NA44 has measured midrapidity deuteron spectra from $\mathrm{AA}$ collisions at $\sqrt{s_{\mathrm{nn}}}\approx 18$ GeV at the CERN SPS. Combining these spectra with published p, $\overline{p},$ and $\overline{d}$ data allows us to calculate, within a coalescence framework, p and $\overline{p}$ source sizes and phase space densities. These results are compared to ${\pi }^{\pm }$ source sizes measured by Hanbury Brown–Twiss (HBT) interferometry and phase densities produced by combining pion spectra and HBT results. We also compare to $\mathrm{pA}$ results and to lower energy (AGS) data. The $\overline{p}$ source is larger than the proton source at $\sqrt{s_{\mathrm{nn}}}=17.3\mathrm{}$ GeV. The phase space densities of ${\pi }^{+}$ and p are not constant but grow with system size. Both ${\pi }^{+}$ and proton radii decrease with $m_T$ and increase with $\sqrt{s_{\mathrm{nn}}}.$ Pions and protons do not freeze out independently. The nature of their interaction changes as $\sqrt{s_{\mathrm{nn}}}$ and the $\pi /p$ ratio increases.

The irreducible representations of the Lie algebra $\mathrm{su}\mathrm{}\left(3\right)\mathrm{}$ describe rotational bands in the context of the nuclear shell and interacting boson models. The density matrices associated with $\mathrm{su}\mathrm{}\left(3\right)\mathrm{}$ provide an alternative theoretical framework for obtaining these bands. The $\mathrm{su}\mathrm{}\left(3\right)\mathrm{}$ density matrix formulation is mathematically simpler than representation theory, yet it yields similar results. Bands are solutions to a system of polynomial equations defined by the quadratic and cubic $\mathrm{su}\mathrm{}\left(3\right)\mathrm{}$ Casimirs. Analytic solutions are found in many physically important cases including rotation about principal axes and spheroids. Numerical solutions are reported in other cases including tilted rotors. The physics of $\mathrm{su}\mathrm{}\left(3\right)\mathrm{}$ rotational bands is more transparent in the density formalism than in representation theory.

We discuss the importance of momentum dependent interactions in explaining the multifragmentation in asymmetric reactions by comparing the results with ${}^{16}\mathrm{O}-\mathrm{induced}$ emulsion data. The reactions are simulated within a quantum molecular dynamics model and the clusterization is performed with the minimum spanning tree method. Our results clearly indicate that the inclusion of momentum dependent forces improves the agreement with the measured atomic number distribution. The simple static interaction fails to explain the experimental data. We also discuss the universal dependence of the effect of momentum dependent interactions on the asymmetry of a reaction.

Using the linear sigma model, we study the evolutions of the quark condensate and of the nucleon mass in the nuclear medium. Our formulation of the model allows the inclusion of both pion and scalar-isoscalar degrees of freedom. It guarantees that the low-energy theorems and the constraints of chiral perturbation theory are respected. We show how this formalism incorporates quantum hadrodynamics improved by the pion loop effects.

We present a separable expansion approximation method for Coulomb-like potentials which is based on Schwinger variational principle and uses Coulomb-Sturmian functions as basis states. The new scheme provides faster convergence with respect to our formerly used nonvariational approach.

The first calculation (to our knowledge) of neutrinoless double beta decay $(0\mathrm{}\nu \beta \beta$-decay) matrix elements within the self-consistent renormalized quasiparticle random phase approximation (SRQRPA) is presented. The contribution from the momentum-dependent induced nucleon currents to $0\nu \beta \beta$-decay amplitude is taken into account. A detailed nuclear structure study includes the discussion of the sensitivity of the obtained SRQRPA results for $0\nu \beta \beta$ decay of ${}^{76}\mathrm{Ge}$ to the parameters of nuclear Hamiltonian, two-nucleon short-range correlations, and the truncation of the model space. A comparison with the standard and renormalized QRPA results is presented. We have found a considerable reduction of the SRQRPA nuclear matrix elements, resulting in less stringent limits for the effective neutrino mass.

