The results of the Doppler-shift attenuation method lifetime measurements in partner bands of ${}^{128}\mathrm{Cs}$ and ${}^{132}\mathrm{La}$ are presented. Experimental reduced transition probabilities in ${}^{128}\mathrm{Cs}$ are compared with theoretical calculations done in the frame of the core-quasiparticle coupling model. The electromagnetic properties, energy and spin of levels belonging to the partner bands show that ${}^{128}\mathrm{Cs}$ is the best known example revealing the chiral symmetry breaking phenomenon.

Elliptic flow measurements at the Brookhaven National Laboratory Relativistic Heavy Ion Collider suggest that quark-gluon fluid flows with very little viscosity compared to weak-coupling expectations, challenging theorists to explain why this fluid is so nearly “perfect.” It is therefore vital to find quantitative experimental information on the viscosity of the fluid. We propose that measurements of transverse momentum fluctuations can be used to determine the shear viscosity. We use current data to estimate the viscosity-to-entropy ratio in the range from 0.08 to 0.3 and discuss how future measurements can reduce this uncertainty.

We analyze recent data from high-momentum-transfer ($p$, $pp$) and ($p$, $ppn$) reactions on carbon. For this analysis, the two-nucleon short-range correlation ($NN$-SRC) model for backward nucleon emission is extended to include the motion of the $NN$ pair in the mean field. The model is found to describe major characteristics of the data. Our analysis demonstrates that the removal of a proton from the nucleus with initial momentum $275–550\mathrm{MeV}/c$ is ${92}_{-18}^{+8}\%$ of the time accompanied by the emission of a correlated neutron that carries momentum roughly equal and opposite to the initial proton momentum. This indicates that the probabilities of $pp$ or $nn$ SRCs in the nucleus are at least a factor of 6 smaller than that of $pn$ SRCs. Our result is the first estimate of the isospin structure of $NN$-SRCs in nuclei, and may have important implication for modeling the equation of state of asymmetric nuclear matter.

Important insight into the symmetry properties of the nuclear ground-state (gs) shape is obtained from the characteristics of low-lying collective energy-level spectra. In the 1950s, experimental and theoretical studies showed that in the gs many nuclei are spheroidal in shape rather than spherical. Later, a hexadecapole component of the gs shape was identified. In the 1970–1995 time frame, a consensus that reflection symmetry of the gs shape was broken for some nuclei emerged. Here we present the first calculation across the nuclear chart of axial symmetry breaking in the nuclear gs. We show that we fulfill a necessary condition: Where we calculate axial symmetry breaking, characteristic gamma bands are observed experimentally. Moreover, we find that, for those nuclei where axial asymmetry is found, a systematic deviation between calculated and measured masses is removed.

A dispersive-optical-model analysis of $p+{}^{40}\mathrm{Ca}$ and $p+{}^{48}\mathrm{Ca}$ interactions has been carried out. The real and imaginary potentials have been constrained from fits to elastic-scattering data, reaction cross sections, and level properties of valence hole states deduced from ($e$, $e^{\prime }p$) data. The surface imaginary potential was found to be larger overall and the gap in this potential on either side of the Fermi energy was found to be smaller for the neutron-rich $p+{}^{48}\mathrm{Ca}$ system. These results imply that protons with energies near the Fermi surface experience larger correlations with increasing asymmetry.

The STAR Collaboration at the Relativistic Heavy Ion Collider reports measurements of azimuthal correlations of high transverse momentum ($p_T$) charged hadrons in $\mathrm{Au}+\mathrm{Au}$ collisions at higher $p_T$ than reported previously. As $p_T$ is increased, a narrow, back-to-back peak emerges above the decreasing background, providing a clear dijet signal for all collision centralities studied. Using these correlations, we perform a systematic study of dijet production and suppression in nuclear collisions, providing new constraints on the mechanisms underlying partonic energy loss in dense matter.

The tensor force is implemented into the mean-field model so that the evolution of nuclear shells can be described for exotic nuclei as well as stable ones. Besides the tensor-force part simulating the meson exchange, the model is an extension of the successful Gogny model. One of the major issues of rare-isotope beam physics is a reduced spin-orbit splitting in neutron-rich exotic nuclei. It will be shown that the effect of the tensor force on this splitting is larger than or about equal to the one due to the neutron skin. We will present predictions for stable and exotic nuclei with comparisons to conventional results and experimental data.

