For (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) double charge exchange on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, an excitation function at 5° has been measured over a range of incident pion energies from 100 to 293 MeV for transitions to both the ground state and to a doublet at 1.75 MeV of excitation in the final nucleus ${}_{}{}^{27}{}_{}{}^{}\mathrm{P}$. The shapes of these excitation functions are strikingly different, with the g.s. data exhibiting an interferencelike dip near 150 MeV and the excited state falling smoothly above 150 MeV.

Large discrepancies have existed, factor of ∼2.5 (∼5σ), between a variety of cascade-type theoretical models and published experimental results for the inclusive protonlike production corss sections at the 20° polar laboratory angle for relativistic La + La collisions. In view of this discrepancy the present work was undertaken to check the experimental cross sections for 0.76 GeV/nucleon La + La collisions using a small-acceptance magnetic spectrometer. The 20° cross sections were determined by measuring the appropriate range of polar laboratory angles and momenta which, when transformed into the projectile frame, produce the cross sections at 20°. Cross sections have been determined from 30° to 75° for protons and light nuclei with rigidities from 0.5 to 2.0 GeV/c in the laboratory frame. Cross sections were also deduced at 15° and 20° in the projectile frame for nucleon momenta from 0.9 to 1.5GeV/c. The original experimental results for the larger polar laboratory angles (40° and 60°) were confirmed; however, the 20° cross sections disagree by a factor of about 1.5 (∼2σ). At large polar laboratory angles (40°-70°) the model calculations disagrees in the low-momentum range with the present data by a factor of 1.5 (∼3σ). The discrepancy at small polar angles (15° and 20°) has been significantly reduced from the original factor of 2.5 down to a value of 1.2 (∼3σ).

Differential cross sections and analyzing powers for scattering of 200 and 318 MeV protons have been measured for states of ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ up to 7 MeV of excitation. The data cover c.m. momentum transfers from approximately 0.4 to 3.0 ${\mathrm{fm}}^{\mathrm{-}1}$. Neutron transition densities were extracted for the $2_1^{+}$,$3_1^{\mathrm{-}}$,$3_2^{\mathrm{-}}$,$4_2^{+}$, and $5_1^{\mathrm{-}}$ states using density-dependent empirical effective interactions previously calibrated upon elastic and inelastic scattering data for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. The corresponding proton transition densities were obtained from electron scattering data and held fixed during the analysis. Fits performed to the data for either energy provide excellent predictions for the other. Neutron densities fitted to data for either energy independently agree very well with each other and with the densities fitted to both data sets simultaneously. These densities are also consistent with earlier data for 500 MeV protons. The energy-independence of the extracted transition densities demonstrates that residual errors in the reaction model are compatible with the error bands estimated by the fitting procedure. Several additional tests of the model dependence of the results were performed also. The proton and neutron transition densities are compared with calculations based upon the extended random phase approximation, which includes 2p2h correlations. These calculations are most successful for densities dominated by 1p1h configurations, whereas densities requiring substantial 2p2h contributions tend to be underestimated.

Coupled channel calculations for proton-nucleus inelastic scattering are performed using the Dirac formalism. The inelastic scattering of 362, 500, and 800 MeV protons from ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are considered. Transition potentials for the low-lying collective states are obtained using a simple collective model. Phenomenological as well as parameter-free relativistic impulse approximation (RIA) optical potentials are used for the direct potentials. It is found that reasonable descriptions of both elastic and inelastic observables are obtained. It is shown that the coupling to low-lying states greatly improves the agreement with the large angle data.

This paper studies the particle correlation effect on hard photon production in heavy ion reactions at intermediate energies. It is indicated that this mechanism is able to increase the high-momentum component in nucleon distribution in phase space, and consequently increase the production of hard photons. A modified version of the Boltzmann-Uehling-Uhlenbeck equation by incorporation of the α-like cluster effect has been developed. As examples, we studied, by using the new model, the photon productions in the reactions of ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$ on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ag}$, and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ targets, respectively, at the same beam energy E/A=44 MeV. The results show that the incorporation of the cluster effect would lead to an enhancement of hard photon emission, especially at backward angles, and improve the agreement between the predicted and measured data. The mechanism underlying such enhancement has been explored.

A description of pp→nX inclusive inelastic scattering data for 8 dominated by Δ (3,3) excitation is presented based on a partial wave expansion model for the reaction pp→n${\mathrm{\Delta }}^{++}$. The data selected for analysis include the total reaction cross section, differential cross sections, analyzing powers, polarization transfers, and spin correlation parameters. A semiquantitative fit to the data is achieved and a phenomenological model for the isospin 1 NN→NΔ transition matrix is presented. The latter quantity is expressed in terms of sixteen parity invariant bilinear combinations of spin operators and accompanying amplitudes. These sixteen amplitudes constitute the first complete phenomenological representation of the NN→NΔ transition which can be used as input fo r distorted wave Born approximation calculations of nucleon and light ion induced Δ excitation in nuclei. Of the sixteen spin operators ten include rank 2 tensors. The effects of these tensor amplitudes on the inelastic NN→NΔ observables are substantial.

