A new type of resonance appears to have been discovered in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{12}$C${,}^{12}$C($0_2^{+}$)${)}^{12}$C($0_2^{+}$) reaction at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=33 MeV. We suggest that it is formed coherently from nearly degenerate resonances with different l values. Taking the individual resonances to be members of a cluster rotational band with 2n+l=const, the coherence can be shown to follow from Levinson’s theorem. The new kind of resonance does not have a definite angular momentum but corresponds to an approximate shape eigenstate.

An unusual low-energy component has been observed in the spectrum of equilibriumlike intermediate-mass fragments (IMFs) emitted from systems formed in high-linear-momentum-transfer reactions of 270-MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ with ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$. The properties of this component include strong focusing of IMFs at an angle perpendicular to the fission fragment separation axis, kinetic energies about one-half those for normal IMFs, and a preference for neutron-excess fragments. This behavior is consistent with emission of IMFs from the neck region of a fissioning nucleus.

Color transparency occurs if a small-sized wave packet, formed in a high momentum transfer process, escapes the nucleus before expanding. The time required for the expansion depends on the masses of the baryonic components of the wave packet. Measured proton diffractive dissociation and electron deep inelastic scattering cross sections are used to examine and severely constrain the relevant masses. These constraints allow significant color transparency effects to occur at experimentally accessible momentum transfers.

Identical rotational bands (i.e., those with surprisingly similar moments of inertia) have been proposed through several analyses of known bands in normally deformed nuclei. In this paper, we analyze bands in odd-proton nuclei (A=150–190) with criteria more stringent than those of previous approaches. The identical bands are found to be associated with up-sloping particle states, suggesting that the cause may be a cancellation between pairing and deformation decreases.

The relativistic cascade code arc is applied to data from the experiment E814 covering projectile rapidities in Si+Pb collisions at 14.6 GeV/c per nucleon. The result is a quantitative theoretical description of the entire range of the experimental rapidity spectrum, as well as of the number and transverse energy dependence of ‘‘punchthrough’’ protons. This plus additional detailed comparisions of transverse mass distributions strongly suggest the cascade approach can be highly useful for understanding energetic ion collisions.

We present results of new measurements of the β spectrum of ${}_{}{}^{35}{}_{}{}^{}\mathrm{S}$, using the Caltech double-focusing, iron-free β spectrometer. Our data show no evidence for a heavy neutrino with a mass between 12 and 22 keV admixed to the usual light neutrino. In particular, we rule out, at the 6σ level, a 17 keV neutrino admixed at 0.85%, and give an upper limit (90% C.L.) of 0.2% for such a neutrino admixture. To demonstrate that our experiment is sensitive to spectral features such as those from heavy neutrinos we have induced an artificial kink by means of an absorber foil covering part of the source.

The problem of the existence of heavy-quarkonia bound states in nuclei is discussed. The method of multipole expansion and low-energy QCD theorems are used to calculate the cc¯-nucleon scattering amplitude. It is shown that an effective interaction is too weak to produce bound states with light nuclei for S-wave cc¯ systems. S-wave quarkonia can be bound in nuclei with A>10 with binding energy of the order of some MeV.

We present novel Monte Carlo methods for treating the interacting shell model that allow exact calculations much larger than those heretofore possible. The two-body interaction is linearized by an auxiliary field; Monte Carlo evaluation of the resulting functional integral gives ground-state or thermal expectation values of few-body operators. The ‘‘sign problem’’ generic to quantum Monte Carlo calculations is absent in a number of cases. We discuss the favorable scaling of these methods with nucleon number and basis size and their suitability to parallel computation.

We consider the effect on baryon-baryon potentials and phase shifts of including quark delocalization and color screening in the nonrelativistic quark cluster model. We find that the inclusion of these additional effects allows a good qualitative description of both.

A comparison between the predictions of a theoretical model describing the giant dipole resonance in hot nuclei, which includes the coupling to time-dependent thermal fluctuations of the nuclear surface, and experimental data on the cross section and the angular distribution associated with the dipole decay of ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}_{}^{\mathrm{*}}{}_{}{}^{}$ is presented. Effects of different time scales for fluctuuations in the deformation and orientation degrees of freedom are observed.

The hadronic spectra of 200A GeV S+S collisions are analyzed assuming thermal emission of particles including resonance decays. While the rapidity distributions suggest a longitudinal flow almost independent of the temperature, the transverse momentum spectra exhibit an ambiguity between transverse flow and temperature, which cannot be resolved by the spectra of the heavier particles. However, in a theoretical model for the global hydrodynamic expansion with a dynamical freeze-out criteron, we find that almost inevitably a sizable transverse flow develops, which is in quantitative agreement with the data.

Nuclear decay via neutrino-pair production is found to have a large density dependence because of intermediate electromagnetic couplings to electrons. These are calculated in a relativistic random phase approximation. The decay rate for vector (Fermi) transitions producing electron type neutrino pairs can be enhanced by ${10}^5$ or more at densities relevant for stellar collapse. Axial-vector (Gamow-Teller) transitions are not enhanced.

