We derive the high energy limit of the momentum distribution associated with the total Born approximation cross section for pair production in a static screened Coulomb field. This high energy distribution is free of the ‘‘large’’ terms which appear in the exact momentum distribution and cancel leaving a remainder of relative order (m/k${)}^2$, the cancellation having been performed analytically. (k is the incident photon energy, m the electron rest mass.) The high energy distribution is used to derive the total pair production cross section both for an unscreened Coulomb field and in the limit of complete screening, and the results are compared with expressions given in the literature. It is shown that the largest corrections to the high energy limit of the total cross section [of relative orders (2m/k${)}^2$${\ln }^3$(2k/m) and (2m/k${)}^2$${\ln }^2$(2k/m)] are independent of screening, and these are given analytically.

The analysis of meson correlations by Hanbury-Brown–Twiss interferometry is tested with a simple model of meson production by resonance decay. We derive conditions which should be satisfied in order to relate the measured momentum correlation to the classical source size. The Bose correlation effects are apparent in both the ratio of meson pairs to singles and in the ratio of like to unlike pairs. With our parameter values, we find that the single particle distribution is too distorted by the correlation to allow a straightforward analysis using pair correlation normalized by the singles rates. An analysis comparing symmetrized to unsymmetrized pairs is more robust, but nonclassical off-shell effects are important at realistic temperatures.

The ${\mathit{q}}^2$ dependence of the ρ-ω mixing amplitude is analyzed with the use of QCD sum rules and dispersion relations. Going off shell the mixing decreases, changes sign at ${\mathit{q}}^2$≃0.4${\mathit{m}}_{\mathrm{\rho }}^2$>0, and is negative in the spacelike region. Implications of this result for the isospin breaking part of the nuclear force are discussed.

The β-delayed neutron decay of ${}_{}{}^{18}{}_{}{}^{}\mathrm{N}$ has been studied using a time-of-flight array with high efficiency. The ${}_{}{}^{18}{}_{}{}^{}\mathrm{N}$ ions were produced by fragmentation of a E/A=75 MeV ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$ beam. Transitions to nine neutron unbound states have been observed with a total branching ratio of 2.2±0.4%. The results are compared with measurements of the decay to γ- and α-emitting states and the differences between the present results and a recent measurement of the ${\mathit{P}}_{\mathit{n}}$ value are discussed.

The self-energies of quasinucleon states in nuclear matter are investigated using a finite-density QCD sum-rule approach developed previously. The sum rules are obtained for a general QCD interpolating field for the nucleon. The key phenomenological inputs are the nucleon σ term, the strangeness content of the nucleon, and quark and gluon distribution functions deduced from deep-inelastic scattering. The emphasis is on testing the sensitivity and stability of sum-rule predictions to variations of the condensates and other input parameters. At nuclear matter saturation density, the Lorentz vector self-energy is found to be positive with a magnitude of a few hundred MeV, which is comparable to that suggested by relativistic nuclear phenomenology. This result is quite stable. The prediction for the scalar self-energy is very sensitive to the undertermined values of the in-medium four-quark condensates.

The Global Color-symmetry Model of QCD is extended to deal with a background electromagnetic field and the associated conserved current is identified for the finite size q¯q pion modes at tree level. We work within a well-defined truncation that factorizes the bilocal pion field into a local field variable and a hadronic form factor having a ladder Bethe-Salpeter content. The associated pion charge form factor is formulated. These developments are used to provide an illustration of how an effective hadronic action containing form factors may be electrmagnetically coupled in a gauge invariant way that is accountable to its field substructure. In particular, the Ward-Takahashi identity for the photon vertex appropriate to the localized pion fields is seen to contain the hadronic form factors. In this context, gauge invariance of the effective hadronic action also requires recognition of the fact that the free inverse propagator for the localized pion field gauge transforms due to the substructure field content that has been absorbed into it.

