The effect nucleon dressing by scattering on the pairing gap in nuclear matter is discussed. Numerical results from self-consistent T-matrix calculations are compared to quasiparticle approximations. The dominant effect of scattering can be accounted for by a renormalization of the quasiparticle strength. The exponential sensitivity of the pairing gap and the critical temperature on the pairing strength makes it strongly dependent on many-body effects.

New solutions of 3+1D covariant kinetic theory are presented for nuclear collisions in the energy domain $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\sim 200A$ GeV. They are obtained using MPC, a new Monte Carlo parton transport technique that employs very high parton subdivision that is necessary to preserve covariance. The transport results are compared with ideal hydrodynamics solutions. We show that the transport evolution differs significantly from hydrodynamics. In addition, we compare the transport freeze-out distributions to those obtained from ideal hydrodynamics with the Cooper-Frye isotherm freeze-out prescription. The transport freeze-out four-volume is shown to be sensitive to the reaction rates and deviates from both timelike and spacelike freeze-out 3D hypersurfaces commonly assumed. In particular, we find that there does not exist a universal freeze-out temperature. Finally, the transverse momentum distributions are found to deviate by up to an order of magnitude from (Cooper-Frye frozen) hydrodynamics for a wide range of possible initial conditions and reaction rates at RHIC energies.

Knowledge of the ${}^{17}\mathrm{F}(p,\gamma {)}^{18}\mathrm{Ne}$ reaction rate is important for understanding stellar explosions, but it was uncertain because the properties of an expected but previously unobserved $3^{+}$ state in ${}^{18}\mathrm{Ne}$ were not known. This state would provide a strong s-wave resonance for the ${}^{17}\mathrm{F}+p$ system and, depending on its excitation energy, could dominate the stellar reaction rate at temperatures above 0.2 GK. We have observed this missing $3^{+}$ state by measuring the ${}^1\mathrm{H}{(}^{17}\mathrm{F}{,p)}^{17}\mathrm{F}$ excitation function with a radioactive ${}^{17}\mathrm{F}$ beam at the ORNL Holifield Radioactive Ion Beam Facility (HRIBF). We find that the state lies at a center-of-mass energy of $E_r=599.8\mathrm{}\pm {1.5}_{\mathrm{stat}}\pm {2.0}_{\mathrm{sys}}$ keV ${(E}_x=4523.7\mathrm{}\pm 2.9\mathrm{keV})$ and has a width of $\Gamma =18\mathrm{}\pm 2_{\mathrm{stat}}\pm 1_{\mathrm{sys}}\mathrm{keV}.$ The measured properties of the resonance are only consistent with a $J^{\pi }{=3\mathrm{}}^{+}$ assignment.

In a recent Rapid Communication [Phys. Rev. C 62, 011301(R) (2000)], Chou, Zamfir, and Casten have pointed out that different interacting boson approximation-2 (IBA-2) Hamiltonians produce similar results provided two specific combinations of Hamiltonian parameters are kept fixed. It is shown here that this is a consequence of the near F-spin purity of low-lying states for their Hamiltonians and that the number of invariants required could be as large as six for the most general IBA-2 Hamiltonian.

Gamma decays from excited states in the $T_z=-\frac{1}{2}$ nucleus ${}^{51}$Fe have been observed for the first time. The differences in excitation energies as compared with those of the mirror partner, ${}^{51}$Mn, have been interpreted in terms of Coulomb effects and the resulting Coulomb energy differences (CED) can be understood intuitively in terms of particle-alignment effects. A new CED effect has been observed, in which different CED trends have been measured for each signature of the rotational structures that characterize these mid-$f_{7/2}$ shell nuclei. Large-scale $\mathrm{fp}$-shell model calculations have been used to compute the trends of the CED as a function of spin. The result of comparing these calculations with the data demonstrates an ability to reproduce the fine details of the Coulomb effects with a precision far greater than has been previously achieved.

Intermediate-energy Coulomb excitation has been used to study excited states in the radioactive $N=19\mathrm{}$ nuclei ${}^{33}\mathrm{Si}$ and ${}^{34}\mathrm{P},$ which are neutron-rich spherical nuclei located along the boundary of the “island of inversion.” The present results for the 1010 keV state in ${}^{33}\mathrm{Si}$ and states up to 2.2 MeV excitation energy in ${}^{34}\mathrm{P}$ can be understood in terms of $0ħ\omega$ (nonintruder) configurations. This suggests that the energy differences between $0ħ\omega$ and $2ħ\omega$ configurations are large enough in ${}^{33}\mathrm{Si}$ and ${}^{34}\mathrm{P}$ that the low-lying $0ħ\omega$ states are not significantly perturbed.

