Differential cross sections of the reactions $(\gamma ,{\pi }^0{\pi }^0)$ and $(\gamma ,{\pi }^0{\pi }^{+/-})$ have been measured for several nuclei (${}^{\mathrm{1}}\mathrm{H}$,${}^{\mathrm{12}}\mathrm{C}$, and ${}^{\mathrm{n}\mathrm{a}\mathrm{t}}\mathrm{P}\mathrm{b}$) at an incident-photon energy of $E_{\gamma }=400–460\mathrm{M}\mathrm{e}\mathrm{V}$ at the tagged-photon facility at MAMI-B using the TAPS spectrometer. A significant nuclear-mass dependence of the $\pi \pi$ invariant-mass distribution is found in the ${\pi }^0{\pi }^0$ channel. This dependence is not observed in the ${\pi }^0{\pi }^{+/-}$ channel and is consistent with an in-medium modification of the $\pi \pi$ interaction in the $I=J=0$ channel. The data are compared to $\pi$-induced measurements and to calculations within a chiral-unitary approach.

This paper describes the measurement of collective flow for charged particles in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$ using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The measured azimuthal hit anisotropy is presented over a wide range of pseudorapidity ($-5.0<\eta <5.3$) for the first time at this energy. The result, averaged over momenta and particle species, is observed to reach 7% for peripheral collisions at midrapidity, falling off with centrality and increasing $|\eta |$. These results call into question the common assumption of longitudinal boost invariance over a large region of rapidity in RHIC collisions.

We introduce the notion of a generalized partial dynamical-symmetry for which part of the eigenstates have part of the dynamical symmetry. This general concept is illustrated with the example of Hamiltonians with a partial dynamical $\mathrm{O}(6)$ symmetry in the framework of the interacting boson model. The resulting spectrum and electromagnetic transitions are compared with empirical data in ${}^{\mathrm{162}}\mathrm{D}\mathrm{y}$.

From experimental observations of limiting temperatures in heavy ion collisions we derive the critical temperature of infinite nuclear matter $T_c=16.6\pm 0.86$. Theoretical model correlations between $T_c$, the compressibility modulus $K$, the effective mass $m^{*}$, and the saturation density ${\rho }_s$ are then exploited to derive the quantity $(K/m^{*}{)}^{1/2}{\rho }_s^{-1/3}$. This quantity together with calculations employing Skyrme and Gogny interactions indicates a value of $K$ in moderately excited nuclei that is in excellent agreement with the value determined from giant monopole resonance data.

Spin-transfer observables for $\overline{p}p\to \overline{\Lambda }\Lambda$ have been measured using a transversely polarized frozen-spin target and a beam momentum of $1.637\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{/}\mathit{c}$. Current models of the reaction near threshold are in good agreement with existing measurements performed with unpolarized particles in the initial state but produce conflicting predictions for the spin-transfer observables $D_{nn}$ and $K_{nn}$ (the normal-to-normal depolarization and polarization transfer), which are measurable only with polarized target or beam. Measurements of $D_{nn}$ and $K_{nn}$ presented here are found to be in disagreement with predictions from these models.

Two-particle azimuthal correlation functions are presented for charged hadrons produced in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at the Relativistic Heavy Ion Collider ($\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$). The measurements permit determination of elliptic flow without event-by-event estimation of the reaction plane. The extracted elliptic flow values ($v_2$) show significant sensitivity to both the collision centrality and the transverse momenta of emitted hadrons, suggesting rapid thermalization and relatively strong velocity fields. When scaled by the eccentricity of the collision zone $\epsilon$, the scaled elliptic flow shows little or no dependence on centrality for charged hadrons with relatively low $p_T$. A breakdown of this $\epsilon$ scaling is observed for charged hadrons with $p_T>1.0\mathrm{G}\mathrm{e}\mathrm{V}/c$.

