Superdeformed bands observed in ${}^{131}$Ce, ${}^{132}$Ce, and ${}^{133}$Ce have sequences of γ-ray transition energies that exhibit a $\Delta I=2\mathrm{}$ staggering. This staggering has different characteristics to that seen in previously known cases in other mass regions. The energy staggering starts at low rotational frequency ( $ħ\omega =3\mathrm{}$ MeV for ${}^{131}$Ce) at a magnitude of $\sim \pm 0.3$ keV, dies away to zero at intermediate frequency ( $ħ\omega =0.6-0.7\mathrm{}$ MeV), and reappears at higher frequencies ( $ħ\omega \sim 0.7$ MeV).

A search for the production of direct photons in $\mathrm{S}+\mathrm{Au}$ collisions at $200A\mathrm{GeV}$ has been carried out in the CERN-WA80 experiment. For central collisions the measured photon excess at each $p_T$, averaged over the range $0.5\le p_T\le 2.5\mathrm{GeV}/c$, corresponded to 5.0% of the total inclusive photon yield with a statistical error of ${\sigma }_{\mathrm{stat}}=0.8\mathrm{}\%$ and a systematic error of ${\sigma }_{\mathrm{syst}}=5.8\mathrm{}\%$. Upper limits on the invariant yield for direct photon production at the 90% C.L. are presented. Possible implications for the dynamics of high-energy heavy-ion collisions are discussed.

The quadrupole moments $Q_0$ of five superdeformed bands in ${}^{131,132}\mathrm{Ce}$ have been established using the Doppler-shift attenuation method; for the first time, we can compare relative deformations of yrast and excited bands in different nuclei to an accuracy of $\simeq (5–7)\%$. Four of the five bands have very similar deformations, while the excited band in ${}^{131}\mathrm{Ce}$ has a somewhat larger quadrupole moment. Important new information is presented on the shape-driving force of the $\nu i_{13/2}$ orbital, the stability of the second minimum with respect to particle excitations, the relative deformations of identical bands, the nature of the sidefeeding, and the time scale of the decay process.

A multiphonon structure, which is known to exist in boson systems [e.g., the U(5) and O(6) limits of the interacting boson model], is shown to arise also in a mixed system of bosons and fermions. This is illustrated with the example of the Spin(6) limit of U( $6|4$) in which a $j=\frac{3}{2}$ fermion is coupled to an O(6) boson core. All states in the supersymmetric multiplet of U( $6|4$) are shown to be multiphonon states obtained by multiple action of a quadrupole operator.

We investigated the energy properties of $\alpha$-cluster matter in a microscopic framework by arranging $\alpha$-clusters in a cubic close-packed configuration in the generator coordinate space, and extracted the surface effects from the total binding energy. The stability of $\alpha$ clusters in matter is probed by allowing the $\alpha$ clusters to be distorted so as to approach uniformly dense nuclear matter. To compare the result for the binding energy per nucleon with that of ordinary nuclear matter, we solve the dynamical problem of an $\alpha$ cluster in a cavity embedded in $\alpha$-cluster matter.

We have searched for a neutral $H$ dibaryon decaying via $H\to \Lambda n$ and $H\to {\Sigma }^{0}n$. Our search has yielded two candidate events from which we set an upper limit on the $H$ production cross section. Normalizing to the inclusive $\Lambda$ production cross section, we find $\frac{\left(\frac{d{\sigma }_H}{d\Omega }\right)}{\left(\frac{d{\sigma }_{\Lambda }}{d\Omega }\right)}<6.3\mathrm{}\times {10}^{-6\mathrm{}}$ at 90% C.L., for an $H$ of mass ≈2.15 GeV/${\mathit{c}}^2$.

Quasicontinuum spectra in coincidence with transitions belonging to the different potential wells of ${}_{}{}^{143}{}_{}{}^{}\mathrm{Eu}$ are studied with increasing number of coincidence folds. An intense bump of rotationally correlated transitions is observed to develop in the high spin region. Fold distributions, angular anisotropies, moment of inertia determinations, and lower limits of lifetimes as function of the rotational frequency show that the bump originates from highly collective rotationally damped $E2\mathrm{}$ transitions generated by superdeformed states.

Measurements of the $\mathrm{D}(\overrightarrow{p},\gamma {)}^3\mathrm{He}$ and $p(\overrightarrow{d},\gamma {)}^3\mathrm{He}$ reactions below $E_{p,d}=80\mathrm{}$ keV are compared to the results of calculations based on correlated hyperspherical harmonic wave functions obtained from realistic interactions with full inclusion of Coulomb distortion in the initial continuum state, and a nuclear current operator with one- and two-body components. Dramatic effects due to the tensor force and the associated two-body (meson-exchange) interaction currents are observed in the vector and, to some extent, tensor analyzing powers for the first time. The extrapolation to zero energy leads to an S-factor value of $S(E=0\mathrm{})=0.165\mathrm{}\pm 0.014$ eV b, in reasonable agreement with theory.

Shell model Monte Carlo techniques are used to calculate two-neutrino double beta decay matrix elements. We test the approach against direct diagonalization for ${}^{48}$Ca in the complete pf shell using the KB3 interaction. The method is then applied to the decay of ${}^{76}$Ge in the $\left({0f}_{5/2}{,1p,0g}_{9/2}\right)$ model space using a newly calculated realistic interaction. Our result for the matrix element is $0.12\pm 0.05{\mathrm{MeV}}^{-1\mathrm{}}$, in reasonable agreement with the experimental value.

