Through the analysis of HELIOS-3 data obtained at the CERN Super Proton Synchrotron (SPS), we demonstrate the importance of secondary processes for dilepton production in heavy-ion collisions in the intermediate invariant mass region. We find that while the dilepton spectra between 1 and 2.5 GeV from proton-induced reactions can be attributed to the decay of primary vector mesons, charmed hadrons, and initial Drell-Yan processes, the strong enhancement seen in the heavy-ion data comes mainly from secondary processes. Furthermore, we find $\pi a_1\to l\overline{l}$ to be the most important process in this mass region, as was found by thermal rate calculations.

The azimuthal angular distribution of $K^{+}$ mesons has been measured in $\mathrm{Au}+\mathrm{Au}$ collisions at $1A\mathrm{GeV}$. In peripheral and semicentral collisions, $K^{+}$ mesons are emitted preferentially perpendicular to the reaction plane. The strength of the azimuthal anisotropy of $K^{+}$ emission is comparable to the one of pions. No in-plane flow was found for $K^{+}$ mesons near projectile and target rapidity.

The Kohn variational principle and the (correlated) hyperspherical harmonics technique are applied to study the $n{-}^3\mathrm{H}$ and $p{-}^3\mathrm{He}$ scattering at zero energy. Predictions for the singlet and triplet scattering lengths are obtained for nonrelativistic nuclear Hamiltonians including two- and three-body potentials. The calculated $n{-}^3\mathrm{H}$ total cross section agrees well with the measured value, while some small discrepancy is found for the coherent scattering length. For the $p{-}^3\mathrm{He}$ channel, the calculated scattering lengths are in reasonable agreement with the values extrapolated from the measurements made above 1 MeV.

The equation of state of symmetric nuclear matter at zero temperature is calculated up to the three hole-line level of approximation in the Bethe-Brueckner-Goldstone expansion. Both the standard and the continuous choices for the single particle auxiliary potential are considered. The resulting equation of state shows independence from the choice of the auxiliary potential to a high degree of accuracy. This result gives strong evidence for the convergence of the expansion and establishes the nuclear matter saturation curve for the adopted nucleon-nucleon interaction, the Argonne $v_{14}$ potential.

The closed shell structure at $N=Z=28\mathrm{}$ is studied by a large-scale shell model calculation by the quantum Monte Carlo diagonalization method. Latest crucial improvements of the method are described. The doubly closed shell probability of ${}^{56}\mathrm{Ni}$ is shown to be only $49\%$ in a full $\mathrm{pf}$ shell calculation, in contrast to the corresponding probability of ${}^{48}\mathrm{Ca}$ which reaches $86\%$.

Neutron-deuteron elastic scattering cross sections are calculated at different energies using modern nucleon-nucleon ( $\mathrm{NN}$) interactions and the Tucson-Melbourne three-nucleon force adjusted to the triton binding energy. Predictions based on $\mathrm{NN}$ forces only underestimate nucleon-deuteron data in the minima at higher energies starting around 60 MeV. Adding the three-nucleon forces fills up those minima and reduces the discrepancies significantly.

The asymptotic $D$- to $S$-state ratio $\eta$ for the $〈d\alpha |{}^6\mathrm{Li}〉$ bound-state overlap is determined from measurements of the tensor analyzing powers for ( ${}^6\overrightarrow{\mathrm{Li}},d$) reactions on medium-heavy targets. The reactions are described by the distorted-wave Born approximation assuming a direct $\alpha$-particle transfer reaction mechanism. The calculations provide good agreement with cross section and vector analyzing power data. A best fit to the tensor analyzing power data results in a new value of $\eta =+0.0003\mathrm{}\pm 0.0009$, much smaller than previous experimental and theoretical determinations.

Recent data provide evidence for coexisting phases at low energy in the spherical-deformed transitional nucleus ${}^{152}\mathrm{Sm}$. The nature of the wave functions at the spherical-deformed phase transition in nuclei is analyzed within the framework of the interacting-boson model. It is shown that in the U(5)-SU(3) transition, two phases coexist in a very small region of parameter space around the critical value of the control parameter $\xi$. The coexistence region with two minima in the potential shrinks to zero as one moves to the U(5)-O(6) transition. Implications for other systems are briefly mentioned.

A Comment on the Letter by B. Tatischeff et al., Phys. Rev. Lett. 79, 601 (1997). The authors of the Letter offer a Reply.

A Reply to the Comment by A. I. L'vov and R. L. Workman.

The emission of ${}^{10}\mathrm{Be}$ in ternary cold neutronless spontaneous fission of ${}^{252}\mathrm{Cf}$ is observed with the Gammasphere consisting of 72 detectors. The $\gamma$ ray corresponding to the decay of the first $2^{+}$ state in ${}^{10}\mathrm{Be}$ is observed in coincidence with the $\gamma$ rays of the fission partners of ${}^{96}\mathrm{Sr}$ and ${}^{146}\mathrm{Ba}$. The yield to the first excited state of ${}^{10}\mathrm{Be}$ in the ${}^{96}\mathrm{Sr}{-}^{146}\mathrm{Ba}$ split is the order of $4.0\times {10}^{-4\mathrm{}}$ per 100 fission events.

