Enhanced population of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ states at $E_x=20.1, 21.3, 23.5, \mathrm{and} 28.2$ MeV is observed in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, \alpha ){}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=26.7\mathrm{}$ MeV, an energy where the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ inelastic channel also exhibits structure. It is suggested that the 28.2-MeV state may be identified with the ${10}^{+}$ member of a postulated excited collective band. $J^{\pi }={10}^{+}$ assignments for the other states are consistent with their decay modes observed in a particle-$\gamma$ coincidence experiment and their excitation energies are suggestively close to recent shell-model calculations.

Two resonances in the photodetachment cross section of ${\mathrm{H}}^{-}$ have been studied in a variable dc electric field by exploiting a relativistic colliding-beam technique. The Feshbach resonance, at a photon energy of 10.930 eV, splits into two and, possibly, a smaller third component for field strengths of about ${10}^5$ V/cm, disappearing entirely for fields greater than 2×${10}^5$ V/cm. The shape resonance, at a photon energy of 10.98 eV, begins to diminish in amplitude and broaden only for fields above 5×${10}^5$ V/cm.

It is shown that in near-resonant $N$-photon ionization, chaotic light can be more efficient than purely coherent light by more than the usual factor of $N!$ ($N$ factorial). This occurs when the resonant intermediate state interferes with another nearby state. Specific results are presented for two-photon ionization.

We present here a phenomenological model calculation that exhibits the realistic qualitative behavior of multiphonon excitation and dissociation of polyatomic molecules. It is also used to show that at least theoretically multiphonon excitation of molecules is not equivalent to thermal heating.

We report the first observation of significant perturbations by external fields of the autoionizing resonance structure of a two-electron atoms. The effects of electric fields up to 20 kV/cm on autoionizing resonances in Sri were observed by three-photon ionization spectroscopy in an atomic beam. In addition to effects analogous to those for bound Stark states of a one-electron Rydberg atom, we observed a new effect: The characteristic shapes and widths of autoionizing resonances (Fano-Beutler profiles) can be strongly influenced by electric fields.

Intensity inversion between the first (3→2) and second (4→2) Balmer series spectral lines of ${\mathrm{C}}^{5+}$ ions has been observed during plasma expansion into a buffer gas. Numerical modeling indicates that the Balmer spectrum is consistent with the Lyman spectrum and with charge-transfer pumping of the $n=4\mathrm{}$ level. Electron-ion recombination alone is insufficient to explain the observed intensity distribution.

We report the results of a neutron scattering study of the magnetization correlation functions in Rb Mn${\mathrm{F}}_3$ for $T<\mathrm{}{T}_{\mathrm{N}}$. We find that the width $\Gamma$ of the spin-diffusion peak in the region $q\xi \lesssim 1$ varies with $q$ as $q^x{C}_s$, where $x=1.45\mathrm{}\pm 0.12$ and $C_s$ is the spin-wave stiffness coefficient. This apparent breakdown of hydrodynamics is consistent with recent predictions of a divergent spin-diffusion coefficient for $T<\mathrm{}{T}_{\mathrm{N}}$ and provides strong indirect evidence for the existence of a divergence in the parallel component of the staggered susceptibility below $T_{\mathrm{N}}$.

We report model calculations of NMR satellite spectra for Cr, Mn, and Fe atoms in Cu which provide, for the first time, a tractable method for relating the experimentally observed Knight shifts to the structure of the magnetic atoms. Based on a three-parameter one-electron screened potential with exchange, the model is also consistent with bulk susceptibility and high-temperature resistivity measurements. We determine the position and widths of the conduction-electron scattering resonances, and the number of $3d$ electrons on the magnetic atoms.

We have measured inclusive particle production in neutron-nucleus collisions at high energies. Data on positive and negative particles produced in nuclei, ranging in size from Be to Pb, are presented for essentially the full forward hemisphere in the center-of-mass system. Fits of the form $A^{\alpha }$ to the invariant production cross section indicate that $\alpha$ changes from ∼0.85 to ∼0.55 for laboratory rapidities ranging from 3 to 8. Multiperipheral models which invoke cut contributions to particle production in nuclei predict such behavior.

In a sample of multihadron events with a ${\pi }^0$ from $e^{+}{e}^{-}$ annihilation data at 3.77-GeV center-of-mass energy, we observe the decay $D^0\to K^{-}{\pi }^{+}{\pi }^0$ with direct observation of the ${\pi }^0$. The observed branching fraction is (12±6)%.