The method for extraction of neutron and matter densities from data on cross sections and spin observables for elastic p-nucleus scattering is presented. The effective nuclear potential was treated to the first order with respect to the t-matrix and density distributions. To eliminate uncertainties associated with the t-matrix, the latter has been determined directly from p${\mathrm{-}}^{40}$Ca scattering data, where the proton and neutron densities are known sufficiently well. The medium modifications in the t- matrix have been included by means of density dependent terms added to the free t matrix. The neutron densities to be found were expressed as a Hartree-Fock (HF) distribution plus a small correction expanded in a Fourier-Bessel series with inclusion of only low-frequency components determined by the data. High-frequency components are presented by the HF term. Expressions for the physical observables were linearized in terms of the expansion coefficients, the latter being determined through an iterative procedure from the ${\mathrm{\chi }}^2$ criterium. The method enables one to obtain statistical fluctuations in those Fourier components as they are generated by experimental error bars. The normalization and model uncertainties have been also estimated. The extracted densities ${\mathrm{of}}^{206,207,208}$Pb and their differences were compared with the HF results calculated by us with the Skyrme interaction. On the whole, pretty good agreement has been achieved.

A set of global optical potentials for alpha particles with energies above 80 MeV has been extended to lower energies and proved appropriate to describe (n,α) reactions. It is found that the transmission coefficients for alpha-particle emission are rather strongly related to the fusion cross sections and elastic scattering at energies above 80 MeV, but not to elastic scattering at lower energy where specific features are comprised within complex optical potential parametrizations.

A time-ordered manifestly covariant relativistic scattering theory for arbitrarily large systems of nucleons and mesons is derived. The S-matrix-type approach is based on clusters rather than individual particles; it provides a recursive hierarchy of Lippmann-Schwinger equations, each describing the dynamical evolution of two-cluster configurations at different levels of the relativistic many-body problem. The present work extends the results of part I to include particle absorption and creation. The resulting effective two-body equations describe all possible absorption and production processes up to the maximum number of initially considered particles; they employ fully dressed cluster propagators and vertices, including all crossed meson contributions. Nonlinear couplings introduce effective contributions from infinitely many mesons. Examples of pion-nucleon, pion-deuteron, and nucleon-nucleon scatterings are discussed. An algorithm for the self-consistent implementation of crossing symmetry and for the determination of the off-shell πN form factor is given. Implications for crossing mechanisms employed in NN potentials and for novel types of three-body forces in three-nucleon calculations are pointed out.

A model for the fragmentation of a nucleus is discussed. A general framework for obtaining the canonical ensemble partition function for a fragmentation process is developed based on simple recursive techniques. Parallels of the description of this process with other areas are shown which include Feynman’s theory of the λ transition in liquid helium, Bose condensation, and Markov process models. These parallels are used to generalize and further develop a previous exactly solvable model of nuclear fragmentation. A comparsion with other models is also given and one of these models is generalized to include a tuning parameter which contains the underlying physical quantities associated with the fragmentation process. A discussion of the behavior of the partion function and phase transitions is given in terms of Lee-Yang zeros of the partition function. An analysis of some experimental data is given.

Fixed energy quantal inverse scattering theory has been used to analyze the differential cross section from the elastic scattering of 200 MeV protons from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. Ambiguities in obtaining the scattering function from the differential cross section are discussed and we illustrate by means of example that not all scattering functions lead to physically reasonable potentials.

Recent data obtained with the quasielastic (e,e’p) reaction, and the (γ,p) reaction at photon energies of about 60 MeV, on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, and ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ are examined. Comparisons are made using disorted-wave impulse-approximation calculations. The (e,e’p) data are used to determined the values of spectroscopic factors and root-mean-square radii of the overlap wave function for each transition considered. These parameters constrain the direct-knockout (DKO) calculations for the (γ,p) reactions which have been performed within the same framework. While the calculations give a very good description of the (e,e’p) data, a discrepancy of typically a factor of six is observed between the DKO calculations and the (γ,p) data. The discrepancy is largely removed when meson exchange current contributions in the (γ,p) reaction are estimated on the basis of the Siegert theorem.

