We have observed the decays ${\mathit{B}}^0$→${\mathit{K}}^{\mathrm{*}}$(892${)}^0$γ and ${\mathit{B}}^{\mathrm{-}}$→${\mathit{K}}^{\mathrm{*}}$(892${)}^{\mathrm{-}}$γ, which are evidence for the quark-level process b→sγ. The average branching fraction is (4.5±1.5±0.9)×${10}^{\mathrm{-}5}$. This value is consistent with standard model predictions from electromagnetic penguin diagrams.

Data taken with the Collider Detector at Fermilab (CDF) during the 1988–1989 run of the Tevatron are used to measure the distribution of the center-of-mass (rest frame of the initial state partons) angle between isolated prompt photons and the beam direction. The shape of the angular distribution for photon-jet events is found to be significantly different from that observed in dijet data. The QCD predictions show qualitative agreement with the observed prompt photon angular distribution.

The polarization transfer observable ${\mathit{D}}_{\mathit{L}\mathit{L}}$(0°) has been measured for ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(p→,n→)2p, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(p→,n→${)}^{12}$N, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$(p→,n→${)}^{14}$N reactions with beam energies of 318 and 494 MeV. The deuterium results are in close agreement with free NN scattering constrained to the Δ${\mathit{J}}^{\mathrm{\pi }}$=$1^{+}$ channel. The results for the carbon targets, however, are systematically more negative than those for deuterium, which suggests a difference between the free and effective nucleon-nucleon interactions. Such a medium modification of the spin-dependent interaction may have important implications for intepretation of other intermediate-energy scattering experiments.

Eight superdeformed rotational bands have been observed in the ${}_{}{}^{149}{}_{}{}^{}\mathrm{Gd}$ nucleus. Several excited bands have partners in neighboring nuclei which differ by up to four nucleons, with nearly identical dynamic moments of inertia and quantized γ-ray phasing. These observations cannot be easily explained by theoretical models including an intrinsic scaling with mass of the moment of inertia. A paired backbend and an interaction due to an accidental degeneracy between two superdeformed levels have also been observed.

We study the multiphoton dissociation of ${\mathrm{H}}_2^{+}$ by a coherent superposition of an intense short pulsed laser radiation and one of its harmonics (second or third), in a phase-locked regime. We show that the total dissociation probability, the energy distribution, and the direction of ejection of the protons are very sensitive to the relative phase of the two radiations. A high degree of control may thus be achieved for the branching ratio between dissociation via bond-softening and above-threshold dissociation, in the realm of current experimental capabilities.

The longitudinal momentum transfer to the recoil ion in collisions of 1 MeV/amu bare F ions with Ne are resolved for final charge states of both projectile and recoil ions. We observe the recoil to be thrown backwards in electron-capture events, reflecting the physical impact of the electron translation factor. The size of the momentum transfer is in agreement with classical trajectory Monte Carlo calculations for low charge state recoil ions but not for high charge state recoil ions.

The size distribution of ${\mathrm{He}}_{\mathit{N}}^{\mathrm{-}}$ ions produced by crossing a low energy beam with an uncharged helium cluster beam exhibits a threshold below which no ions are detected. The threshold region is unexpectedly structured, however, and exhibits a sharp ‘‘magic’’ mass peak at N=(2.0±0.1)×${10}^5$ atoms. We suggest that this behavior derives from the dynamics of the conduction band instability which leads to the formation of a metastably trapped bubble electron in the droplet.

We have observed up to 8 orders (n) in the spectra of parametric x-radiation (PXR) in the range 5–40 keV, produced by the interaction of a 90 MeV electron beam with mosaic graphite and single silicon crystals. The measured yields and intensity ratios, I(n≥2)/I(n=1), in graphite are not in agreement with the theory of PXR for mosaic crystals. In comparison, the ratios of intensities in silicon are close to the predictions of PXR theory for perfect crystals. The bandwidths of spectral lines measured in both silicon and graphite are in good agreement with theoretical predictions.

Using a two-photon interferometer, we have measured the time delay for a photon to tunnel across a barrier consisting of a 1.1-μm-thick 1D photonic band-gap material. The peak of the photon wave packet appears on the far side of the barrier 1.47±0.21 fs earlier than it would if it were to travel at the vacuum speed of light c. Although the apparent tunneling velocity (1.7±0.2)c is superluminal, this is not a genuine signal velocity, and Einstein causality is not violated. The measured tunneling time is consistent with the group delay (‘‘phase time’’), but not with the semiclassical time.

A new theoretical approach to the unsteady detonation in condensed explosives was developed in our laboratory. The experimental results presented in this paper represent the first study of the propagation of front waves moving transverse to the detonation front. It also appears that the velocity of these waves does not depend on the explosive confinement.