The decay of the very neutron-rich nucleus ${}^{100}\mathrm{Rb}$ has been studied by γ spectroscopy of online mass-separated samples. Schemes for β decay to ${}^{100}\mathrm{Sr}$ and $\beta n$ decay to ${}^{99}\mathrm{Sr}$ are presented. New sets of transitions in ${}^{99}\mathrm{Sr}$ and ${}^{100}\mathrm{Sr}$ with identical energies are observed. All identical bands so far observed in neutron-rich Sr isotopes obey a simple energy rule valid for even-even, odd-even, and odd-odd bands.

In order to determine the relative importance of the role played by inelastic excitations and transfer channels of the colliding nuclei, in near-barrier fusion enhancement, the fusion cross sections have been measured for ${}^{12}\mathrm{C}{+}^{194,198}\mathrm{Pt}$ in the energy range of $0.9<~{E/V}_B<~\mathrm{1.2.}$ Additional data of quasielastic and nucleon(s)-exchange cross sections have also been measured at an energy of ${1.2V}_B.$ The strength of transfer form factors required for the simplified coupled-channels calculations has been obtained from the transfer reaction measurements using a semiclassical approach and calculations based on complex WKB approximations. Coupled-reaction-channels calculations have been performed to explain the complete data set that included fusion, quasielastic, and transfer cross sections. The dominant contributions to the enhancement of fusion cross section compared to a one-dimensional barrier-penetration model arise from coupling to inelastic channels. It has been shown for the first time that the lighter isotope ${(}^{194}\mathrm{Pt})$ of a given nuclide that has a relatively larger collectivity $\left({\beta }_{\lambda }\right)$ and a larger neutron separation energy compared to the heavier isotope ${(}^{198}\mathrm{Pt}),$ exhibits larger enhancement of fusion cross section. The experimental fusion-barrier distributions were obtained from fusion and quasielastic scattering data.

Alpha particle emission spectra have been measured from a number of heavy ion induced nuclear reactions populating compound nuclei in the mass range $A=112\mathrm{}–208.$ The data have been analyzed using the statistical model code PACE2 with an aim to determine the values of the inverse level density parameter $\mathrm{}\left(K\right).$ The K values thus determined have been compared with the calculations based on the static path approximation method taken from the literature. Also the diminishing of the shell effects in closed shell Pb nuclei has been discussed.

Cross sections for coherent rho production in the ${(p,p}^{\prime })$ reaction on ${}^{12}\mathrm{C}$ have been calculated in the beam energy range $1.8-2.5\hspace{0.5em}\mathrm{GeV}.$ The rho meson produced at the ${\mathrm{pp}}^{\prime }$ vertex is brought on-shell by the coherent effect of the target nucleus through an optical potential. The latter is constructed using the high energy ansatz with the elementary $\rho N$ scattering amplitude coming from the vector dominance model and the resonance model, and the coupled channel calculations on the meson-nucleon scattering. The cross sections are found to be significant and sensitive to the strength of the potential and the beam energy. The rho mesons are found to come mostly in the forward direction.

