First $\beta$- and $\gamma$-spectroscopic decay studies of the $N=82$ $r$-process “waiting-point” nuclide ${}^{130}\mathrm{C}\mathrm{d}$ have been performed at CERN/ISOLDE using the highest achievable isotopic selectivity. Several nuclear-physics surprises have been discovered. The first one is the unanticipatedly high energy of 2.12 MeV for the [$\pi g_{9/2}\otimes \nu g_{7/2}]$ $1^{+}$ level in ${}^{130}\mathrm{I}\mathrm{n}$, which is fed by the main Gamow-Teller transition. The second surprise is the rather high $Q_{\beta }$ value of 8.34 MeV, which is in agreement only with recent mass models that include the phenomenon of $N=82$ shell quenching. Possible implications of these new results on the formation of the $A\simeq 130$ $r$-process abundance peak are presented.

The one-proton knockout channel from ${}^6\mathrm{H}\mathrm{e}$ ($240\mathrm{M}\mathrm{e}\mathrm{V}/u$) impinging on a carbon target has been investigated. The triton fragments originating from this channel were detected in coincidence with the two neutrons. A broad structure, peaked at 3 MeV above the $t+2n$ threshold, is observed in the $t+n+n$-relative energy spectrum. It is shown that this structure is mainly due to a $I^{\pi }=1/2^{+}$ resonance as expected for the ${}^5\mathrm{H}$ ground state, and from the observed angular and energy correlations, being used for the first time in ${}^5\mathrm{H}$ studies, that the neutrons to a large extent occupy the $p$ shell.

Source images are extracted from two-particle correlations constructed from strange and nonstrange hadrons produced in $6A\mathrm{G}\mathrm{e}\mathrm{V}$ $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions. Very different source images result from $pp$ vs $p\Lambda$ vs ${\pi }^{-}{\pi }^{-}$ correlations. Scaling by transverse mass can describe the apparent source size ratio for $p/{\pi }^{-}$ but not for $\Lambda /{\pi }^{-}$ or $\Lambda /p$. These observations suggest important differences in the space-time emission histories for protons, pions, and neutral strange baryons produced in the same events.

Lifetimes of states in the lowest lying positive parity band in ${}^{106}\mathrm{C}\mathrm{d}$ have been measured using the Doppler shift attenuation method. The deduced $B(E2)$ transition rates show a marked decrease with increasing spin. Cranking and semiclassical model calculations suggest that the structure has the character of a shears-type band resulting from the coupling of $g_{9/2}$ proton holes to aligned pairs of $h_{11/2}$ and $g_{7/2}$ neutron particles. This is the first clear evidence for the phenomenon of “antimagnetic” rotation in nuclei.

We study the quantum phase transition mechanisms that arise in the interacting boson model. We show that the second-order nature of the phase transition from U(5) to O(6) may be attributed to quantum integrability, whereas all the first-order phase transitions of the model are due to level repulsion with one singular point of level crossing. We propose a model Hamiltonian with a true first-order phase transition for finite systems due to level crossings.

We report a new measurement of the neutron decay lifetime by the absolute counting of in-beam neutrons and their decay protons. Protons were confined in a quasi-Penning trap and counted with a silicon detector. The neutron beam fluence was measured by capture in a thin ${}^6\mathrm{L}\mathrm{i}\mathrm{F}$ foil detector with known absolute efficiency. The combination of these simultaneous measurements gives the neutron lifetime: ${\tau }_n=(886.8\pm 1.2[\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}]\pm 3.2[\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}])\mathrm{s}$. The systematic uncertainty is dominated by uncertainties in the mass of the ${}^6\mathrm{L}\mathrm{i}\mathrm{F}$ deposit and the ${}^6\mathrm{L}\mathrm{i}(n,t)$ cross section. This is the most precise measurement of the neutron lifetime to date using an in-beam method.

