We have searched for resonances in the reaction $e^{+}{e}^{-}\to \mathrm{hadrons}, \gamma \gamma , \mu \mu , \mathrm{and} \mathrm{ee}$, in the energy range $39.79<\mathrm{}\sqrt{s}<45.52\mathrm{}$ GeV, using the Mark J detector at PETRA. We obtain stringent upper limits on the production of toponium and particles postulated to explain $Z^0\to \mathrm{lepton}\mathrm{pair}+\gamma$ events observed at the CERN $\bar{p}p$ collider. We also set limits on the mass and coupling constant of excited electrons.

A new signature for quark-matter formation in relativistic heavy-ion collisions, in terms of the emission spectra in the fragmentation regions, is proposed.

A new lower limit of 3.2×${10}^{22}$ yr has been obtained for the half-life of neutrinoless double $\beta$ decay of ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$ to the ground state of ${}_{}{}^{76}{}_{}{}^{}\mathrm{Se}$, by use of a Ge detector of 208 ${\mathrm{cm}}^3$ active volume running in a salt mine for 2363 h. This is the largest detector used to date in such an experiment. A limit for decay to the first excited state has also been obtained.

We have measured a complete set of polarization-transfer observables in the inclusive scattering of 500-MeV protons from ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ and Pb at $q=1.75\mathrm{}$ ${\mathrm{fm}}^{-1\mathrm{}}$. Axial longitudinal and transverse response functions derived from these data show no differences between Pb and ${}_{}{}^2{}_{}{}^{}\mathrm{H}$. This implies no enhancement of the nuclear pion field in heavy nuclei and consequently that models of the low-$x$ $A$ dependence of certain nuclear structure functions requiring such an enhancement are unlikely to be correct.

High-energy gamma rays from the deexcitation of giant dipole resonance modes have been measured for the decay of ${}_{}{}^{108}{}_{}{}^{}\mathrm{Sn}_{}^{*}{}_{}{}^{}$ and ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}_{}^{*}{}_{}{}^{}$. The structure of the observed resonances can be correlated with the shapes of these nuclei at high excitation energy ($E^{*}\simeq 60$ MeV). For the deformed system ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}_{}^{*}{}_{}{}^{}$ a shape change with increasing temperature is suggested.

Results of the first measurements of the form factors for the electroexcitation of the $0_2^{+}$ state at 3.352 MeV in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ in the momentum-transfer region from 0.3 to 2.7 ${\mathrm{fm}}^{-1\mathrm{}}$ are described. It is shown that the model-independent densities obtained from these measurements provide a sensitive test of the nuclear structure models of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. The essential premise of the coexistence model of Gerace and Green is verified.

An identity-forbidden two-photon transition has been observed for the first time, between the $I^1{\Sigma }^{-}$ and $X^1{\Sigma }^{+}$ states in carbon monoxide. Such transitions are dipole allowed only for the absorption of two photons with different frequencies and polarization states. Only $P$ and $R$ rotational branches of the (7-0) band are observed, and the line intensities are maximized for perpendicular photon polarizations. This is the first experimental demonstration of the two-photon electric-dipole selection rule ${\Sigma }^{+}\to {\Sigma }^{-}$.

The use of a low-pressure discharge lamp has permitted us to discover many new emission bands of ${\mathrm{N}}_2$ at short wavelengths, in the vacuum ultraviolet. Strong evidence of predissociation is afforded by the sharp breaking off in the rotational structure of some bands corresponding to transitions originating from an electronic state different in ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}_2^{}{}_{}{}^{}$ and ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}_2^{}{}_{}{}^{}$. The respective limits give, directly, an improved upper limit for the dissociation into $\mathrm{N}\left({}_{}{}^2{}_{}{}^{}D\right)+\mathrm{N}\left({}_{}{}^2{}_{}{}^{}D\right)$, furnishing clear-cut evidence for setting definitely the dissociation energies of ${\mathrm{N}}_2$.

The quadrupole photoionization cross sections for hydrogen are shown to contain minima at kinetic energies of the free electron that are less than 2 eV. These minima are the result of zeros that occur in some of the quadrupole transition strengths between bound excited ($|n,l〉$) and continuum ($|W,l+2\mathrm{}〉$) states for atomic hydrogen. These minima are compared with Cooper minima which occur in the photoionization cross sections for some multielectron systems.

We report on the first observation of an electron beam formed in an argon gas-puff $Z$ pinch at the time of pinch. An on-axis Faraday cup in conjunction with thin foil filters was used to measure the beam parameters. The beam has a pulse width of 4 ns, a peak current on the order of 10 kA, and an energy of 20 keV.

