Coulomb activation of the four quasiparticle $K^{\pi }={16}^{+}$ ${}^{178}\mathrm{Hf}$ isomer ($t_{1/2}=31\mathrm{y}$) has led to the measurement of a set of $E\lambda$ matrix elements coupling the isomer band to the ground band. The present data combined with earlier ${}^{178}\mathrm{Hf}$ Coulomb excitation data have probed the $K$ components in the wave functions and revealed the onset and saturation of $K$ mixing in low-$K$ bands, whereas the mixing is negligible in the high-$K$ bands. The implications can be applied to other quadrupole-deformed nuclei.

Atomic masses of ${}^{95–100}\mathrm{Sr}$, ${}^{98–105}\mathrm{Zr}$, and ${}^{102–110}\mathrm{Mo}$ have been measured with a precision of 10 keV employing a Penning trap setup at the IGISOL facility. Masses of ${}^{104,105}\mathrm{Zr}$ and ${}^{109,110}\mathrm{Mo}$ are measured for the first time. Our improved results indicate significant deviations from the previously published values deduced from beta end point measurements. The most neutron-rich studied isotopes are found to be significantly less bound (1 MeV) compared to the 2003 atomic mass evaluation. A strong correlation between nuclear deformation and the binding energy is observed in the two-neutron separation energy in all studied isotope chains.

It was recently suggested that the error with respect to experimental data in nuclear mass calculations is due to the presence of chaotic motion. The theory was tested by analyzing the typical error size. A more sensitive quantity, the correlations of the mass error between neighboring nuclei, is studied here. The results provide further support to this physical interpretation.

The mixed occurrence of $s$-wave and $p$-wave contributions in a first forbidden unique Gamow-Teller $\beta$ decay has been investigated for the first time by measuring the beta environmental fine structure (BEFS) in a ${}^{187}\mathrm{Re}$ crystalline compound. The experiment has been carried out with an array of eight ${\mathrm{AgReO}}_4$ thermal detectors operating at a temperature of $\sim 100\mathrm{mK}$. A fit of the observed BEFS spectrum indicates the $p$-wave electron emission as the dominant channel. The complete understanding of the BEFS distortion of the ${}^{187}\mathrm{Re}$ $\beta$ decay spectrum is crucial for future experiments aiming at the precise calorimetric measurement of the antineutrino mass.

The 10.15 MeV resonance in ${}^{10}\mathrm{Be}$ has been probed via resonant ${}^6\mathrm{He}+{}^4\mathrm{He}$ elastic scattering. It is demonstrated that it is the $J^{\pi }=4^{+}$ member of a rotational band built on the 6.18 MeV $0^{+}$ state. A ${\Gamma }_{\alpha }$ of 0.10–0.13 MeV and ${\Gamma }_{\alpha }/\Gamma =0.35–0.46$ were deduced. The corresponding reduced $\alpha$ width, ${\gamma }_{\alpha }^2$, indicates one of the largest $\alpha$-cluster spectroscopic factors known. The deformation of the band, including the 7.54 MeV, $2^{+}$ member, is large (${\hslash }^2/2I=200\mathrm{keV}$). Such a deformation and the significant degree of clusterization signals a well-developed $\alpha :2n:\alpha$ molecular structure.

We compute by numerical integration of the Dirac equation the number of quark-antiquark pairs initially produced in the classical color fields of colliding ultrarelativistic nuclei. While the number of $q\overline{q}$ pairs is parametrically suppressed in the coupling constant, we find that in this classical field model their production rate is comparable to the thermal ratio of $\mathrm{\text{gluons}}/\mathrm{\text{pairs}}=9N_{\mathrm{f}}/32$. After isotropization one thus would have a quark-gluon plasma in chemical equilibrium.