Evaporation residue cross sections have been measured with neutron-rich radioactive ${}^{132}\mathrm{S}\mathrm{n}$ beams on ${}^{\mathrm{64}}\mathrm{N}\mathrm{i}$ in the vicinity of the Coulomb barrier. The average beam intensity was $2\times {10}^4$ particles per second and the smallest cross section measured was less than 5 mb. Large sub-barrier fusion enhancement was observed. Coupled-channel calculations taking into account inelastic excitation significantly underpredict the measured cross sections below the barrier. The presence of several neutron transfer channels with large positive $Q$ values suggests that multinucleon transfer may play an important role in enhancing the fusion of ${}^{132}\mathrm{S}\mathrm{n}$ and ${}^{\mathrm{64}}\mathrm{N}\mathrm{i}$.

Differential production cross sections of $K^{-}$ and $K^{+}$ mesons have been measured in $\mathrm{N}\mathrm{i}+\mathrm{N}\mathrm{i}$ and $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at a beam energy of $1.5\mathrm{A}\mathrm{G}\mathrm{e}\mathrm{V}$. The $K^{-}/K^{+}$ ratio is found to be nearly constant as a function of the collision centrality and system size. The spectral slopes and the polar emission pattern differ for $K^{-}$ and $K^{+}$ mesons. These observations indicate that $K^{+}$ mesons decouple earlier from the fireball than $K^{-}$ mesons.

The apparent discrepancy between the Rosenbluth and the polarization transfer methods for the ratio of the electric to magnetic proton form factors can be explained by a two-photon exchange correction which does not destroy the linearity of the Rosenbluth plot. Though intrinsically small, of the order of a few percent of the cross section, this correction is accidentally amplified in the case of the Rosenbluth method.

Two-photon exchange contributions to elastic electron-proton scattering cross sections are evaluated in a simple hadronic model including the finite size of the proton. The corrections are found to be small in magnitude, but with a strong angular dependence at fixed $Q^2$. This is significant for the Rosenbluth technique for determining the ratio of the electric and magnetic form factors of the proton at high $Q^2$, and partly reconciles the apparent discrepancy with the results of the polarization transfer technique.

We report the first observation of the charge symmetry breaking $d+d\to {}^4\mathrm{H}\mathrm{e}+{\pi }^0$ reaction near threshold. Measurements using a magnetic channel (gated by two photons) of the ${}^4\mathrm{H}\mathrm{e}$ scattering angle and momentum (from time of flight) permitted reconstruction of the ${\pi }^0$ “missing mass,” the quantity used to separate ${}^4\mathrm{H}\mathrm{e}+{\pi }^0$ events from the continuum of double radiative capture ${}^4\mathrm{H}\mathrm{e}+\gamma +\gamma$ events. We measured total cross sections for neutral pion production of $12.7\pm 2.2\mathrm{p}\mathrm{b}$ at 228.5 MeV and $15.1\pm 3.1\mathrm{p}\mathrm{b}$ at 231.8 MeV. The uncertainty is dominated by statistical errors. These cross sections arise fundamentally from the down-up quark mass difference and quark electromagnetic effects that contribute in part through meson mixing (e.g., ${\pi }^0-\eta$) mechanisms.

We study the effect of spatially homogeneous and inhomogeneous shadowing on $J/\psi$ production in deuterium-nucleus collisions. We discuss how the shadowing and its spatial dependence can be measured by comparing central and peripheral $dA$ collisions. These event classes may be selected by using gray protons from heavy ion breakup and events where the proton or neutron in the deuterium does not interact. We find that inhomogeneous shadowing has a significant effect on central $dA$ collisions, larger than expected in central $AA$ collisions. Results are presented for $d\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$ and $d\mathrm{P}\mathrm{b}$ collisions at $\sqrt{s_{NN}}=6.2\mathrm{T}\mathrm{e}\mathrm{V}$.

Phase transitions in angle variables are studied. An example of angular phase transition, an axially to triaxially deformed “shape” transition in nuclei, is discussed. Spectroscopic signatures for the occurrence of these transitions are suggested. Preliminary experimental evidence is presented.

High-spin states in ${}^{135}\mathrm{N}\mathrm{d}$ were populated with the ${}^{110}\mathrm{P}\mathrm{d}({}^{30}\mathrm{S}\mathrm{i},5n){}^{135}\mathrm{N}\mathrm{d}$ reaction at a ${}^{30}\mathrm{S}\mathrm{i}$ bombarding energy of 133 MeV. Two $\Delta I=1$ bands with close excitation energies and the same parity were observed. These bands are directly linked by $\Delta I=1$ and $\Delta I=2$ transitions. The chiral nature of these two bands is confirmed by comparison with three-dimensional tilted axis cranking calculations. This is the first observation of a three-quasiparticle chiral structure and establishes the primarily geometric nature of this phenomenon.