The fragmentation resulting from peripheral $\mathrm{Au}+\mathrm{Au}$ collisions at an incident energy of $E=35\mathrm{}\mathrm{MeV}/\mathrm{nucleon}$ is investigated. A power-law charge distribution, $A^{-\tau }$ with $\tau \approx 2.2$, and an intermittency signal are observed for events selected in the region of the Campi scatter plot where “critical” behavior is expected.

A Comment on the Letter by J. Pochodzalla, et al., Phys. Rev. Lett. 75, 1040 (1995). The authors of the Letter offer a Reply.

A Reply to the Comment by L. G. Moretto et al.

We report on the first measurement in heavy-ion collisions of hard photons of extremely high energies that extend the photon spectrum to 5 times the beam energy per nucleon. The photon spectrum was measured for the systems ${}^{86}\mathrm{Kr}{+}^{\mathrm{nat}}\mathrm{Ni}$ at $60A\mathrm{MeV}$ and ${}^{181}\mathrm{Ta}{+}^{197}\mathrm{Au}$ at $40A$ MeV. The data are interpreted using the Dubna cascade model. The radiative channel of pion-nucleon interaction $\pi +N\to N+\gamma$, involving subthreshold pions produced in the nuclear medium, dominates all other processes considered for the production of the very energetic photons. This channel was never considered so far at beam energies below the pion threshold.

The $J^{\pi }{=0\mathrm{}}^{+}$ ground state of a drop of 8 neutrons and the lowest $1/2^{-}$ and $3/2^{-}$ states of 7-neutron drops, all in an external well, are computed accurately with variational and Green's function Monte Carlo methods for a Hamiltonian containing the Argonne $v_{18}$ two-nucleon and Urbana IX three-nucleon potentials. These states are also calculated using Skyrme-type energy-density functionals. Commonly used functionals overestimate the central density of these drops and the spin-orbit splitting of 7-neutron drops. Improvements in the functionals are suggested.

We present a novel quantum Monte Carlo method based on a path integral in Fock space, which allows the computation of finite-temperature properties of a many-body nuclear system with a monopole pairing interaction in the canonical ensemble. It enables an exact calculation of the thermodynamic variables such as the internal energy, the entropy, or the specific heat, from the measured moments of the number of hops in a path of nuclear configurations. Monte Carlo calculations for a single-shell $(h_{11/2}{)}^6$ model are consistent with an exact calculation from the many-body spectrum in the seniority model.

A simultaneous description of the NN and YN interactions is attempted in the resonating-group formulation of the spin-flavor S${\mathrm{U}}_6$ quark model, in which the full Fermi-Breit interaction with explicit quark-mass dependence acts between quarks, and all the mesons of scalar and pseudoscalar nonets couple directly to quarks. An overall agreement with the existing data is obtained with few adjustable parameters. In the $\Lambda p$ elastic total cross sections, the cusp structure at the $\Sigma N$ threshold is strongly enhanced by the antisymmetric ${\mathrm{LS}}^{\left(-\right)}$ force generated from the Fermi-Breit interaction.

A novel implantation-decay technique has been employed to measure the magnetic moments of the $2_1^{+}$ states in the neutron-deficient nuclei ${}^{184}\mathrm{Pt}$, ${}^{186}\mathrm{Pt}$, and ${}^{188}\mathrm{Pt}$. The magnetic moment systematics for the even Pt isotopes now extend from ${}_{78}^{184}{\mathrm{Pt}}_{106}$ to ${}_{78}^{198}{\mathrm{Pt}}_{120}$, spanning the upper half of the valence neutron shell. Despite the prolate-to-oblate shape transition near $A=190\mathrm{}$, they remain remarkably constant. The $g\left(2_1^{+}\right)$ values for ${}^{184,186,188}\mathrm{Pt}$ are consistent with shape-coexistence models in which the deformed configuration has a larger effective number of valence protons than the less-deformed configuration.

Production of the $\phi$ meson in central $\mathrm{Si}+\mathrm{Au}$ collisions has been measured by $E859\mathrm{}$ at the Brookhaven Alternating Gradient Synchrotron by selecting events with identified $K^{+}{K}^{-}$ pairs. The mass and width of the $\phi$, obtained from the invariant mass distribution of kaon pairs, are consistent with those of free $\phi$ mesons. The transverse mass and rapidity distributions are presented. The inverse slope parameter for an exponential fit to the invariant transverse mass distribution is $179\pm 10\pm 17\mathrm{MeV}$.

High energy γ rays from the decay of the giant resonance in hot ${}^{120}$Sn nuclei were measured in the excitation energy range of 30–130 MeV. The excited nuclei were populated by inelastic scattering of α particles at 40 and 50 MeV/nucleon. The resonance width was observed to increase monotonically with increasing excitation energy, from 5 MeV at the ground state to $\sim 12$ MeV at the largest excitation energy. Inelastic scattering predominantly populates low angular momentum states, and the observed width increase is thus attributed to fluctuations in the nuclear shape induced by temperature.

A nuclear resonance fluorescence experiment with one of the newly developed highly efficient EUROBALL cluster detectors has been performed on the $\gamma$-soft nucleus ${}^{196}\mathrm{Pt}$. Magnetic dipole excitations were observed between 2 and 3.5 MeV excitation energy. They are interpreted as the main fragments of the scissors mode based on the measured excitation strengths and branching ratios. A strong $\gamma$ decay, which we believe to be an $E2\mathrm{}$ decay of the scissors mode to the $2_1^{+}$ state, is observed. It allows an extraction of the effective boson quadrupole charges in the interacting boson model.