In a beam-dump experiment at Fermilab the cross section for charm-particle production has been deduced from a measurement of the prompt neutrino flux. The reaction cross section, if we assume only $D\overline{D}$ and the dependence on atomic weight $A^{0.75}$, is 57.2 ± 2.9 ± 8.5 μb/nucleon and the dependence on Feynman $x$ and transverse momentum is $\frac{E_D{d}^3\sigma }{d{p}_D^3}\propto {\mathrm{}(1-x)\mathrm{}}^{3.2}{e}^{-1.5\mathrm{}{p}_{\perp }}$ ($p_{\perp }$ in GeV/c). The data are consistent with as much as 40% diffractive production of ${\Lambda }_c\overline{D}$.

We have used the spin-precession technique to measure the ${\Sigma }^{-}$ magnetic moment (${\mu }_{\Sigma }$). A ${\Sigma }^{-}$ beam with a polarization of 22% was produced by a 400-GeV proton beam striking a Cu target at nominal production angles of ±3 mrad. We simultaneously recorded 21 000 ${\Sigma }^{-}\to n{e}^{-}\overline{\nu }$ decays and 650 000 ${\Sigma }^{-}\to n{\pi }^{-}$ decays at ${\Sigma }^{-}$ beam momenta of 253 and 308 GeV/c. We find ${\mu }_{\Sigma }=-1.166\mathrm{}\pm 0.014\pm 0.010$ nuclear magnetons, where the quoted errors are statistical and systematic, respectively.

The chiral Ward identities for the pseudoscalar nonet including the glueball candidate $\iota \mathrm{}\left(1450\right)\mathrm{}$, together with the requirement that the topological susceptibility be positive, imply that $\Gamma (\iota \to \gamma \gamma )$ is typically small (< 1 keV), in agreement with recent experimental values. The topological susceptibility is, as expected, much smaller than pure-gauge-field estimates.

A novel analysis technique of $\overline{p}n$ annihilations at rest has recently brought strong evidence for a new state, called here $\zeta$, of mass 1477 ± 5 and width 116 ± 9 MeV/${\mathit{c}}^2$, which contributes dominantly to the $3{\pi }^{-}2{\pi }^{+}$ final state. An analysis has been made of the $3{\pi }^{-}2{\pi }^{+}$ considering all known intermediate states. It is found that only the cascade $\overline{p}n\to {\pi }^{-}\zeta$ and $\zeta \to 2{\rho }^0$ with $\zeta$ quantum numbers $0^{+}$, $2^{++}$ ($I^G,J^{\mathrm{PC}}$) describes $3{\pi }^{-}2{\pi }^{+}$. The product branching ratio $B(\overline{p}n\to {\pi }^{-}\zeta )B(\zeta \to 2\rho )$ is large, equal to (11.1 ± 0.8)%. The $\zeta$ is a good candidate as a quasinuclear $\overline{N}N$ bound state or as a ${\overline{Q}}^2{Q}^2$ state or, perhaps, as a glueball.

Observations of a strong dependence of nucleon-antinucleon annihilation modes, particularly $\pi \rho$ and $\pi f$, on orbital angular momentum and spin-isospin are interpreted in a quark-gluon description of the reaction dynamics.

The total cross section for deuteron photodisintegration has been measured in the $\gamma$-ray energy range between 15 and 75 MeV, by use of the monochromatic LADON photon beam of the Frascati National Laboratories and detection of the proton. The results are in substantial agreement with the standard theory and do not provide evidence for contributions of quark degrees of freedom.

A significant energy dependence was observed in the region of the first diffraction minimum of the form factor for elastic electron scattering from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ between 238 and 419 (and 431) MeV. This effect might be attributed to dispersive (two-step) processes.

It is shown that inelastic $\alpha$-particle scattering to the well-known isovector giant dipole excitation, when computed with a neutron radius greater than the proton radius and including isovector Coulomb excitation, is predicted to give an angular dependence similar to that of an isoscalar monopole excitation claimed to exist at the same nuclear excitation energy. A much smaller fraction of the monopole sum-rule transition strength is then required by these data, perhaps altering the conclusions for nuclear compressibility.

The correspondence between the $\mathrm{SD}$ fermion and $\mathrm{sd}$ boson spaces is studied. A procedure is discussed to derive boson images of fermion operators. Spectra in the two spaces are compared. $E2\mathrm{}$ operators are also studied.

The ${}_{}{}^1{}_{}{}^{}P$ shape resonance of ${\mathrm{H}}^{-}$ has been populated in collisions between ${\mathrm{H}}^{-}$ and Xe. We report on the decay ${\mathrm{H}}^{-}\left({}_{}{}^1{}_{}{}^{}P\right)\to {\mathrm{H}}^0\mathrm{}(n=2\mathrm{})+e^{-}$, which for the first time is measured by high-resolution electron spectroscopy. New information on the angular distribution of ejected electrons is obtained by use of a Shore parametrization to describe the cross section. The Shore parameters are related to matrix elements of the transition operator. The obtained resonance energy and width are in good agreement with recent theoretical calculations as well as other experimental results.

