We report, with good statistics, the $\pi$ momentum distributions from the reaction $K^{+}+p\to {\pi }^{-}+$ anything at 11.8 $\frac{\mathrm{GeV}}{c}$. We compare the shape of the distribution in longitudinal momentum of the ${\pi }^{-}$ with that of ${\pi }^{-}$ mesons produced in the reaction ${\pi }^{-}+p\to {\pi }^{-}+$ anything at 25 $\frac{\mathrm{GeV}}{c}$ and ${\pi }^{+}+p\to {\pi }^{-}+$ anything at 18.5 $\frac{\mathrm{GeV}}{c}$ in terms of the scaling variable $x=\frac{2p_L}{\sqrt{s}}$. The backward distributions are found to be independent of the nature of the projectile. The forward distributions are different in shape from the backward, but are remarkably similar for $K^{+}p$ and ${\pi }^{+}p$ interactions. The distribution in longitudinal momentum in the center-of-mass system is not independent of the value of the transverse momentum.

It is shown that the trilinear (or Yukawa-type) vertex of a nonstrange, neutral boson with a spin-½ baryon vanishes unless the boson has the quantum numbers of the quarkantiquark ($q\overline{q}$) system, as long as this vertex satisfies the usual analyticity conditions and $C$ and $P$ are good quantum numbers. Thus, the quantum numbers of the observed nonstrange bosons may be explained without the quark.

The low-energy behavior of the pion-mass form factors is derived using stress-tensor—current commutation relations. The results indicate significant deviations from tensor-meson and scalar-meson pole dominance of the stress tensor. The stress-tensor—$\epsilon$-meson coupling and the scale dimension of the pion field are obtained in terms of $g_{A_1\epsilon \pi }$. Numerical estimates are given.

Results are presented for the production of electron pairs by the collision of high-energy bremsstrahlung and high-intensity laser beams. With Stanford linear accelerator bremsstrahlung parameters, it is found that the laser must be focused to about ${10}^{18}$ W/${\mathrm{cm}}^2$ to produce pairs. Approximately 25 laser photons participate in each event, and the required laser intensity is outside the known radius of convergence of perturbation theory for this process. The electron mass shift may also be determined.

We discuss the Regge prediction for the behavior of inclusive cross sections near the kinematic boundary, and we compare it with a recent conjecture of Chou and Yang. Some existing experimental data are analyzed and, in particular, we find no evidence yet for diffraction dissociation into high masses (three-Pomeranchon coupling).

We show that, contrary to present practice and belief, double-particle-exchange contributions to hadronic scattering amplitudes are not negligible. We introduce a hierarchy of exchange mechanisms: (i) Pomeranchon; (ii) single pole exchange (including pole-Pomeranchon cuts), (iii) double particle exchange, etc. The relative strength of any pair of consecutive terms in this hierarchy of amplitudes is of order $\eta ={\eta }_0{\nu }^{\frac{-1\mathrm{}}{2}}$, where ${\eta }_0\sim 0.6$ Be${\mathrm{V}}^{1/2}$. At $\nu =5\mathrm{}$ BeV, double-particle-exchange amplitudes may contribute to 25-50% of the cross section for inelastic processes and should not be ignored.

A model suggested by Sudarshan which relates strong, weak, and electromagnetic interactions through vector and axial-vector currents is adapted to nucleon-nucleon scattering. Strong time-reversal violation is predicted in $n-p$ scattering above 100 MeV through the same mechanism assumed to cause $\mathrm{CP}$-invariance violation in weak hadronic decays. Where a $T$-invariance violation has been sought for and not found, i.e., in $p-p$ scattering up to 635 MeV and low-energy $n-p$ scattering, the model predicts very little $T$-invariance violation.

A transmission experiment is used to observe the structure in the total electron-impact cross section in CO and ${\mathrm{O}}_2$. The structure in the cross sections is enhanced by measuring directly the derivative of the transmitted current. An isolated resonance in CO is observed at an electron energy of 10.04±0.03 eV. In ${\mathrm{O}}_2$, structure is observed which correlates well with the absorption spectra in the energy range 8-10 eV. In addition, two very sharp resonances (30-meV width) are observed at 8.02±0.03 and at 8.25±0.03 eV.

