The distribution of energy eigenvalues in the irregular spectrum is derived in the semiclassical limit $\hslash \to 0$ by use of a plausible assumption on the spatial distribution of the corresponding eigenfunctions.

A quantum Kolmogorov-Arnol'd-Moser-like theorem is formulated with use of an existence condition of a unique transformation between eigenstates of integrable and nonintegrable Hamiltonians. This condition determines the ability to assign local quantum numbers to eigenstates of nonintegrable Hamiltonians and explains localization phenomena.

${{\Xi }^{*}}^{-}$ production was studied in the reaction $K^{-}+p\to {K^{+}}_{\mathrm{slow}}+X^{-}$ at 5 GeV/c. The slow $K^{+}$ was electronically detected, while the $X^{-}$ was observed as a missing mass, thus allowing for observation of all ${\Xi }^{*}$ independent of decay mode. The observed $\Xi$ states were $\Xi \mathrm{}\left(1320\right)\mathrm{}$, $\Xi \mathrm{}\left(1530\right)\mathrm{}$, $\Xi \mathrm{}\left(1820\right)\mathrm{}$, $\Xi \mathrm{}\left(2030\right)\mathrm{}$, $\Xi \mathrm{}\left(2250\right)\mathrm{}$, $\Xi \mathrm{}\left(2370\right)\mathrm{}$, and $\Xi \mathrm{}\left(2500\right)\mathrm{}$. These data establish and confirm the existence of $\Xi \mathrm{}\left(2250\right)\mathrm{}$ and indicate a peculiar production-cross-section behavior for the ${\Xi }^{*}\mathrm{}\left(2370\right)\mathrm{}$.

The $\tau$ lifetime was measured with the Mark II vertex detector at the storage ring PEP. ${\tau }_{\tau }=(3.20\mathrm{}\pm 0.41\pm 0.35)\times {10}^{-13\mathrm{}}$ sec was found, which agrees well with $e-\mu -\tau$ university.

The scattering of fermions from a magnetic monopole is analyzed in a theory with $\mathrm{CP}$ nonconservation. The dyon charge that arises can be understood as a Friedel sum rule from the theory of alloys, as the data for a Riemann-Hilbert problem in the theory of integral equations, and as a consequence of specifying Wigner's $R$ matrix at the monopole core.

Measurements of $\psi \mathrm{}\left(3097\right)\mathrm{}$ and ${\psi }^{\prime }\mathrm{}\left(3686\right)\mathrm{}$ branching fractions for selected hadronic decays are presented. The ratio of ${\psi }^{\prime }$ to $\psi$ branching fractions for these decays is consistent with the ratio of branching fractions to lepton pairs, with the exception of the decays to $p\pi$ and $K^{*}K$ for which this ratio is substantially smaller.

The authors have measured the large-$p_T$ inclusive cross sections for ${\pi }^0$ and $\eta$ production near 90° in the center-of-mass system in 200-GeV/c ${\pi }^{+}$ and proton collisions with beryllium, carbon, and aluminum targets. The cross section for both ${\pi }^0$ and $\eta$ mesons rises with increasing nucleon number ($A$) of the target nucleus as $A^{\alpha }$, with $\alpha >1\mathrm{}$. The ratio of the ${\pi }^0$ yield in $\mathrm{pA}$ collisions to that in ${\pi }^{+}A$ collisions decreases with increasing $p_T$.

The authors have measured the inclusive production of direct photons in the transverse momentum ($p_T$) range 2.1-5.0 GeV/c in 200-GeV/c collisions of protons and ${\pi }^{+}$ mesons on a carbon target. A significant yield of direct photons was observed for $p_T>2.5\mathrm{}$ GeV/c. The invariant cross section for direct-photon production, when compared with measurements from the CERN intersecting storage rings, can be expressed in terms of $p_T$ and $x_T=2\mathrm{}{p}_T\sqrt{s} \mathrm{as} (42\mathrm{}\pm 14){(1-x_T)}^{8.1\pm 1.0}{p_T}^{-6.6\mathrm{}\pm 0.3}$ μb/${\mathrm{GeV}}^2$ for the c.m. energy range from $\sqrt{s}=19.4\mathrm{} \mathrm{to} 63$ GeV, and for the $x_T$ range from 0.2 to 0.5.

An ultralow-energy $K$-capture branch has been discovered in the decay of ${}_{}{}^{158}{}_{}{}^{}\mathrm{Tb}$ with an energy release of only 156(17) eV above the $K$-shell threshold, the smallest known so far for a weak-decay process. It thus offers a new neutrino "balance" with close-to-ideal decay energetics.

By use of the molecular-beam microwave-optical double-resonance technique the first high-precision Stark-effect measurement of an alkaline-earth monohalide has been performed. Low-field Stark shifts of rotational transitions in the $v=0\mathrm{}$, $X{}_{}{}^2{}_{}{}^{}\Sigma$ state of CaCl exhibited an unexpectedly complicated field dependence which, however, has been shown to be in complete agreement with an exact theoretical calculation.