The newly developed nonadiabatic method based on the coupled-channel Schrödinger equation with Gamow states is used to study the phenomenon of proton radioactivity. The new method, adopting the weak coupling regime of the particle-plus-rotor model, allows for the inclusion of excitations in the daughter nucleus. This can lead to rather different predictions for lifetimes and branching ratios as compared to the standard adiabatic approximation corresponding to the strong coupling scheme. Calculations are performed for several experimentally seen, nonspherical nuclei beyond the proton dripline. By comparing theory and experiment, we are able to characterize the angular momentum content of the observed narrow resonance.

We report on precision measurements of the cross sections for the reactions $\overline{p}\overrightarrow{p}\overline{\Lambda }\Lambda ,$ $\overline{p}\overrightarrow{p}\overline{\Lambda }{\Sigma }^0,$ and $\overline{p}\overrightarrow{p}{\overline{\Sigma }}^0\Lambda$ in the region below 5 MeV excess kinetic energy above reaction threshold. For the $\overline{p}\overrightarrow{p}\overline{\Lambda }\Lambda$ measurement, the data represent a third and definitive scan through the threshold region by this experiment. Improvements in the detector system and analysis techniques, coupled with greatly increased statistics, have negated the question of the existence of a near-threshold resonance as had been indicated in our earlier, lower-statistics studies. The high statistics permit the first extraction of the polarization information at these low energies. We also report the first measurement of the cross section for the complementary reactions $\overline{p}\overrightarrow{p}\overline{\Lambda }{\Sigma }^0+\mathrm{c}.\mathrm{c}.\mathrm{}$ at excess energies up to 2.5 MeV. This allows a comparison of the onset of $\overline{\Lambda }\Lambda$ production to that of $\overline{\Lambda }{\Sigma }^0$ and ${\overline{\Sigma }}^0\Lambda .$ The data show no evidence for near-threshold resonance structures in either reaction channel. Further, the $\overline{p}\overrightarrow{p}\overline{\Lambda }{\Sigma }^0+\mathrm{c}.\mathrm{c}.\mathrm{}$ reactions exhibit a larger P-wave fraction close to threshold compared to $\overline{p}\overrightarrow{p}\overline{\Lambda }\Lambda .$

$\mathrm{pd}$ capture processes at various energies have been analyzed based on solutions of three-nucleon (3N)-Faddeev equations and using modern $\mathrm{NN}$ forces. The application of the Siegert theorem is compared to the explicit use of $\pi$- and $\rho$-like exchange currents connected to the AV18 $\mathrm{NN}$ interaction. Overall good agreement with cross sections and spin observables has been obtained but leaving room for improvement in some cases. Feasibility studies for three-nucleon forces (3NF’s) consistently included in the 3N continuum and the 3N bound state have been performed as well.

We investigate chemical and thermal freeze-out time dependencies of strange baryon production for CERN SPS heavy ion collisions in the framework of a dynamical hadronic transport code. We show that the $\Lambda$ yield changes considerably after hadronization in the case of Pb+Pb collisions, whereas for smaller system sizes (e.g., S+S) the direct particle production dominates over production from inelastic rescattering. Chemical freeze-out times for strange baryons in Pb+Pb are smaller than for nonstrange baryons, but they are still sufficiently long for hadronic rescattering to contribute significantly to the final $\Lambda$ yield.

High-spin states of the nucleus ${}^{88}\mathrm{Sr}$ have been studied via the reaction ${}^{80}\mathrm{Se}{(}^{11}\mathrm{B},p2n)$ at a beam energy of 45 MeV. Gamma rays were detected with the six-detector array OSIRIS CUBE. The level scheme of ${}^{88}\mathrm{Sr}$ has been extended up to $E\approx 11\hspace{0.5em}\mathrm{MeV}$ and $J=17.\mathrm{}$ Mean lifetimes of three levels have been determined using the Doppler-shift-attenuation method. The level structures in ${}^{88}\mathrm{Sr}$ have been interpreted in terms of the shell model. The calculations were performed in the configuration space ${(0f}_{5/2}{,1p}_{3/2}{,1p}_{1/2}{,0g}_{9/2})$ for the protons and ${(1p}_{1/2}{,0g}_{9/2}{,1d}_{5/2})$ for the neutrons. These calculations describe the high-spin level sequences linked by $M1\mathrm{}$ transitions with strengths of $B\left(M1\mathrm{}\right)\mathrm{}\approx 0.3$ to 1.4 W.u. as multiplets of seniority $\upsilon =4\mathrm{}$ and 6 states including proton configurations and neutron-core excitations.

