We have measured the proton elliptic flow excitation function for the $\mathrm{Au}+\mathrm{Au}$ system spanning the beam energy range $(2–8)A\mathrm{GeV}$. The excitation function shows a transition from negative to positive elliptic flow at a beam energy, $E_{\mathrm{tr}}\sim 4A\mathrm{GeV}$. Detailed comparisons with calculations from a relativistic Boltzmann equation are presented. The comparisons suggest a softening of the nuclear equation of state from a stiff form ( $K\sim 380\mathrm{MeV}$) at low beam energies ( $E_{\mathrm{beam}}\le 2A\mathrm{GeV}$) to a softer form ( $K\sim 210\mathrm{MeV}$) at higher energies ( $E_{\mathrm{beam}}\ge 4A\mathrm{GeV}$) where the calculated baryon density $\rho \sim 4{\rho }_0$.

The positron-neutrino correlation in the $0^{+}\to 0^{+}$ $\beta$ decay of ${}^{32}\mathrm{Ar}$ was measured at ISOLDE by analyzing the effect of lepton recoil on the shape of the narrow proton group following the superallowed decay. Our result is consistent with the standard model prediction. For vanishing Fierz interference we find $a=0.9989\mathrm{}\pm 0.0052\pm 0.0039$, which yields improved constraints on scalar weak interactions.

The nucleus ${}^{94}\mathrm{Mo}$ was investigated using a powerful combination of $\gamma$-singles photon scattering experiments and $\gamma \gamma$-coincidence studies following the $\beta$ decay of ${}^{94}{\mathrm{Tc}}^m$. The data survey short-lived $J^{\pi }{=1\mathrm{}}^{+}{,2\mathrm{}}^{+}$ states and include branching ratios, $E2\mathrm{}/M1\mathrm{}$ mixing ratios, lifetimes, and transition strengths. The proton-neutron mixed-symmetry (MS) $1^{+}$ scissors mode and the $2^{+}$ MS state are identified from $M1\mathrm{}$ strengths. A $\gamma$ transition between MS states was observed and its rate was measured. Nine $M1\mathrm{}$ and $E2\mathrm{}$ strengths involving MS states agree with the O(6) limit of the interacting boson model-2 using the proton boson $E2\mathrm{}$ charge as the only free parameter.

Following a prediction by Smolańczuk [Phys. Rev. C 59, 2634 (1999)], we searched for superheavy element formation in the bombardment of ${}^{208}\mathrm{Pb}$ with 449-MeV ${}^{86}\mathrm{Kr}$ ions. We have observed three decay chains, each consisting of an implanted heavy atom and six subsequent $\alpha$ decays, correlated in time and position. In these decay chains, a rapid (ms) sequence of high energy $\alpha$ particles ( $E_{\alpha }\ge 10\mathrm{MeV}$) indicates the decay of a new high- $Z$ element. The observed chains are consistent with the formation of ${}_{}{}^{293}{}_{}{}^{}118$ and its decay by sequential $\alpha$-particle emission to ${}_{}{}^{289}{}_{}{}^{}116$, ${}_{}{}^{285}{}_{}{}^{}114$, ${}_{}{}^{281}{}_{}{}^{}112$, ${}_{}{}^{277}{}_{}{}^{}110$, ${}^{273}\mathrm{Hs}$ ( $Z=108\mathrm{}$) and ${}^{269}\mathrm{Sg}$ ( $Z=106\mathrm{}$). The production cross section is ${2.2}_{-0.8\mathrm{}}^{+2.6\mathrm{}}\mathrm{pb}$.

Structure of the odd- $N$ superheavy elements with $Z\lesssim 118$ and $N\lesssim 175$ is investigated using the self-consistent Skyrme-Hartree-Fock-Bogoliubov method with pairing. Microscopic analysis of one-quasiparticle neutron states, alpha-decay energies, and deformations is performed. Good agreement was obtained with the recently reported $\alpha$-decay chains of ${}^{289}114$ and ${}^{293}118$.

