The incomplete-fusion–fragmentation model is modified to analyze ALADIN multifragmentation data of the projectile remnant in reactions of 600 MeV/nucleon Au on different targets. Since the incomplete-fusion–fragmentation model includes both the dynamical formation and the statistical disassembly of a hot nucleus, the ALADIN observables can be reproduced quite well when the model parameter concerning the excitation energy is somewhat adjusted to account for the mean multiplicity of intermediate mass fragments as a function of the total bound charge. © 1996 The American Physical Society.

We study the evolution of density waves in an expanding nuclear system taking into account nonlinearity and finiteness effects. The main differences with the standard spinodal decomposition are that the transition from the stable to the nonstable region is gradual, and that it takes place at densities higher than those associated to the spinodal line. © 1996 The American Physical Society.

We analyze the multifractal structure in one and two dimensions of multihadronic final states produced in proton interactions with AgBr nuclei at 800 GeV in terms of modified G moments. Explicit corrections have been made for the finite statistical sample. The generalized dimensions ${\mathit{D}}_{\mathit{q}}$ have been determined for q=1–5. The observed multifractal structure of multiparticle production is well represented by the p model of self-similar cascading. The phenomenological parameter p drops in value in going from two to one dimensions, and shows weaker dependence on multiplicity for high multiplicity events compared to low multiplicity events. © 1996 The American Physical Society.

The rate of quark-gluon plasma droplet nucleation in superheated hadronic matter is calculated within the MIT bag model. The requirements of color singletness and (to less extent) fixed momentum suppress the nucleation rate by many orders of magnitude, making thermal nucleation of quark-gluon plasma droplets unlikely in ultrarelativistic heavy-ion collisions if the transition is first order and reasonably described by the bag model. © 1996 The American Physical Society.

We review results on leading particles from hadron-nuclear collisions. We conclude that the partons (quarks or diquarks) which produce the leading particles are not strongly absorbed as they emerge from the struck nucleus. In contrast an examination of the partons that give rise to the low energy pions and nucleons seems to indicate some kind of cascade occurs in the struck nucleus. There is on the average only one massive string produced in these collisions. The multiplicity produced by the hadronization of the massive strings is quite consistent with that produced in ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ annihilations. © 1996 The American Physical Society.

The thermalization process is studied in an expanding parton gas using the Boltzmann equation with two types of collision terms. In the relaxation time approximation we determine the criteria under which a time-dependent relaxation time leads to thermalization of the partons. We calculate the entropy production due to collisions for the general time-dependent relaxation time. In a perturbative QCD approach on the other hand, we can, given the initial conditions, estimate the effective relaxation time due to elastic collisions; this will be an upper limit only since radiative processes will also contribute to thermalization. We find that the parton gas does thermalize eventually but only after having undergone a phase of free streaming and gradual equilibration where considerable entropy is produced (‘‘after burning’’). The final entropy and thus particle density depends on the collision time as well as the initial conditions (a ‘‘memory effect’’). Results for entropy production are presented based upon various model estimates of early parton production. © 1996 The American Physical Society.

A comprehensive study of the properties of strangelets at zero and finite temperature is presented within the framework of liquid drop model, including the essential finite size effects. Strong parameter dependences of the properties are found and discussed. © 1996 The American Physical Society.

The finite temperature and finite density dependence of the neutron-proton mass difference is analyzed in a purely hadronic framework where the ρ-ω mixing is crucial for this isospin symmetry breakdown. The problem is handled within thermofield dynamics. The present results, consistent with partial chiral and charge symmetry restoration, improve the experimental data fit for the energy difference between mirror nuclei. © 1996 The American Physical Society.

Proton-nucleus collisions, where the beam proton gets excited to the Δ resonance and then decays to p${\mathrm{\pi }}^{+}$, either inside or outside the nuclear medium, are studied. Cross sections for various kinematics for the (p,${\mathit{p}}^{\prime }$${\mathrm{\pi }}^{+}$) reaction between 500 MeV and 1 GeV beam energy are calculated to see the effects of the nuclear medium on the propagation and decay of the resonance. The cross sections studied include proton energy spectra in coincidence with the pion, four momentum transfer distributions, and the invariant p${\mathrm{\pi }}^{+}$ mass distributions. We find that the effect of the nuclear medium on these cross sections mainly reduces their magnitudes. Comparing these cross sections with those considering the decay of the Δ outside the nucleus only, we further find that at 500 MeV the two sets of cross sections have large differences, while by 1 GeV the differences between them become much smaller. © 1996 The American Physical Society.

