The experimental results on hadron production obtained recently at RHIC offer a new prospective on the energy dependence of the nuclear collision dynamics. In particular, it is possible that parton saturation—the phenomenon likely providing initial conditions for the multiparticle production at RHIC energies—may have started to set in central heavy ion collisions already around the highest CERN SPS energy. We examine this scenario, and make predictions based on high density QCD for the forthcoming $\sqrt{s}=22$ GeV run at RHIC.

Excited low-spin states of ${}^{92}\mathrm{Zr}$ have been studied with the $(n,n^{\text{'}}\gamma )$ reaction. Comprehensive data on the electromagnetic decay of states with excitation energies up to about 3.8 MeV in particular, lifetimes, γ-ray branching ratios, multipole mixing ratios, and absolute transition strengths have been obtained. The detailed spectroscopic information about the low-spin level scheme enables us to address the predominant proton-neutron symmetry for low-spin states of ${}^{92}\mathrm{Zr}$. These data are compared to those of corresponding states in the $N=52$ isotone ${}^{94}\mathrm{Mo}$ and to a shell model calculation using ${}^{88}\mathrm{Sr}$ as an inert core. However, neither a purely collective picture nor the restricted shell model calculation yields a fully satisfactory description of the observed structures.

We study medium modifications of $J/\psi$ production in cold nuclear media in deuterium-nucleus collisions. We discuss several parametrizations of the modifications of the parton densities in the nucleus, known as shadowing, an initial-state effect. We also include absorption of the produced $J/\psi$ by nucleons, a final-state effect. Both spatially homogeneous and inhomogeneous shadowing and absorption are considered. We use the number of binary nucleon-nucleon collisions as a centrality measure. Results are presented for d+Au collisions at $\sqrt{S_{NN}}=200\hspace{1em}\mathrm{GeV}$ and for d+Pb collisions at $\sqrt{S_{NN}}=6.2\hspace{1em}\mathrm{TeV}$. To contrast the centrality dependence in pA and $dA$ collisions, we also present p+Pb results at $\sqrt{S_{NN}}=8.8\hspace{1em}\mathrm{TeV}$.

Values calculated by Fortune and Sherr [Phys. Rev. C 68, 034309 (2003)] for the width of the ${}^{12}\mathrm{O}$ ground state because of either sequential decay through ${}^{11}\mathrm{N}$(g.s.) or ${}^2\mathrm{He}$ decay are appreciably larger than earlier estimates. This may be at least in part because of incorrect normalization of their convolution functions.

We analyze how the spatial localization properties of pairing correlations are changing in a major neutron shell of heavy nuclei. It is shown that the radial distribution of the pairing density depends strongly on whether the chemical potential is close to a low or a high angular momentum level and has little sensitivity to whether the pairing force acts at the surface or in the bulk. The pairing density averaged over one major shell is, however, rather flat, exhibiting little dependence on the pairing force. Hartree-Fock-Bogoliubov calculations for the isotopic chain ${}^{100-132}\mathrm{Sn}$ are presented for demonstration purposes.

A semianalytic connection between matter and charge radii for Borromean halo nuclei is derived. It is based on the three-body core $+N+N$ cluster structure of those halo nuclei and knowledge of corresponding radii for the constituents. The charge form factor of ${}^6\mathrm{He}$ is predicted.

We develop polarization observables for the processes $\gamma N\to \pi \pi N$ and $\pi N\to \pi \pi N$, using both a helicity and hybrid helicity-transversity basis. Such observables are crucial if processes that produce final states consisting of a spin-1/2 baryon and two pseudoscalar mesons are to be fully exploited for baryon spectroscopy. We derive relationships among the observables, as well as inequalities that they must satisfy. We also discuss the observables that must be measured in “complete” experiments and briefly examine the prospects for measurement of some of these observables in the near future.

The screening potential in the ${}^1{S}_0$ and ${}^3{S}_1$ pairing channels in neutron and nuclear matter in different approximations is discussed. It is found that the vertex corrections to the potential are much stronger in nuclear matter than in neutron matter.

γ-ray spectroscopy of high-spin states of the neutron-deficient nucleus ${}^{189}\mathrm{Pb}$ has been conducted with the ${}^{158}\mathrm{Gd}({}^{36}\mathrm{Ar},5n)$ and ${}^{164}\mathrm{Er}({}^{29}\mathrm{Si},4n)$ reactions. With the first of these, detection of evaporation residues and mass gating were used to unambiguously assign a number of prompt γ-ray transitions to ${}^{189}\mathrm{Pb}$. With the second reaction and a pulsed beam, an isomer with a mean life of 32 μs was found. Although inconclusive, the available evidence favors identification of the isomer with the ${\frac{33}{2}}^{+}$ state of the $\nu (i_{13/2}){}^{-3}$ configuration. The levels observed below the isomer can be identified with states involving three different structures: the neutron $(i_{13/2}){}^{-3}$ multiplet in the spherical well; a prolate-deformed band involving mixed $i_{13/2}$ neutron orbitals; and a state with the oblate $\pi (2p\text{−}2h){}_{0^{+}}\otimes \nu (i_{13/2}){}^{-1}$ configuration. The evidence for structures associated with different shapes is supported by the observation of $E0$ components in some of the $J^{\pi }\to J^{\pi }$ transitions linking them.

