect to neutron and proton emission. This gives us the opportunity to investigate the properties of exotic hypernuclei, as well as the properties of normal nuclei beyond the drip lines, which can be produced after weak decay of such hypernuclei.

We show that within a hybrid two-stage approach one can explain novel experimental data on the production of hypernuclei emitted from projectile residues in relativistic ion collisions. This reaction proceeds via formation of intermediate moderately excited hypernuclear systems, which decay into conventional nuclei and hyperfragments afterward. With a similar reaction mechanism one can also obtain weakly bound exotic hypernuclei (such as $\ensuremath{\Lambda}n$ and H-dibaryons), which may not be easily accessible in other processes.

The N/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at the GSI Schwerionen Synchrotron (SIS). Stable and radioactive Sn and La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. For the interpretation of the data, calculations with the statistical multifragmentation model for a properly chosen ensemble of excited sources were performed. The parameters of the ensemble, representing the variety of excited spectator nuclei expected in a participant-spectator scenario, are determined empirically by searching for an optimum reproduction of the measured fragment-charge distributions and correlations. An overall very good agreement is obtained. The possible modification of the liquid-drop parameters of the fragment description in the hot freeze-out environment is studied, and a significant reduction of the symmetry-term coefficient is found necessary to reproduce the mean neutron-to-proton ratios /Z and the isoscaling parameters of Z, 23 pages, 29 figures, published in Physical Review C

Ternary breakup of an excited projectile-like fragment produced in mid-peripheral collisions of $^{124}\mathrm{Xe}$ projectiles with $^{112}\mathrm{Sn}$ nuclei at $E/A=50$ MeV is examined. Charge correlations reveal that symmetric breakups occur with significant probability. By selecting on the parallel velocity of the heaviest fragment we minimize the entrance channel dynamics. Calculations with the statistical decay code GEMINI failed to reproduce the experimental charge correlations for any suitable combination of excitation energy and spin considered. A statistical multifragmentation model (SMM) in which breakup of low-density nuclear matter is assumed was able to reproduce the observed charge correlations. The $\ensuremath{\langle}N\ensuremath{\rangle}/Z$ and isotope distributions of fragments were compared to the results of the SMM calculations. Describing the $\ensuremath{\langle}N\ensuremath{\rangle}/Z$ of heavy fragments ($Zg6$) within SMM suggests that a reduction of the symmetry energy parameter from $\ensuremath{\gamma}=25$ to $14$ MeV is necessary. We observe that the yield of neutron-rich isotopes of heavy fragments is particularly sensitive to the symmetry energy.

Experimental analyses of moderate temperature nuclear gases produced in the violent collisions of 35 MeV/nucleon$^{64}$Zn projectiles with $^{92}$Mo and $^{197}$Au target nuclei reveal a large degree of alpha particle clustering at low densities. For these gases, temperature and density dependent symmetry energy coefficients have been derived from isoscaling analyses of the yields of nuclei with A $\leq 4$. At densities of 0.01 to 0.05 times the ground state density of symmetric nuclear matter, the temperature and density dependent symmetry energies are 10.7 to 13.5 MeV. These values are much larger than those obtained in mean field calculations. They are in quite good agreement with results of a recently proposed Virial Equation of State calculation., 9 pages, 7 figures. This is the version taking into account referee comments

The symmetry energy and the isoscaling properties of the fragments produced in the multifragmentation of $^{40}\mathrm{Ar}$, $^{40}\mathrm{Ca}+^{58}\mathrm{Fe}$, $^{58}\mathrm{Ni}$ reactions at 25, 33, 45, and 53 MeV/nucleon were investigated within the framework of statistical multifragmentation model. The isoscaling parameters \ensuremath{\alpha}, from the primary (hot) and secondary (cold) fragment yield distributions, were studied as a function of excitation energy, isospin (neutron-to-proton asymmetry), and fragment symmetry energy. It is observed that the isoscaling parameter \ensuremath{\alpha} decreases with increasing excitation energy and decreasing symmetry energy. The parameter \ensuremath{\alpha} is also observed to increase with increasing difference in the isospin of the fragmenting system. The sequential decay of the primary fragments into secondary fragments, when studied as a function of excitation energy and isospin of the fragmenting system, show very little influence on the isoscaling parameter. The symmetry energy, however, has a strong influence on the isospin properties of the hot fragments. The experimentally observed scaling parameters can be explained by symmetry energy that is significantly lower than that for the ground-state nuclei near saturation density. The results indicate that the properties of hot nuclei at excitation energies, densities, and isospin away from the normal ground-state nuclei could be significantly different.