The complete hyperfine structure of the $P\left(117\right)\mathrm{}$ line of the 21-1 band of the $B\leftarrow X$ transition of ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}_2^{}{}_{}{}^{}$ is observed at 568.2 nm. A resolution in excess of ${10}^8$ is obtained by a sensitive technique of saturation spectroscopy using a krypton-ion laser. The spectrum can be fitted by a model which includes both a nuclear electric quadrupole and a magnetic hyperfine interaction.

Electrostatic instabilities in a plasma having electrons flowing along a magnetic field are generated by a shear in the electron drift velocity. This can cause an effective resistivity much higher than the Buneman value and consequently increase the rates of penetration of a skin current and of heating.

We investigate equilibria and compression of thin electron rings in cylindrically symmetric guide fields. It is found that particle energies are smaller and ring radii different from values obtained ignoring self-fields.

Molecular vibrations are coherently excited by an intense light pulse of duration $t_p$. The rise and decay of the vibrational amplitude is measured with delayed pulses of the same time dependence. The molecular dephasing time $\tau$ is obtained when $\tau \gtrsim t_p$, while the shape of the light pulse is found for $\tau \ll t_p$.

A simple lattice gas, of the familiar kind with only short-range pair interactions, is proved to have a coexistence curve whose diameter is singular at the critical point. Particle-hole symmetry is violated only because the range of interaction energies a molecule can experience depends on which of two nonequivalent sets its lattice site belongs to.

Experiments with a pulsed beam of charged, quantized vortex rings show that it evolves into a steady-state distribution. This behavior is shown to follow from the Coulomb interaction among the vortices and a negative effective pressure arising from the vortex dispersion law.

${\mathrm{He}}^3$ and ${\mathrm{He}}^4$ adsorbed on graphite have heat capacities qualitatively different from monolayers on other substrates. Both isotopes have quasiclassical two-dimensional gas behavior at low fractional coverage $x$ and $T\gtrsim 2$°K. At lower $T$ and $0.14<~x<~0.39$, ${\mathrm{He}}^3$ shows quantum degeneracy, with Fermi temperatures of several degrees Kelvin. The specific heat per atom of ${\mathrm{He}}^4$ at the same coverages rises above $k$ and has pronounced peaks at low $T$.

Heat capacities of He monolayers on graphite show qualitative differences between ${\mathrm{He}}^3$ and ${\mathrm{He}}^4$, contrary to the usual theories of two-dimensional quantum gases. We attribute the differences to weak lateral fields due to substrate inhomogeneities, and using a two-dimensional ideal-gas model show qualitative agreement between theoretical and observed heat capacities.

We describe a new method for observing magnetic periodicities, both spatial and temporal, ultimately capable of resolving wavelengths between 100 and ${10}^5$ Å and frequencies between 0.5 and 500 MHz. We have used this method to observe the periodic magnetic field above the surface of a type-II superconductor containing a lattice of flux lines which moves under transport currents. We believe that the measurements are the first direct observations of the flux-flow velocity in a type-II superconductor.

We consider the problem of interacting particles occupying random sites on either a plane square or a simple cubic lattice. The critical concentration $p_c$ is defined as that concentration below which the cooperative transition which normally occurs in the system can no longer take place. In this paper we obtain an expression for $p_c$ as a function of the interaction range $\mathbf{r}$, exact when ${\mathbf{r}}^{\mathbf{d}}\gg 1$ ($d$=dimensionality, $\mathbf{r}$ measured in units of lattice constant).

We report the first definite observations of the magnetic field dependence of centralcell corrections in shallow donors. Exploiting the extreme resolution inherent in magnetospectroscopy employing infrared gas laser sources, we have observed previously unresolved transitions arising from four distinct "hydrogenic" donor species occurring in high-purity epitaxial GaAs. We show that the species-dependent differences in transition energies are directly proportional to the probability of finding an electron at the donor site to which it is loosely bound. This probability increases with increasing magnetic field because of magnetic squeezing of the wave function of the bound electron.

Isospin mixing in the $2^{+}$, $1^{+}$, and $3^{+}$ states of ${\mathrm{Be}}^8$ has been calculated with correlated radial wave functions obtained from reference-spectrum solutions of the Bethe-Gold-stone equation. The off-diagonal matrix elements are approximately a factor of 2 larger than those calculated with oscillator wave functions and provide a very reasonable interpretation of the experimental data.