We report measurements of $e^{+}{e}^{-}\to e^{+}{e}^{-}$, $e^{+}{e}^{-}\to \gamma \gamma$, and $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ at angles close to 90°, relative to Bhabha scattering at 3.7°, at a center-of-mass energy equal to 5.2 GeV. The results are found to be consistent with the predictions of quantum electro-dynamics.

Quantum field theory is shown to give an energy-dependent $R=\frac{\sigma (e^{+}{e}^{-}\to \mathrm{hadrons})}{\sigma (e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-})}$, as a result of creation of slow particles in the c.m. system. A simple model which predicts power growth for $R$ is given and further experimental consequences are discussed.

In an external magnetic field, quantum beats at the Larmor frequency $\omega$ are observed in circularly polarized light as a result of coherent orientation of fast He i and ii states by a thin foil with exit-surface normal not coincident with the beam direction. Effects resulting from variation of detection geometry, quantum state, incident ion energy, foil tilt angle, and foil material are discussed. An interpretation in terms of an impulsive asymmetric electric interaction is considered.

In an experiment at the Clinton P. Anderson Meson Physics Facility, no muonium formation was found in pure He or Ne, and abundant formation in Ar and Xe. A small Xe admixture (0.1%) in He and Ne resulted in abundant muonium formation, due to the process in which Xe serves as an electron donor to a low-energy positive muon. These results are qualitatively consistent with our knowledge of relevant atomic collision cross sections.

Searches were made with positive muons stopped in liquid helium for free-muon precession, for muonium precession, and for depolarization of the muon spin. The muons behaved as free muons both above and below the $\lambda$ point. There was no muonium formation (<2%) and no depolarization of the muon spin (depolarization time >20 μsec).

Efficient injection (>80%) of an intense relativistic electron beam into a torus has been achieved using curvature drift injection. Drift was stabilized with a supplemental dipole magnetic field but beam loss in the radial direction due to the defocusing effect of the dipole field limited containment time. We propose a system for beam trapping and confinement which employs drift injection and beam energy losses in a toroidal-plus-betatron-type field.

Tunable monochromatic phonon pulses (130 to 870 GHz) were scattered at solid surfaces covered with various amounts of helium. A strong phonon loss due to only 3 atomic layers was observed which was independent of frequency and did not exhibit structure due to the helium dispersion. The results indicate strong frequency conversion at the interface, and thus suggest a new approach to the Kapitza-resistance problem.

A method of calculating local-field effects in the time-dependent Hartree-Fock approximation utilizing the Wannier representation is presented and applied to the optical spectrum of diamond. The results establish the importance of including both the local-field effects and the exchange effects beyond the random-phase approximation.

We describe direct method for surface-structure determination from low-energy electron-diffraction (LEED) intensities. Fourier transforms of LEED intensities are shown to contain convolution products of functions of the interatomic vectors with data truncation and potential windows. A deconvolution method and substrate-subtraction procedure is described, yielding an accurate structural determination of clean surfaces and overlayer systems. Applicability of the method to experimental data is demonstrated by using LEED intensities from A1(100)

An exact solution to the one-dimensional electron gas with a particular attractive-interaction strength for scattering across the Fermi "surface" is given. It is shown that conductivity enhancement occurs for physically interesting values of the coupling constants. Scaling arguments are advanced to demonstrate that this solution applies generally for attractive backward scattering. In addition, the spinless problem is solved exactly for arbitrary couplings.

The average number of continuum $\gamma$ rays above 0.6 MeV has been measured for each of several final products in the reactions $p$+${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{150}{}_{}{}^{}\mathrm{Sm}$, and ${}_{}{}^{84}{}_{}{}^{}\mathrm{Kr}$ + Se. This number ranges from 2 to 20 and is shown to correlate mainly with the average angular momentum leading to each product.

Heavy ion (HI, $\mathrm{xN}$) reactions leading to ${}_{}{}^{158}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{160,162,164}{}_{}{}^{}\mathrm{Er}$, and ${}_{}{}^{170,172}{}_{}{}^{}\mathrm{Hf}$ were studied in order to determine the average multiplicity of the unresolved photons underlying discrete spectra of rotational band transitions observed in rare-earth even-even nuclei. The average multiplicity is found to be small (6), independent (to the accuracy of this experiment) of the ground-state rotational band level in which the cascade terminates.

The nucleus-nucleus optical potential is calculated by using a density-dependent two-body effective interaction where the local density takes into account the contribution of both the projectile and the target densities. The results indicate that it is important to use such an interaction when the densities of the colliding nuclei overlap significantly.

In the reaction ${\pi }^{-}p\to {A_2}^{-}p$, we observe a dip in the differential cross section at $t\approx 1.2$ Ge${\mathrm{V}}^2$. Analysis in terms of $t$-channel contributions from isospin-0 and -1, natural- and unnatural-parity exchanges suggest that the dip is mainly due to natural-$\stackrel{\mathrm{`}}{\mathrm{p}}$arity, $I=0\mathrm{}$ exchange.

We consider the information available about nonelectromagnetic lepton interactions in experiments which are relatively insensitive to the loop structure of the underlying theory. Further experiments which would clarify the role of exotic interactions are proposed and discussed.

The $A_2-A_1$ phase difference observed in ${\pi }^{-}p\to {\pi }^{+}{\pi }^{-}{\pi }^{-}p$ is compared with the ${A_2}^{-}$ phase from a Regge fit to the $\frac{d\sigma }{\mathrm{dt}}$ data for ${A_2}^{-}$ and the ${A_1}^{-}$ phase given by a Reggeized Deck model. The agreement (∼30°) depends crucially on the contribution of the Reggeized pion propagator to the $A_1$ phase and requires equal signs for the $f$ and $P$ residues in the $A_2$ amplitude.

The fluorescence rise time for dimethyl 1, 4-bis[2(4-methyl-5-phenyl-oxazolyl)] benzene (POPOP) and perylene molecules in the vapor phase is measured with a streak camera to be less than 20 and 30±10 psec, respectively. These results are direct evidence that large polyatomic molecules can rapidly relax, even in the absence of collisions.

The complete energy spectrum for electron bremsstrahlung has been obtained, by using a numerical calculation in partial waves with numerical potentials corresponding to neutral atoms. Sample spectra are presented for electrons of kinetic energy 50 keV incident on Au and Al. The connections between elastic electron scattering and the low-frequency region of the bremsstrahlung spectrum and between photoeffect and the high-frequency region of the bremsstrahlung spectrum are demonstrated.

We show that the implantation and anneal behavior of Gd implanted into iron is strongly affected by the process of "internal oxidation." This result is used to clear up discrepancies in earlier measurements on rare-earth ions implanted into iron.

We report the first observation of a marked temperature dependence in the optical properties of TTF-TCNQ, based on thermoreflectance spectroscopy. The structure just above the plasma edge exhibits an abrupt 25% drop with $\overrightarrow{\mathrm{e}}\parallel \overrightarrow{\mathrm{b}}$ as the temperature is lowered past 45-50 K; simultaneously, a strong response for this transition with $\overrightarrow{\mathrm{e}}\perp \overrightarrow{\mathrm{b}}$ emerges. This supports the suggestion that a librational distortion of the TCNQ ion may be responsible for a Peierls transition in the complex.