A compact expression for one-loop radiative corrections to lepton lines in positronium and muonium hyperfine splitting is presented. It is valid for hyperfine-splitting contributions of order ${\alpha }^2{E}_{\mathrm{F}}$, including the effects of recoil to all orders. For muonium, known nonrecoil parts of this contribution are easily evaluated analytically, as is a previously calculated radiative-recoil contribution of order ${\alpha }^2{E}_{\mathrm{F}}\left(\frac{m_e}{m_{\mu }}\right)\ln \left(\frac{m_{\mu }}{m_e}\right)$. Nonlogarithmic radiative-recoil corrections obtained by numerical evaluation of this expression yield new contributions of 2.64 ± 0.07 kHz for muonium and -11.12 ± 0.02 MHz positronium.

A perturbative expansion of the electron's Dirac Coulomb propagator around a nonrelativistic form is used to evaluate the one-loop nonrecoil corrections to ground-state hyperfine splitting in hydrogenic atoms. A contribution previously estimated as $\left(\frac{\alpha }{\pi }\right){\left(Z\alpha \right)}^2\times (18.36\mathrm{}\pm 5)E_{\mathrm{F}}$ is found to be $\left(\frac{\alpha }{\pi }\right){\left(Z\alpha \right)}^2$ $(15.10\mathrm{}\pm 0.29)E_{\mathrm{F}}$. Theory and experiment are compared for muonium hyperfine splitting and consequences for the fine-structure constant are discussed.

The authors report strong repulsive van der Waals and dipole-quadrupole interactions in the $\Sigma$ and $\Pi$ potentials of the LiCs molecule dissociating into Li $2P$ and Cs $6S$ atoms. Theoretical results derived from second-order perturbation theory are verified by investigating experimentally the wavelength dependence of the quasistatic wings of the Li resonance lines broadened by Cs ground-state atoms.

The stability properties of high-beta tokamak equilibria with $\epsilon {\beta }_p\gtrsim 1$ and $〈\beta 〉$ in the range of 10% have been studied with use of a dual-beam C${\mathrm{O}}_2$-laser interferometer system. Two equilibria with $〈\beta 〉$ of 9% and 13% were observed to be stable. Another equilibrium with $〈\beta 〉$ of 10% was observed to be unstable with the characteristics of a high-toroidal-modenumber ballooning mode.

A centered rectangular lattice-gas model for the chemisorption of H on Fe(110) is studied by transfer-matrix scaling. The results indicate a new type of phase transition to a uniaxial modulated "(3×1)" phase with anisotropic critical behavior.

A statistical model of interacting linear domain walls (occurring, e.g., in monolayer adsorbates) is solved on the square lattice with use of exact and numerical results of an equivalent eight-vertex model. For attractive walls a commensurate and an incommensurate phase are separated by a first-order line for stiff walls and by a fluid phase for flexible walls. The phase boundaries with the fluid phase are Ising-like. For repulsive stiff walls an intermediate striped phase with a nonuniversal boundary occurs which vanishes for higher flexibilities. Moreover, disorder lines are located.

An exact equivalence is established between the directed-site animals-enumeration (DSAE) problem in $d$ dimensions and a crystal-growth model defined on the same lattice. In special cases, the latter reduces to the calculation of the free energy of a ($d-1\mathrm{}$)-dimensional lattice gas with extended hard cores. The author solves a DSAE problem with $d=3\mathrm{}$ exactly by using its equivalence to the hard-hexagon problem, and shows that the exponent $\theta =\frac{5}{6}$. A new and simpler solution to the DSAE problem on the square and triangular lattices is given.

The observation of four $Z$'s in a sample of events containing 32 charged $W$'s improves terrestrial bounds on the number of neutrinos by roughly one order of magnitude. Also a bound on the production cross section of $Z$'s relative to $W$'s is obtained. These bounds do not depend on the determination of the $Z$ width.

The radiative decay $\frac{J}{\psi }\to \gamma \eta \pi \pi$ has been studied with data taken with the crystal-ball detector at the SPEAR $e^{+}{e}^{-}$ storage ring. In addition to the well-known ${\eta }^{\prime }$, the $\eta \pi \pi$ mass spectrum shows a broad enhancement centered at ∼ 1700 MeV. The authors have searched for the $\iota \mathrm{}\left(1440\right)\mathrm{}$ in the $\eta \pi \pi$ mass spectrum and find $\frac{R(\frac{J}{\psi }\to \gamma \iota )(\iota \to \eta \pi \pi )}{R(\frac{J}{\psi }\to \gamma \iota )(\iota \to K\overline{K}\pi )}<0.5\mathrm{}$ (90% confidence level).