The decay mode ${\psi }^{\prime }\to \gamma \gamma \psi$ has been studied with the Mark-II detector at SPEAR. New measurements of branching ratios for decays of the type ${\psi }^{\prime }\to \gamma \chi$, $\chi \to \gamma \psi$ involving known $\chi$ states are presented. The existence of a $\chi$ state of mass near 3455 MeV/${\mathit{c}}^2$ produced in this decay chain is not confirmed, and the upper limit (90% confidence level) of the product of branching ratios is measured to be 0.13%. A new decay mode, ${\psi }^{\prime }\to {\pi }^0\psi$, which violates isospin conservation is observed with branching ratio (0.15±0.06)%.

The role of higher-order isovector modes and of the mass asymmetry in the charge distributions of deep inelastic products is studied in the weak-coupling limit.

The interference between the $E_p=14.23\mathrm{}$ MeV $M1\mathrm{}\left(E2\mathrm{}\right)\mathrm{}$ $T=\frac{3}{2}$ resonance and the $E1\mathrm{}$ giant-dipole-resonance "background" in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(p_{\mathrm{pol}}, {\gamma }_0){}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ is used to determine uniquely the $E1\mathrm{}$ reaction amplitudes. The $E1\mathrm{}$ capture is found to be predominantly $d$ wave, in agreement with the basic shell-model description of the nuclear giant dipole resonance.

This paper reports the first detection and measurement of spin-destruction rates due to collisions between atoms in ${}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ states. The spin-destruction rates are about 1% of the well-known spin-exchange rates. Magnetic dipole spin-spin interactions are large enough to account for the observed spin destruction.

This paper presents measurements of the influence of magnetic fields on the plastic deformation of zinc. In particular it is shown that both slip processes and twinning are affected by the presence or absence of magnetic fields. Furthermore, it is shown that the motion of dislocations is required for twinning and that twinning can be altered through a change in magnetic field which determines the dislocation velocity. These results are explained by treating the dislocations as underdamped oscillators.

The phase diagram for a staged intercalation compound is calculated in mean-field theory. At low temperatures, the dependence of the staging on the chemical potential is related to the interlayer interactions responsible for staging. At high temperatures, a dilute stage-1 phase is predicted for all values of the chemical potential. The stage-2-stage-1 transition is second order for temperatures greater than the tricritical temperature. The predicted phase diagrams are related to recent experiments.

Computer simulations of crack properties were performed on a two-dimensional triangular lattice with a Lennard-Jones interatomic interaction. The use of a long-range potential and an unconstrained sample revealed novel features compared to earlier simulations. The Griffith energy treatment for fracture was found wanting. This system is brittle at low stresses in agreement with the Rice-Thomson criterion and shows dislocation formation at elevated stresses.

The first high-resolution observation of the ${\nu }_1$ vibrational mode of H chemisorbed on W(100) at saturation coverage has been obtained by surface electromagnetic wave spectroscopy.

The dispersion of the $B$-exciton polariton is CdS for $\overrightarrow{\mathrm{k}}\perp \overrightarrow{\mathrm{c}}$ was measured using resonant Brillouin scattering. Data taken with $\overrightarrow{\mathrm{E}}\parallel \overrightarrow{\mathrm{c}}$ were interpreted within the conventional two-branch polariton model; however, with $\overrightarrow{\mathrm{E}}\perp \overrightarrow{\mathrm{c}}$, the spectra provided direct evidence for three simultaniously propagating exciton-polariton modes. The $B$-exciton effective mass, $m_{\perp }$, and the $k$-linear term of the second valence band, $C^h$, were directly derived. The value of $C^h$ casts doubt on the theoretical explanation of the physical origin of the $k$-linear terms.

This paper reports measurement of bulk plasmon dispersion in single-crystal silicon along the [100] and [110] directions using electron energy-loss spectroscopy. An electron beam energy of 250 keV allows one to observe the plasmon peak up to wave vectors of $q=2.55\mathrm{}$ ${\mathrm{\AA }}^{-1\mathrm{}}$ along [100]. It is shown that the plasmon is still dispersive at large $q$, contrary to what has been reported.