The dynamical model developed by us [Phys. Rev. C 54, 2660 (1996)] has been applied to investigate the pion electroproduction reactions on the nucleon. It is found that the model can describe to a very large extent the recent data of ${p(e,e}^{\prime }{\pi }^0)$ reaction from Jefferson Laboratory and MIT-Bates. The extracted magnetic dipole $\mathrm{}\left(M1\mathrm{}\right),$ electric dipole $\mathrm{}\left(E2\mathrm{}\right),$ and Coulomb $\mathrm{}\left(C2\mathrm{}\right)\mathrm{}$ strengths of the $\gamma \overrightarrow{N}\Delta$ transition are presented. It is found that the $C2/M1\mathrm{}$ ratio drops significantly with $Q^2$ and reaches about $-14\%$ at $Q^2=4\mathrm{}\hspace{0.5em}(\mathrm{GeV}{/c)}^2,$ while the $E2/M1\mathrm{}$ ratio remains close to the value $\sim -3\%$ at the $Q^2=0\mathrm{}$ photon point. The determined $M1\mathrm{}$ transition form factor drops faster than the usual dipole form factor of the proton. We also find that the nonresonant interactions can dress the $\gamma \overrightarrow{N}\Delta$ vertex to enhance strongly its strength at low $Q^2,$ but much less at high $Q^2.$ Predictions are presented for future experimental tests. Possible developments of the model are discussed.

We use light-front dynamics to calculate the electromagnetic form factor for the Hulthén model of the deuteron. For a small momentum transfer $Q^2<5\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^2,$ the relativistic effects are quite small. For $Q^2\sim 11$ ${\mathrm{GeV}}^2$ there is a $\sim 13\%$ discrepancy between the relativistic and nonrelativistic approaches. For asymptotically large momentum transfer, however, the light-front form factor $\sim \ln Q^2{/Q}^4$ differs markedly from the nonrelativistic version $\sim {1/Q}^4.$ This behavior is also present for any wave function, such as those obtained from realistic potential models, which can be represented as a sum of Yukawa functions. Furthermore, the asymptotic behavior is in disagreement with the Drell-Yan-West relation. We investigate precisely how to determine the asymptotic behavior, and confront the problem underlying troublesome form factors on the light front.

Resonance states are introduced into the Hartree-Fock BCS model using a complex scaling method in order to take into account the effect of pair scattering into continuum states. The applicability of the state-dependent BCS model based on bound and resonance states is checked at the proton drip-line region around the double magic nuclei ${}^{48}\mathrm{Ni}$ by comparing with Hartree-Fock-Bogoliubov calculations.

Hartree-Fock-Bogoliubov calculations for the $N=Z$ nucleus ${}^{80}\mathrm{Zr}$ give a ground state band with $T=1\mathrm{}$ Cooper pairs and an excited band with $T=0\mathrm{}$ Cooper pairs. The bands cross at spin $I\approx 5ħ,$ providing a “phase transition” from $T=1\mathrm{}$ pairs for $I<\mathrm{}5\mathrm{}ħ$ to $T=0\mathrm{}$ pairs for $I>\mathrm{}5\mathrm{}ħ.$ There is also a $T=0+T=1\mathrm{}$ pair band, which forms an envelope to the $T=1\mathrm{}$ pair band and the $T=0\mathrm{}$ pair band. In this band there is a more gradual transition from $T=1\mathrm{}$ pairs at $I=0\mathrm{}$ to $T=0\mathrm{}$ pairs at high spins, with $T=0\mathrm{}$ pairs and $T=1\mathrm{}$ pairs coexisting at intermediate spins. The Coriolis antipairing (CAP) effect breaks the $T=1\mathrm{}$ pairs, but there is no CAP effect for $T=0\mathrm{}$ pairs in which the n and p occupy identical space-spin orbitals. The $T=1\mathrm{}$ pair band has a moment of inertia $\mathcal{I}\left(\omega \right)$ which backbends at spins between $8ħ$ and $14ħ,$ but the $T=0\mathrm{}$ pair band does not backbend. Both bands have $g_{9/2}$ spin alignments. For the $T=0\mathrm{}$ pair band, the dominant angular momentum of a pair is $J=5,$ not $J=1\mathrm{}$ or ${J=J}_{\max }=9\mathrm{}$ as was anticipated. For a rotating $N=Z=\mathrm{even}$ nucleus, $T=0\mathrm{}$ pairing produces a twofold degeneracy in the canonical orbital occupation probability $v^2,$ although $T=1\mathrm{}$ pairing produces a fourfold degeneracy in $v^2.$

