The neutron-nucleus cross section at Fermi lab energies is computed using Glauber-Gribov multiple scattering theory. The effects of higher moments in the cross section fluctuations are included and their physical origin discussed. The validity of the frozen approximation is critically examined. These studies of the nucleon-nucleus total cross sections provide a test of the pp→Xp diffractive amplitudes used in calculations of color transparency effects.

The effect of Coulomb interaction in quasifree scattering and quasifree reactions has been investigated under different kinematical conditions for the processes involving up to two charges per particle and a total of six nucleons in the incoming channel, and three particles in the outgoing channel. The differential cross section was calculated using the plane wave impulse approximation. The influence of the Coulomb interaction on the magnitiude and shape of these spectra were determined and compared with experimental data. It has been found that for the quasifree peak of the Coulomb effect within this model depends only on the outgoing particles in quasifree vertex and on energy between them. At low energies the influence of the Coulomb interaction cannot account for the discrepancy between the quasifree data and the impulse approximation predictions, although it can produce effects of several orders of magnitiude, depending on the energy and the charges of particles. The Coulomb interaction changes only the magntiude, and has a very weak influence on the shape of the quasifree spectra. At high energies the Coulomb influence on the maxima of the spectra is in the 5–20% range. When those Coulomb effects are taken into account and when a proper wave function for the spectator-transfer particle system is used, then at energies above 200 MeV this model agrees with data.

We study two-body currents in the noninteracting relativistic Fermi gas model. Special emphasis is put on the role of the Δ isobar. Due to a resonance behavior, relativistic two-body isobar currents are found to be important in comparison with experimental data. Real-pion production is studied within the same framework, and the importance and physical implications of the energy dependence of the Δ-isobar decay width are stressed.

A model for the meson exchange in the scalar (σ) and vector (ρ) channel in the πN interaction based on correlated 2π exchange is presented, which is obtained by using quasiempirical information about the NN¯→2π amplitudes. Due to chiral symmetry constraints it turns out that σ exchange is repulsive in S waves but attractive in P waves. The specific feature seems to be favored by the πN data. Concerning ρ exchange our result is roughly twice as large as used in former more phenomenological treatments. Our model is supplemented by conventional (direct and exchange) pole diagrams involving a (bare) nucleon and Δ isobar, and is then unitarized by means of the relativistic Schrödinger equation, giving the Δ isobar a width determined by the dynamics of the model. Resulting πN phase shifts in the elastic region agree well with empirical information, as do scattering lengths and the πN Σ term.

The use of the Coulomb dissociation method to obtain the cross sections for the radiative capture reactions ${}_{}{}^3{}_{}{}^{}\mathrm{C}$(α,γ) ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$(p,γ) ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ is investigated. The contribution of the nuclear interaction to the breakup is included. Due to the low binding of the proton in ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ the second reaction is dominated by Coulomb breakup. The effects of Coulomb reacceleration of the fragments and of the excitation of states in the fragments are also studied. Ideal kinematical conditions for the experiments are investigated.

The response functions for the unpolarized (e,e’p) and polarized (e→,e’p) reaction are calculated for medium-heavy nuclei under quasifree conditions. The formalism presented here incorporates both electron distortion effects and two-body currents related to meson-exchange and the Δ(1232) excitation. The final-state interaction of the outgoing nucleon with the residual nucleus is handled in a self-consistent Hartree-Fock random phase approximation formalism. The effect of Coulomb distortion of the incoming and outgoing electron is included within a fully distorted wave calculation. The sensitivity of the results to the two-body currents is discussed for the five structure functions in quasielastic (e→,e’p) scattering off the target nuclei ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. A selective sensitivity to the two-body currents is obtained in the longitudinal-transverse interference term ${\mathit{W}}_{\mathit{L}\mathit{T}}$ for which two-body currents can explain part of the discrepancy between the impulse-approximation calculations and the data.

