The correlation coefficients $a$, $A$, and $B$ in neutron $\beta$ decay are proportional to the ratio of the axial-vector-to-vector weak coupling constants, $g_A{/g}_V$, to leading recoil order. With the advent of the next generation of neutron-decay experiments, the recoil-order corrections to these expressions become experimentally accessible, admitting a plurality of standard model (SM) tests. The measurement of both $a$ and $A$, e.g., allows one to test the conserved-vector-current (CVC) hypothesis and to search for second-class currents (SCC) independently. The anticipated precision of these measurements suggests that the bounds on CVC violation and SCC from studies of nuclear $\beta$ decay can be qualitatively bettered.

We measured the cross section and response functions for the quasielastic ${}^{16}\mathrm{O}\left({e,e}^{\prime }p\right)$ reaction for missing energies $25\le E_m\le 120\mathrm{MeV}$ at missing momenta $P_m\le 340\mathrm{MeV}/c$. For $25<\mathrm{}{E}_m<50\mathrm{}\mathrm{MeV}$ and $P_m\approx 60\mathrm{MeV}/c$, the reaction is dominated by a single ${1s}_{1/2}$ proton knockout. At larger $P_m$, the single-particle aspects are increasingly masked by more complicated processes. Calculations which include pion exchange currents, isobar currents, and short-range correlations account for the shape and the transversity, but for only half of the magnitude of the measured cross section.

A kinetic master equation for multiplicity distributions is formulated for charged particles which are created or destroyed only in pairs due to the conservation of their Abelian charge. It allows one to study time evolution of the multiplicity distributions in a relativistic many-body system with arbitrary average particle multiplicities. It is shown to reproduce the equilibrium results for both canonical (rare particles) and grand canonical (abundant particles) systems. For canonical systems, the equilibrium multiplicity is much lower and the relaxation time is much shorter than the naive extrapolation from grand canonical results. Implications for chemical equilibration in heavy-ion collisions are also discussed.

The dipole response of stable and unstable neutron-rich oxygen nuclei of masses $A=17\mathrm{}$ to $A=22\mathrm{}$ has been investigated experimentally utilizing electromagnetic excitation in heavy-ion collisions at beam energies about $600\mathrm{MeV}/\mathrm{nucleon}$. A kinematically complete measurement of the neutron decay channel in inelastic scattering of the secondary beam projectiles from a Pb target was performed. Differential electromagnetic excitation cross sections $d\sigma /dE$ were derived up to 30 MeV excitation energy. In contrast to stable nuclei, the deduced dipole strength distribution appears to be strongly fragmented and systematically exhibits a considerable fraction of low-lying strength.

New electron scattering measurements have been made that extend data on the ${}^3\mathrm{He}$ elastic magnetic form factor up to $Q^2=42.6\mathrm{}{\mathrm{fm}}^{-2\mathrm{}}$. These new data test theoretical conjectures regarding non-nucleonic effects in the three-body system. The very small cross sections, as low as ${10}^{-40\mathrm{}}{\mathrm{cm}}^2/\mathrm{sr}$, required the use of a high-pressure cryogenic gas target and a detector system with excellent background rejection capability. No existing theoretical calculation satisfactorily accounts for all the available data.

Standard analyses of low-energy $\mathrm{NN}$ and nuclear parity-violating observables have been based on a $\pi$-, $\rho$-, and $\omega$-exchange model capable of describing all five independent $s-p$ partial waves. Here a parallel analysis is performed for the one-body, exchange-current, and nuclear polarization contributions to the anapole moments of ${}^{133}\mathrm{Cs}$ and ${}^{205}\mathrm{Tl}$. The resulting constraints are not consistent, though there remains some degree of uncertainty in the nuclear structure analysis of the atomic moments.

Pseudospin symmetry in nuclei is investigated considering the Dirac equation with a Lorentz structured Woods-Saxon potential. The isospin correlation of the energy splittings of pseudospin partners with the nuclear potential parameters is studied. We show that, in an isotopic chain, the pseudospin symmetry is better realized for neutrons than for protons. This behavior comes from balance effects among the central nuclear potential parameters. In general, we found an isospin asymmetry of the nuclear pseudospin interaction, opposed to the nuclear spin-orbit interaction which is quasi-isospin symmetric.

We measured the invariant mass spectra of electron-positron pairs in the target rapidity region of 12-GeV $p+A$ reactions. We have observed a significant difference in the mass spectra below the $\omega$ meson between $p+\mathrm{C}$ and $p+\mathrm{Cu}$ interactions. This difference indicates that the spectral shape of mesons is modified at normal nuclear-matter density.

A three parameter scaling relationship between isotopic distributions for elements with $Z\le 8$ has been observed. This allows a simple description of the dependence of such distributions on the overall isospin of the system. This scaling law (termed isoscaling) applies for a variety of reaction mechanisms that are dominated by phase space, including evaporation, multifragmentation, and deeply inelastic scattering. The origins of this scaling behavior for the various reaction mechanisms are explained. For multifragmentation processes, the systematics is influenced by the density dependence of the asymmetry term of the equation of state.

We report results on the ratio of midrapidity antiproton-to-proton yields in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$ per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of $|y|<0.5\mathrm{}$ and $0.4<\mathrm{}{p}_t<1.0\mathrm{}\mathrm{GeV}/c$, the ratio is essentially independent of either transverse momentum or rapidity, with an average of $0.65\pm {0.01}_{\left(\mathrm{stat}\right)}\pm {0.07}_{\left(\mathrm{syst}\right)}$ for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the $p-\overline{p}$ pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.

