Data are presented for the charge-exchange scattering of negative pions on protons at high momentum transfer for incident pion momenta in the range 2-6 GeV/c. They are compared with predictions from a Reggeized baryon-exchange model of the process.

We discuss low-mass enhancements observed in the $p{\pi }^{+}{\pi }^{-}$ and in the $\overline{p}{\pi }^{+}{\pi }^{-}$ systems produced in the reaction $\overline{p}p\to \overline{p}p{\pi }^{+}{\pi }^{-}$ at 3-4 GeV/c. We conclude that these enhancements near the mass of the $N\left(1470\right)\mathrm{}$, at our energy, are associated with the ${\Delta }^{++}\mathrm{}\left(1236\right)\mathrm{}-{\overline{\Delta }}^{--}\mathrm{}\left(1236\right)\mathrm{}$ channel.

We describe a way to include unitarity in dynamical calculations that may involve indefinitely rising Regge trajectories. As an illustrative application we study the sigma meson in $\pi -\pi$ scattering.

Two models of rising trajectories are contrasted. The first, based on single-channel rotational excitations, leads to a mean square particle radius which increases linearly with angular momentum for excitations on a trajectory. The second model, which makes use of a conjectured weakly violated selection rule, gives a particle radius which is constant along a trajectory. The approximate selection rule explains the narrowness of the higher resonances.

A form of exchange degeneracy for mesons and baryons is derived from duality and the absence of resonances in exotic channels. The implications of this structure for the hadron spectrum are discussed.

The electroproduction function $F_2(-\frac{\nu }{q^2})$, defined as the limit of the structure function $\nu W_2(q^2,\nu )$ for $\nu \to \infty$, $\frac{\nu }{q^2}$ fixed, is experimentally observed to approach a constant for $-\frac{\nu }{q^2}\to \infty$. We derive this result from an integral representation of the scattering amplitude and the assumption of Regge behavior for the limit $\nu \to \infty$, $q^2$ fixed.

A new type of $l$-plane branch point, heretofore unnoticed, is found, which may become more important than the Amati, Fubini, and Stanghellini branch points. When the multiperipheral bootstrap model is employed, this new type of branch point implies an asymptotic lower bound of Regge trajectories, i.e., $\alpha \mathrm{}\left(t\right)\mathrm{}>~-a{\mathrm{}(-t)\mathrm{}}^{\frac{1}{2}}$, as $t\to -\infty$. A linear trajectory will violate this bound.

A systematic procedure for applying the hypothesis of the partial conservation of the axial-vector current to the Regge-pole models of the Veneziano type is illustrated by a discussion of the matrix element of the axial-vector current for the weak process $A_{\mu }+\pi \to \pi +\pi$. Additional information is obtained which relates the reactions $\pi +\pi \to \pi +\pi$ and $\pi +\pi \to \pi +A_1$.

Hard-meson partial conservation of axial-vector current and partial conservation of vector current are imposed upon the Veneziano amplitudes. It is seen that these determine inelastic amplitudes (e.g., $\pi \pi \to \pi A_1$, etc.) in terms of corresponding elastic amplitudes (e.g., $\pi \pi \to \pi \pi$). Mass formulas for the $\kappa$ and $\delta$ meson, equality of many trajectory slopes of either normality, and $\pi K$ scattering lengths are obtained, in good agreement with experiment.

A partial-wave description is employed to calculate the cross sections for fine-structure transitions in the ${}_{}{}^2{}_{}{}^{}P$ state of sodium in collisions with helium. The cross sections show an oscillatory behavior with energy that is related to the occurrence of shape resonances in the elastic-scattering channels.

Unusually large inelastic energy losses have been measured for single collisions of argon ions with argon atoms and of iodine ions with xenon atoms using ion energies from 0.5 to 6 MeV and scattering angles from 4 to 20 deg. These losses, as high as 28 keV, are attributed in part to the production of inner-shell vacancies. The measurement of the energies of x rays from these collisions support this hypothesis.

A low-energy excitation process in CO at approximately 2.3 eV is investigated near threshold by a trapped-electron method. Structure has been observed in this excitation for the first time. An upper limit to the electron affinity of CO is established at -1.8 ± 0.1 eV.

A nonarbitrary method is presented for the calculation of inelastic-scattering wave functions by an expansion technique. The method can be applied for any incident energy, including values at resonances resulting from stable or metastable bound states. Calculations are presented for an exactly soluble two-channel model problem which illustrates the utility of the method.

The shear viscosity of the system aniline-cyclohexane has been measured for a mixture at the critical concentration. Above the critical temperature the experimental points are well fitted over three decades by a logarithmic law. A discussion of the relevance of this result on some recent theoretical work is also included.

The collisional dissociation of a beam of energetic ${\mathrm{H}}_2^{+}$ ions provides a localized and rapid measurement of plasma density and perturbation of plasma density, yet leaves the plasma undisturbed.

The Bogoliubov inequality is employed to obtain bounds on the density dependence of the free energy and energy of a wide class of interacting many-particle systems including the realistic case of multicomponent Coulomb-interacting systems.

Data on elastic diffraction and inelastic scattering of electrons by Cs adsorbed on W in monolayer lattices suggest that at monolayer densities equal to about half the bulk density the decay rate of surface plasmons is much greater than for similarly situated monolayers of approximately bulk density. The enhanced decay rate is interpreted as evidence for nonmetallic character of the low-density layer, as proposed by Wigner for a low-density gas and by Mott for low-density aggregates of odd-valence atoms.

Phonon-exchange pumping of nuclear magnon pairs in low-anisotropy flopped antiferromagnets is proposed and the effective threshold fields given. Although the electronic sublattice magnetizations are driven, magnetoelastically, far below their resonance frequency, the lower pump frequency compensates for the weakened dynamic coupling between nuclear and electronic magnons. The required phonon power density is thus low and well within experimental reach.

It is shown that the ion-neutralization spectroscopy determines the orbital energy spectra of surface molecules formed of adsorbed foreign atoms and surface atoms of the substrate. For free molecules such a spectrum yields information concerning molecular symmetry and structure as well as ionicity within the molecule. Using also measured work-function change in adsorption, specific conclusions are drawn concerning O, S, and Se adsorbed in $p(2\mathrm{}\times 2)$ and $c(2\mathrm{}\times 2)$ arrangements on Ni (100).

A sharp optical absorption edge has been found at about 0.5 eV for amorphous Ge on a quartz substrate. The edge is comparable in sharpness with the direct edge of crystalline Ge. No evidence for tailing of the band edges into the forbidden band or for a high density of states in the forbidden band is found by these optical measurements. A new density determination gives a value of 4.54± 0.14 g/${\mathrm{cm}}^3$.