The isotopic properties of the primary and secondary fragment yield distribution in the multifragmentation of {sup 58}Fe+{sup 58}Ni and {sup 58}Fe+{sup 58}Fe reactions are studied with respect to the {sup 58}Ni+{sup 58}Ni reaction at 30, 40, and 47 MeV/nucleon. The reduced neutron and proton densities from the observed fragment yield distribution show primary fragment yield distribution to undergo strongly secondary deexcitations. The effect is small at the lowest excitation energy and smallest neutron-to-proton ratio and becomes large at higher excitation energies and higher neutron-to-proton ratio. The symmetry energy of the primary fragments deduced from the reduced neutron density is significantly lower than that for the normal nuclei at saturation density, indicating that the fragments are highly excited and formed at a reduced density. Furthermore, the symmetry energy is also observed to decrease slowly with increasing excitation energy. The observed effect is explained using the statistical multifragmentation model.

New experimental results on the kinematics and the residue production are obtained for the interactions of $^{56}\mathrm{Fe}$ projectiles with protons and $^{\mathrm{nat}}\mathrm{Ti}$ target nuclei, respectively, at the incident energy of $1\phantom{\rule{0.3em}{0ex}}A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$. The titanium-induced reaction serves as a reference case for multifragmentation. Already in the proton-induced reaction, the characteristics of the isotopic cross sections and the shapes of the velocity spectra of light residues indicate that high thermal energy is deposited in the system during the collision. In the $^{56}\mathrm{Fe}+p$ system the high excitation seems to favor the onset of fast break-up decays dominated by very asymmetric partitions of the disassembling system. This configuration leads to the simultaneous formation of one or more light fragments together with one heavy residue.

The paper is devoted to the experimental determination of the space-time characteristics for the target multifragmentation in p(8.1GeV) + Au collisions. The experimental data on the fragment charge distribution and kinetic energy spectra are analyzed within the framework of the statistical multifragmentation model. It is found that the partition of hot nuclei is specified after expansion of the target spectator to a volume equal to Vt = (2.9 +- 0.2) Vo, with Vo as the volume at normal density. However, the freeze-out volume is found to be Vf = (11 +- 3) Vo. At freeze-out, all the fragments are well separated and only the Coulomb force should be taken into account. The results are in accordance with a scenario of spinodal disintegration of hot nuclei., 11 pages, 4 figures, submitted to Phys.Rev.C

Characteristics of the primary fragments produced in central collisions of ${}^{129}\mathrm{Xe}{+}^{\mathrm{nat}}\mathrm{Sn}$ from 32 to 50 A MeV have been obtained. By using the correlation technique for the relative velocity between light charged particles (LCP) and fragments, we were able to extract the multiplicities and average kinetic energy of secondary evaporated LCP. We then reconstructed the size and excitation energy of the primary fragments. For each bombarding energy a constant value of the excitation energy per nucleon over the whole range of fragment charge has been found. This value saturates at 3A MeV for beam energies 39A MeV and above. The corresponding secondary evaporated LCP represent less than 40% of all produced particles and decreases down to 23% for 50A MeV. The experimental characteristics of the primary fragments are compared to the predictions of statistical multifragmentation model (SMM) calculations. Reasonable agreement between the data and the calculation has been found for any given incident energy. However SMM fails to reproduce the trend of the excitation function of the primary fragment excitation energy and the amount of secondary evaporated LCP's.

A Comment on the Letter by Al. H. Raduta and Ad. R. Raduta, Phys. Rev. Lett. 87, 202701 (2001). The authors of the Letter offer a Reply.

Invariant transverse-velocity spectra of intermediate-mass fragments were measured with the 4-pi multi-detector system INDRA for collisions of Au on Au at incident energies between 40 and 150 MeV per nucleon. Their scaling properties as a function of incident energy and atomic number Z are used to distinguish and characterize the emissions in (i) peripheral collisions at the projectile and target rapidities, and in (ii) central and (iii) peripheral collisions near mid-rapidity. The importance of dynamical effects is evident in all three cases and their origin is discussed.

The relationship between nuclear temperature and excitation energy of hot nuclei formed by 8 GeV/c negative pion and antiproton beams incident on 197Au has been investigated with the ISiS 4-pidetector array at the BNL AGS accelerator. The double-isotope-ratio technique was used to calculate the temperature of the hot system. The two thermometers used (p/d-3He/4He) and (d/t-3He/4He) are in agreement below E*/A ~ 7 MeV when corrected for secondary decay. Comparison of these caloric curves to those from other experiments shows some differences that may be attributable to instrumentation and analysis procedures. The caloric curves from this experiment are also compared with the predictions from the SMM multifragmentation model.

