We give a systematic microscopic description of the $\alpha$ decay to excited states in spherical nuclei. Low-lying collective excitations are considered within the quasiparticle random phase approximation. As a residual force we use the surface delta interaction. It turns out that this simple approach is able to reproduce the available experimental hindrance factors for transitions to $2^{+}$ states in Po isotopes. We predict a linear dependence between the logarithm of the hindrance factor and the excitation energy of the $2^{+}$ state.

A normal mode analysis of rotating equilibrium densities is made in the su(3) mean field approximation. The su(3) self-consistent mean field solutions are stable equilibria for rotations of a triaxial body about a short or long principal axis and unstable equilibria for rotations about the middle axis. The wobbling frequencies are determined for the short and long axis cases. Bands of stable equilibrium solutions are found for tilted rotation in a principal plane. The normal modes for tilted rotors are oscillations of the axis lengths together with wobbling off the principal plane. The frequencies for these normal modes are determined.

The exclusive ${}^{16}\mathrm{O}(\gamma {,pn)}^{14}{\mathrm{N}}_{0,1,2,\dots }$ reaction was measured for the photon energy range $E_{\gamma }=98.5\mathrm{}$ to 141.0 MeV with an excitation energy resolution of 2.8 MeV. Protons were detected at $76°$ and $82°$ and coincident neutrons were detected at the opening angle for quasifree deuteron photodisintegration. Only the $T=0,$ $1^{+},$ 3.95 MeV state in the residual ${}^{14}\mathrm{N}$ nucleus was significantly populated. This corresponds to a preferred $L=0\mathrm{}$ angular momentum transfer to the recoil nucleus as is expected for quasifree kinematics. The absence of significant population to other discrete states is evidence that absorption on correlated proton-neutron pairs with an angular momentum transfer of $L>~2$ is largely suppressed for the low recoil momentum range of the current measurement. As a consequence of this fact, and the absence of unnatural parity states, only absorption on proton-neutron pairs in relative motion $l=0,2\mathrm{}$ is expected for all possible shell model couplings. No significant population of the $T=1\mathrm{}$ state at 2.31 MeV is consistent with previous measurements, demonstrating that absorption on proton-neutron pairs in an isospin triplet is suppressed. The results of the measurement to discrete states in the residual ${}^{14}\mathrm{N}$ nucleus are compared to microscopic calculations which include contributions above that of the mean field due to the short range and tensor parts of the nuclear potential. Clear separation in the contribution of ${\mathrm{}\left(1p\right)\mathrm{}}^{-2}$ and ${\mathrm{}\left(1p\right)\mathrm{}}^{-1}{\mathrm{}\left(1s\right)\mathrm{}}^{-1}$ proton-neutron pairs is seen to occur at an excitation energy of $20\pm 2\hspace{0.5em}\mathrm{MeV}.$ Significant population of the ${\mathrm{}\left(1p\right)\mathrm{}}^{-1}{\mathrm{}\left(1s\right)\mathrm{}}^{-1}$ continuum above 20 MeV indicates that absorption on $L=1\mathrm{}$ nucleon pairs is also important near quasifree kinematics.

Microscopic optical potentials for nucleon-nucleus $\mathrm{}\left(\mathrm{NA}\right)\mathrm{}$ scattering obtained from the folding of the effective g matrices, solutions of the Bruckner-Bethe-Goldstone equation, with the densities of the target, are applied to the case of neutron-nucleus scattering. Given that the optical potentials are specified in all two-body angular momentum, spin and isospin channels available to the $\mathrm{NA}$ scattering, the only difference in this model description of proton and neutron scattering observables for a given nucleus is in the inclusion of the Coulomb interaction. A priori microscopic optical model predictions for neutron and proton elastic scattering are compared with results from a phenomenological optical model and with data. New measurements are recommended to reduce discrepancies in the existing database, and to differentiate between different theoretical predictions.