A general scheme is proposed here to describe the production of semihard and soft quarks and gluons that form the bulk of the plasma in ultrarelativistic heavy-ion collisions. We show how to obtain the production rates in the extended phase space, including the color part, as a function of time in a consistent manner and without having to make ad hoc assumptions. All the required features—the back reaction on QCD vacuum, the non-Markovian nature of the production, and the quasi particle nature of the partons—are naturally incorporated. We illustrate the results with a realistic albeit toy model and also show how physically tenable source terms may be obtained.

By combining a one-meson-exchange model for the $\Lambda N\to nN$ transition in finite nuclei with an intranuclear cascade code, we have obtained nucleon-nucleon (angular and energy) coincidence distributions from the nonmesonic weak decay of ${}_{\Lambda }{}^5\mathrm{H}\mathrm{e}$ and ${}_{\Lambda }{}^{12}\mathrm{C}$ hypernuclei. Although, due to the elimination of interferences, two-nucleon coincidences are expected to give a cleaner extraction (with respect to single nucleon observables) of the ratio ${\Gamma }_n/{\Gamma }_p\equiv \Gamma (\Lambda n\to nn)/\Gamma (\Lambda p\to np)$, we show that the effect of the final state interactions is still important even when applying favorable energy and angular cuts. The agreement of our results for the ratio $N_{nn}/N_{np}$ between the number of $nn$ and $np$ emitted pairs with preliminary KEK coincidence data allows us to conclude that ${\Gamma }_n/{\Gamma }_p$ for ${}_{\Lambda }{}^5\mathrm{H}\mathrm{e}$ should be small and close to the value of 0.46 predicted by our meson-exchange model.

A low-energy coexisting band $J^{\pi }$ ($E_x\mathrm{k}\mathrm{e}\mathrm{V}$) $0^{+}$ (1182), $2^{+}$ (1418), $4^{+}$ (1701) is identified in the deformed nucleus, ${}^{154}\mathrm{G}\mathrm{d}$. Detailed $\gamma$-ray spectroscopy following the $\beta$ decays of ${}^{154}\mathrm{E}\mathrm{u}$ ($J=3$), ${}^{154g,m_1,m_2}\mathrm{T}\mathrm{b}$ ($J=0,3,7$) is used to establish this structure. The structure is explained in terms of the pairing and deformation degrees of freedom, a “pairing isomer,” which results from the $\nu [505]\uparrow$ Nilsson intruder orbital.

A new expression for the branching ratio for the decay via the $E1$ process in the normal-deformed band of superdeformed nuclei is given within a simple two-level model. Using this expression, the spreading or tunneling width ${\Gamma }^{\downarrow }$ for superdeformed decay can be expressed entirely in terms of experimentally known quantities. We show how to determine the tunneling matrix element $V$ from the measured value of ${\Gamma }^{\downarrow }$ and a statistical model of the energy levels. The accuracy of the two-level approximation is verified by considering the effects of the other normal-deformed states.

Data are presented for the reaction ${\pi }^{-}p\to {\pi }^0{\pi }^{0}n$ in the range from threshold to $p_{{\pi }^{-}}=750\mathrm{M}\mathrm{e}\mathrm{V}/c$. The systematics of the data and multipole analyses are examined for sensitivity to a $f_0(600)$ (“$\sigma$”) meson. A one-pion-exchange mechanism is found to be very weak, or absent. The reaction appears to become dominated by sequential ${\pi }^0$ decays through the $\Delta (1232)$ resonance as the beam momentum increases, along with substantial interference effects from several competing mechanisms.

The emission time chronology of neutrons, protons, and deuterons from the $E/A=61\mathrm{M}\mathrm{e}\mathrm{V}$ ${}^{36}\mathrm{A}\mathrm{r}+{}^{27}\mathrm{A}\mathrm{l}$ reaction is deduced from two-particle correlation functions.