Long range intercluster structural order has been observed in the late, diffusion-limited stages of cluster-cluster aggregation of colloidal monolayers at liquid surfaces. The structure factor S(q,t) scales as ${\mathit{q}}_{\mathit{m}\mathit{f}}^{\mathrm{-}\mathit{d}}$(t)F(q/${\mathit{q}}_{\mathit{m}}$), the exponent being the fractal dimension of two dimensional diffusion-limited cluster aggregation. Such scaling is not observed when the aggregation is reaction limited.

Synchro-betatron coupling in a proton storage ring with electron cooling was studied experimentally by modulating a transverse dipole field close to the synchrotron frequency. The combination of the electron cooling and transverse field modulation on the synchrotron oscillation is equivalent to a dissipative parametric resonant system. The proton bunch was observed to split longitudinally into two pieces, or beamlets, converging toward attractors of the dissipative system. These phenomena might be important in understanding the effect of ground vibration on the Superconducting Super Collider beam, and the effect of power supply ripple on the Relativistic Heavy-Ion Collider beam.

The stimulated Brillouin scattering (SBS) of intense laser light is considered. We present experimental data demonstrating SBS nonstationarity of radiation directed at thick targets. The results are explained in terms of the interaction of light scattered and reflected from the critical surface. Numerical simulations supporting this interpretation are presented. It is demonstrated that the SBS evolution is neither sensitive to plasma density, size of plasma slab, or beam intensity variations. But it is sensitive enough to changes in the reflection coefficient and variations of the critical surface velocity.

We propose an explanation for the experimentally observed transition in the shape of silicon clusters of size 20≤N≤40: Elongated shapes of low energy can be obtained by stacking stable subunits, while concurrent optimization of surface-to-volume ratio and surface structure leads to compact shapes. A transition in shape from elongated to compact structures is expected as the size increases beyond a critical value at which interior atoms become stable. Our proposal is backed by extensive first-principles calculations on the energetics of two classes of Si clusters, which suggest a critical size bounded by 24≤N≤28, in good agreement with experimental observations.

By high-temperature ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy on single crystals the diffusion mechanism in an ordered structure (stoichiometric ${\mathrm{Fe}}_3$Si) has been studied on an atomic scale. From the widths and the weights of the quasielastic lines in appropriately chosen crystal directions one can directly infer the elementary diffusion jump mechanism: For the stoichiometric alloy ${\mathrm{Fe}}_3$Si jumps via the three iron sublattices dominate. At only slightly higher iron concentrations (off stoichiometry), however, jumps via antistructure sites on the silicon sublattice contribute strongly.

The ferroelectric domain wall is an ideal interface for studies of the boundary scattering of high frequency acoustic phonons. These internal interfaces have no contamination and can be reversibly created and destroyed by application of an electric field at the phase transition—122 K in KDP. Images of phonons in single- and multiple-domain cases show remarkable differences in the ballistic heat flux. Theoretical modeling based on acoustic wave reflection reveals that the domain walls act as nearly perfect grain boundaries.

We report sorption isotherms and optical measurements for fullerite ${\mathrm{C}}_{60}$/${\mathrm{C}}_{70}$ crystals and ${\mathrm{C}}_{60}$ films exposed to helium. The low temperature isotherms show excess sorption above that expected for surface films. We interpret this as intercalation of helium in the fullerite lattice. Our observations suggest that helium is mobile within the crystal, and opens up the possibility of realizing a new type of three-dimensional quantum fluid. Raman measurements are inconclusive on the issue of intercalation.

Scanning tunneling microscopy images of the equilibrium structure of A- and B-type steps on vicinal GaAs(001) with the (2×4)/c(2×8) reconstruction have been analyzed to determine edge and kink energies. The values of the edge energies are low (implying that the equilibrium steps will be quite rough at room temperature), and anisotropic by a ratio of ∼6:1. The data provide evidence for a kink-kink interaction, found only in the A steps, which is short range and repulsive.

We introduce a novel three-dimensional Toom model on a bcc lattice, and study its physical properties. In the low-noise limit, the model leads to an effective solid-on-solid type model, which exhibits a stationary interface via depositions and evaporations with an avalanche process. We find that the model is described by the Edwards-Wilkinson equation for the unbiased case and the anisotropic Kardar-Parisi-Zhang equation in the weak-coupling limit for the biased case. Thus the square of the surface width diverges logarithmically with space and time for both unbiased and biased cases.

Results of an x-ray-scattering study of the (3×1)-to-disordered phase transformation of the Si(113) surface are reported. A continuous commensurate-solid to incommensurate-fluid transformation occurs at ${\mathit{T}}_{\mathit{c}}$=959 K. A new two-dimensional universality class is identified and characterized. Specifically, we find that the correlation lengths in the disordered phase scale anisotropically, and that the product of the incommensurability and the correlation length along the incommensurate direction is constant.