We analyze the centrality dependence of thermal parameters deduced from hadron multiplicities in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=130\hspace{1em}\mathrm{GeV}$. Although the chemical freeze-out temperature and chemical potentials are found to be roughly centrality independent, the strangeness saturation factor ${\gamma }_S$ increases with participant number toward unity, supporting the assumption of equilibrium freeze-out conditions in central collisions.

The ${}^{17}\mathrm{O}(p,\gamma ){}^{18}\mathrm{F}$ and ${}^{17}\mathrm{O}(p,\alpha ){}^{14}\mathrm{N}$ reactions have a profound influence on hydrogen-burning nucleosynthesis in a number of stellar sites, including red giants, asymptotic giant branch (AGB) stars, massive stars, and classical novae. Previously evaluated thermonuclear rates for both reactions carry large uncertainties. We investigated the proton-capture reaction on ${}^{17}\mathrm{O}$ in the bombarding energy range of $E_p^{\mathrm{lab}}=180\text{−}540\text{keV}$. We observed a previously undiscovered resonance at $E_R^{\mathrm{lab}}=193.2\pm 0.9\text{keV}$. The resonance strength amounts to $(\omega \gamma ){}_{p\gamma }=(1.2\pm 0.2)\times {10}^{-6}\mathrm{eV}$. With this value, the uncertainties of the ${}^{17}\mathrm{O}(p,\gamma ){}^{18}\mathrm{F}$ reaction rates are reduced by orders of magnitude in the peak temperature range of classical novae $(T=0.1\text{−}0.4\mathrm{GK})$. We also report on a reevaluation of the ${}^{17}\mathrm{O}(p,\gamma ){}^{18}\mathrm{F}$ reaction rates at lower temperatures that are pertinent to red giants, AGB stars, or massive stars. The present work establishes the ${}^{17}\mathrm{O}(p,\gamma ){}^{18}\mathrm{F}$ reaction rates over a temperature range of $T=0.01\text{−}1.5\mathrm{GK}$ with statistical uncertainties of 10–50%. The new recommended reaction rates deviate from the previously accepted values by an order of magnitude around $T\approx 0.2\mathrm{GK}$ and by factors of 2–3 at $T<0.1\mathrm{GK}$.

Both hyperfine states of muonic ${}^{23}\mathrm{Na}$ and the rate R of conversion between them have been observed directly in a high field negative muon spin precession experiment using a backward muon beam with transverse spin polarization. The result in metallic sodium, $R=13.7\pm 2.2\mu s^{-1}$, is consistent with Winston's prediction in 1963 based on Auger emission of core electrons, and with the measurements of Gorringe et al. in Na metal, but not with their smaller result in NaF. In NaOH we find $R=23.5\pm 8\mu s^{-1}$, leaving medium-dependent effects ambiguous.

The proton analyzing power $A_y$ in the pion production reaction $\overrightarrow{p}d\to {\pi }^0{}^3\mathrm{He}$ has been calculated including one- and two-body meson production mechanisms with a proper treatment of the three-nucleon dynamics and an accurate solution of the 3N bound-state problem for phenomenological two-nucleon potentials. In the region around the Δ resonance, the structure of the analyzing power can be understood once interference effects among amplitudes describing intermediate $\Delta N$ formation in different orbital states are considered along with the additional interference with the S-wave pion-production amplitudes. Then, the inclusion of three-nucleon dynamics in the initial state produces the structure of the analyzing power that has been observed experimentally.

A coexisting band structure is identified in ${}^{152}\mathrm{Sm}$ through γ-ray coincidence spectroscopy following β decay of ${}^{152m,g}\mathrm{Eu}$ and following multistep Coulomb excitation. This structure is interpreted as a pairing isomer analogous to a similar band identified in ${}^{154}\mathrm{Gd}$, based on relative $B(E2)$ values for transitions out of the band and two-neutron transfer reaction population of the $0^{+}$ and $2^{+}$ band members. Systematics for odd-$A$ isotopes near $N=90$ suggest that there should be a low-lying pairing isomer in ${}^{156}\mathrm{Dy}$ and similar structures at higher energy in ${}^{150}\mathrm{Nd}$ and ${}^{158}\mathrm{Er}$.