The extremely neutron-rich nucleus ${}^{19}\mathrm{C}$ has been studied by Coulomb dissociation into ${}^{18}\mathrm{C}+n$ at $67A\mathrm{MeV}$. A large $E1\mathrm{}$ strength of $0.71\pm 0.07e^2\mathrm{fm}{}^2$ has been observed at low excitation energies. An analysis of the angular distribution of ${}^{18}\mathrm{C}+n$ center of mass has led to a determination of the neutron separation energy of ${}^{19}\mathrm{C}$ to be $530\pm 130\mathrm{keV}$. The $E1\mathrm{}$ strength distribution can be well reproduced for a ${}^{19}\mathrm{C}$ ground state structure with a dominant $s$-wave valence neutron, providing a consistent picture of the neutron halo structure of ${}^{19}\mathrm{C}$.

Fine structure in the ground-state proton radioactive decay of highly deformed ${}^{131}\mathrm{Eu}$ has been identified. In addition to the previously observed ground-state line, measured here with a proton energy of 932(7) keV, a second proton peak with energy 811(7) keV was observed. We interpret this line as proton decay from the ${}^{131}\mathrm{Eu}$ ground state to the first excited $2^{+}$ state of the daughter nucleus ${}^{130}\mathrm{Sm}$. Comparing the measured branching ratio with calculations enables the ground-state configuration of ${}^{131}\mathrm{Eu}$ to be unambiguously assigned to the $3/2^{+}$[411] Nilsson configuration.

We study the connection between the Fourier transforms of one- and two-body observations and the excitation of multiple vibrations. We show that one-body observables give information on the excitation of a single vibration while two-body operators are needed to measure the excitation of double vibrations. Therefore, while mean-field approaches correctly predict the excitation of a single vibration, the study of multiple vibrations requires the estimation of many-body observables which goes beyond the mean-field approximation. These findings are illustrated in an algebraical model.

A Comment on the Letter by G. M. Irwin and K. H. Kim, Phys. Rev. Lett. 79, 990 (1997). The authors of the Letter offer a Reply.

A Reply to the Comment by F. F. Karpeshin, et al.

Neutral pion production in central $158A\mathrm{GeV}$ ${}^{208}\mathrm{Pb}+{}^{208}\mathrm{Pb}$ collisions has been studied in the WA98 experiment at the CERN Super Proton Synchrotron. The ${\pi }^0$ transverse mass spectrum has been analyzed in terms of a thermal model with hydrodynamic expansion. The high accuracy and large kinematic coverage of the measurement allow one to limit previously noted ambiguities in the extracted freeze-out parameters. The results are shown to be sensitive to the shape of the velocity distribution at freeze-out.

We note that, in the limit where the $\mathrm{NN}$ ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ and ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ scattering lengths, $a^{{(}^1{S}_0)}$ and $a^{{(}^3{S}_1)}$, go to infinity, the leading terms in the effective field theory for strong $\mathrm{NN}$ interactions are invariant under Wigner's SU(4) spin-isospin symmetry. This explains why the leading effects of radiation pions on the $S$-wave $\mathrm{NN}$ scattering amplitudes vanish as $a^{{(}^1{S}_0)}$ and $a^{{(}^3{S}_1)}$ go to infinity. The implications of Wigner symmetry for $\mathrm{NN}\to \mathrm{NN}$ axion and $\gamma d\to \mathrm{np}$ are also considered.

We have measured the hyperfine structure of the ${7P}_{1/2}$ level for ${}^{208-212}\mathrm{Fr}$ to a precision of 300 ppm. These measurements along with previous ground state hyperfine structure measurements reveal a hyperfine anomaly. The hyperfine anomaly exhibits a strong sensitivity to the radial distribution of the neutron magnetization, providing a good way to probe this quantity. We use neutron radial distributions from recent theories to qualitatively explain the measurements.

Threshold measurements of the associated strangeness production reactions $\mathrm{pp}\to {\mathrm{pK}}^{+}\Lambda$ and $\mathrm{pp}\to {\mathrm{pK}}^{+}{\Sigma }^0$ are presented. The most remarkable feature of the data is that at the same excess energy the total cross section for the ${\Sigma }^0$ production appears to be about a factor of ${28}_{-9\mathrm{}}^{+6\mathrm{}}$ smaller than for the $\Lambda$ particle. It is concluded that strong ${\Sigma }^{0}p$ final state interactions, and in particular the $\Sigma N\to \Lambda p$ conversion reaction, are the likely cause of the depletion in the $\Sigma$ signal. This hypothesis is in line with other experimental evidence in the literature.