The transverse momenta of hadrons in central nucleus-nucleus collisions are evaluated in a boost invariant hydrodynamics with transverse expansion. Quark gluon plasma is assumed to be formed in the initial state which expands and cools via a first-order phase transition to a rich hadronic matter and ultimately undergoes a freeze-out. The average transverse momentum of pions, kaons, and protons is estimated for a wide range of multiplicity densities and transverse sizes of the system. For a given system it is found to scale with the square root of the particle rapidity density per unit transverse area, and consistent with the corresponding values seen in $p\overline{p}$ experiments at 1800 GeV, suggesting a universal behavior. The average transverse momentum shows only an approximate scaling with multiplicity density per nucleon which is at variance with the $p\overline{p}$ data.

We numerically determine the full complex Lyapunov spectrum of SU(2) Yang-Mills fields on a three-dimensional lattice from classical chaotic dynamics using eigenvalues of the monodromy matrix. The microcanonical equation of state is determined as the entropy-energy relation utilizing the Kolmogorov-Sinai entropy extrapolated to the large size limit.

In a recent publication Ernst et al. [Phys. Rev. C 62, 024305 (2000)] suggest a shell structure description of Ti and Cr nuclei from systematic g factor and lifetime measurements of the $2^{+}$ and $4^{+}$ states of these nuclei, pointing out a disagreement between previous measurements and shell model calculations. We show that the systematics of previous and present g-factor measurements are not in significant disagreement, and they do not exclude the possibility of an onset of collectivity in the middle of the $\mathrm{fp}$ shell. The theoretical interpretation of the data is still an open question. A conflict between the ${}^{50}\mathrm{Cr}\hspace{0.5em}{g(4\mathrm{}}_1^{+})$ measurements may be attributed to statistical fluctuations, as large errors are assigned to both existing measurements, but not to the fusion excitation technique adopted in one of the measurements. It is suggested that the moments of the higher spin states must be determined with better precision to shed more light on the situation.

We investigate the scenario of homogeneous nucleation for a first order quark-hadron phase transition in a rapidly expanding background of quark gluon plasma. Using an improved preexponential factor for homogeneous nucleation rate, we solve a set of coupled equations to study the hadronization and the hydrodynamical evolution of the matter. It is found that significant supercooling is possible before hadronization begins. This study also suggests that spinodal decomposition competes with nucleation and may provide an alternative mechanism for phase conversion particularly if the transition is strong enough and the medium is nonviscous. For weak enough transition, the phase conversion may still proceed via homogeneous nucleation.

Polarized beam $\overrightarrow{\gamma }p$ Compton scattering provides a theoretically clean way to extract the isovector parity violating pion-nucleon coupling constant $h_{\pi \mathrm{NN}}^{\mathrm{}\left(1\right)\mathrm{}}$. This channel is more tractable experimentally than the recently proposed extraction of $h_{\pi \mathrm{NN}}^{\mathrm{}\left(1\right)\mathrm{}}$ from the Bedaque-Savage process—polarized target $\gamma \overrightarrow{p}$ Compton scattering. The leading parity violating effect is calculated using heavy baryon chiral perturbation theory. The size of the asymmetry is estimated to be $\sim 4\times {10}^{-8}$ for 120 MeV photon energy.

We study the vector-meson density matrix and the associated polarization asymmetries in $\phi$ photoproduction near threshold. In order to study the Okubo-Zweig-Iizuka (OZI) violating processes, we consider the direct $\phi \mathrm{NN}$ coupling as well as the knockout processes arising from the nonvanishing $s\overline{s}$ sea quarks in the nucleon. The polarization asymmetries in $\phi$ meson decays are found to be very useful to constrain the $\phi \mathrm{NN}$ coupling constant. The hidden strangeness of the nucleon can also be studied by these asymmetries, but mostly at large $|t|$ region.

Coherent states are introduced as test functions to formulate the statistical mechanics of fermions and bosons interacting via schematic forces. Finite temperature solutions to the Lipkin model and to the Schütte–Da Providencia model are obtained by performing the statistical sum $à\mathrm{la}$ Hecht, e.g., by using coherent states. Comparison between present and exacts results is discussed.

