A systematic analysis of the spherical-to-deformed shape phase transition in even-even rare-earth nuclei from ${}^{58}\mathrm{Ce}$ to ${}^{74}\mathrm{W}$ is carried out in the framework of the interacting boson model. These results are then used to calculate nuclear radii and electric monopole ($E0$) transitions with the same effective operator. The influence of the hexadecapole degree of freedom ($g$ boson) on the correlation between radii and $E0$ transitions thus established is discussed.

A remarkably simple regularity in the energies of $0^{+}$ states in a broad class of collective models is discussed. A single formula for all $0^{+}$ states in flat-bottomed infinite potentials that depends only on the number of dimensions and a simpler expression applicable to all three interacting boson approximation symmetries in the large $N_B$ limit are presented. Finally, a connection between the energy expression for $0^{+}$ states given by the X(5) model and the predictions of the interacting boson approximation near the critical point of the first order phase transition is explored.

We investigate the hydrodynamic evolution of the system formed in ultrarelativistic heavy-ion collisions and find that an appropriate choice of the initial condition, specifically a simple two-dimensional Gaussian profile for the transverse energy, in conjunction with a realistic equation of state, leads to a uniform description of soft observables measured at the relativistic heavy-ion collider. In particular, the transverse-momentum spectra, the elliptic-flow, and the Hanbury-Brown–Twiss correlation radii, including the ratio $R_{\mathrm{out}}/R_{\mathrm{side}}$ as well as the dependence of the radii on the azimuthal angle, are all properly described.

Incoherent $\eta$ photoproduction in nuclei is evaluated at forward angles within 4 to 9 GeV using a multiple scattering Monte Carlo cascade calculation with full $\eta$-nucleus final-state interactions. The Primakoff, nuclear coherent and nuclear incoherent components of the cross sections fit remarkably well previous measurements for Be and Cu from Cornell, suggesting a destructive interference between the Coulomb and nuclear coherent amplitudes for Cu. The inelastic background of the data is consistently attributed to the nuclear incoherent part, which is clearly not isotropic as previously considered in Cornell’s analysis. The respective Primakoff cross sections from Be and Cu give ${\Gamma }_{\eta \to \gamma \gamma }=0.476(62)\mathrm{keV}$, where the quoted error is only statistical. This result is consistent with the Particle Data Group average of 0.510(26) keV and in sharp contrast ($\sim 50\%$) with the value of 0.324(46) keV obtained at Cornell.

The reduced transition probabilities, $B(E2;0_{\mathrm{gs}}^{+}\to 2_1^{+})$, have been measured in the radioactive isotopes ${}^{108,106}\mathrm{Sn}$ using subbarrier Coulomb excitation at the REX-ISOLDE facility at CERN. Deexcitation $\gamma$ rays were detected by the highly segmented MINIBALL Ge-detector array. The results, $B(E2;0_{\mathrm{gs}}^{+}\to 2_1^{+})=0.222(19)e^2{b}^2$ for ${}^{108}\mathrm{Sn}$ and $B(E2;0_{\mathrm{gs}}^{+}\to 2_1^{+})=0.195(39)e^2{b}^2$ for ${}^{106}\mathrm{Sn}$ were determined relative to a stable ${}^{58}\mathrm{Ni}$ target. The resulting $B(E2)$ values are $\sim 30\%$ larger than shell-model predictions and deviate from the generalized seniority model. This experimental result may point towards a weakening of the $N=Z=50$ shell closure.

A high-precision Penning trap mass measurement of the exotic ${}^8\mathrm{He}$ nuclide ($T_{1/2}=119\mathrm{ms}$) has been carried out resulting in a reduction of the uncertainty of the halo binding energy by over an order of magnitude. The new mass, determined with a relative uncertainty of $9.2\times {10}^{-8}$ ($\delta m=690\mathrm{eV}$) is 13 keV less bound than the previously accepted value. The mass measurement is of great relevance for the recent charge-radius measurement of ${}^8\mathrm{He}$ [P. Mueller et al., Phys. Rev. Lett. 99, 252501 (2007).]. The ${}^8\mathrm{He}$ mass is the first result from the newly-commissioned Penning trap: TITAN (TRIUMF’s Ion Trap for Atomic and Nuclear science) at the ISAC (Isotope Separator and Accelerator) radioactive beam facility at TRIUMF.

Because of long chemical equilibration times for standard hadronic reactions in a hadron gas in relativistic heavy ion collisions, it was suggested that hadrons are born into equilibrium after the quark gluon plasma is formed. We develop a dynamical scheme, using master equations, in which Hagedorn states contribute to fast chemical equilibration times of baryons and kaons, just below the critical temperature, estimates of which are derived analytically. The hadrons quickly equilibrate for an initial over- or underpopulation of Hagedorn states. Our particle ratios compared to BNL Relativistic Heavy Ion Collider show a close match.