Fusion cross sections and barrier distributions are discussed and calculated in the framework of a semiclassical approximation for a variety of systems. An overall good description of the data is achieved.

Using general baryon interpolating fields $J_B$ for $B=N,\Xi ,\Sigma ,$ without derivative, we study QCD sum rules for meson-baryon couplings and their dependence on Dirac structures for the two-point correlation function with a meson $i\int d^4{\mathrm{xe}}^{\mathrm{iqx}}〈0|\mathrm{T}\left[J_B\mathrm{}\right(x\left)\mathrm{}{J}_B\mathrm{}\right(0\left)\mathrm{}\right]|\mathcal{M}\mathrm{}\left(p\right)\mathrm{}〉.$ Three distinct Dirac structures are compared: $i{\gamma }_5,$ $i{\gamma }_{5}p/,$ and ${\gamma }_5{\sigma }_{\mu \nu }{q}^{\mu }{p}^{\nu }$ structures. From the dependence of the OPE on general baryon interpolating fields, we propose criteria for choosing an appropriate Dirac structure for the coupling sum rules. The ${\gamma }_5{\sigma }_{\mu \nu }{q}^{\mu }{p}^{\nu }$ sum rules satisfy the criteria while the $i{\gamma }_5$ sum rules beyond the chiral limit do not. For the $i{\gamma }_{5}p/$ sum rules, the large continuum contributions prohibit reliable prediction for the couplings. Thus, the ${\gamma }_5{\sigma }_{\mu \nu }{q}^{\mu }{p}^{\nu }$ structure seems pertinent for realistic predictions. In the SU(3) limit, we identify the OPE terms responsible for the $F/D$ ratio. We then study the dependence of the ratio on the baryon interpolating fields. We decide on the ratio $F/D\sim 0.6$–0.8 for appropriate choice of the interpolating fields.

We have made new and improved measurements of the neutron capture and total cross sections for ${}^{88}\mathrm{Sr}$ at the Oak Ridge Electron Linear Accelerator (ORELA). Improvements over previous measurements include a wider incident neutron energy range, better resolution, the use of metallic rather than carbonate samples, better background subtraction, reduced sensitivity to sample-dependent backgrounds, and better pulse-height weighting functions. Because of its small cross section, the ${}^{88}\mathrm{Sr}(n,\gamma )$ reaction is an important bottleneck during s-process nucleosynthesis. Hence, an accurate determination of this rate is needed to better constrain the neutron exposure in s-process models and to better understand the recently discovered isotopic anomalies in certain meteorites. We performed an $\mathcal{R}$-matrix analysis of our capture and transmission data to extract parameters for 101 resonances between 100 eV and 350 keV. In addition, we fitted our transmission data alone to extract parameters for 342 additional resonances between 350 and 950 keV. We used this information to calculate average properties of the ${}^{88}\mathrm{Sr}+n$ system for comparison to previous work. Although previous data and resonance analyses were much less extensive, they are, in general, in good agreement with our results except that the average radiation widths as well as the p-wave correlation coefficients we determined are significantly smaller, and the s-wave correlation coefficient we determined has opposite sign from that reported in previous work. We used these resonance parameters together with a calculation of the small, but significant direct-capture contribution to determine the astrophysical reaction rate for the ${}^{88}\mathrm{Sr}(n,\gamma )$ reaction to approximately 3% accuracy across the entire range of temperatures needed by s-process models. Our new rate is in good agreement with the results from a high-precision activation measurement at kT=25 keV, but it is approximately 9.5% lower than the rate used in most previous nucleosynthesis calculations in the temperature range (kT=6–8 keV), where most of the neutron exposure occurs in current stellar models of the s process. We discuss the possible astrophysical impact of this new, lower rate.