The pion-nucleon and kaon-nucleon scattering lengths are studied in the QCD sum rule. We show that the leading and next-to-leading order terms of the operator product expansion (OPE) give rise to the Tomozawa-Weinberg and σ terms, respectively in the pion-nucleon and kaon-nucleon scattering lengths. We discuss phenomenological contributions which should be added to the experimental scattering lengths to be compared with the theoretical calculation by the OPE: we estimate the Λ(1405) contribution in the kaon-nucleon channel by using the effective coupling strength determined by the analysis of the scattering data. We also estimate the continuum contribution above the threshold in the pion-nucleon channel by using the nonlinear σ model. It turns out that the results of the QCD sum rule for the pion-nucleon scattering lengths are consistent with those of the low energy theorem and therefore with experiments and those for the kaon-nucleon scattering lengths differ from the results of naive partial conservation of axial-vector current–plus-current-algebra approach by the contribution from Λ(1405). © 1996 The American Physical Society.

We describe an extended version of the Nambu–Jona-Lasinio (NJL) model that includes a description of confinement. It is necessary to incorporate some description of confinement in order to discuss the properties of the sigma, rho, and omega mesons in the NJL model. These mesons, in addition to the pion, are the minimum needed to describe the salient features of the nucleon-nucleon interaction. In previous work we considered the relation between the bosonized NJL model and the one-boson-exchange (OBE) model of the nucleon-nucleon force. Most of our attention was given to pion and sigma exchange. We provide a review of that work and extend our discussion to a consideration of rho and omega exchange. We also present a more detailed discussion of the bosonization procedure. Our results depend upon the strength of the confining interaction. Once that is fixed, we obtain good values for the omega-nucleon coupling constant, ${\mathit{G}}_{\mathrm{\omega }\mathit{NN}}$, and for the tensor coupling constant ${\mathit{f}}_{\mathrm{\rho }}$, in the rho-nucleon interaction. (One limitation of the present version of the model is that the ratio ${\mathit{f}}_{\mathrm{\rho }}$/${\mathit{g}}_{\mathrm{\rho }}$=3.70, instead of the empirical value of ${\mathit{f}}_{\mathrm{\rho }}$/${\mathit{g}}_{\mathrm{\rho }}$≃6.1.) If we consider nucleon-nucleon scattering for relatively small momentum transfer, we obtain good results for the processes of sigma, pion, rho, and omega exchange. Remarkably, the description of pion exchange is very accurate up to ${\mathit{q}}^2$∼-2 ${\mathrm{GeV}}^2$. That is, the microscopic model reproduces the pion-exchange amplitude of the boson-exchange model over a broad range of momentum transfer when we specify a single parameter than governs the momentum-transfer dependence of the pseudoscalar-isovector form factor of the nucleon. In the other channels (σ,ρ,ω), the nucleon form factors may be treated in the same manner. However, if we calculate the form factors in our model, we find that they are too ‘‘soft’’ to fit the OBE amplitudes away from ${\mathit{q}}^2$≃0. Further work is needed to obtain good fits for the various amplitudes for large momentum transfer, although the OBE amplitudes are well reproduced in the case of scattering at small momentum transfer (‖${\mathit{q}}^2$‖≤0.1 ${\mathrm{GeV}}^2$). © 1996 The American Physical Society.

The ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$${(}^3$He,d${)}^{27}$Si reaction was measured from 0°≤${\mathrm{\theta }}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$≤35° at E${(}^3$He)=20 MeV using a quadrupole-dipole-dipole-dipole magnetic spectrometer. States in ${}_{}{}^{27}{}_{}{}^{}\mathrm{Si}$ were observed above the background at 7652 and 7741 keV and upper limits were set for the state at 7592 keV. Implications for the ${}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$(p,γ${)}^{27}$Si stellar reaction rate are discussed. © 1996 The American Physical Society.

An excitation function for the ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$(p,α${)}^{15}$O reaction has been measured in the energy range ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=600–800 keV using a radioactive ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$ beam. A resonant state with a spin value of 3/$2^{+}$ has been found at an energy of 652 keV above threshold. This ${\mathit{l}}_{\mathit{p}}$=0 resonance is found to dominate the astrophysical reaction rate at temperatures ${\mathit{T}}_9$≳0.5. © 1996 The American Physical Society.