The newly discovered resonance $\Upsilon \mathrm{}\left(9.5\right)\mathrm{}$ is studied as a bound state of a heavy quark and its antiquark. From the estimate of the production cross section, it is argued that the charge of the constituent quark is likely to be $-\frac{1}{3}$.

Observed universality among the known quarks and leptons requires that additional quarks be mixed little, or not at all, with the four conventional quarks. Discrete symmetries can result in the latter possibility and give rise to absolutely stable (pseudoscalar) hadrons. These particles would produce remarkable $\beta$ decays, x-ray spectra, and hypernuclei.

A generalization of Wilson's loop prescription to include spin is proposed. Instantons are shown to generate a spin-spin interaction between quarks. The large splitting between $\frac{J}{\psi }\mathrm{}\left(3100\right)\mathrm{}$ and ${\eta }_c\mathrm{}\left(2830\right)\mathrm{}$ may, in fact, be dominated by this mechanism and thus may provide a vivid demonstration of the physical effects of instantons. Heuristic arguments are presented which explain the sign and form of the interaction.

We present the results of a detailed study of ${\omega }^{\prime }\mathrm{}\left(1675\right)\mathrm{}$ production in the reaction ${\pi }^{+}p\to {\Delta }^{++}{\pi }^{+}{\pi }^{-}{\pi }^0$ from a high-statistics bubble-chamber experiment at 15 GeV/c. We have measured the mass, width, and cross section as well as differential cross section and spin density matrix elements and compare then to ${A_2}^0$ production in the same reaction. We show clear evidence for the resonant phase increase of the $3^{-}$ $\left(\rho \pi \right)f_{I=0\mathrm{}}$ amplitude with ${\omega }^{\prime }\mathrm{}\left(1675\right)\mathrm{}$ production.

We measured the inclusive production of ${\rho }^0$ mesons in virtual-photon-nucleon collisions. The extracted structure functions are $Q^2$ independent and approximately equal to those observed in photoproduction, if one excludes the diffractive (elastic) region where a large decrease is observed. A significant fraction of the inclusive ${\pi }^{\pm }$ distribution results from the decay of these ${\rho }^0\text{'}\mathrm{s}$.

In a recent publication, McNulty et al. reported a very high pion multiplicity in relatively low-energy heavy-ion interactions in nuclear emulsion. Using an emulsion stack virtually identical to theirs we find a pion multiplicity at least a factor of 30 smaller. We show here that the previously reported multiplicity was based on an erroneous identification of high-energy protons as pions.

Nuclear pion single charge exchange has been studied using a method of ${\pi }^0$ detection based on the spectroscopy of the band-angle decay $\gamma$ ray. For incident 100-MeV positive pions, charge-exchange scattering from nuclei ranging from Be to Pb was studied. For all targets the ${\pi }^0$ spectra were broad, extending over the entire range 0-100 MeV. Data were taken at 40° and 120° and in all cases the data show a backward peaking. The yields vary about as $A^{\frac{2}{3}}$.

A coincidence measurement of the quasifree scattering of 255-MeV pions by ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ targets has been made. The measured results for the ratio of ${\pi }^{+}$ to ${\pi }^{-}$ cross sections of 7.0 ± 0.7 for ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ and 4.5 ± 0.5 for ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are substantially below the classical impulse-approximation value of 9, showing the influence of charge exchange by the outgoing nucleons. The observed $A$ dependence of this cross-section ratio is in agreement with the predictions of a simplified calculation based on the semiclassical charge-exchange theory for the knockout process.

The transfer mechanism for the exotic (${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$) reaction has been investigated by measuring the angular distribution for the reaction ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$(${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$)${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$. The structure in the angular distribution is reproduced by a direct four-neutron-cluster transfer. In addition, the relative (${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$) cross sections from ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ are predicted correctly if collective effects are included in the spectroscopic factors.

Differential cross sections for the excitation of the $2^{+}$ state in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ by 230-MeV pions are found to be about 70% larger for ${\pi }^{-}$ than for ${\pi }^{+}$. Since the $\pi$-nucleon interaction at this energy is dominated by the (3,3) resonance, it is concluded that the results imply that ${〈\beta R〉}_n\approx 1.3{〈\beta R〉}_p$, or alternatively, that ${\left(\beta R\right)}_n \left(\mathrm{valence}\mathrm{neutrons}\right)\approx 3{\left(\beta R\right)}_c\left(\mathrm{core}\right)$, where $\beta$ is the deformation parameter and $R$ the equilibrium radius of the deformed potential. We believe that these results constitute the first example of measurement of the neutron deformation parameter.