For nearly fifty years theoretical and experimental efforts in nucleon-nucleon bremsstrahlung ( $\mathrm{NN}\gamma$) have been devoted to measuring off-shell amplitudes and distinguishing among various $\mathrm{NN}$ potentials on the basis of their off-shell behavior. New experiments are underway, designed specifically to attain kinematics further off shell than in the past, and thus to be more sensitive to the off-shell behavior. This Letter shows that, contrary to these expectations, and due to the invariance of the $S$ matrix under transformations of the fields, the off-shell $\mathrm{NN}$ amplitude is as a matter of principle an unmeasurable quantity in $\mathrm{NN}\gamma$.

The hard contributions to the heavy quarkonium-nucleon cross sections are calculated based on the QCD factorization theorem and the nonrelativistic quarkonium model. We evaluate the nonperturbative cross sections which dominates at $\sqrt{s_{\mathrm{NN}}}\approx 20\mathrm{GeV}$ at the CERN Super Proton Synchrotron (SPS) and becomes a correction at $\sqrt{s_{\mathrm{NN}}}\approx 6\mathrm{TeV}$ at the CERN Large Hadron Collider. $\mathrm{J}/\Psi$ production at the CERN SPS is well described by hard QCD, when the larger absorption cross sections of the $\chi$ states predicted by QCD are taken into account. We predict an $A$-dependent polarization of the $\chi$ states. The expansion of small wave packets is discussed.

New isomeric states in the neutron-rich nuclei near the $Z=28\mathrm{}$ and $N=40\mathrm{}$ shell closures have been identified among the reaction products of a $60.3A$ MeV ${}^{86}\mathrm{Kr}$ beam on a ${}^{\mathrm{nat}}\mathrm{Ni}$ target. From the measured isomeric decay properties information about the excited states and their nuclear structure has been obtained. The isomerism is related mostly to the occupation of the neutron $g_{9/2}$ orbital, an intruder level in the $N=3\mathrm{}$ $\mathrm{fp}$ shell. It is illustrated with the decay properties of ${}^{69}{\mathrm{Ni}}^m$, ${}^{70}{\mathrm{Ni}}^m$, and ${}^{71}{\mathrm{Cu}}^m$ interpreted within the nuclear shell model.

We explore the natural limit of binomial reducibility in nuclear multifragmentation by constructing excitation functions for intermediate mass fragments of a given element $Z$. The resulting multiplicity distributions for each window of transverse energy are Poissonian. Thermal scaling is observed in the linear Arrhenius plots made from the average multiplicity of each element. “Emission barriers” are extracted from the slopes of the Arrhenius plots and their possible origin is discussed.

At the tagged photon facility PHOENICS at the Bonn accelerator ELSA a measurement of the target asymmetry of the reaction $\gamma p\to p\eta$ from threshold to 1150 MeV has been performed. Simultaneously the reaction $\gamma p\to p{\pi }^0$ has been measured in the first resonance region. Results are presented for both reactions. The target asymmetry data are suited to put considerable constraints on the model parameters used for the theoretical description of meson photoproduction.

The absolute decay width of a single-particle level in a deformed potential is evaluated exactly. Experimental data are analyzed by using the formalism developed here. It is found that proton decay is a powerful tool to determine the deformation of nuclei as well as to probe small components of the wave functions of the decaying states. This will allow one to study the behavior of single-particle resonances in nuclei close to the drip line, and may guide future experiments.

We study the systematics of the giant dipole resonance width $\Gamma$ in hot rotating nuclei as a function of temperature $T$, spin $J$, and mass $A$. We compare available experimental results with theoretical calculations that include thermal shape fluctuations in nuclei ranging from $A=45\mathrm{}$ to $A=208\mathrm{}$. Using the appropriate scaled variables, we find a simple phenomenological function $\Gamma (A,T,J)$ which approximates the global behavior of the giant dipole resonance width in the liquid drop model. We reanalyze recent experimental and theoretical results for the resonance width in Sn isotopes and ${}^{208}\mathrm{Pb}$.

The nucleus ${}^{54}\mathrm{Mn}$, observed in cosmic rays, decays there dominantly by the ${\beta }^{-}$ branch with an unknown rate. The branching ratio of its ${\beta }^{+}$ decay was determined recently. We use the shell model with only a minimal truncation and calculate both ${\beta }^{+}$ and ${\beta }^{-}$ decay rates. Good agreement for the ${\beta }^{+}$ branch suggests that the calculated partial half-life of the ${\beta }^{-}$ decay, $4.94\times {10}^5\mathrm{yr}$, should be reliable. However, this half-life is noticeably shorter than the range $1–2\times {10}^6\mathrm{yr}$ indicated by the fit based on the ${}^{54}\mathrm{Mn}$ abundance in cosmic rays. We also evaluate other known unique second forbidden $\beta$ decays from the $p$ and $\mathrm{sd}$ shells and show that the shell model can describe them with reasonable accuracy as well.

New high-precision measurements of the neutron total cross section for hydrogen and the deuterium-hydrogen cross section difference were performed for neutron energies between 7 and 600 MeV. The results are compared with state-of-the-art Faddeev calculations of the neutron-deuterium system up to 300 MeV. Above 100 MeV, this comparison reveals significant limitations of the nonrelativistic $3N$ Hamiltonian using nucleon-nucleon forces only.