The first evidence for excited states in ${}_{}{}^{101}{}_{}{}^{}\mathrm{In}$ is presented. ${}_{}{}^{101}{}_{}{}^{}\mathrm{In}$ is the lightest In isotope observed in an in-beam experiment. Two γ-ray transitions at 1309 and 341 keV, respectively, are strong candidates for a cascade to the ground state in this nucleus. In shell-model terms it has one proton hole and two neutron particles outside the double shell closure at ${}_{}{}^{100}{}_{}{}^{}\mathrm{Sn}$. New ideas for improving the peak to background ratio in certain γ-ray spectra from fusion evaporation reactions are introduced. © 1996 The American Physical Society.

Emission of charged particles from a compressed reaction zone is studied for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$${+}^{197}$Au collisions at E/A=100, 250, and 400 MeV. Using a modified coalescence invariant weighting, squeeze-out ratios are determined and compared to predictions of cascade and BUU transport-model calculations. © 1996 The American Physical Society.

Two theoretical papers have suggested the existence of an ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{16}$O${+}^{16}$O configuration in ${}_{}{}^{48}{}_{}{}^{}\mathrm{Cr}$. We report on three experimental searches for the ternary breakup of ${}_{}{}^{48}{}_{}{}^{}\mathrm{Cr}$ to the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{16}$O${+}^{16}$O channel. No evidence is seen for the process. Upper limits for the cross section are reported. © 1996 The American Physical Society.

We have searched for the reaction d(α,γ${)}^6$Li at an α-d center-of-mass energy of 53 keV. An upper limit on the reaction S factor is 2.0×${10}^{\mathrm{-}7}$ MeV b at the 90% confidence level, corresponding to a limit on the synthesis of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ from a standard big bang of 0.9% of the present abundance for a total baryon-to-photon ratio 2.86<${\mathrm{\eta }}_{10}$<3.77. Equivalently, the ${}_{}{}^6{}_{}{}^{}\mathrm{-}_{}^7{}_{}{}^{}$Li isotopic abundance ratio immediately after a standard big bang is constrained to be less than 0.85%, considerably less than a recent measurement of this ratio in a metal-poor, Population II halo star. © 1996 The American Physical Society.

The lifetime of the neutron-unstable nucleus ${}_{}{}^{16}{}_{}{}^{}\mathrm{B}$ was investigated to search for evidence of delayed neutron emission (neutron radioactivity). The lifetime was inferred to be less than 191 ps (68% C.L.) based upon the lack of ${}_{}{}^{16}{}_{}{}^{}\mathrm{B}$ fragments observed in the fragmentation of 52 MeV/nucleon ${}_{}{}^{17}{}_{}{}^{}\mathrm{C}$ nuclei. © 1996 The American Physical Society.

We report precision measurements of the polarization transfer parameter ${\mathit{D}}_{\mathit{NN}}$ for 500 MeV polarized proton elastic scattering from ${}_{}{}^{12,13}{}_{}{}^{}\mathrm{C}$ at the first diffractive minima in the differential cross sections. The ratio ${\mathit{D}}_{\mathit{NN}}$${(}^{13}$C)/${\mathit{D}}_{\mathit{NN}}$${(}^{12}$C) (1.000±0.028) is consistent with zero spin-flip probability (S) for ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$, where S (1-${\mathit{D}}_{\mathit{NN}}$). Comparisons are made with results of theoretical calculations reported in the literature. © 1996 The American Physical Society.

We have measured the thick-target yield and analyzing power for the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$(p→,γ) reaction to the ground and first excited state of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ below ${\mathit{E}}_{\mathit{p}}$=80 keV. High-purity-germanium detectors were used to acquire data at five angles from θ=0° to 124°. For both states the yield, integrated from the beam energy of 80 keV down to 0 keV, is nearly isotropic and the integrated analyzing power shows only small deviations from zero. This is taken as an indication that, unlike the case of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p→,${\gamma }_0$${)}^8$Be reaction, the p-wave-capture process is unimportant compared to the s-wave process. Transition-matrix-element analyses of the ground-state data yield p-wave contributions of a few percent. Under the assumption of a constant astrophysical S factor, consistent with direct s-wave capture, a value of S=(2.69±0.54)×${10}^{\mathrm{-}5}$ MeV b has been deduced. © 1996 The American Physical Society.