The subtle interplay between the two nuclear superfluids, isovector $T=1,$ and isoscalar $T=0\mathrm{}$ phases are investigated in an exactly soluble model. It is shown that $T=1\mathrm{}$ and $T=0\mathrm{}$ pair modes decouple in the exact calculations with the $T=1\mathrm{}$ pair energy being independent of the $T=0\mathrm{}$ pair strength and vice versa. In the rotating field, the isoscalar correlations remain constant in contrast to the well-known quenching of isovector pairing. An increase of the isoscalar $\mathrm{}(J=1,T=0\mathrm{})\mathrm{}$ pair field results in a delay of the band crossing frequency. This behavior is shown to be present only near the $N=Z$ line and its experimental confirmation would imply a strong signature for isoscalar pairing collectivity. The solutions of the exact model are also discussed in the Hartree-Fock-Bogoliubov approximation.

Gamma-ray cascades from nanosecond isomers in neutron-rich nuclei ${}^{67}\mathrm{Cu}$ and ${}^{64}\mathrm{Co}$ have been observed through heavy-ion deep-inelastic collisions of ${}^{198}\mathrm{Pt}{+}^{76}\mathrm{Ge}$ (8 MeV/nucleon) using an isomer-scope. In ${}^{67}\mathrm{Cu},$ an isomeric state at 3464 keV and its decay scheme have been established. The isomeric transition is a hindered $M1\mathrm{}$ transition between the ${15/2}^{+}$ and the ${13/2}^{+}$ states with main components of $(\pi p_{3/2}\nu g_{9/2}\nu f_{5/2}^{-1}{)}_{{15/2}^{+}}$ and $(\pi p_{3/2}\nu g_{9/2}\nu p_{1/2}{)}_{{13/2}^{+}},$ respectively. A fast $E3\mathrm{}$ transition between the $\pi g_{9/2}$ and the $\pi p_{3/2}$ single-particle states indicates strong particle-octupole vibration coupling in ${}^{67}\mathrm{Cu}.$ An isomeric state at 834 keV with $T_{1/2}=6.4\mathrm{}\left(3\right)\mathrm{}\mathrm{ns}$ has been identified in ${}^{64}\mathrm{Co}.$ Proton-neutron configurations of the levels established in ${}^{64}\mathrm{Co}$ are discussed.

Using a multiphase transport model, we study the relative importance of $J/\psi$ suppression mechanisms due to plasma screening, gluon scattering, and hadron absorption in heavy ion collisions at the Relativistic Heavy Ion Collider. We find that for collisions between heavy nuclei such as Au+Au, both plasma screening and gluon scattering are important. As a result, the effect due to absorption by hadrons becomes relatively minor. The final $J/\psi$ survival probability in these collisions is only a few percent. In the case of collisions between light nuclei such as S+S, the effect of plasma screening is, however, negligible in spite of the initial high parton density. The final $J/\psi$ survival probability thus remains appreciable after comparable absorption effects due to gluons and hadrons.

A parameter-free investigation of the moments of inertia of ground-state rotational bands in well-deformed rare-earth nuclei is carried out using cranked relativistic Hartree-Bogoliubov (CRHB) and nonrelativistic cranked Hartree-Fock-Bogoliubov (CHFB) theories. In CRHB theory, the relativistic fields are determined by the nonlinear Lagrangian with the NL1 force and the pairing interaction by the central part of a finite-range Gogny D1S force. In CHFB theory, the properties in particle-hole and particle-particle channels are defined solely by Gogny D1S forces. Using an approximate particle number projection before variation by means of the Lipkin-Nogami method improves the agreement with the experimental data, especially in CRHB theory. The effect of the particle number projection on the moments of inertia and pairing energies is larger in relativistic than in nonrelativistic theory.

The conditions for the pseudospin symmetry hidden in the Dirac equation are found for the case of the deformed potential both from the large and small components of the Dirac wave function. The numerical analysis based on the relativistic mean-field theory is carried out for ${}^{154}\mathrm{Sm}.$ It is confirmed that the conditions found from the large components of the Dirac wave function are satisfied better than those from its small components. As long as these conditions are satisfied, the pseudospin symmetry appears in the amplitudes with the unnatural $l_z$ $(z$ component of orbital angular momentum) in both large and small components.

Properties like the excitation energy with respect to the ground state, moments of inertia, $B\left(E2\mathrm{}\right)\mathrm{}$ transition probabilities, and stability against quadrupole fluctuations at low spin of the predicted superdeformed band of ${}^{32}\mathrm{S}$ are studied with the Gogny force D1S using the angular momentum projected generator coordinate method for the axially symmetric quadrupole moment. The self-consistent cranking method is also used to describe the superdeformed rotational band. In addition, properties of some collective normal deformed states are discussed.