The lightest superdeformed nuclei of the mass-60 region are described using the projected shell model. In contrast to the heaviest superdeformed nuclei where a coherent motion of nucleons often dominates the physics, it is found that alignment of $g_{9/2}$ proton and neutron pairs determines the high spin behavior for superdeformed rotational bands in this mass region. It is predicted that, due to the systematics of shell fillings along the even-even Zn isotopic chain, observation of a regular superdeformed yrast band sequence will be unlikely for certain nuclei in this mass region.

The isovector electric monopole resonance (IVMR) was studied by the ${}^{60}\mathrm{Ni}{(}^7\mathrm{Li}{,}^7\mathrm{Be}{)}^{60}\mathrm{Co}$ reaction at 65A MeV and at forward scattering angles including zero degrees. We confirmed the existence of the IVMR at an excitation energy of $20\pm 2\mathrm{MeV}$ with a width of $10\pm 2\mathrm{MeV}$ in ${}^{60}\mathrm{Co}$, which is an analog of the $T_0+1\mathrm{}$ isospin component of the IVMR estimated at $E_x\approx 31\mathrm{MeV}$ in ${}^{60}\mathrm{Ni}$. The result presently obtained is consistent with previous results using the pion charge-exchange reaction.

The total cross section for $\omega$ production in the $\mathrm{pp}\to \mathrm{pp}\omega$ reaction has been measured at 5 c.m. excess energies from 3.8 to 30 MeV. The energy dependence is easily understood in terms of a strong proton-proton final state interaction combined with a smearing over the width of the state. The ratio of near-threshold $\phi$ and $\omega$ production is, to within relatively large uncertainties, consistent with the predictions of a simple one-pion-exchange model. The degree of violation of the Okubo-Zweig-Iizuka rule is similar to that found in the ${\pi }^{-}p\to n\omega /\phi$ reactions.

Peripheral fragmentation of a 287 MeV/nucleon beam of the halo nucleus ${}^{11}\mathrm{Li}$ incident on a carbon target has been studied in a fragment-neutron coincidence experiment. The momentum distribution of the ${}^{10}\mathrm{Li}$ fragments gives access to the momentum distribution of the removed neutron in ${}^{11}\mathrm{Li}$. From the shape of the distribution, the $({1s}_{1/2}{)}^2$ contribution to the mixture of $({1s}_{1/2}{)}^2$ and $({0p}_{1/2}{)}^2$ components in the ground-state wave function was determined to be $(45\pm 10)\%$. The angular correlation between the knocked out neutron and the one from the decay of ${}^{10}\mathrm{Li}$ shows a skew distribution signaling interference of these two different parity states.

Lifetimes of states of a magnetic dipole band in each of the nuclei ${}^{106,108}\mathrm{Sn}$ have been obtained using the Doppler shift attenuation method. The deduced $B\left(M1\mathrm{}\right)$ transition rates show the characteristic behavior associated with the shears mechanism. A simplified semiclassical analysis yields $B\left(M1\mathrm{}\right)$ values in qualitative agreement with those expected for previously assigned configurations. The results suggest extremely low deformations for these dipole structures. In particular, the ${}^{106}\mathrm{Sn}$ band appears to be the first example of almost pure magnetic rotation in a spherical nucleus.

Nonstatistical structures observed in ${}^{24}\mathrm{Mg}{+}^{24}\mathrm{Mg}$ and ${}^{28}\mathrm{Si}{+}^{28}\mathrm{Si}$ elastic and inelastic excitation functions produce channel-channel correlations and damped oscillations in the cross section energy autocorrelation functions. We present an interpretation of these nonstatistical effects assuming the formation of a highly excited dinucleus with strongly overlapping resonances in these scattering processes. We show that the essential features of the nonstatistical behavior of the excitation functions can be reproduced in terms of a slow spin decoherence of $\simeq (4:1)$ hyperdeformed coherent rotational states excited in ${}^{24}\mathrm{Mg}{+}^{24}\mathrm{Mg}$ and ${}^{28}\mathrm{Si}{+}^{28}\mathrm{Si}$ scattering.