The two previously published Hartree-Fock (HF) mass formulas, HFBCS-1 and HFB-1 (HF-Bogoliubov), are shown to be in poor agreement with new Audi-Wapstra mass data. The problem lies first with the prescription adopted for the cutoff of the single-particle spectrum used with the $\delta$-function pairing force, and second with the Wigner term. We find an optimal mass fit if the spectrum is cut off both above $E_F+15\mathrm{}\hspace{0.5em}\mathrm{MeV}$ and below $E_F-15\hspace{0.5em}\mathrm{MeV},$ $E_F$ being the Fermi energy of the nucleus in question. In addition to the Wigner term of the form $V_W\hspace{0.5em}\exp (-\lambda |N-Z|/A)$ already included in the two earlier HF mass formulas, we find that a second Wigner term linear in $|N-Z|$ leads to a significant improvement in lighter nuclei. These two features are incorporated into our new Hartree-Fock-Bogoliubov model, which leads to much improved extrapolations. The 18 parameters of the model are fitted to the 2135 measured masses for $N,Z>~8$ with an rms error of 0.674 MeV. With this parameter set a complete mass table, labeled HFB-2, has been constructed, going from one drip line to the other, up to $Z=120.\mathrm{}$ The new pairing-cutoff prescription favored by the new mass data leads to weaker neutron-shell gaps in neutron-rich nuclei.

The differences between the excitation energies of isobaric analog states deduced from experimental data have been studied. (i) Isospin inversion is indicated for several nuclei with $N=Z=\mathrm{odd}$ up to $A=98\mathrm{}$ based on experimental information including the systematics of the above energy differences. It is shown that the related approximate equality of the symmetry and pairing energies also extends to this mass region. A recently reported theoretical description of this behavior seems to involve a complex interplay between isoscalar and isovector pairing. (ii) An expression combining three of these excitation energy differences for nuclei with $N\approx Z$ displays residuals up to 8 MeV in the lightest nuclei only when nuclei with $N=Z$ = odd are included. These residuals appear to be related to a combination of isoscalar and isovector $p-n$ interactions. However, other theoretical interpretations have also been reported. (iii) A ratio of excitation energy differences has been introduced. It provides a signature for shell-model or quartet structures in nuclei with $N\approx Z.\mathrm{}$ Shell-model behavior dominates over the entire range of nuclei except for a region in the $\mathrm{fp}$ shell with $A\approx 70$ to 90 where quartet structure is observed. This result is in agreement with the reported theoretical prediction of a coexistence of $T=0\mathrm{}$ and $T=1\mathrm{}$ nucleon pairs.

The ${}^{14}\mathrm{N}(p,\gamma {)}^{15}\mathrm{O}$ reaction regulates the energy produced by the CN cycle in main-sequence stars and in red giants. Recently, preliminary evidence was presented for a new resonance in this reaction, which would significantly increase the reaction rate for temperatures near ${10}^8\mathrm{K}.$ We have attempted to confirm this result and find no indication of a resonance near $E_p^{\mathrm{lab}}=127\mathrm{}\mathrm{keV}.$ Our upper limit on its strength is $\omega \gamma <~32\mathrm{neV}$ (95% C.L.), which is more than 2 orders of magnitude below the previously reported value.

Variational Monte Carlo calculations for ${}_{\Lambda }^4\mathrm{H}$ (ground and excited states) and ${}_{\Lambda }^5\mathrm{He}$ are performed to decipher information on Λ-nuclear interactions. Appropriate operatorial nuclear and Λ-nuclear correlations have been incorporated to minimize the expectation values of the energies. We use the Argonne ${\upsilon }_{18}$ two-body NN along with the Urbana IX three-body NNN interactions. The study demonstrates that a large part of the splitting energy in ${}_{\Lambda }^4\mathrm{H}$ ${(0\mathrm{}}^{+}{-1\mathrm{}}^{+})$ is due to the three-body $\Lambda \mathrm{NN}$ forces. ${}_{\Lambda }^{17}\mathrm{O}$ hypernucleus is analyzed using the s-shell results. Λ binding to nuclear matter is calculated within the variational framework using Fermi-hypernetted-chain technique. There is a need to correctly incorporate the three-body $\Lambda \mathrm{NN}$ correlations for Λ binding to nuclear matter.