Substantial collective flow is observed in collisions between large nuclei at BNL RHIC (Relativistic Heavy Ion Collider) as evidenced by single-particle transverse momentum distributions and by azimuthal correlations among the produced particles. The data are well reproduced by perfect fluid dynamics. A calculation of the dimensionless ratio of shear viscosity $\eta$ to entropy density $s$ by Kovtun, Son, and Starinets within anti-de Sitter space/conformal field theory yields $\eta /s=\hslash /4\pi k_B$, which has been conjectured to be a lower bound for any physical system. Motivated by these results, we show that the transition from hadrons to quarks and gluons has behavior similar to helium, nitrogen, and water at and near their phase transitions in the ratio $\eta /s$. We suggest that experimental measurements can pinpoint the location of this transition or rapid crossover in QCD.

Transverse momentum spectra of ${\pi }^{\pm }$, $p$, and $\overline{p}$ up to $12\mathrm{GeV}/c$ at midrapidity in centrality selected $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ are presented. In central $\mathrm{Au}+\mathrm{Au}$ collisions, both ${\pi }^{\pm }$ and $p(\overline{p})$ show significant suppression with respect to binary scaling at $p_T\gtrsim 4\mathrm{GeV}/c$. Protons and antiprotons are less suppressed than ${\pi }^{\pm }$, in the range $1.5\lesssim p_T\lesssim 6\mathrm{GeV}/c$. The ${\pi }^{-}/{\pi }^{+}$ and $\overline{p}/p$ ratios show at most a weak $p_T$ dependence and no significant centrality dependence. The $p/\pi$ ratios in central $\mathrm{Au}+\mathrm{Au}$ collisions approach the values in $p+p$ and $d+\mathrm{Au}$ collisions at $p_T\gtrsim 5\mathrm{GeV}/c$. The results at high $p_T$ indicate that the partonic sources of ${\pi }^{\pm }$, $p$, and $\overline{p}$ have similar energy loss when traversing the nuclear medium.

Measurements of the production of forward ${\pi }^0$ mesons from $p+p$ and $d+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ are reported. The $p+p$ yield generally agrees with next-to-leading order perturbative QCD calculations. The $d+\mathrm{Au}$ yield per binary collision is suppressed as $\eta$ increases, decreasing to $\sim 30\%$ of the $p+p$ yield at $⟨\eta ⟩=4.00$, well below shadowing expectations. Exploratory measurements of azimuthal correlations of the forward ${\pi }^0$ with charged hadrons at $\eta \approx 0$ show a recoil peak in $p+p$ that is suppressed in $d+\mathrm{Au}$ at low pion energy. These observations are qualitatively consistent with a saturation picture of the low-$x$ gluon structure of heavy nuclei.

Gamma decays from excited states up to $J^{\pi }=6^{+}$ in the $N=Z-2$ nucleus ${}^{54}\mathrm{Ni}$ have been identified for the first time. Level energies are compared with those of the isobars ${}^{54}\mathrm{Co}$ and ${}^{54}\mathrm{Fe}$ and of the cross-conjugate nuclei of mass $A=42$. The good but puzzling $f_{7/2}$ cross-conjugate symmetry in mirror and triplet energy differences is analyzed. Shell model calculations reproduce the new data but the necessary nuclear charge-dependent phenomenology is not fully explained by modern nucleon-nucleon potentials.

The quasifree $pn\to d\varphi$ reaction has been studied at the Cooler Synchrotron COSY—Jülich, using the internal proton beam incident on a deuterium cluster-jet target and detecting a fast deuteron in coincidence with the $K^{+}{K}^{-}$ decay of the $\varphi$ meson. The energy dependence of the total and differential cross sections are extracted for excess energies up to 80 MeV by determining the Fermi momentum of the target neutron on an event-by-event basis. Though these cross sections are consistent with $s$-wave production, the kaon angular distributions show the presence of $p$ waves at quite a low energy. Production on the neutron is found to be stronger than on the proton but not by as much as for the $\eta$ meson.

We report the measurements of $\Sigma (1385)$ and $\Lambda (1520)$ production in $p+p$ and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ from the STAR Collaboration. The yields and the $p_T$ spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central $\mathrm{Au}+\mathrm{Au}$ collisions. Our results indicate that there may be a time span between chemical and thermal freeze-out during which elastic hadronic interactions occur.

Excited states have been observed in the $N=Z-2$ odd-odd nucleus ${}^{48}\mathrm{Mn}$ for the first time. Through comparison with the structure of ${}^{48}\mathrm{V}$, a first high-spin study of an odd-odd mirror pair has been achieved. Differences between the $T=1$ analogue states in this pair have been interpreted in terms of Coulomb effects, with the aid of shell-model calculations in the full $pf$ valence space. Unlike other mirror pairs, the energy differences have been interpreted almost entirely as due to a monopole effect associated with smooth changes in radius (or deformation) as a function of angular momentum. In addition, the large energy shift between analogue negative-parity states is interpreted in terms of the electromagnetic spin-orbit interaction in nuclei.