The barrier distributions extracted from quasielastic excitation functions are analyzed in terms of a semiclassical model that incorporates both the excitation of the surface degrees of freedom and the exchange of neutrons and protons. It is shown that quasielastic cross sections receive sizable contributions from transfer reactions in all measured energy range.

Neutral pion transverse momentum spectra were measured in $p+\mathrm{C}$ and $p+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=17.4\mathrm{GeV}$ at midrapidity ($2.3\lesssim {\eta }_{\mathrm{lab}}\lesssim 3.0$) over the range $0.7\lesssim p_T\lesssim 3.5\mathrm{GeV}/c$. The spectra are compared to ${\pi }^0$ spectra measured in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=17.3\mathrm{GeV}$ in the same experiment. For a wide range of $\mathrm{Pb}+\mathrm{Pb}$ centralities ($N_{\mathrm{part}}\lesssim 300$), the yield of ${\pi }^0$’s with $p_T\gtrsim 2\mathrm{GeV}/c$ is larger than or consistent with the $p+\mathrm{C}$ or $p+\mathrm{Pb}$ yields scaled with the number of nucleon-nucleon collisions ($N_{\mathrm{coll}}$), while for central $\mathrm{Pb}+\mathrm{Pb}$ collisions with $N_{\mathrm{part}}\gtrsim 350$, the ${\pi }^0$ yield is suppressed.

A three-dimensional correlation function obtained from midrapidity, low $p_T$, pion pairs in central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ is studied. The extracted model-independent source function indicates a long range tail in the directions of the pion pair transverse momentum (out) and the beam (long). A proper breakup time ${\tau }_0\sim 9\mathrm{fm}/c$ and a mean proper emission duration $\Delta \tau \sim 2\mathrm{fm}/c$, leading to sizable emission time differences ($⟨|\Delta t_{\mathrm{LCM}}|⟩\approx 12\mathrm{fm}/c$), are required to allow models to be successfully matched to these tails. The model comparisons also suggest an outside-in “burning” of the emission source reminiscent of many hydrodynamical models.

The photoresponse of the semimagic $N=82$ nucleus ${}^{136}\mathrm{Xe}$ was measured up to the neutron separation energy $S_n$ using the $(\gamma ,{\gamma }^{\prime })$ reaction. A concentration of strong dipole excitations is observed well below $S_n$ showing a fragmented resonancelike structure. Microscopic calculations in the quasiparticle phonon model including complex configurations of up to three phonons agree well with the experimental data in the total integrated strength, in the shape and the fragmentation of the resonance, which allows us to draw conclusions on the damping mechanism of the pygmy dipole resonance.

We propose the enhancement of ${\Lambda }_c$ as a novel quark-gluon plasma signal in heavy ion collisions at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider. Assuming a stable bound diquark state in the strongly coupled quark-gluon plasma near the critical temperature, we argue that the direct two-body collision between a $c$ quark and a $[ud]$ diquark would lead to an enhanced ${\Lambda }_c$ production in comparison with the normal three-body collision among independent $c$, $u$, and $d$ quarks. In the coalescence model, we find that the ${\Lambda }_c/D$ yield ratio is enhanced substantially due to the diquark correlation.

Forming the same heavy compound nucleus with different isotopes of the projectile and target elements allows nuclear structure effects in the entrance channel (resulting in static deformation) and in the dinuclear system to be disentangled. Using three isotopes of Ti and W, forming ${}^{232}\mathrm{Cm}$, with measurement spanning the capture barrier energies, alignment of the heavy prolate deformed nucleus is shown to be the main reason for the broadening of the mass distribution of the quasifission fragments as the beam energy is reduced. The complex, consistently evolving mass-angle correlations that are observed carry more information than the integrated mass or angular distributions, and should severely test models of quasifission.

The branching ratio for the superallowed ${\beta }^{+}$ decay of ${}^{38}\mathrm{K}^m$ was measured at TRIUMF’s ISAC radioactive ion beam facility. The $M3$ internal transition between the isomer and the ground state of ${}^{38}\mathrm{K}^m$ was observed with a branching ratio of 330(43) ppm. A search for the nonanalogue $\beta$-decay branch to the first excited $0^{+}$ state in ${}^{38}\mathrm{Ar}$ was also performed and yielded an upper limit of $\le 12\mathrm{ppm}$ at 90% C.L. These measurements lead to a revised superallowed branching ratio for ${}^{38}\mathrm{K}^m$ of 99.967(4)%, and increase the ${}^{38}\mathrm{K}^m$ $ft$ value by its entire quoted uncertainty to $ft=3052.1(10)\mathrm{s}$. Implications for tests of the nuclear-structure dependent corrections in superallowed $\beta$ decays and the extraction of the Cabibbo-Kobayashi-Maskawa matrix element $V_{\mathrm{ud}}$ are discussed.