Experimental data from the reaction of an $8.0\mathrm{GeV}/c$ ${\ensuremath{\pi}}^{\ensuremath{-}}$ beam incident on a ${}^{197}\mathrm{Au}$ target have been analyzed in order to investigate the breakup time scale for hot residues. Helium nuclei angular distributions and energy spectra supported by a momentum tensor analysis suggest that at large excitation energy, above $3\ensuremath{-}5\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n},$ highly excited heavy fragments are separated promptly after the thermalization. A binary fission-like mechanism fits the experimental data at low excitation energies, but seems unable to reproduce the data at excitation energies above $3\ensuremath{-}5\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}.$

Fragment kinetic energy spectra for reactions induced by 8.0 $\mathrm{GeV}/c{\ensuremath{\pi}}^{\ensuremath{-}}$ beams on a ${}^{197}\mathrm{Au}$ target have been analyzed. The average fragment kinetic energies are observed to increase systematically with fragment charge but are nearly independent of excitation energy. Near $E*/A=5$ MeV, the data are well accounted for by two statistical multifragmentation models, SMM and SIMON-explosion. However, at higher excitation energies, a small amount of extra energy, proportional to the fragment mass, is required in the models in order to match the experimental fragment's kinetic energies. This extra expansion energy is small relative to the radial expansion observed in heavy-ion-induced reactions, consistent with the interpretation that the latter expansion may be driven primarily by collective dynamical effects that are not present in light-ion-induced collisions.

Results of experiments performed to investigate the Xe1Cu 30 MeV/nucleon reaction are presented. The decay products coming from the disassembly of the unique source formed in central collisions and those coming from the decay of the quasiprojectile in peripheral and midperipheral ones have been identified through a careful data selection taking into account the experimental efficiency distortion on energy and angular distributions. The nuclear temperatures of these decaying systems have been measured from the relative isotopic abundances; the excitation energies of the fragment sources have been extracted by means of model calculations. The results have been compared to those obtained in the study of the Au1Au 35 MeV/nucleon in order to probe the effects of the finite size of the intermediate mass fragment emitting source on the relationship between its excitation energy and temperature. The studied fragment emitting sources have mass A1 .130, A2.200, A3.300; moreover, the A2 system have been investigated via two different reaction channels: the quasiprojectile of peripheral Au1Au and the unique fused system of the Xe1Cu central collisions. The relationship between temperature and excitation energy seems to be almost independent on the size of the emitting source and on the reaction entrance channel. On the contrary a weak dependence arises when individual thermometers are considered. @S0556-2813~99!03009-5#

Exclusive studies of angular distributions for intermediate-mass fragments (IMFs) produced in GeV hadron-induced reactions have been performed with the Indiana Silicon Sphere (ISiS) 4[pi] detector array. Special emphasis has been given to understanding the origin of sideways peaking, which becomes prominent in the angular distributions for beam momenta above about 10 GeV/c. Both the magnitude of the effect and the peak angle increase as a function of fragment multiplicity and charge. When gated on IMF kinetic energy, the angular distributions evolve from forward-peaked to near isotropy as the fragment kinetic energy decreases. Fragment-fragment angular-correlation analyses show no obvious evidence for a dynamic mechanism that might signal shock wave effects or the breakup of exotic geometric shapes such as bubbles or toroids. Moving-source and intranuclear cascade simulations suggest that the observed sideways peaking is of kinematic origin, arising from significant transverse momentum imparted to the heavy recoil nucleus during the fast cascade stage of the collision. A two-step cascade and statistical multifragmentation calculation is consistent with this assumption. [copyright] [ital 1999] [ital The American Physical Society]

To investigate the source size and time dependence of multifragmentation reactions, small- and large-angle relative velocity correlations between coincident complex fragments have been measured for the 1.8[endash]4.8 GeV [sup 3]He+[sup nat]Ag, [sup 197]Au systems. The results support an evolutionary scenario for the fragment emission process in which lighter IMFs (Z[approx lt]6) are emitted from a hot, more dense source prior to breakup of an expanded residue. For the most highly excited residues, for which there is a significant yield of fragments with very soft energy spectra (E/A[le]3 MeV), comparisons with an [ital N]-body simulation suggest a breakup time of [tau][approximately]50 fm/c for the expanded residue. Comparison of these data with both the evolutionary expanding emitting source model and the Copenhagen statistical multifragmentation model shows good agreement for heavier IMF[close quote]s formed in the final breakup stage, but only the evolutionary model is successful in accounting for the lighter IMFs. thinsp [copyright] [ital 1999] [ital The American Physical Society]