The similarities in the experimental indications for multinucleon mechanisms in (γ,p) and (e,e’p) processes are pointed out. For both types of reactions, the substantial role of two-nucleon emission processes for transitions to high excitation energies in the residual nucleus is stressed. A microscopic model for the calculation of the two-body knockout contributions to the inclusive (γ,N) reaction is presented. It is based on an unfactorized formalism for the calculation of electromagnetically induced two-nucleon emission cross sections. The model is shown to yield a reasonable description of the overall behavior of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(γ,p) and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(γ,n) data at high excitation energies in the residual nucleus. In the calculations, effects from nonresonant and resonant pion exchange currents are included. Photoabsorption on these currents is predicted to produce the major contributions to the exclusive ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(γ,${\mathit{n}}_0$${)}^{15}$O process at photoenergies above the pion threshold. Double differential cross sections for photon induced pp and pn emission from ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ are calculated and compared with the data.

The ${\mathit{M}}_{\mathrm{\perp }}$ scaling property of the dilepton spectrum from early parton matter in ultrarelativistic heavy collisions is analyzed for various mechanisms of initial parton production. If there is no essentially additional scale in the parton distribution, we find even for strong off-equilibrium parton matter approximate scaling, while such scales as low-momentum cutoff or parton masses cause strong scaling violations.

Heavy ion collisions at ultrarelativistic energies are expected to provide an environment where quarks and gluons replace hadrons as the appropriate degrees of freedom. As the excited region expands and cools, the transition to the hadronic state might be characterized by phase separation with hadrons being emitted from dense droplets of quark-gluon matter. Here we study four techniques to search for such droplets: rapidity correlations, identical kaon correlations, φ meson production, and proton correlations. We conclude that rapidity correlations are the clearest signal of such fluctuations, and that proton correlations and φ production can also be strongly affected by drop formation.

We have performed a set of partial-wave analyses of the pion-nucleon elastic scattering data to 2 GeV employing rigorous constraints from simultaneous forward and fixed-t dispersion relations. Constraints were generated from the forward ${\mathit{C}}^{\pm }$ amplitudes and the invariant amplitudes A and B at fixed t in the range 0 to -0.3 ${\mathrm{GeV}}^2$. Solutions were generated for a range of pion-nucleon coupling constants (${\mathit{g}}^2$/4π) and isoscalar scattering lengths (${\mathit{a}}^{\mathrm{}(+)\mathrm{}}$). A chi-squared map for these (${\mathit{g}}^2$/4π,${\mathit{a}}^{\mathrm{}(+)\mathrm{}}$) solutions exhibits a clear minimum near ${\mathit{g}}^2$/4π=13.75 (${\mathit{f}}^2$/4π=0.076) for both the fits to the data and the dispersion relations. While favoring a particular ${\mathit{g}}^2$/4π, this work shows that it is possible to obtain good, stable fits for nearby values, but at the cost of increased chi squared. Consequently, this approach provides a criterion for defining the preferred value and uncertainty of ${\mathit{g}}^2$/4π from pion-nucleon scattering data. On this basis, we conclude that ${\mathit{g}}^2$/4π=13.75±0.15 (${\mathit{f}}^2$/4π=0.076±0.001).

The EMC-type effects observed in lepton, hadron-nucleus collisions have revised the conventional high energy picture of the nucleus as a collection of semi-independent nucleons interacting via a meson field. For high momentum transfers deviations from this picture can be accounted for by a QCD treatment in which the nuclear dependence, attributed to overlapping of bound nucleons, is introduced through the nonperturbative parton momentum distributions. These phenomena must be more pronounced in nucleus-nucleus interactions to be studied at the Relativistic Heavy Ion Collider. We calculate the ratio of the Drell-Yan cross section for collisions of two large nuclei to that for interactions of two protons or deuterium nuclei to order ${\mathrm{\alpha }}_{\mathit{s}}$. We predict that in the invariant mass range between the heavy quarkonium peaks this ratio is less (greater) than one for small (large) values of the pair longitudinal and transverse momentum. For fixed nucleon energy the depletion at low lepton momenta decreases with increase of the invariant mass and disappears well beyond the meson resonances. We investigate the dependence of these effects on the choice of ocean and gluon momentum distributions.

