This Letter describes the measurement of the energy dependence of elliptic flow for charged particles in $\mathrm{Au}+\mathrm{Au}$ collisions using the PHOBOS detector at the Relativistic Heavy Ion Collider. Data taken at collision energies of $\sqrt{s_{NN}}=19.6$, 62.4, 130, and 200 GeV are shown over a wide range in pseudorapidity. These results, when plotted as a function of ${\eta }^{\prime }=|\eta |-y_{\mathrm{beam}}$, scale with approximate linearity throughout ${\eta }^{\prime }$, implying no sharp changes in the dynamics of particle production as a function of pseudorapidity or increasing beam energy.

Electromagnetic transition rates provide an important test for nuclear structure models. The nucleus ${}^8\mathrm{Be}$ exhibits a pronounced alpha-cluster structure and is a building block for more complex cluster nuclei. Here we report on the first observation of the gamma transition between the $4^{+}$ and $2^{+}$ states of ${}^8\mathrm{Be}$ in the ${}^4\mathrm{He}+{}^4\mathrm{He}$ reaction. The measured on-resonance cross section of $165\pm 54\mathrm{nb}$ leads to a $B(E2)$ of$25\pm 8e^2\mathrm{f}{\mathrm{m}}^4$, in good agreement with alpha-cluster models and sophisticated ab initio structure calculations.

A multichannel algebraic scattering theory, to find solutions of coupled-channel scattering problems with interactions determined by collective models, has been structured to ensure that the Pauli principle is not violated. By tracking the results in the zero coupling limit, a correct interpretation of the subthreshold and resonant spectra of the compound system can be made. As an example, the neutron-${}^{12}\mathrm{C}$ system is studied defining properties of ${}^{13}\mathrm{C}$ to 10 MeV excitation. Accounting for the Pauli principle in collective coupled-channels models is crucial to the outcome.

We discuss different sources of hadron correlations in relativistic heavy ion collisions. We show that correlations among partons in a quasithermal medium can lead to the correlated emission of hadrons by quark recombination and argue that this mechanism offers a plausible explanation for the dihadron correlations in the few $\mathrm{GeV}/c$ momentum range observed in $\mathrm{Au}+\mathrm{Au}$ collisions at the BNL Relativistic Heavy Ion Collider.

The $B(E2;0_1^{+}\to 2_1^{+})$ values for the radioactive neutron-rich germanium isotopes ${}^{78,80}\mathrm{Ge}$ and the closed neutron shell nucleus ${}^{82}\mathrm{Ge}$ were measured at the HRIBF using Coulomb excitation in inverse kinematics. These data allow a study of the systematic trend between the subshell closures at $N=40$ and $50$. The $B(E2)$ behavior approaching $N=50$ is similar to the trend observed for heavier isotopic chains. A comparison of the experimental results with a shell model calculation demonstrates persistence of the $N=50$ shell gap and a strong sensitivity of the $B(E2)$ values to the effective interaction.

Nuclei with magic numbers serve as important benchmarks in nuclear theory. In addition, neutron-rich nuclei play an important role in the astrophysical rapid neutron-capture process ($r$ process). ${}^{78}\mathrm{N}\mathrm{i}$ is the only doubly magic nucleus that is also an important waiting point in the $r$ process, and serves as a major bottleneck in the synthesis of heavier elements. The half-life of ${}^{78}\mathrm{N}\mathrm{i}$ has been experimentally deduced for the first time at the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory at Michigan State University, and was found to be ${110}_{-60}^{+100}\mathrm{ms}$. In the same experiment, a first half-life was deduced for ${}^{77}\mathrm{N}\mathrm{i}$ of ${128}_{-33}^{+27}\mathrm{ms}$, and more precise half-lives were deduced for ${}^{75}\mathrm{N}\mathrm{i}$ and ${}^{76}\mathrm{N}\mathrm{i}$ of ${344}_{-24}^{+20}\mathrm{ms}$ and ${238}_{-18}^{+15}\mathrm{ms}$, respectively.