Two-proton decay from ${}^{18}\mathrm{Ne}$ excited states has been studied by complete kinematical reconstruction of the decay products. The ${}^{18}\mathrm{Ne}$ nucleus has been produced as a radioactive beam by ${}^{20}\mathrm{Ne}$ primary projectile fragmentation at $45A\mathrm{MeV}$ incident energy on a Be target. The ${}^{18}\mathrm{Ne}$ at $33A\mathrm{MeV}$ incident energy has been excited via Coulomb excitation on a ${}^{\mathrm{nat}}\mathrm{Pb}$ target. The obtained results unambiguously show that the 6.15 MeV ${}^{18}\mathrm{Ne}$ state two-proton decay proceeds through a ${}^2\mathrm{He}$ diproton resonance (31%) and democratic or virtual sequential decay (69%). The quoted branching ratio has been deduced from relative angle and momentum correlations of the emitted proton pairs.

We discuss the three-body decay mechanisms of many-body resonances. Sequential decays proceed via two-body configurations after emission of the third particle. In direct decay all three particles leave their interaction regions simultaneously. The intermediate paths within the interaction regions are not observables and are only accessible through models. The momentum distributions carry, apart from polarization, all possible information about decay modes and resonance structure. In this context we discuss detailed results for the decay of the ${}^9\mathrm{Be}(5/2^{-})$ resonance.

The $p({}^{11}\mathrm{Li},{}^9\mathrm{Li})t$ reaction has been studied for the first time at an incident energy of $3A\mathrm{MeV}$ at the new ISAC-2 facility at TRIUMF. An active target detector MAYA, built at GANIL, was used for the measurement. The differential cross sections have been determined for transitions to the ${}^9\mathrm{Li}$ ground and first excited states in a wide range of scattering angles. Multistep transfer calculations using different ${}^{11}\mathrm{Li}$ model wave functions show that wave functions with strong correlations between the halo neutrons are the most successful in reproducing the observation.

We evaluate heavy-quark (HQ) transport properties in a quark-gluon plasma (QGP) within a Brueckner many-body scheme employing interaction potentials extracted from thermal lattice QCD. The in-medium $T$ matrices for elastic charm- and bottom-quark scattering off light quarks in the QGP are dominated by attractive meson and diquark channels which support resonance states up to temperatures of $\sim 1.5T_c$. The resulting drag coefficient increases with decreasing temperature, contrary to expectations based on perturbative QCD scattering. Employing relativistic Langevin simulations we compute HQ spectra and elliptic flow in $\sqrt{s_{NN}}=200\mathrm{GeV}$ Au-Au collisions. A good agreement with electron decay data supports our nonperturbative computation of HQ diffusion, indicative for a strongly coupled QGP.

Information on hadron properties in the nuclear medium has been derived from the photoproduction of $\omega$ mesons on the nuclei C, Ca, Nb, and Pb using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the $\omega$-meson cross section on the nuclear mass number has been compared with three different types of models: a Glauber analysis, a Boltzmann-Uehling-Uhlenbeck analysis of the Giessen theory group, and a calculation by the Valencia theory group. In all three cases, the inelastic $\omega$ width is found to be $130–150\mathrm{MeV}/c^2$ at normal nuclear matter density for an average 3-momentum of $1.1\mathrm{GeV}/c$. In the rest frame of the $\omega$ meson, this inelastic $\omega$ width corresponds to a reduction of the $\omega$ lifetime by a factor $\approx 30$. For the first time, the momentum dependent $\omega N$ cross section has been extracted from the experiment and is in the range of 70 mb.

The generalized two-center cluster model, which can treat static structures and dynamical reactions in excited states, is applied to the light neutron-rich system, ${}^{12}\mathrm{Be}=\alpha +\alpha +4N$. We discuss the change of the neutrons’ configuration around two $\alpha$ cores from the covalent structure to the ionic one. We show that, in the unbound region above particle-decay thresholds, the ionic configurations appear as the molecular resonances of $\alpha +{}^8\mathrm{He}$, ${}^6\mathrm{He}+{}^6\mathrm{He}$, and ${}^5\mathrm{He}+{}^7\mathrm{He}$. A new type of superdeformation is possible, and we find here a covalent superdeformation with a hybrid configuration of both the covalent and ionic structures. The excitation of these exotic structures through the two-neutron transfer reaction is also discussed.