Color transparency (CT) in high momentum transfer (e,e’p→) and (e,e’p→) reactions is explored. The vector nature of the photon and the spin of the proton and photon are treated explicitly by describing the initial bound proton and the ejected wave packet as four-component Dirac spinors. Such effects, ignored in previous calculations, yield several results: (1) The use of Dirac-based optical potentials in the ‘‘standard calculation’’ (ignoring CT) leads to smaller cross sections than predicted before. (2) The normal component of the ejectile polarization, which vanishes in the limit of full CT, is found to approach zero very slowly as the energy increases. (3) Due to the presence of the 1${\mathit{H}}_{11/2}$ orbital, a measurement of the normal-transverse response in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ could afford the opportunity to see CT at quite low momentum transfers ∼1 GeV/c. (4) The four-component nature of our formalism allows us to determine that our calculations are roughly consistent with current conservation, except when the momentum of the struck nucleon is greater than about 150 MeV/c.

We investigate πρ scattering in the pseudoscalar (π), vector (ω), and axial-vector (${\mathit{A}}_1$) channel using a model based on a s- as well as t-channel meson exchange. We start with the realistic case of a broad ρ meson and illustrate the application of three-body methods in this approach. In a second step our calculation is simplified by treating the ρ as a stable particle. Our model is adjusted to reproduce ω- and ${\mathit{A}}_1$-resonance parameters and we are able to resolve in a natural way apparent discrepancies occurring in the analysis of the ${\mathit{A}}_1$.

We discuss heavy-meson exchange corrections in the context of parity violating quasielastic electron-deuteron scattering. We compute the meson exchange contributions to the isoscalar vector response function of the deuteron. In contrast to the case of heavy targets the corrections are found to be small.

There are several known T=1 states in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ in the region of 24 to 27 MeV excitation. We observe the alpha-particle decay to the ground state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ of many excited states in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, some of which reside between 24 to 27 MeV. Either we have observed new states in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ or there is a very strong admixture of T=0 in these previously assigned T=1 states.

This paper is an extension of a previous study of the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ nucleus in the framework of the homology concept. It is concerned with the multiplet of states homologous to the 1.484 MeV, 11/$2^{\mathrm{-}}$ level of ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$, due to ‖9/$2^{\mathrm{-}}$⊗ 11) / 2 ${}_{}{}^{\mathrm{-}}{}_{}{}^{}\mathrm{〉}$ coupling. The results obtained and the new assignments attributed to ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ confirm the importance of the homology concept in the spectroscopy of high excitation energy levels.

Two-proton correlation functions for the inverse kinematics reaction ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$${+}^{27}$Al at E/A=31 MeV have been reanalyzed to search for differences between longitudinal and transverse correlations indicative of emission from a long-lived composite system. Evidence for such differences is found when tight angular cuts are applied in the compound nucleus rest frame and when the correlation functions are constructed by the event mixing technique.

The excited states of ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ were studied by means of the decays of the 15.8-min, $3^{+}$ ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sb}$ ground state, and the 60.3-min, $8^{\mathrm{-}}$ ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sb}$ isomer. Over 50 γ rays were observed; these were incorporated into a level scheme consisting of 32 excited states. Except for one new level proposed at 3.986 MeV, the current study fully supports an exhaustive study of levels in ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ reported earlier. The previous study was an attempt to develop a nearly ‘‘complete’’ level scheme of ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ up to an excitation energy of 4.3 MeV.

Partial differential equations are derived for the densities of the grand canonical ensemble. By using an expansion in Planck’s constant, semiclassical solutions are obtained for the phase space distributions. Integration of these solutions over all values of momenta gives the Wigner-Kirkwood densities derived previously with a convolution method and used extensively to study hot nuclei.

In view of the recent interest in the problem of the nuclear interactions of charmonium, we consider the role of higher order multiple scattering and nucleon-nucleon correlation effects in charmonium${\mathrm{-}}^4$He interaction at zero energy. We find a remarkably large enhancement of the calculated low-energy cross section over the standard coherent impulse approximation. This is a consequence of large collectivity induced by the higher order effects in the multiple scattering expansion which appear to play a crucial role for the case of a real and negative (corresponding to attraction) elementary scattering length.