The quasielastic scattering of the exotic ‘‘halo’’ nucleus ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ has been studied at an energy of 60 MeV/nucleon and compared with that of the A=11 isobar ${}_{}{}^{11}{}_{}{}^{}\mathrm{C}$. The prediction of enhanced refraction in the former system is confirmed, as is the need for very long-range absorption. No evidence is found for an Airy minimum in the far-side scattering.

Entry distributions leading to normal and superdeformed (SD) states in ${}_{}{}^{192}{}_{}{}^{}\mathrm{Hg}$ have been measured. A model, based on Monte Carlo simulations of γ cascades, successfully reproduces the entry distribution for SD states, as well as all other known observables connected with the population of SD states. Comparison of experimental and model results, together with the measured SD entry distribution, suggest that the SD band lies 3.3–4.3 MeV above the normal yrast line when it decays around spin 10 and that the SD well depth is 3.5–4.5 MeV at spin 40.

Double beta decay of ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$ has been confirmed and the ratio of half-lives for ββ decay of ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$ and ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$ has been determiend as ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}_{1/2}^{}{}_{}{}^{}$${/}^{128}$${\mathrm{Te}}_{1/2}$=(3.52±0.11)×${10}^{\mathrm{-}4}$ by ion-counting mass spectrometry of Xe in ancient Te ores. The Xe measurements, combined with common Pb dating, yield a ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$ half-life of (2.7±0.1)×${10}^{21}$ yr and thus a ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$ half-life of (7.7±0.4)×${10}^{24}$ yr. These results give limits on the effective Majorana mass of the neutrino (<1.1-1.5 eV) and right-handed currents (‖〈η〉‖>5.3×${10}^{\mathrm{-}8)}$ comparable to the best obtained from direct neutrinoless ββ-decay searches. They also imply new limits on nonstandard Majorons not constrained by measurements of the ${\mathit{Z}}^0$ decay width.

We report measurements of d¯, p¯, ${\mathit{K}}^{\mathrm{-}}$, and ${\mathrm{\pi }}^{\mathrm{-}}$ produced at 0° in collisions of 14.6A GeV/c ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ on Al, Cu, and Au targets. A beam-line focusing spectrometer was used to identify particles at rigidities from -2 to -8 GV. The ratio of d¯/p¯ invariant cross sections at midrapidity (y=1.7) is (1±0.7)×${10}^{\mathrm{-}5}$, larger than expected from a calculation of dd¯ direct production but smaller than predicted by a simple coalescence model. We also report limits on the production of exotic particles.

Contrary to the conventional view of spherical nuclei as being chaotic in nature, we find, by means of level statistics, that some heavy nuclei exhibit deviations toward regularity unlike the predictions of the random matrix theory. We show that the degree of regularity is closely connected to the ratio of the nuclear size to the range of the nuclear force.

Bound-state ${\mathrm{\beta }}^{\mathrm{-}}$ decay was observed for the fist time by storing bare ${}_{66}{}^{163}{}_{}{}^{}\mathrm{Dy}_{}^{66+}{}_{}{}^{}$ ions in a heavy-ion storage ring. From the number of ${}_{67}{}^{163}{}_{}{}^{}\mathrm{Ho}_{}^{66+}{}_{}{}^{}$ daughter ions, measured as a function of the storage time, a half-life of ${47}_{\mathrm{-}5}^{+5\mathrm{}}$ d was derived. By comparing this result with reported half-lives for electron capture (EC) from the ${\mathit{M}}_1$ and ${\mathit{M}}_2$ shells of neutral ${}_{67}{}^{163}{}_{}{}^{}\mathrm{Ho}$, bounds for both the ${\mathit{Q}}_{\mathrm{EC}}$ value of neutral ${}_{67}{}^{163}{}_{}{}^{}\mathrm{Ho}$ and for the electron-neutrino mass were set.

A new method, use of a fragment separator as an energy-loss spectrometer, has been developed and used to make the first measurements of the parallel momentum distributions of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ nuclei produced in the breakup of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$. Measurements were made for 66-MeV/nucleon ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ projectiles on ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$, and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ targets. Distributions with Gaussian width of ${\mathrm{\sigma }}_{\mathrm{\parallel }}$≊19 MeV/c were observed for all targets—the first time such a narrow structure has been observed for medium and high mass targets. From the weak dependence of width on breakup target it appears that the paralell momentum distributions are relatively insensitive to the interaction governing the breakup and reflect an extended neutron distribution for ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$.

Cross section (σ), analyzing power (${\mathrm{A}}_{\mathrm{y}}$), induced polarization (P), and normal polarization transfer ${\mathrm{coefficientD}}_{\mathrm{N}{\mathrm{N}}^{\prime }}$) data have been measured for scattering of 200-MeV polarized protons from ${\mathrm{B}}^{10}$. Data for the $3^{+}$, T=0 to $0^{+}$, T=1 (1.74 MeV) isovector 0ħω stretched transition are compared to results of distorted-wave calculations. While σ, ${\mathrm{A}}_{\mathrm{y}}$, and P are reasonably described by calculations based on the free nucleon-nucleon(NN)t matrix, the ${\mathrm{D}}_{\mathrm{N}{\mathrm{N}}^{\prime }}$ data are not. The results suggest a larger transverse to longitudinal spin-dependent interaction ratio than is expected from free NN scattering. © 1992 The American Physical Society