The breaking of the $N=8$ shell-model magic number in the ${}^{12}\mathrm{Be}$ ground state has been determined to include significant occupancy of the intruder $d$-wave orbital. This is in marked contrast with all other $N=8$ isotones, both more and less exotic than ${}^{12}\mathrm{Be}$. The occupancies of the $0\hslash \omega$ $\nu p_{1/2}$ orbital and the $1\hslash \omega$, $\nu d_{5/2}$ intruder orbital were deduced from a measurement of neutron removal from a high-energy ${}^{12}\mathrm{Be}$ beam leading to bound and unbound states in ${}^{11}\mathrm{Be}$.

Proton and neutron densities from Skyrme-Hartree-Fock calculations of a number of nuclei with masses ranging from 28 to 58 have been used to generate optical potentials for proton elastic scattering. Those potentials, generated by folding the structure functions with effective in-medium nucleon-nucleon ($NN$) interactions, have been used to evaluate proton total reaction cross sections; cross sections that reveal signatures of the structures.

The PHENIX experiment has measured midrapidity ($|\eta |<0.35$) transverse momentum spectra ($0.4<p_T<5.0\mathrm{GeV}/c$) of electrons as a function of centrality in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of ${\pi }^0$ and $\eta$ mesons, were removed. The resulting nonphotonic electron spectra are primarily due to the semileptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to nonphotonic electrons in $p+p$ collisions. A significant suppression of electrons at high $p_T$ is observed in central $\mathrm{Au}+\mathrm{Au}$ collisions, indicating substantial energy loss of heavy quarks.

The azimuthal distribution of identified ${\pi }^0$ and inclusive photons has been measured in $\sqrt{s_{NN}}=200\mathrm{GeV}$ $\mathrm{Au}+\mathrm{Au}$ collisions with the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The second-harmonic parameter ($v_2$) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon $v_2$ is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured $p_T$ range $1–6\mathrm{GeV}/c$. An attempt is made to extract $v_2$ of direct photons.

We show that a sizable azimuthal asymmetry, characterized by a coefficient $v_2$, is to be expected for large $p_T$ direct photons produced in noncentral high energy nuclear collisions. This signal is generated by photons radiated by jets interacting with the surrounding hot plasma. The anisotropy is out of phase by an angle $\pi /2$ with respect to that associated with the elliptic anisotropy of hadrons, leading to negative values of $v_2$. Such an asymmetry, if observed, could be a signature for the presence of a quark gluon plasma and would establish the importance of jet-plasma interactions as a source of electromagnetic radiation.

An approximate solution at the critical point of the pairing transition from harmonic vibration to deformed rotation in gauge space is found by analytic solution of the collective pairing Hamiltonian. The eigenvalues are expressed in terms of the zeros of Bessel functions of integer order. The results are compared to the pairing bands based on the Pb isotopes.

The ground state of three flavor quark matter at asymptotically large density is believed to be the color-flavor-locked (CFL) phase. At nonasymptotic density the effect of the nonzero strange quark mass cannot be neglected. If the strange quark mass exceeds $m_s\sim m_u^{1/3}{\Delta }^{2/3}$, the CFL state becomes unstable toward the formation of a neutral kaon condensate. Recently, several authors discovered that for $m_s\sim (2\Delta p_{\mathrm{F}}{)}^{1/2}$ the CFL state contains gapless fermions, and that the gapless modes lead to an instability in current-current correlation functions. Using an effective theory of the CFL state, we demonstrate that this instability can be resolved by the formation of a meson supercurrent, analogous to Migdal’s $p$-wave pion condensate. This state has a nonzero meson current that is canceled by a backflow of gapless fermions.

We study the transverse momentum distribution of vector mesons produced in ultraperipheral relativistic heavy ion collisions (UPCs). In UPCs there is no strong interaction between the nuclei, and the vector mesons are produced in photon-nucleus collisions where the (quasireal) photon is emitted from the other nucleus. Exchanging the role of both ions leads to interference effects. A detailed study of the transverse momentum distribution, which is determined by the transverse momentum of the emitted photon, the production process on the target, and the interference effect, is done. We study the unrestricted cross section and the one with an additional electromagnetic excitation of one or both ions; in the latter case small impact parameters are emphasized.