We have completed a new set of total cross section measurements of 31 elements and isotopes spanning the periodic table from A=1 to 238. We employed the same technique as in Finley et al. [Phys. Rev. C 47, 237 (1993)] with refinements intended to allow measurements on separated isotopes and improved systematic error control. The goal of the new measurement was 1% statistical accuracy in 1% energy bins with systematic errors less than 1%. This was achieved for all but the thinnest samples. Stringent checks of systematic errors in this measurement resulted in a reassignment of systematic uncertainties to the neutron total cross sections reported in Finley et al. Microscopic optical model calculations were carried out to interpret the results of the experiment. Two specific types of optical models were employed. The Jeukenne-Lejeune-Mahaux model was used in the range of 5–160 MeV, and a model based on the empirical effective interaction of Kelly was used from 135 to 650 MeV. These models are shown to be useful for predicting both neutron total cross sections and proton reaction cross sections. They are particularly important for light nuclei, for which standard global phenomenological parametrizations of the optical potential are insufficiently accurate.

We present a formalism of distorted wave impulse approximation for analyzing spin observables in nucleon inelastic and charge-exchange reactions leading to the continuum. It utilizes response functions calculated by the continuum random-phase approximation, which include the effective mass, the spreading widths, and the $\Delta$ degrees of freedom. The Fermi motion is treated by the optimal factorization, and the nonlocality of the nucleon-nucleon t matrix by an averaged reaction plane approximation. By using the formalism we calculated the spin-longitudinal and the spin-transverse cross sections, ${\mathrm{ID}}_q$ and ${\mathrm{ID}}_p,$ of ${}^{12}\mathrm{C},$ ${}^{40}\mathrm{Ca}$ $(\overrightarrow{p},\overrightarrow{n})$ at 494 and 346 MeV. The calculation reasonably reproduced the observed ${\mathrm{ID}}_q,$ which is consistent with the predicted enhancement of the spin-longitudinal response function $R_{\mathrm{L}}.$ However, the observed ${\mathrm{ID}}_p$ is much larger than the calculated one, which was consistent with neither the predicted quenching nor the spin-transverse response function $R_{\mathrm{T}}$ obtained by the ${(e,e}^{\prime })$ scattering. The Landau-Migdal parameter $g_{N\Delta }^{\prime }$ for the $N\Delta$ transition interaction and the effective nucleon mass at the nuclear center $m_N^{*}\mathrm{}(r=0\mathrm{})\mathrm{}$ are treated as adjustable parameters. The present analysis indicates that the smaller $g_{N\Delta }^{\prime }(\approx 0.3)$ and $m_N^{*}\mathrm{}\left(0\right)\mathrm{}\approx 0.7$ $m_N$ are preferable. We also investigate the validity of the plane-wave impulse approximation with the effective nucleon number approximation for the absorption, by means of which $R_{\mathrm{L}}$ and $R_{\mathrm{T}}$ have conventionally been extracted.

Evaporation residue (ER) cross sections for ${}^{82}\mathrm{Se}{+}^{\mathrm{nat}}\mathrm{Ce}{(Z}_1{Z}_2=1972)$ were measured in the vicinity of the Coulomb barrier and the fusion probability was obtained with the aid of calculated survival probability. This fusion probability was compared with that for ${}^{76}\mathrm{Ge}{+}^{150}\mathrm{Nd}{(Z}_1{Z}_2=1920),$ which was determined with the same manner by using the data published by us. The former system represents fusion of two spherical nuclei, the latter fusion involving the prolately deformed target ${}^{150}\mathrm{Nd}.$ The collision of ${}^{76}\mathrm{Ge}$ with the side of ${}^{150}\mathrm{Nd}$ is the most compact configuration at touching. The system ${}^{82}\mathrm{Se}{+}^{\mathrm{nat}}\mathrm{Ce}$ showed fusion hindrance in the form of extra-extra-push energy of $27\pm 5\mathrm{MeV},$ whereas the system ${}^{76}\mathrm{Ge}{+}^{150}\mathrm{Nd}$ does not show fusion hindrance at and above the Coulomb barrier energy, suggesting that the reaction starting from the compact touching point results in a higher fusion probability.