Radial and elliptic flow in noncentral heavy-ion collisions can constrain the effective equation of state (EOS) of the excited nuclear matter. To this end, a model combining relativistic hydrodynamics and a hadronic transport code [Sorge, Phys. Rev. C 52, 3291 (1995)] is developed. For an EOS with a first-order phase transition, the model reproduces both the radial and elliptic flow data at the SPS. With the EOS fixed from SPS data, we quantify predictions at RHIC where the quark-gluon plasma (QGP) pressure is expected to drive additional radial and elliptic flows. Currently, the strong elliptic flow observed in the first RHIC measurements does not conclusively signal this nascent QGP pressure.

Recently developed chiral nucleon-nucleon $\left(\mathrm{NN}\right)$ forces at next-to-leading order (NLO), that describe $\mathrm{NN}$ phase shifts up to about 100 MeV fairly well, have been applied to $3N$ and $4N$ systems. Faddeev-Yakubovsky equations have been solved rigorously. The resulting $3N$ and $4N$ binding energies are in the same range as found using standard $\mathrm{NN}$ potentials. In addition, low-energy $3N$ scattering observables are very well reproduced as for standard $\mathrm{NN}$ forces. The long-standing $A_y$ puzzle is absent at NLO. The cutoff dependence of the scattering observables is rather weak.

We introduce an exactly solvable model for interacting bosons that extend up to high spin and interact through a repulsive pairing force. The model exhibits a phase transition to a state with almost complete $\mathrm{sd}$ dominance. The repulsive pairing interaction that underlies the model has a natural microscopic origin in the Pauli exclusion principle between constituent nucleons. As such, repulsive pairing between bosons seems to provide a new mechanism for the enhancement of $\mathrm{sd}$ dominance, giving further support for the validity of the $\mathrm{sd}$ interacting boson model.

We report an analysis of the nuclear dependence of the yield of Drell-Yan dimuons from the $800\mathrm{GeV}/c$ proton bombardment of ${}^2\mathrm{H}$, C, Ca, Fe, and W targets. Employing a new formulation of the Drell-Yan process in the rest frame of the nucleus, this analysis examines the effect of initial-state energy loss and shadowing on the nuclear-dependence ratios versus the incident proton's momentum fraction and dimuon effective mass. The resulting energy loss per unit path length is $-dE/dz=2.32\mathrm{}\pm 0.52\pm 0.5\mathrm{GeV}/\mathrm{fm}$. This is the first observation of a nonzero energy loss of partons traveling in a nuclear environment.

The $T=2\mathrm{}$ excitations in even-even $N=Z$ nuclei are calculated within the isospin cranked mean-field approach. The response of pairing correlations to rotation in isospace is investigated. Whereas the isovector pairing rather modestly modifies the single-particle moment of inertia in isospace, the isoscalar pairing strongly reduces its value. This reduction of the isomoments of inertia with respect to its rigid body value is a strong indicator of collective isoscalar pairing correlations. These results are further generalized yielding beautiful analogies between the role of isovector pairing for the case of spatial rotations and the role of isoscalar pairing for the case of isorotations.

We derive stability conditions of asymmetric nuclear matter (ANM) and discuss the relation to mechanical and chemical instabilities of general two-component systems. We show that the chemical instability may appear as an instability of the system against isoscalarlike rather than isovectorlike fluctuations if the interaction between the two constituent species has an attractive character as in the case of ANM. This leads to a new kind of liquid-gas phase transition, of interest for fragmentation experiments with radioactive beams.

No conventional picture of nucleus-nucleus collisions has yet been able to explain the abundance of $\Omega$ and $\overline{\Omega }$ hadrons in central collisions between Pb nuclei at $158A\mathrm{GeV}$ at the CERN SPS. We argue that this is evidence that they are produced as topological defects arising from the formation of disoriented chiral condensates with an average domain size of about 2 fm.

The spin-orbit splitting of $\Lambda$ single-particle states in ${}_{\Lambda }^{13}\mathrm{C}$ was measured. The ${}^{13}\mathrm{C}(K^{-},{\pi }^{-}{)}_{\Lambda }^{13}\mathrm{C}$ reaction was used to excite both the $1/2^{-}$ and $3/2^{-}$ states simultaneously, which have predominantly ${}^{12}\mathrm{C}\left(0^{+}\right)\times p_{\Lambda }$ configuration. $\gamma$ rays from the states to the ground state were measured in coincidence with the ${\pi }^{-}$'s, by which $\ell s$ splitting was found to be $152\pm 54\left(\mathrm{stat}\right)\pm 36\left(\mathrm{syst}\right)\mathrm{keV}$. The value is 20–30 times smaller than exhibited by the $\ell s$ splitting in the nuclear shell model. This value gives us new insight into the YN interaction.

The $Q$ value of the ${}^{76}\mathrm{Ge}$ double beta decay has been determined by measuring the masses of ${}^{76}\mathrm{Ge}$ and ${}^{76}\mathrm{Se}$ in a Penning trap using neon- and fluorinelike ions. The obtained masses are 75.921 402 758(96) u and 75.919 213 795(81) u, respectively. The systematic errors of these two determinations are nearly equal, and therefore, the remaining systematic uncertainty of the $Q$ value is drastically reduced. A $Q$ value of 2 039.006(50) keV was obtained improving the accuracy of the accepted value by a factor of 6.