Nuclear effects in the small x region of hadron-nucleus Drell-Yan processes at 800 GeV are analyzed. We employ the parton recombination model to describe the suppression in the ${\mathit{R}}_{\mathrm{DY}}^{\mathit{p}\mathit{A}}$(${\mathit{x}}_2$) ratio and we compare it with ${\mathit{R}}_{\mathrm{EMC}}$(x), in the same kinematical region. Our results show that shadowing effects in Drell-Yan and deep inelastic scattering processes admit a description based on this model in both cases but with different characteristic parameters. Good agreement with experimental results is obtained.

A method is described for solving relativistic quasipotential equations in configuration space. The Blankenbecler-Sugar-Logunou-Tavkhelidze-Logunov and an equal-time equation, both relativistic covariant two-body equations containing the full Dirac structure of positive and negative energy states, are studied in detail. These equations are solved for a system of two constituent quarks interacting through a potential consisting of a one-gluon exchange part with running coupling constant plus a linear confining potential which is mostly scalar and partly vector, and the spectrum of all light and heavy mesons is calculated.

The projectile-target system ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$${+}^{58}$Ni has been used to produce the neutron deficient N=49 isotones ${}_{}{}^{92}{}_{}{}^{}\mathrm{Tc}$, ${}_{}{}^{93}{}_{}{}^{}\mathrm{Ru}$, ${}_{}{}^{94}{}_{}{}^{}\mathrm{Rh}$, and ${}_{}{}^{95}{}_{}{}^{}\mathrm{Pd}$. The multidetector array NORDBALL including particle selection was used. The yrast level scheme could in three cases be determined up to and above spin values corresponding to the highest angular momenta attainable in the previously used configuration spaces for shell model calculations. The yrast level schemes of the N=49 isotones bear a striking relationship to those of the corresponding N=50 isotones. By interpreting the experimental high spin yrast structure in shell model configurations we hope to facilitate the choice of a restricted configuration space to be used for calculations. Generally, there is an intrinsic simplicity in most of the observed yrast or near-yrast states.

We examine the applicability of a class of relativistic two-body equations, the quasipotential equations (QPE's), as a tool for investigating hadronic physics. We show that the QPE's traditionally used in nuclear physics may be viewed as special cases of a more general QPE written in terms of three parameters. The behavior of the QPE's is analyzed in terms of these parameters in the small, intermediate, and large coupling regimes, including fits to light and heavy meson spectra. A subset of QPE's is identified which provide fits to the heavy mesons with rms deviations from experiment of 32-36 MeV.

We have studied the helium plasma in the hypernetted chain approximation considering both short-ranged internuclear and long-ranged Coulomb interactions. The optimal two-particle wave function has been determined in fourth order; fifth-order corrections have been considered in the calculation of the two-body and three-body correlation functions. The latter has been used to determine the pycnonuclear triple-alpha-fusion rate in the density regime ${10}^8$ g/${\mathrm{cm}}^3$≤ρ≤${10}^{10}$ g/${\mathrm{cm}}^3$, which is of importance for the crust evolution of an accreting old neutron star. The influence of three-particle terms in the many-body wave function on the rate is estimated within an additional variational hypernetted chain calculation. Our results support the idea that the helium liquid undergoes a phase transition to stable ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ matter at densities ρ≊3×${10}^9$ g/${\mathrm{cm}}^3$ as the plasma induced screening potential then becomes strong enough to bind the ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ ground state.

The multipole mixing ratios for the 198 and 177 keV γ-ray transitions in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ are determined as δ(198)=-6.$1_{\mathrm{-}0.6}^{+0.4\mathrm{}}$ and δ(177)=-0.${20}_{\mathrm{-}0.03}^{+0.04\mathrm{}}$ from new measurements of angular correlation of the 63-198 and 63-177 keV cascades in addition to measurements on the cascades passing through the 118 and 139 keV levels. The present value of δ(198) indicates an almost pure E2 character for the 198 keV γ ray while from earlier measurements an admixture of only 9% E2 was reported for this γ ray. For both the 198 and 177 keV transitions the results do not agree with the conversion electron measurements and indicate that the conversion processes in these transitions are not normal. From time-differential measurement on the 63-198 keV cascade, the relaxation constant ${\lambda }_2$=(0.31±0.21)×${10}^7$ ${\sec }^{\mathrm{-}1}$ is obtained using the source in acetic acid solution. The integral attenuation coefficients for the 316 keV level are found to be ${\mathit{G}}_2$=0.19±0.04 in liquid chloride source and ${\mathit{G}}_2$=0.57±0.06 in liquid acetate source.