Important goals of BNL RHIC and CERN LHC experiments with ion beams include the creation and study of new forms of matter, such as the quark gluon plasma. Heavy quark production and attenuation provide unique tomographic probes of that matter. We predict the suppression pattern of open charm and beauty in $\mathrm{Au}+\mathrm{Au}$ collisions at RHIC and LHC energies based on the DGLV formalism of radiative energy loss. A cancellation between effects due to the $\sqrt{s}$ energy dependence of the high $p_T$ slope and heavy quark energy loss is predicted to lead to surprising similarity of heavy quark suppression at RHIC and LHC.

We present a relativistic quantum-mechanical treatment of opacity and refractive effects that allows reproduction of observables measured in two-pion Hanbury Brown–Twiss (HBT) interferometry and pion spectra at RHIC. The inferred emission duration is substantial. The results are consistent with the emission of pions from a system that has a restored chiral symmetry.

Non-Abelian plasma instabilities may be responsible for the fast apparent quark-gluon thermalization in relativistic heavy-ion collisions if their exponential growth is not hindered by nonlinearities. We study numerically the real-time evolution of instabilities in an anisotropic non-Abelian plasma with an SU(2) gauge group in the hard-loop approximation. We find exponential growth of non-Abelian plasma instabilities both in the linear and in the strongly nonlinear regimes, with only a brief phase of subexponential behavior in between.

We calculate correlation energies associated with the quadrupole shape degrees of freedom with a view to improving the self-consistent mean-field theory of nuclear binding energies. Systematic results are presented for 605 even-even nuclei from mass number 16 to the heaviest whose mass has been measured, using the Skyrme SLy4 interaction and the generator coordinate method. Correlation energies range from 0.5 to 6.0 MeV, and their inclusion improves two qualitative deficiencies of the mean-field theory, namely, the exaggerated shell effect at neutron magic numbers and the failure of mean-field theory to describe mutually enhanced magicity. For the mass table as a whole, the quadrupolar correlations improve binding energies, separation energies, and separation energy differences by $20\%30\%$.

It has been suggested that chaotic motion inside the nucleus may significantly limit the accuracy with which nuclear masses can be calculated. Using a power spectrum analysis we show that the inclusion of additional physical contributions in mass calculations, through many-body interactions or local information, removes the chaotic signal in the discrepancies between calculated and measured masses. Furthermore, a systematic application of global mass formulas and of a set of relationships among neighboring nuclei to more than 2000 nuclear masses allows one to set an unambiguous upper bound for the average errors in calculated masses, which turn out to be almost an order of magnitude smaller than estimated chaotic components.

We present a theory that accurately describes the counting of excited states of a noninteracting fermionic gas. At high excitation energies the results reproduce Bethe’s theory. At low energies oscillatory corrections to the many-body density of states, related to shell effects, are obtained. The fluctuations depend nontrivially on energy and particle number. Universality and connections with Poisson statistics and random matrix theory are established for regular and chaotic single-particle motion.

Produced partons have a large local relative orbital angular momentum along the direction opposite to the reaction plane in the early stage of noncentral heavy-ion collisions. Parton scattering is shown to polarize quarks along the same direction due to spin-orbital coupling. Such global quark polarization will lead to many observable consequences, such as left-right asymmetry of hadron spectra and global transverse polarization of thermal photons, dileptons, and hadrons. Hadrons from the decay of polarized resonances will have an azimuthal asymmetry similar to the elliptic flow. Global hyperon polarization is studied within different hadronization scenarios and can be easily tested.

A general but simple method is proposed to eliminate the quantum fluctuations generated by selected one-body operators in the excitation spectrum of a discrete random phase approximation (RPA) Hamiltonian. This method provides an outstanding tool for the removal of the contaminating spurious effects originated from symmetry violations. It can be also applied as a mode filter for analyzing RPA response functions.

The ${}^{62}\mathrm{N}\mathrm{i}(n,\gamma ){}^{63}\mathrm{N}\mathrm{i}(t_{1/2}=100\pm 2\mathrm{y}\mathrm{r})$ reaction plays an important role in the control of the flow path of the slow neutron-capture ($s$) nucleosynthesis process. We have measured for the first time the total cross section of this reaction for a quasi-Maxwellian ($kT=25\mathrm{k}\mathrm{e}\mathrm{V}$) neutron flux. The measurement was performed by fast-neutron activation, combined with accelerator mass spectrometry to detect directly the ${}^{63}\mathrm{N}\mathrm{i}$ product nuclei. The experimental value of $28.4\pm 2.8\mathrm{m}\mathrm{b}$, fairly consistent with a recent calculation, affects the calculated net yield of ${}^{62}\mathrm{N}\mathrm{i}$ itself and the whole distribution of nuclei with $62<A<90$ produced by the weak $s$ process in massive stars.