Based on the quark coalescence model for the parton-to-hadron phase transition in relativistic heavy ion collisions, we relate the elliptic flow ($v_2$) of high $p_{\mathrm{T}}$ hadrons to that of high $p_{\mathrm{T}}$ quarks. For high $p_{\mathrm{T}}$ hadrons produced from an isospin-symmetric and quark-antiquark–symmetric partonic matter, magnitudes of their elliptic flows follow a flavor ordering as $(v_{2,\pi }=v_{2,N})>(v_{2,\Lambda }=v_{2,\Sigma })>v_{2,K}>v_{2,\Xi }>(v_{2,\varphi }=v_{2,\Omega })$ if strange quarks have a smaller elliptic flow than light quarks. The elliptic flows of high $p_{\mathrm{T}}$ hadrons further follow a simple quark counting rule if strange quarks and light quarks have the same high $p_{\mathrm{T}}$ spectrum and coalescence probability.

Inclusive transverse momentum distributions of charged hadrons within $0.2<p_T<6.0\mathrm{G}\mathrm{e}\mathrm{V}/c$ have been measured over a broad range of centrality for $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$. Hadron yields are suppressed at high $p_T$ in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high-$p_T$ hadron production in heavy-ion collisions at high energy.

The spectrum of prompt conversion electrons emitted by excited ${}^{\mathrm{254}}\mathrm{N}\mathrm{o}$ nuclei has been measured, revealing discrete lines arising from transitions within the ground state band. A striking feature is a broad distribution that peaks near 100 keV and comprises high multiplicity electron cascades, probably originating from $M1$ transitions within rotational bands built on high $K$ states.

The effective interaction problem in nuclear physics is believed to be highly nonperturbative, requiring extended high-momentum spaces for accurate solution. We trace this to difficulties that arise at both short and long distances when the included space is defined in terms of a basis of harmonic oscillator Slater determinants. We show, in the simplest case of the deuteron, that both difficulties can be circumvented, yielding highly perturbative results in the potential even for modest $(\sim 4\hslash \omega )$ included spaces.

We first define a series of $NN$ interaction models ranging from very simple to fully realistic. We then present Green’s function Monte Carlo calculations of light nuclei to show how nuclear spectra evolve as the nuclear forces are made increasingly sophisticated. We find that the absence of stable five- and eight-body nuclei depends crucially on the spin, isospin, and tensor components of the nuclear force.

We show that the second-order phase transition between spherical and deformed shapes of atomic nuclei is an isolated point following from the Landau theory of phase transitions. This point can occur only at the junction of two or more first-order phase transitions which explains why it is associated with one special type of structure and requires the recently proposed first-order phase transition between prolate and oblate nuclear shapes. Finally, we suggest the first empirical example of a nucleus located at the isolated triple-point.

Evidence for particle stability of ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{\mathrm{4}}\mathrm{H}$ has been suggested by the BNL-AGS E906 experiment. We report on Faddeev-Yakubovsky calculations for the four-body $\Lambda \Lambda pn$ system using $\Lambda N$ interactions which reproduce the observed binding energy of ${}_{\mathrm{\Lambda }}{}^{\mathrm{3}}\mathrm{H}({\frac{1}{2}}^{+})$ within a Faddeev calculation for the $\Lambda pn$ subsystem. No ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{\mathrm{4}}\mathrm{H}$ bound state is found over a wide range of $\Lambda \Lambda$ interaction strengths, although the Faddeev equations for a three-body $\Lambda \Lambda d$ model of ${}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{\mathrm{4}}\mathrm{H}$ admit a $1^{+}$ bound state for as weak a $\Lambda \Lambda$ interaction strength as required to reproduce $B_{\Lambda \Lambda }({}_{\mathrm{\Lambda }\mathrm{\Lambda }}{}^{\mathrm{6}}\mathrm{H}\mathrm{e})$.