$J/\psi$ production in $d+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ has been measured by the PHENIX experiment at rapidities $-2.2<y<+2.4$. The cross sections and nuclear dependence of $J/\psi$ production versus rapidity, transverse momentum, and centrality are obtained and compared to lower energy $p+A$ results and to theoretical models. The observed nuclear dependence in $d+\mathrm{Au}$ collisions is found to be modest, suggesting that the absorption in the final state is weak and the shadowing of the gluon distributions is small and consistent with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-based parametrizations that fit deep-inelastic scattering and Drell-Yan data at lower energies.

The stiffness of the hadronic equation of state has been extracted from the production rate of $K^{+}$ mesons in heavy-ion collisions around $1A\mathrm{GeV}$ incident energy. The data are best described with a compression modulus $K$ around 200 MeV, a value which is usually called “soft.” This is concluded from a detailed comparison of the results of transport theories with the experimental data using two different procedures: (i) the energy dependence of the ratio of $K^{+}$ from $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{C}+\mathrm{C}$ collisions and (ii) the centrality dependence of the $K^{+}$ multiplicities. It is demonstrated that input quantities of these transport theories which are not precisely known, such as the kaon-nucleon potential, the $\Delta N\to N{K}^{+}\Lambda$ cross section, or the lifetime of the $\Delta$ in matter, do not modify this conclusion.

We examine the two-photon exchange contribution to the $eN\to e\Delta (1232)\to e\pi N$ process with the aim of a precision study of the ratios of electric quadrupole $(E2)$ and Coulomb quadrupole $(C2)$ to the magnetic dipole $(M1)$ ${\gamma }^{*}N\Delta$ transitions. We relate the two-photon exchange amplitude to the $N\to \Delta$ generalized parton distributions and obtain a quantitative estimate of the two-photon effects. The two-photon exchange corrections to the $C2/M1$ ratio depend strongly on whether this quantity is obtained from an interference cross section or from the Rosenbluth-type cross sections, in similarity with the elastic, $eN\to eN$, process.

The fine structure of the Gamow-Teller resonance in a medium-heavy nucleus is observed for the first time in a high-resolution ${}^{90}\mathrm{Zr}({}^3\mathrm{He},t){}^{90}\mathrm{Nb}$ experiment at the Research Center for Nuclear Physics, Osaka. Using a novel wavelet analysis technique, it is possible to extract characteristic energy scales and to quantify their relative importance for the generation of the fine structure. This method combined with the selectivity of the reaction permits an extraction of the level density of $1^{+}$ states in ${}^{90}\mathrm{Nb}$.

To investigate the behavior of the $N=14$ neutron gap far from stability with a neutron-sensitive probe, proton elastic and $2_1^{+}$ inelastic scattering angular distributions for the neutron-rich nucleus ${}^{22}\mathrm{O}$ were measured using the MUr à STrip detector array at the Grand Accélérateur National d’Ions Lourds facility. A deformation parameter ${\beta }_{p,p^{\prime }}=0.26\pm 0.04$ is obtained for the $2_1^{+}$ state, much lower than in ${}^{20}\mathrm{O}$, showing a weak neutron contribution to this state. A microscopic analysis was performed using matter and transition densities generated by continuum Skyrme-Hartree-Fock-Bogoliubov and quasiparticle random phase approximation calculations, respectively. The ratio of neutron to proton contributions to the $2_1^{+}$ state is found close to the $N/Z$ ratio, demonstrating a strong $N=14$ shell closure in the vicinity of the neutron drip line.

A variational method is developed to determine configuration interaction wave functions. The method is straightforward and is applied to a pairing Hamiltonian with constant matrix elements, for which exact eigenvalues are available. Comparisons are made with the exact results. Calculations can be carried out to any desired degree of accuracy. The method is also applied to a Hamiltonian that has neutron-neutron, proton-proton, and neutron-proton pairing. No difficulties are found in extending the method to this Hamiltonian that has many collective modes. In practice, the method scales linearly with $N$, where $N$ is the number of variational basis states.