Hard and semihard processes lead to a copious production of partons at the early stage of ultrarelativistic heavy-ion collisions. Since the parton momentum distribution is strongly anisotropic, the system can be unstable with respect to the specific plasma modes. The conditions of instability are found and the characteristic time of its development is estimated. Then, the screening of the static chromoelectric field in the nonequilibrium plasma is studied. Importance of the two phenomena for heavy-ion collisions at the Brookhaven Relativistic Heavy Ion Collider and the CERN Large Hadron Collider is critically discussed.

The decay width of a phi meson is reduced from its vacuum value as its mass decreases in hot hadronic matter as a result of the partial restoration of chiral symmetry. This reduction is, however, cancelled by collisional broadening through the reactions φπ→${\mathit{KK}}^{\mathrm{*}}$, φK→φK, φρ→KK, and φφ→KK. The resulting phi meson width in hot hadronic matter is found to be less than about 10 MeV for temperatures below 200 MeV. If hadronic matter has a strong first-order phase transtion, this narrow phi meson with reduced mass will appear as a second peak in the dilepton spectrum in ultrarelativistic heavy-ion collisions. We discuss use of this second phi peak to determine the transition temperature and the lifetime of the two-phase coexistence region in the case of a strong first-order phase transition. We also discuss using the peak to determine the range of temperatures over which the transition occurs in the case of a smooth but fast change in the entropy density.

Hot gluons are the dominant components of the QCD plasma to be formed in future high energy heavy ion experiments. In this paper we study the elementary processes in the plasma medium for gluon multiplication based on all orders of the tree diagrams in perturbative QCD. When applying to the chemical equilibration in the expanding system, we found that the gluon reaches chemical equilibrium well within its plasma phase. The inclusion of all the next-to-leading-order processes makes the equilibration considerably faster than the simple gg⇆ggg one considered previously.

The scalar, isoscalar piece of the two-pion exchange force between two nucleons is calculated in the linear σ model. A large contribution to this force is found to come from terms involving direct coupling of the σ field to the nucleons. This part of the interaction can be related to the partial restoration of chiral symmetry experienced by a nucleon in nuclear matter, and it has a strength determined by the σ commutator. Even if the ‘‘elementary’’ σ is taken to be heavy (${\mathit{m}}_{\mathrm{\sigma }}$>1GeV), the effect has a longer range, determined by the mass of the pair of pions. Although the σ fields used in relativistic models of nuclei have a similar strength and range, no simple relationship is found between such fields and partial restoration of chiral symmetry.

In this work, we investigate the question whether the conventional analysis of the electromagnetic form factors of the nucleon, evaluated in the framework of the cloudy bag model (CBM) or other chirally invariant hybrid quark models utilizing the same philosophy, is gauge invariant? In order to address that point, we first formulate the CBM in a style that resembles the technique of loop integrals. Evaluating the self-energy and the electromagnetic form factors of the nucleon in that manner, and comparing with the standard analysis where nonrelativistic perturbation theory is used, allows us to show that our approach is appropriate and to point out what approximations are made in the standard derivation of the model. From the form of those loop integrals, we then show that additional diagrams are needed to preserve electromagnetic gauge invariance and we assess the corresponding corrections.

Differential cross sections for the elastic scattering of 20 and 40 MeV ${\mathrm{\pi }}^{\mathrm{-}}$ by nuclei ranging from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ to ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ are reported. Comparisons are made with the predictions of the Michigan State University (MSU) optical potential.

The fine structure in the alpha decay of ${}_{}{}^{231}{}_{}{}^{}\mathrm{U}$ has been studied for the first time. The alpha branching ratio in ${}_{}{}^{231}{}_{}{}^{}\mathrm{U}$ is determined as (4±1)×${10}^{\mathrm{-}5}$. Levels in ${}_{}{}^{227}{}_{}{}^{}\mathrm{Th}$ are deduced and tentative spins and parities suggested.

We have performed quasiparticle random phase approximation (QRPA) calculations for the 2νββ decay matrix element ${\mathit{M}}_{\mathrm{GT}}^{2\nu }$ of ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ using realistic effective interactions derived from the Paris, Bonn, and Reid potentials. Unlike earlier QRPA calculations where the BCS self-energies were suppressed, we have retained these self-energies together with the use of the single-particle levels provided by a ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ core. Different choices for the single-particle levels are employed, and their effects on ${\mathit{M}}_{\mathrm{GT}}^{2\nu }$ are compared. A majority of our calculated ${\mathit{M}}_{\mathrm{GT}}^{2\nu }$ matrix elements are in good agreement with the experimental bounds of ‖${\mathit{M}}_{\mathrm{GT}}$${\mathrm{\Vert }}^{2\nu }$<0.05 ${\mathrm{MeV}}^{\mathrm{-}1}$, and exhibit good stability with respect to the variation of the particle-particle interaction strength ${\mathit{g}}_{\mathit{p}\mathit{p}}$.