Energy levels of the double-Λ hypernuclei ${}_{\Lambda \Lambda }^7\mathrm{He},$ ${}_{\Lambda \Lambda }^7\mathrm{Li},$ ${}_{\Lambda \Lambda }^8\mathrm{Li},$ ${}_{\Lambda \Lambda }^9\mathrm{Li},$ ${}_{\Lambda \Lambda }^9\mathrm{Be},$ and ${}_{\Lambda \Lambda }^{10}\mathrm{Be}$ are predicted on the basis of an $\alpha +x+\Lambda +\Lambda$ four-body model, where ${x=n,p,d,t,}^3\mathrm{He},$ and $\alpha ,$ respectively. Interactions between the constituent particles are determined so as to reproduce reasonably the observed low-energy properties of the $\alpha +x$ nuclei ${(}^5\mathrm{He},{}^5\mathrm{Li},{}^6\mathrm{Li},{}^7\mathrm{Li},{}^7\mathrm{Be},{}^8\mathrm{Be})$ and the existing data for Λ-binding energies of the $x+\Lambda$ and $\alpha +x+\Lambda$ systems ${(}_{\Lambda }^3\mathrm{H},{}_{\Lambda }^4\mathrm{H},{}_{\Lambda }^5\mathrm{He},{}_{\Lambda }^6\mathrm{He},{}_{\Lambda }^6\mathrm{Li},{}_{\Lambda }^7\mathrm{Li},{}_{\Lambda }^8\mathrm{Li},{}_{\Lambda }^8\mathrm{Be},{}_{\Lambda }^9\mathrm{Be}).\mathrm{}$ An effective ΛΛ interaction is constructed so as to reproduce, within the α+Λ+Λ model, the $B_{\Lambda \Lambda }$ of ${}_{\Lambda \Lambda }^6\mathrm{He},$ which was extracted from the emulsion experiment, the NAGARA event. With no adjustable parameters for the $\alpha +x+\Lambda +\Lambda$ system, $B_{\Lambda \Lambda }$ of ground and bound excited states of the double-Λ hypernuclei with $A=7\mathrm{}–10$ are calculated within the Gaussian-basis coupled-rearrangement-channel method. The Demachi-Yanagi event, identified recently as ${}_{\Lambda \Lambda }^{10}\mathrm{Be},$ is interpreted as an observation of its $2^{+}$ excited state on the basis of the present calculation. Structural changes in the $\alpha +x$ core nuclei, due to the interaction of the Λ particles, are found to be substantial, and these play an important role in estimating the ΛΛ bond energies of those hypernuclei.

The process ${}^3\overrightarrow{H}\mathrm{e}\left(\overrightarrow{e}{,e}^{\prime }n\right)$ is theoretically analyzed with the aim to search for sensitivity to the electric form factor of the neutron, $G_E^n.$ Faddeev calculations based on five high precision nucleon-nucleon force models are employed, and stability versus exchange of the nucleon-nucleon forces is demonstrated.

The contractor renormalization (CORE) method is applied in combination with modern effective-theory techniques to the nuclear many-body problem. A one-dimensional—yet “realistic”—nucleon-nucleon potential is introduced to test these novel ideas. It is found that the magnitude of “model-space” (CORE) corrections diminishes considerably when an effective potential that eliminates the hard-momentum components of the potential is first introduced. As a result, accurate predictions for the ground-state energy of the three-body system are made with relatively little computational effort when both techniques are used in a complementary fashion.

The excitation cross sections to the first collective excitations in ${}^{28,30}\mathrm{Na}$ have been measured with the technique of intermediate-energy heavy-ion scattering. The trends in the deduced intrinsic electromagnetic quadrupole moments obtained in the present study and in a previous study of ${}^{31}\mathrm{Na}$ suggest that the ground state of ${}^{31}\mathrm{Na}$ is dominated by intruder configurations, while the lighter sodium isotopes are not. This conclusion is supported by data on binding energies.