We investigate the effects of an external magnetic field in the gluon dynamics of a color superconductor with three massless quark flavors. In the framework of gluon mean-field theory at asymptotic densities, we show that the long-range component $\tilde{H}$ of the external magnetic field that penetrates the color-flavor locked phase produces an instability when its strength becomes larger than the Meissner mass of the charged gluons. As a consequence, the magnetic field causes the formation of a vortex state characterized by the condensation of charged gluons and the creation of magnetic flux tubes. Inside the flux tubes, the magnetic field is stronger than the applied one. This antiscreening effect is connected to the anomalous magnetic moment of the gluon field. We suggest how this same mechanism could serve to remove the chromomagnetic instabilities existing in gapless color superconductivity.

The nuclear physics input from the ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ cross section is a major uncertainty in the fluxes of ${}^7\mathrm{Be}$ and ${}^8\mathrm{B}$ neutrinos from the Sun predicted by solar models and in the ${}^7\mathrm{Li}$ abundance obtained in big-bang nucleosynthesis calculations. The present work reports on a new precision experiment using the activation technique at energies directly relevant to big-bang nucleosynthesis. Previously such low energies had been reached experimentally only by the prompt-$\gamma$ technique and with inferior precision. Using a windowless gas target, high beam intensity, and low background $\gamma$-counting facilities, the ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ cross section has been determined at 127, 148, and 169 keV center-of-mass energy with a total uncertainty of 4%. The sources of systematic uncertainty are discussed in detail. The present data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ astrophysical $S$ factor to solar energies.

A $K^{\pi }={13}^{+}$, 280 ns four-quasiparticle isomer in the odd-odd nucleus ${}^{174}\mathrm{Lu}$ has been identified and characterized. The isomer decays to both $K^{\pi }=7^{+}$ and $K^{\pi }=0^{+}$ rotational bands obtained from the parallel and antiparallel coupling of the proton $7/2^{+}[404]$ and neutron $7/2^{+}[633]$ orbitals. $K$ mixing caused by particle-rotation coupling explains the anomalously fast transition rates to the $7^{+}$ band but those to the $0^{+}$ band are caused by a chance degeneracy between the isomer and a collective state, allowing the mixing matrix element for a large $K$ difference to be deduced.

Excited states in ${}^{40}\mathrm{Si}$ have been established by detecting $\gamma$ rays coincident with inelastic scattering and nucleon removal reactions on a liquid hydrogen target. The low excitation energy, 986(5) keV, of the $2_1^{+}$ state provides evidence of a weakening in the $N=28$ shell closure in a neutron-rich nucleus devoid of deformation-driving proton collectivity.

Employing thermal dilepton rates based on a medium-modified electromagnetic correlation function we show that recent dimuon spectra of the NA60 Collaboration in central In-In collisions at the CERN-SPS can be understood in terms of radiation from a hot and dense hadronic medium. Earlier calculated in-medium $\rho$-meson spectral functions provide an accurate description of the data up to dimuon invariant masses of about $M\simeq 0.9\mathrm{GeV}$, with good sensitivity to the predicted $\rho$-meson line shape, identifying baryon-induced modifications as the prevalent ones. A reliable evaluation of the contribution enables the study of further medium effects: at masses $M>0.9\mathrm{GeV}$, 4-pion type annihilation accounts for the experimentally observed excess (possibly augmented by effects of “chiral mixing”), while predictions for thermal emission from in-medium $\omega$ and $\varphi$ mesons may be tested in the future.

A high-precision branching ratio measurement for the superallowed ${\beta }^{+}$ decay of ${}^{62}\mathrm{Ga}$ was performed at the Isotope Separator and Accelerator radioactive ion beam facility. Nineteen $\gamma$ rays emitted following ${\beta }^{+}$ decay of ${}^{62}\mathrm{Ga}$ were identified, establishing the dominant superallowed branching ratio to be $(99.861\pm 0.011)\%$. Combined with recent half-life and $Q$-value measurements, this branching ratio yields a superallowed $ft$ value of $3075.6\pm 1.4\mathrm{s}$ for ${}^{62}\mathrm{Ga}$ decay. These results demonstrate the feasibility of high-precision superallowed branching ratio measurements in the $A\ge 62$ mass region and provide the first stringent tests of the large isospin-symmetry-breaking effects predicted for these decays.