In the universe prior to recombination the plasma conductivity $\lambda$ can range ∼${10}^{12}$-${10}^3$ mho/m. Plasma instabilities of a frozen-in magnetic field couple to the fluid motion to augment perturbations in density depending exponentially on the conductivity. Ultimately this leads to exponential growth of the density perturbations in an anisotropic, spatially homogeneous, magnetohydrodynamic background model at the rate $t\exp \left(\lambda t\right)$ for isothermal and $t\exp \left(4\mathrm{}\lambda t^{\frac{1}{4}}\right)$ for adiabatic perturbations.

In a recent paper Thornton and Clay strongly suggest a very early development in the atmosphere for small cosmic-ray showers and consequently require a change in primary mass composition in the energy range ${10}^{15}$-${10}^{17}$ eV. It is suggested here that when allowance is made for inconsistencies in the data the necessity for the early development of small showers-and hence the inferred rapid change in primary composition-is removed.

Differential renormalization equation for the $q$-state Potts model are proposed, and the critical behavior of the model near $q=q_c$ discussed. The equations give rise to critical and tricritical fixed points which merge at $q=q_c$ when a dilution field becomes marginal, to an essential singularity in the latent heat as a function of $q=q_c$, in accordance with the exact result of Baxter, and, for $q=q_c$, to a logarithm correction to the power-law behavior of the free energy as a function of $T-T_c$.

An Ising model on a square lattice is studied, where one row of horizontal bonds has an energy ${E_1}^{\prime }$ different from all other horizontal bonds. The correlation of two spins is calculated in this row, resulting in exponents $\beta$ and $\eta$ which depend on ${E_1}^{\prime }$. The long-distance behavior of the correlation for fixed $T\ne T_c$ is found to have different forms depending upon the value of ${E_1}^{\prime }$.

This paper reports on the results of an extensive analysis of baryon couplings in a quark model with chromodynamics. The amplitudes which emerge from the analysis resolve the problem of "missing" baryon resonances by showing that a very large number of states essentially decouple from the partial-wave analyses; those resonances which remain are in remarkable correspondence to the observed states in both their masses and decay amplitudes.

We study the classical solutions of Yang-Mills equations of motion where the field tensor $G_{\mu \nu }$ is assumed to decrease exponentially with $\mathcal{r}$, as $\mathcal{r}$, the spatial distance, goes to infinity. Sources are introduced and they are also assumed to decrease exponentially fast at infinity. We find that $G_{\mu \nu }$ has to decrease at least as fast as the sources at infinity. If we think that within a classical approach to confinement the size of the sources should not matter, then our result is an indication that quantum effects are necessary to achieve it.

Vibrational states, which are expected (in the string picture) in addition to ordinary $Q\overline{Q}$ bound states, are investigated in the $\Upsilon$ spectroscopy by use of a phenomenalogical approach. The lowest $1^{--}$ vibrational state is predicted to be below the continuum threshold, between the radial excitations ${\Upsilon }^{\prime \prime }$ and ${\Upsilon }^{\prime \prime \prime }$. Its mass is estimated to be 990 (±90) MeV above $\Upsilon$ with a leptonic width of 0.20 (±0.15) keV.

A missing-mass experiment in $\mathrm{pd}\to \mathrm{NX}$, where $X$ is the system whose mass $M_X$ is measured, was performed for interactions of antiprotons at rest and in flight below 500 MeV/c. The 4-standard-deviation upper limit for the production of narrow states, in the mass interval $M_X=1650-1930\mathrm{}$ MeV/${\mathit{c}}^2$, is 2 mb for annihilations in flight and 0.3% of the annihilations at rest.

Natural-parity high-spin states of $J^{\pi }={12}^{+}$ (6.10 MeV) and ${10}^{+}$ (4.89, 5.07, and 5.92 MeV) were observed and identified via inelastic electron scattering. Dominant single-particle-hole configurations in these excitations were deduced. The measured cross sections indicate a reduction of the transverse transition amplitude to 65% of the shell-model prediction, and the absence of an effective charge for the neutron.

$K$-shell autoionization accompanying internal bremsstrahlung in the decay of ${}_{}{}^{204}{}_{}{}^{}\mathrm{Tl}$ has been observed. Its probability was determined to be $P_{\mathrm{IB}, K}=(8\mathrm{}\pm 3)\times {10}^{-8\mathrm{}}$ per $\beta$ decay for internal bremsstrahlung in the energy range from 88 to 394 keV. A comparison with theoretical expectations is presented.