We study signatures of critical behavior in microscopic simulations of small, highly excited Lennard-Jones drops. We focus our attention on the behavior of the system at the time of fragment formation (which takes place in phase space) and compare the results with the corresponding ones obtained at asymptotic times (experimentally accessible). The four critical exponents (τ, β, σ, and γ) found at fragmentation time have shown to be stable against time evolution, indicating that the asymptotic stage reflects accurately the physics at fragmentation time. Even though evidence of critical behavior arises from the calculations, we cannot affirm that the system is performing a second-order-like phase transition.

The properties of two measures of charge fluctuations $\tilde{D}$ and $\Delta {\Phi }_q$ are discussed within several toy models of nuclear collisions. In particular their dependence on mean particle multiplicity, multiplicity fluctuations, and net electric charge are studied. It is shown that the measure $\Delta {\Phi }_q$ is less sensitive to these trivial biasing effects than the originally proposed measure $\tilde{D}.$ Furthermore the influence of resonance decay kinematics is analyzed and it is shown that it is likely to shadow a possible reduction of fluctuations due to QGP creation.

Analyzing powers for $\pi p$ elastic scattering at bombarding energies below the $\Delta \mathrm{}\left(1232\right)\mathrm{}$ resonance were measured at TRIUMF using the CHAOS spectrometer and a polarized spin target. This work presents ${\pi }^{-}$ data at six incident energies of 57, 67, 87, 98, 117, and 139 MeV, and a single ${\pi }^{+}$ data set at 139 MeV. The higher energy measurements cover an angular range of $72°<~{\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~180°$ while the lower energies were limited to $101°<~{\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~180°.$ There is a high degree of consistency between this work and the predictions of the VPI/GWU group’s SM95 partial wave analysis.

Searches have been made for states in ${}^{16}\mathrm{C}$ with a structural overlap with an $\alpha :2n:\alpha :2n:\alpha$ configuration using reactions of a 130 MeV ${}^{18}\mathrm{O}$ beam with a ${\mathrm{Li}}_2\mathrm{O}$ target. Upper limits of $1.9\pm 0.4\mu \mathrm{b},$ $0.012\pm 0.003\mu \mathrm{b},$ and $15.5\pm 3.9\mu \mathrm{b}$ have been set on the total cross sections for the ${}^{16}\mathrm{O}{(}^{18}\mathrm{O}{,}^{10}{\mathrm{Be}}^{*}(6\mathrm{}\mathrm{MeV}{)+}^6\mathrm{He}{)}^{18}\mathrm{Ne},$ ${}^7\mathrm{Li}{(}^{18}\mathrm{O}{,}^{10}{\mathrm{Be}}^{*}(6\mathrm{}\mathrm{MeV}{)+}^6\mathrm{He}{)}^9\mathrm{B},$ and ${}^{16}\mathrm{O}{(}^{18}\mathrm{O}{,}^6\mathrm{He}{+}^6\mathrm{He}+\alpha {)}^{18}\mathrm{Ne}$ reactions, respectively.

We discuss a simple generic model of “jet quenching” in which matter absorption is defined by one parameter. We show that as absorption grows, the azimuthal asymmetry parameter $v_2$ grows as well, reaching the finite limit $v_2^{*}$ which has a simple geometric interpretation. We show that this limit is still below the experimental values for $6>\mathrm{}{p}_t>2\mathrm{}\hspace{0.5em}\mathrm{GeV},$ according to preliminary data from the STAR experiment at RHIC. We thus conclude that jet quenching models alone cannot account for the observed phenomenon, and speculate about alternative scenarios.

In this work we present a calculation of the $2p-2h$ preequilibrium escape width of giant resonances for the nuclei ${}^{40}\mathrm{Ca},$ ${}^{90}\mathrm{Zr},$ and ${}^{208}\mathrm{Pb}.$ The problem studied here involves an excited nucleus in the $1p-1h$ configuration, evolving to the $2p-2h$ configuration with the $1p$ in the continuum. The theoretical approach used for our calculations is based on the statistical multistep compound theory of Feshbach, Kerman, and Koonin (FKK) and on the particle-hole state densities given by Obložinský. Our calculations show that although different state densities supply a similar result for the damping width, the escape width is strongly dependent on the nuclei, on the binding energy of the emitted nucleon, and the excitation energy of the giant resonance.