We report the first observation of forbidden atomic absorptions to Rydberg final states in laser-assisted single-collision processes. These free-free transitions, which occur at unusually low laser power densities, are characterized by narrow absorption linewidths.

X-ray photoabsorption measurements were carried out on krypton near the $1s$ ionization threshold, by use of synchrotron radiation. A rich, well resolved spectrum of simultaneous two- and three-electron excitations is detected. Feature identification is supported by both relativistic and nonrelativistic calculations. The data support in detail the $Z+1\mathrm{}$ approximation for both two- and three-electron excitations. No indication of a preferred Coster-Kronig decay channel for $1s4s$ hole states is found, in contrast with argon. The partial cross sections are in good accord with shakeup theory and photoelectron data on other noble gases.

Bell and Seaton's ab initio theory of dielectronic recombination is extended to include the influence of arbitrary electric fields in the $S$ matrix. Rydberg series of resonances are treated in quantum-defect-Stark theory. The zero-field rate of an $n$, $m$ manifold is enhanced up to a factor $\frac{({\Gamma }_R+{\Gamma }_A)}{\left(\frac{{\Gamma }_R+{\Gamma }_A}{n}\right)}$ as seen in a simple model. Previously ignored interference effects reduce the enhancement for interacting manifolds.

Time-resolved fluorescence studies of ${\mathrm{Ar}}_2$ formed by supersonic jet expansion and excited by monochromatic, tunable, vacuum-ultraviolet radiation have been used to measure the radiative lifetimes of selected high vibronic levels of the $A{1}_{\mathrm{u}}$ state. Lifetimes of levels $v^{\prime }=24\mathrm{} \mathrm{to} 30$ were found to have an average value of 160 ± 10 ns. This differs by a factor of ∼ 20 from the lifetime of 2.88 ± 0.06 μs obtained earlier for the $v^{\prime }\sim 0$ level with high gas pressures and excitation by charged particles. It is shown that this large difference in lifetimes arises from a sixfold increase in the electronic transition moment for a change of internuclear distance from 2.5 to 3.5 Å.

High-quality polarized-emission cross sections for the ${\left\{\alpha \right\}}_5=|J=1,M_J〉\to {\left\{\alpha \right\}}_7$ and ${\left\{\alpha \right\}}_5\to {\left\{\alpha \right\}}_4$ transitions in the $\left\{\alpha \right\}=\left\{{\mathrm{}\left(2p\right)\mathrm{}}^5\mathrm{}\right(3p\left)\right\}$ multiplet (lifetime 20 ns) have been measured in a crossed-beam experiment. For the ${\left\{\alpha \right\}}_5\to {\left\{\alpha \right\}}_7$ transition we observe a strong preference for the $\left|M_J\right|=0\mathrm{}$ orientation. The small cross section for the $\left|M_J\right|=1\mathrm{}$ orientation can be understood qualitatively from the model potentials of Hennecart and Masnou-Seeuws by the strong coupling to the ${\left\{\alpha \right\}}_4$ and ${\left\{\alpha \right\}}_6$ states (avoided crossings), which is absent for the $\Omega =\left|M_J\right|=0^{-}$ molecular potentials because of the constraint of reflection symmetry.

A novel two-laser technique for photoabsorption studies of refractory and corrosive elements is described and applied to observe for the first time the absorption spectrum of atomic thorium. Results on the giant $5d$ dipole resonance in the extreme uv are found to be in good qualitative agreement with recent theoretical predictions. The spectrum is very similar to that reported for the metal, indicating that the $5f$ wave function is largely unaffected by its solid environment.

By the measurement of doubly differential distributions of electrons emitted downstream when 170-keV protons pass through thin carbon foils, besides the convoy electron peak and the characteristic ridge, centered in the beam direction and found also in gas targets, a lateral structure is observed at larger angles. The location of this structure can be uniquely and quantitatively attributed to electron diffraction in the three-dimensional reticule of the polycrystalline foil. Electrons in the central ridge are found to diffract, while the convoy electrons do not.

We present high-resolution electron spectra for electrons ejected in the forward direction by protons and neutral hydrogen in collisions with He gas. The spectra show the expected electron transfer to the continuum peak, but also show a 0° ridge extending to the lowest electron energies measured. We propose that this new secondary-electron component represents electrons which propagate on the saddle of the potential surface produced by the two positive ions ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ in the intermediate collision complex.

The recently demonstrated technique of laser guiding has been used to propagate successfully a 10-kA relativistic electron beam 95 m through the Advanced Test Accelerator and postaccelerator beamline. The maximum transverse displacement of the beam at the end of the Advanced Test Accelerator was 1 mm while the maximum beam breakup amplitude was 0.1 mm. The use of laser guiding constitutes a breakthrough in accelerator technology in that it is able to reduce greatly or even suppress the beam breakup instability, which is the most serious obstacle to high-current beam transport in linear induction accelerators.

The ac electrical conductivity of a dense plasma is studied by use of reflectivity measurements on the rear surface of a laser-irradiated planar target. The results show general agreement with theory in which a minimum collision mean free path is assumed, yielding correspondingly a minimum conductivity. However, the results also suggest that the minimum mean free path is greater than the interatomic radius.