Two approaches (exact and approximate) to the isobaric analog resonance (IAR) theory within the random phase approximation in the continuum are considered. Both of them are based on the partial self-consistency condition which is the result of the isospin symmetry of the nuclear Hamiltonian. The evaluations of the IAR partial proton widths for near magic nuclei over a wide atomic mass region are performed. The results obtained within the framework of these approaches are compared with each other and with the experimental data. The method of the calculation of the Coulomb correction to the IAR transition density is also given.

Extraction of the nuclear matter incompressibility ${\mathit{K}}_{\mathrm{\infty }}$ from the experimental giant monopole resonance (GMR) data via liquid drop type expansion of compression modulus of finite nuclei ${\mathit{K}}_{\mathit{A}}$ is found to be fraught with uncertainties. Hence a realistic finite range effective interaction is constructed that reproduces the bulk properties of nuclear systems as well as the GMR data in the Thomas-Fermi approximation. The nuclear matter incompressibility calculated with this interaction is found to be 226 MeV. A numerical scheme is also proposed which enables us to extract the various coefficients occurring in the expansion of ${\mathit{K}}_{\mathit{A}}$ employing this effective interaction.

The vacuum-polarization (VP) corrections to rates for nuclear-fusion reactions in the pp chain and in the CNO cycle are calculated. For the reactions of particular importance to the solar-neutrino problem, the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$${(}^3$He,2p${)}^4$He, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(α,γ${)}^7$Be, ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$(p,γ${)}^8$B, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$(p,γ${)}^{15}$O reactions, we find the magnitude of the effect to be less than 2%. The effect of VP on all the other reaction rates is expected to be of a similar order of magnitude. We discuss how these results affect the predicted fluxes of solar neutrinos.

We reexamine a recent calculation of the effect of dressing on the pion propagator in the one-pion-exchange potential. Our results confirm the qualitative features of the earlier work, namely that the correction can be represented as the exchange of an effective π’ meson. However, at a quantitative level this approximation does not work well over a wide range of momentum transfer unless the mass of the π’ is made too large to be of significance in nucleon-nucleon scattering.

The pair-hopping model of large amplitude motion is applied to the calculation of the frequency of low-lying quadrupole and octupole vibrations in atomic nuclei. Theory provides an overall account of the experimental findings.

Recent ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$(e,e’) data at momentum transfer ‖q‖=1.14 GeV display behavior which is qualitatively different from that of lower momentum transfers. An explanation of this difference is offered based on an analysis of the longitudinal response in nuclear matter. An ansatz is made for the momentum dependence of the nucleon self-energy functions in the nuclear medium which suppresses medium effects for momenta above the nucleon mass scale. This suppression is shown to improve the agreement with the high momentum transfer data, and offers a motivation for further experimental investigation in the momentum transfer region between 0.5 and 1.0 GeV.

It is suggested that collective bands in ${}_{}{}^{186,188}{}_{}{}^{}\mathrm{Pb}$ built on a $0^{+}$ intruder configuration, belong to a four-particle–four-hole (4p-4h) intruder analog spin I=2 multiplet. The multiplet structure is presented and a suggestion for the energy of the 2p-2h $0^{+}$ intruder bandhead in ${}_{}{}^{186,188}{}_{}{}^{}\mathrm{Pb}$ is made.

Resonances in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{12}$C and ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$${+}^{24}$Mg scattering have been associated with hyperdeformed configurations in the harmonic oscillator shell model and the alpha-cluster model. Resonances in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{28}$Si scattering do not seem to fit into this picture so well. We present alpha-cluster model calculations for superdeformed and hyperdeformed states in ${}_{}{}^{56}{}_{}{}^{}\mathrm{Ni}$. One configuration identified in our calculations corresponds to a 2:1 harmonic oscillator configuration. The others are more complex; however, none gives a totally satisfactory explanation of the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$${+}^{28}$Si resonances.