We have studied the transfer reaction ${}^{14}\mathrm{N}{(}^7\mathrm{Be}{,}^8\mathrm{B}{)}^{13}\mathrm{C}$ at $E_{\mathrm{lab}}=84\mathrm{}\hspace{0.5em}\mathrm{MeV},$ paying special attention to the effects of the coupling to the continuum in the exit channel. Using the continuum discretized coupled channels (CDCC) formalism, we find that these effects are important for the description of the elastic scattering observables. However, for the transfer process, differences between the predictions of the differential cross section within the distorted wave Born approximation (DWBA) and the CDCC-Born approximation (CDCC-BA) are found to be negligible. This result supports the use of the DWBA method as a reliable tool to extract the $S_{17}\mathrm{}\left(0\right)\mathrm{}$ factor in this case.

A study of the low-lying levels of ${}^{128}\mathrm{Ba}$ was performed using three clover detectors in a compact arrangement. The levels were populated by beta decay of ${}^{128}\mathrm{La}$ which was produced by the fusion evaporation reaction ${}^{116}{\mathrm{S}\mathrm{n}(}^{16}\mathrm{O},1p3n).\mathrm{}$ $\gamma -\gamma$ angular correlations and polarization measurements were performed. The decay properties of several low-lying states were investigated. Spin assignments were made for two states, and several $E2/M1\mathrm{}$ mixing ratios were determined. The results are in good agreement with predictions of the O(6) limit of the interacting boson approximation. One of the states is unambiguously determined to be the hitherto unobserved member of the $\tau =4\mathrm{}$ multiplet.

The elastic scattering of the ${}^{16}\mathrm{O}{+}^{28}\mathrm{Si}$ system has been analyzed with a modified potential within the framework of the optical model over a wide energy range in the laboratory system from 29.0 to 142.5 MeV. This system has been extensively studied over the years and a number of serious problems has remained unsolved: The explanation of the anomalous large angle scattering data; the out-of-phase problem between theoretical predictions and experimental data; the reproduction of the oscillatory structure near the Coulomb barrier; and the consistent description of angular distributions together with the excitation functions data. These are just some of the problems. We propose the use of a modified potential method to explain these problems over this wide energy range. This new method consistently improves the agreement with the experimental data and achieves a major improvement on all the previous optical model calculations for this system.

The parton distribution functions determined by CTEQ at low $Q^2$ are used as inputs to test the validity of the valon model. The valon distributions in a nucleon are first found to be nearly Q independent. The parton distributions in a valon are shown to be consistent with being universal, independent of the valon type. The momentum fractions of the partons in the valon add up separately to one. These properties affirm the validity of the valon model. The various distributions are parametrized for convenient application of the model.

Inclusive distributions of soft production of mesons in hadronic collisions are calculated in the valon-recombination model. The new determination of the valon distributions from hard scattering data makes possible a tightly interrelated treatment of pion and kaon production in the fragmentation regions of proton, pion, and kaon. Only one free parameter is used in the determination of the valon distribution in the kaon. No other adjustable parameter is needed to fit the x distributions of the data on inclusive cross sections, except for the normalizations since the data are at fixed $p_T.$ The success of the model in reproducing seven inclusive distributions suggests that there are two important mechanisms at work in soft production. One is that the structure of the hadron that fragments is highly relevant. The other is that the produced particles are formed by the recombination of quarks and antiquarks. These two aspects about hadrons in soft processes can be well described in the framework of the valon-recombination model.

Nucleon structure and the origin and nature of the nuclear force are investigated in the context of a quantum chromodynamics motivated effective Lagrangian for quark and diquark fields and the path-integral method of hadronization. We start from a microscopic model of quarks and diquarks where the gluons have been integrated out. In particular, we use the chiral Nambu–Jona-Lasinio model to describe quark dynamics and assume that the nucleon can be conceived as a quark-diquark relativistic bound state. The hadronization method is then used to rewrite the problem in terms of the physical meson and nucleon degrees of freedom. Next, by employing a loop expansion of the resulting quark/diquark determinants, we arrive at an effective chiral meson-nucleon Lagrangian. Nucleon properties such as mass, coupling constants, electromagnetic radii, anomalous magnetic moments, and form factors are derived using a theory of at most two free parameters.