Prompt $\gamma$ rays from the neutron-induced fission of ${}^{235}\mathrm{U}$ have been studied using the GEANIE spectrometer situated at the LANSCE/WNR “white” neutron facility. Transitions characteristic of specific fission fragments were identified using a combination of single-fold and coincidence $\gamma$-ray analysis. Gamma-ray production cross sections were obtained as a function of incident neutron energy using the time-of-flight technique. Yields were extracted for 206 $\gamma$ rays produced by 56 distinct fission fragments for $1<~E_n\left(\mathrm{MeV}\right)<~250.$ Fission-channel cross sections were deduced for a subset of 22 even-even fragments, where the measured $\gamma$-ray yields represent a large fraction of the full de-excitation strength of the fragment. Independent yields were deduced from these cross sections and fitted with standard formulations of the fragment charge and mass distributions. The results were used to study the transition from asymmetric to symmetric fission as a function of internal excitation energy of the fissioning system. This transition is interpreted in the context of the disappearance of shell structure at high excitation energies.

Neutron-induced reactions on ${}^{196}\mathrm{Pt}$ were studied over the neutron energy range from 1 to 250 MeV. A “white” neutron beam was provided by the spallation neutron source of the Weapons Neutron Research facility at the Los Alamos Neutron Science Center. The prompt reaction $\gamma$ rays were measured with the large-scale Compton-suppressed Ge spectrometer GEANIE. The incident neutron energy was determined by the time-of-flight technique. Excitation functions for $\gamma$-ray transitions in ${}^{184,186,188,190-196}\mathrm{Pt}$ and ${}^{189,191,193}\mathrm{Ir}$ isotopes are compared with enhanced Hauser-Feshbach reaction modeling, as implemented in the reaction code GNASH. Overall, the model predictions agree well with the measured $\gamma$-ray yields. Discrepancies appear, however, due to inadequate discrete-level information in the calculations describing the preequilibrium process.

Different statistical multifragmentation models have been used to study isoscaling, i.e., the factorization of the isotope ratios from two reactions, into fugacity terms of proton and neutron number, $R_{21}{\mathrm{}(N,Z)=Y}_2{\mathrm{}(N,Z)/Y}_1\mathrm{}(N,Z)=C\exp (\alpha N+\beta Z).\mathrm{}$ Even though the primary isotope distributions are quite different from the final distributions due to evaporation from the excited fragments, the values of $\alpha$ and $\beta$ are not much affected by sequential decays. $\alpha$ is shown to be mainly sensitive to the proton-to-neutron composition of the emitting source and may be used to study isospin-dependent properties in nuclear collisions, such as, the symmetry energy in the equation of state of asymmetric nuclear matter.

The event-by-event $p_{\perp }$ fluctuations due to the temperature variations are considered. The so-called $\Phi$ measure is computed and shown to be a linear function of temperature variance. The fluctuations of temperature naturally explain the data on $\Phi {(p}_{\perp })$ in proton-proton and central Pb-Pb collisions, but independent measurements of temperature fluctuations are needed to confirm the explanation. Feasibility of such an event-by-event measurement is discussed.

We calculate prompt photon production in high-energy nuclear collisions. We focus on the broadening of the intrinsic transverse momenta of the partons in the initial state from nuclear effects, and their influence on the prompt photon $p_t$ distribution. Comparing to WA98 data from Pb-Pb collisions at $\sqrt{s}=17.4A\mathrm{GeV}$ we find evidence for the presence of nuclear broadening at high $p_t$ in this hard process. Below $p_t\sim 2.7$ GeV the photon distribution is due to small momentum transfer processes. At RHIC energy, $\sqrt{s}=200A\mathrm{GeV},$ the effect of intrinsic transverse momentum on the spectrum of prompt photons is less prominent. The region $p_t=3\mathrm{}–4$ GeV would be the most promising for studying the nuclear broadening effects at that energy. Below $p_t=2\mathrm{}-3$ GeV the contribution from large momentum transfer flattens out, and we expect that region to be dominated by soft contributions.