Regular structures generated by random interactions in energy centroids defined over irreducible representations (irreps) of some of the group symmetries of the interacting boson models sdIBM, sdgIBM, sdIBM-T, and sdIBM-ST are studied by deriving trace propagation equations for the centroids. It is found that, with random interactions, the lowest and highest group irreps in general carry most of the probability for the corresponding centroids to be lowest in energy. This generalizes the result known earlier, via numerical diagonalization, for the more complicated fixed spin J centroids where simple trace propagation is not possible.

High spin levels in ${}^{108}\mathrm{Cd}$ have been populated through ${}^{100}\mathrm{Mo}({}^{13}\mathrm{C},5n\gamma ){}^{108}\mathrm{Cd}$ reaction using a 65 MeV ${}^{13}\mathrm{C}$ beam. The lifetime of the ${14}^{+},{16}^{+},{18}^{+}$, and ${20}^{+}$ levels of the positive parity yrast band of ${}^{108}\mathrm{Cd}$ have been measured using the Doppler shift attenuation method. The evaluated B(E2) values from the measured lifetimes have been compared with the B(E2) values calculated using the semiclassical model, which assume shears mechanism, and the values obtained from total Routhian surface (TRS) calculations. Both calculations show good agreement with the measured values. In addition, the large ${\mathcal{J}}^{(2)}/B(E2)$ ratio may indicate that a large contribution to the angular momentum of this band is generated by shears mechanism. Thus, the present work indicates that the states of the positive parity yrast band from ${16}^{+}$ onwards in ${}^{108}\mathrm{Cd}$, originate due to antimagnetic rotation.

The fission fragment mass ratio distributions of fusion-fission events have been measured for the reactions of ${}^{19}\mathrm{F}+{}^{232}\mathrm{Th},{}^{16}\mathrm{O}+{}^{235}\mathrm{U}$, and ${}^{16}\mathrm{O}+{}^{238}\mathrm{U}$ at energies near and below the fusion barrier. It is found that the mass ratio widths follow a decreasing trend with decreasing energy, contrary to recent claims of anomalous mass widths attributed to a quasifission mechanism.

Motivated by ongoing developments at High-Intensity Gamma Source (HIγS) at Triangle Universities Nuclear Laboratory (TUNL) that include increased photon flux and the ability to circularly polarize photons, we calculate several beam-polarization and/or target-spin-dependent observables for elastic Compton scattering on the deuteron. This is done at energies of the order of the pion mass within the framework of heavy-baryon chiral perturbation theory. Our calculation is complete to $\mathcal{O}(Q^3)$ and at this order there are no free parameters. Consequently, the results reported here are predictions of the theory. We discuss paths that may lead to the extraction of neutron polarizabilities. We find that the photon/beam polarization asymmetry is not a good observable for the purpose of extracting ${\alpha }_n$ and ${\beta }_n$. However, one of the double polarization asymmetries, ${\Sigma }_x$, shows appreciable sensitivity to ${\gamma }_{1n}$ and could be instrumental in pinning down the neutron spin polarizabilities.

A measurement of the ${}^2\mathrm{H}(d,{}^2\mathrm{He}){}^{2}n$ charge-exchange reaction at $E_d=171$ MeV has been performed in order to study the interaction of the di-neutron system. Spectroscopy of the neutron-neutron final-state interaction with a resolution of about 115 keV (FWHM) was achieved by measuring the momentum of ${}^2\mathrm{He}$ at forward scattering angles. In the experiment the two protons of the unbound ${}^2\mathrm{He}$ are momentum analyzed with a magnetic spectrometer and detected with the same detector. A simple reaction theory is employed in order to obtain information about the neutron-neutron interaction from the measured cross section data. The validity of the impulse approximation for the $d\to {}^2\mathrm{He}$ transition at intermediate energies is discussed and compared to the Watson-Migdal theory of the proton-proton final-state interaction. Predictions of the impulse approximation for the analog transition $d\to {}^{2}n$ are confronted with experimental data. A procedure to extract the neutron-neutron scattering length $a_{nn}$ from this comparison is presented. The result is compatible with the recommended value of $a_{nn}=-18.6(\pm 0.4)$ fm.

Three-neutron resonances are investigated using realistic nucleon-nucleon interaction models. The resonance pole trajectories are explored by first adding an additional interaction to artificially bind the three-neutron system and then gradually removing it. The pole positions for the three-neutron states up to $J=5/2$ are localized in the third energy quadrant—$\mathrm{Im}(E)⩽0,\mathrm{Re}(E)⩽0$—well before the additional interaction is removed. Our study shows that realistic nucleon-nucleon interaction models exclude any possible experimental signature of three-neutron resonances.