The liquid-vapor coexistence boundary of submonolayer C${\mathrm{H}}_4$ adsorbed on graphite was mapped out in an extensive ac heat-capacity study. The order-parameter exponent $\beta$ that describes the shape of the liquid-vapor coexistence boundary was found to be 0.127 ± 0.020. This is in good agreement with $\frac{1}{8}$, the exact value calculated for a two-dimensional Ising-model system.

The dilute $n\to 0$ vector model, recently used to model the phase equilibria in sulfur solutions and living polymers, possesses a nonsymmetrical tricritical point of the sort found in three- and more-component solutions at a small nonzero value of the magnetic field as well as the symmetric tricritical point at zero field. This has interesting consequences for the phase diagrams of sulfur solutions and suggests a resolution of a number of discrepancies between the earlier (zero-field) theory of Scott and experiments on sulfur solutions.

A direct connection is proposed between the "dynamic" transport properties and the "static" topological structure for branched polymers in any number $d$ of spatial dimensions. Specifically, the resistivity exponent $\tilde{\zeta }$ is given by $\tilde{\zeta }=\frac{d_f}{d_l}$, where $d_f$ and $d_l$ are the fractal and topological dimensions (the number of sites within path length $l$ of a given site scales as $M\sim l^{d_l}$). To confirm this new result, we carry out extensive exact and Monte Carlo calculations for $d=2, 3, 4, \mathrm{and} 8$.

Direct measurements of the silicon liquid/solid interface velocity have been made during both melt-in and regrowth for crystalline silicon irradiated with a pulsed (15 psec) ultraviolet laser. The liquid films produced were up to 40 nm thick and were fully amorphized upon resolidification. Above threshold, the regrowth velocity was 25 m/sec, independent of laser fluence. The results imply a nonlinear relationship between supercooling and interface velocity.

We present the local-band theory of the temperature dependence of up- and down-spin Green's functions in itinerant-electron ferromagnets. The results, calculated for a temperature-independent, local, exchange field strength, and under the assumption of the existence of short-range magnetic order, agree with recent measurements of angle-, energy-, and spin-resolved photoemission in nickel. States which contribute to the magnetization, not seen in the measurements, remain split in energy even at $T_C$. Split states at $T_C$ are also expected in iron.

The first use of linear magnetic birefringence (optical Cotton-Mouton effect) to observe a magnetic resonance is reported. This allows us to make the first direct observation of resonant motion of a ferromagnetic vortex. This vortex is present in an easy-plane garnet film at the intersection of two 90° Néel walls. Agreement between the resonant frequencies and our theory confirms a previously proposed equation of vortex motion.

The infrared conductivities of four organic conductors with partially filled one-electron bands are compared. The behavior ranges from near Drude type in the best metal to semiconductorlike in the moderate conductor. Electron-molecular-vibration coupling effects of varying degree are seen in all materials. It is suggested that the combined effect of electron-electron interaction and electron-phonon interaction in producing $4k_{\mathrm{F}}$ charge-density waves is essential for interpreting the results.

High-resolution soft-x-ray excitation spectra are reported for free CO, CO condensed on Au at ∼ 20 K, and CO chemisorbed on Ni(111). Chemisorption increases dramatically the widths of the C and O $1s\to 2{\pi }^{*}$ transitions from < 0.2 to 2.2 eV for C $1s$ and from 1.15 to 3.5 eV for O $1s$. Shifts of 0.3 eV (for C $1s$) and 1.7 eV (for O $1s$) towards lower energy are resolved for the first time and are explained in terms of the electronic distribution in excited CO.

The occupied and empty electronic states of the insulator Ce${\mathrm{O}}_2$ have been studied by high-energy spectroscopies. The outer-level spectra reveal empty localized $4f^1$ states within the band gap. The core-level spectra display different final-state populations of the $4f$ localized states which are well predicted by a many-body calculation taking into account the presence of $f$-symmetry admixture in the valence band. A mixed valence can be definitely excluded in Ce${\mathrm{O}}_2$.

The majority- and minority-spin states of the exchange-split virtual bound state of Mn impurities in Cu and Ag are studied with high-resolution photoemission and bremsstrahlung isochromat spectroscopy. The exchange splitting is found to be close to the atomic value. The majority-spin state is strongly hybridized with the host-metal $d$ band resulting in its delocalization. The minority-spin states are localized but close to the Fermi level so that a description of the physical properties in terms of a spin Hamiltonian is not appropriate.