A new survey of all world data on superallowed $\beta$ decays provides demanding tests of, and tight constraints on, the weak interaction. In confirmation of the conserved vector current hypothesis, the vector coupling constant $G_V$ is demonstrated to be constant to better than three parts in ${10}^4$, and any induced scalar current is limited to $f_S\le 0.0013$ in electron rest-mass units. Any possible fundamental scalar current is similarly limited to $|C_S/C_V|\le 0.0013$. The superallowed data also determine the up-down element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix to be $V_{ud}=0.9738(4)$. With Particle Data Group values for $V_{us}$ and $V_{ub}$, the top-row test of CKM unitarity yields $|V_{ud}{|}^2+|V_{us}{|}^2+|V_{ub}{|}^2=0.9966(14)$; if $V_{us}$ comes instead from two recent results on $K_{e3}$ decay, this sum becomes 0.9996(11). Either unitarity result can be used to constrain the possible existence of right-hand currents.

Double differences of masses can be used to isolate specific nucleonic interactions. With the new 2003 mass tabulation a significant increase in the number of empirical average proton-neutron interactions of the last nucleons can be extracted. It is shown that they exhibit dramatic and distinctive patterns, especially near doubly magic nuclei, that these patterns can be interpreted with a simple ansatz based on overlaps of proton and neutron orbits, and that the trends in $p\mathrm{\text{−}}n$ interactions across entire shells can be understood if they are correlated with the fractional shell filling. It is shown how these empirical interactions can be sensitive to changes in shell structure in exotic nuclei. Finally, these results are used to suggest criteria for future mass measurements with new exotic beam facilities.

We have measured transverse momentum distributions of charged hadrons produced in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=62.4\mathrm{G}\mathrm{e}\mathrm{V}$. The spectra are presented for transverse momenta $0.25<p_T<4.5\mathrm{G}\mathrm{e}\mathrm{V}/c$, in a pseudorapidity range of $0.2<\eta <1.4$. The nuclear modification factor $R_{AA}$ is calculated relative to $p+p$ data at the same collision energy as a function of collision centrality. For $2<p_T<4.5\mathrm{G}\mathrm{e}\mathrm{V}/c$, $R_{AA}$ is found to be significantly larger than in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=$ 130 and 200 GeV. In contrast to the large change in $R_{AA}$, we observe a very similar centrality evolution of the $p_T$ spectra at $\sqrt{s_{NN}}=62.4$ and 200 GeV. The dynamical origin of this surprising factorization of energy and centrality dependence of particle production in heavy-ion collisions remains to be understood.

Results of the Jefferson Lab Hall A quasielastic ${}^3\mathrm{H}\mathrm{e}(e,e^{\prime }p)pn$ measurements are presented. These measurements were performed at fixed transferred momentum and energy, $q=1502\mathrm{M}\mathrm{e}\mathrm{V}/c$ and $\omega =840\mathrm{M}\mathrm{e}\mathrm{V}$, respectively, for missing momenta $p_m$ up to $1\mathrm{G}\mathrm{e}\mathrm{V}/c$ and missing energies in the continuum region, up to pion threshold; this kinematic coverage is much more extensive than that of any previous experiment. The cross section data are presented along with the effective momentum density distribution and compared to theoretical models.

We report on charged hadron production in deuteron-gold reactions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. Our measurements in the deuteron direction cover $1.4<\eta <2.2$, referred to as forward rapidity, and in the gold direction $-2.0<\eta <-1.4$, referred to as backward rapidity, and a transverse momentum range $p_T=0.5–4.0\mathrm{G}\mathrm{e}\mathrm{V}/c$. We compare the relative yields for different deuteron-gold collision centrality classes. We observe a suppression relative to binary collision scaling at forward rapidity, sensitive to low momentum fraction ($x$) partons in the gold nucleus, and an enhancement at backward rapidity, sensitive to high momentum fraction partons in the gold nucleus.