The low-energy ${}^6\mathrm{H}\mathrm{e}+p,$ ${}^6\mathrm{H}\mathrm{e}\left({p,n)}^6\mathrm{Li}{(1\mathrm{}}^{+}{,0\mathrm{}}^{+}\right),$ and ${}^6\mathrm{H}\mathrm{e}(p,\alpha )t$ reactions are studied in the framework of a microscopic multicluster model. The ${}^6\mathrm{He},$ ${}^6\mathrm{Li},$ and t wave functions are calculated variationally with microscopic three-cluster structures. The different thresholds are fairly well reproduced. The model provides the experimentally known states and resonances of ${}^7\mathrm{Li}$ up to $E_x=12\mathrm{}\hspace{0.5em}\mathrm{MeV}$ except the second ${7/2}^{-}$ state. A ${3/2}^{-};T=3/2\mathrm{}$ resonance is obtained which should correspond to the experimental ${3/2}^{-};3/2\mathrm{}$ resonance at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=1.27\mathrm{}\hspace{0.5em}\mathrm{}\mathrm{MeV}.$ This resonance might have a halo structure. The ${}^6\mathrm{H}\mathrm{e}({p,n)}^6\mathrm{Li}{(0\mathrm{}}^{+};$ 3.56 MeV) cross section should be strongly affected by this resonance. Cross sections are also calculated for the ${}^6\mathrm{H}\mathrm{e}+p$ elastic scattering and for the ${}^6\mathrm{H}\mathrm{e}(p,\alpha )t$ transfer reaction. The ${}^6\mathrm{H}\mathrm{e}+n$ elastic phase shifts are determined with a similar model and provide the isobaric analog ${3/2}^{-}$ ground state of ${}^7\mathrm{He}$ and a ${1/2}^{-}$ excited state.

We use Dirac’s constraint dynamics to obtain a Hamiltonian formulation of the relativistic N-body problem in a separable two-body basis in which the particles interact pairwise through scalar and vector interactions. The resultant N-body Hamiltonian is relativistically covariant. It can be easily separated in terms of the center of mass and the relative motion of any two-body subsystem. It can also be separated into an unperturbed Hamiltonian with a residual interaction. In a system of two-body composite particles, the solutions of the unperturbed Hamiltonian are relativistic two-body internal states, each of which can be obtained by solving a relativistic Schrödinger-like equation. The resultant two-body wave functions can be used as basis states to evaluate reaction matrix elements in the general N-body problem. We prove a relativistic version of the post-prior equivalence which guarantees a unique evaluation of the reaction matrix element, independent of the ways of separating the Hamiltonian into unperturbed and residual interactions. Since an arbitrary reaction matrix element involves composite particles in motion, we show explicitly how such matrix elements can be evaluated in terms of the wave functions of the composite particles and the relevant Lorentz transformations.

We apply recently developed effective field theory nuclear models in mean field approximation (parameter sets G1 and G2) to describe ground-state properties of nuclei from the valley of $\beta$ stability up to the drip lines. For faster calculations of open-shell nuclei we employ a modified BCS approach which takes into account quasibound levels owing to their centrifugal barrier, with a constant pairing strength. We test this simple prescription by comparing with available Hartree-plus-Bogoliubov results. Using the new effective parameter sets we then compute separation energies, density distributions, and spin-orbit potentials in isotopic (isotonic) chains of nuclei with magic neutron (proton) numbers. The new forces describe the experimental systematics similarly to conventional nonlinear $\sigma -\omega$ relativistic force parameters like NL3.