The formation of $K^{-}$ and $K^0$ condensation in $\beta$-equilibrated hyperonic matter is investigated within a relativistic mean field model. In this model, baryon-baryon and (anti)kaon-baryon interactions are mediated by the exchange of mesons. It is found that antikaon condensation is not only sensitive to the equation of state but also to the antikaon optical potential depth. For large values of the antikaon optical potential depth, $K^{-}$ condensation sets in before the appearance of negatively charged hyperons. We treat $K^{-}$ condensation as a first-order phase transition. The Gibbs criteria and global charge conservation laws are used to describe the mixed phase. Nucleons and $\Lambda$ hyperons behave dynamically in the mixed phase. A second-order phase transition to $K^0$ condensation occurs in the pure $K^{-}$ condensed phase. Along with $K^{-}$ condensation, $K^0$ condensation makes the equation of state softer, thus resulting in smaller maximum mass stars compared with the case without any condensate. This equation of state also leads to a stable sequence of compact stars called the third family branch, beyond the neutron star branch. The compact stars in the third family branch have different compositions and smaller radii than that of the neutron star branch.

We studied the exclusive reaction $e\overrightarrow{p}{e}^{\prime }{p}^{\prime }\phi$ using the $\overrightarrow{\phi }{K}^{+}{K}^{-}$ decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in $Q^2$ from 0.7 to 2.2 ${\mathrm{GeV}}^2,$ and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of $\phi$ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time $c\Delta \tau$ below 2 fm. At $〈c\Delta \tau 〉=0.6\mathrm{}$ fm, we measure $b_{\phi }=2.27\mathrm{}\pm 0.42$ ${\mathrm{GeV}}^{-2}.$ The cross section dependence on W as $W^{0.2\pm 0.1}$ at $Q^2=1.3\mathrm{}$ ${\mathrm{GeV}}^2$ was determined by comparison with $\phi$ production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction.

The time-dependent mesh method is applied to the calculation of the Coulomb breakup of a projectile into two charged fragments. The projectile is described in the potential model and its center of mass is assumed to follow a classical trajectory. The approach is compared with the first-order time-dependent perturbation approximation based on an electric dipole interaction under the same model assumptions. The numerical technique is applied to the ${}^{17}\mathrm{F}{+}^{208}{\overrightarrow{\mathrm{Pb}}}^{16}\mathrm{O}{+p+}^{208}\mathrm{Pb}$ breakup in order to test the validity of the extraction of the $E1\mathrm{}$ astrophysical S factor for the ${}^{16}\mathrm{O}(p,\gamma {)}^{17}\mathrm{F}$ radiative capture reaction to the ${}^{17}\mathrm{F}$ ground state. After carefully testing the validity of the numerical technique, we show that the accuracy of the astrophysical S factor extracted in such a way is better than $5\%$ for projectile velocities above about $0.25c$ in large domains of impact parameters and relative energies between the fragments. Breakup cross sections are also calculated as a function of the relative energy between the fragments at different projectile velocities. A test calculation is performed for the breakup of the weakly bound ${1/2}^{+}$ excited state of ${}^{17}\mathrm{F}.$ A comparison is presented and discussed with the only existing experimental differential cross section at the projectile energy of 10 MeV/nucleon.

We update our chemical analysis of (strange) hadrons produced at the SPS in Pb-Pb collisions at 158A GeV and discuss chemical analysis of RHIC results. We report that the shape of (anti)hyperon $m_{\perp }$ spectra in a thermal freeze-out analysis leads to freeze-out conditions found in chemical analysis, implying sudden strange-hyperon production. We discuss how a combined analysis of several strange-hadron resonances of differing lifespan can be used to understand the dynamical process present during chemical and thermal freeze-outs. In medium resonance quenching is considered.