The differential cross section for electron-induced neutron knockout in the reaction ${}^{\mathrm{4}}\mathrm{H}\mathrm{e}(e,e^{\prime }n){}^{\mathrm{3}}\mathrm{H}\mathrm{e}$ has been measured for the first time with a statistical accuracy of 11%. The experiment was performed in quasielastic kinematics at a momentum transfer of $300\mathrm{M}\mathrm{e}\mathrm{V}/c$ and in the missing-momentum range of $25–70\mathrm{M}\mathrm{e}\mathrm{V}/c$. The comparison of the data with theoretical calculations shows an impressive increase of the cross section resulting from final state interaction effects. Specifically , the $p\mathrm{\text{−}}n$ charge-exchange process dominates the cross section in this kinematical regime.

Modification of parton fragmentation functions by multiple scattering and gluon bremsstrahlung in nuclear media is shown to describe very well the recent HERMES data in deeply inelastic scattering, giving the first evidence of the $A^{2/3}$ dependence of the modification. The energy loss is found to be $⟨dE/dL⟩\approx 0.5\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{f}\mathrm{m}$ for a 10-GeV quark in an Au nucleus. Including the effect of expansion, analysis of the ${\pi }^0$ spectra in central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s}=130\mathrm{G}\mathrm{e}\mathrm{V}$ yields an averaged energy loss equivalent to $⟨dE/dL⟩\approx 7.3\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{f}\mathrm{m}$ in a static medium. Predictions for central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s}=200\mathrm{G}\mathrm{e}\mathrm{V}$ are also given.

The physical interpretation of nuclear rainbow scattering within the frame of the optical model is critically investigated. Starting from the properties of the Luneburg lens, a gradient index device that displays refractive features similar to those of the nuclear potential, important differences between the mechanisms producing the nuclear and optical rainbows are pointed out.

Using a multiphase transport model that includes both initial partonic and final hadronic interactions, we study the pion interferometry at the Relativistic Heavy-Ion Collider. We find that the two-pion correlation function is sensitive to the magnitude of the parton-scattering cross section, which controls the parton density at which the transition from the partonic to hadronic matter occurs. Also, the emission source of pions is non-Gaussian, leading to source radii that can be more than twice larger than the radius parameters extracted from a Gaussian fit to the correlation function.

Variational calculations for $s$-shell hypernuclei are performed by explicitly including $\Sigma$ degrees of freedom. Four sets of $YN$ interactions [SC97d(S), SC97e(S), SC97f(S), and SC89(S)] are used. The bound-state solution of ${}_{\mathrm{\Lambda }}{}^{\mathrm{5}}\mathrm{H}\mathrm{e}$ is obtained and a large energy expectation value of the tensor $\Lambda N\mathrm{\text{−}}\Sigma N$ transition part is found. The internal energy of the ${}^{\mathrm{4}}\mathrm{H}\mathrm{e}$ subsystem is strongly affected by the presence of a $\Lambda$ particle with the strong tensor $\Lambda N\mathrm{\text{−}}\Sigma N$ transition potential.

The isovector and isotensor energy differences between yrast states of isobaric multiplets in the lower half of the $pf$ region are quantitatively reproduced in a shell model context. The isospin nonconserving nuclear interactions are found to be at least as important as the Coulomb potential. Their isovector and isotensor channels are dominated by $J=2$ and $J=0$ pairing terms, respectively. The results are sensitive to the radii of the states, whose evolution along the yrast band can be accurately followed.

The nucleus ${}^{\mathrm{163}}\mathrm{L}\mathrm{u}$ has been populated through the reaction ${}^{\mathrm{139}}\mathrm{L}\mathrm{a}({}^{\mathrm{29}}\mathrm{S}\mathrm{i},5n)$ with a beam energy of 157 MeV. Three triaxial, strongly deformed (TSD) bands have been observed with very similar rotational properties. The first excited TSD band has earlier been assigned as a one-phonon wobbling excitation built on the lowest-lying (yrast) TSD band. The large $B(E2{)}_{\mathrm{o}\mathrm{u}\mathrm{t}}/B(E2{)}_{\mathrm{i}\mathrm{n}}$ value obtainable for one of four observed transitions between the second and first excited TSD bands is in good agreement with particle-rotor calculations for a two-phonon wobbling excitation.