In the very heavy collision system ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$${+}^{197}$Au the ${\mathit{K}}^{+}$ production process was studied as a function of impact parameter at 1 GeV/nucleon, a beam energy well below the free N-N threshold. The ${\mathit{K}}^{+}$ multiplicity increases more than linearly with the number of participant nucleons and the ${\mathit{K}}^{+}$/${\mathrm{\pi }}^{+}$ ratio rises significantly when going from peripheral to central collisions. The measured ${\mathit{K}}^{+}$ double differential cross section is enhanced by a factor of 6 compared to microscopic transport calculations if secondary processes (ΔN→KΛN and ΔΔ→KΛN) are ignored.

In the framework of the relativistic quantum molecular dynamics approach we investigate antiproton (p¯) observables in Au+Au collisions at 10.7A GeV. The rapidity dependence of the in-plane directed transverse momentum ${\mathbf{p}}_{\mathit{x}}$(y) of p¯’s shows the opposite sign of the nucleon flow, which has indeed recently been discovered at 10.7A GeV by the E877 group. The ‘‘antiflow’’ of p¯’s is also predicted at 2A GeV and at 160A GeV and appears at all energies also for π’s and ${\mathit{K}}^{\mathrm{-}}$’s. These predicted p¯ anticorrelations are a direct proof of strong p¯ annihilation in massive heavy ion reactions.

Using the FOPI facility at GSI Darmstadt complete data of Au on Au collisions at 150A MeV were collected for charged products (Z=1–15) at laboratory angles 1°≤${\mathrm{\Theta }}_{\mathrm{lab}}$≤30°. Central collisions were selected by applying various criteria. The kinetic energy spectra of fragments from an isolated midrapidity source are investigated in detail for center-of-mass angles 25°≤${\mathrm{\Theta }}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$≤45°. The heavy products (Z≥3) are used to determine the collective energy which is found to be at least 10A MeV.

We report measurements of the rates and hyperfine (HF) dependences of ${\mathrm{\mu }}^{\mathrm{-}}$ capture on ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$, and the HF transition rate in Na metal. The measured capture rates are in general agreement with the predictions of the 1s-0d shell model. The measured HF dependences of the 1017 and 1823 keV γ rays from ${}_{}{}^{23}{}_{}{}^{}\mathrm{Ne}$ yield ${\mathit{g}}_{\mathit{p}}$/${\mathit{g}}_{\mathit{a}}$=7.6${\pm }_{2.5}^{2.1}$ and ${\mathit{g}}_{\mathit{p}}$/${\mathit{g}}_{\mathit{a}}$≤7.1(1σ), consistent with partial conservation of axial-vector current, but in disagreement with claims of an enhancement of ${\mathit{g}}_{\mathit{p}}$/${\mathit{g}}_{\mathit{a}}$ in light nuclei. The measured HF transition rate ${\mathrm{\Delta }}_{\mathit{h}}$=15.5±1.1 μ${\mathrm{s}}^{\mathrm{-}1}$ is in agreement with the theory of Auger emission but twice the rate previously obtained in NaF (a∼3σ effect).

We have measured (γ,p) and (γ,n) differential yields at 90° for the two-body photodisintegration of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ using tagged photons of energy ${\mathit{E}}_{\gamma }$=25–60 MeV. Data for both channels were obtained simultaneously using windowless ΔE-E telescopes to detect the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ recoils. The ration of our angle-integrated yields, which is insensitive to systematic uncertainies due to the simultaneity of the measurements, agrees with calculations employing only charge-symmetric nuclear interactions. Thus, within the present errors, our data show no evidence of a significant charge-symmetry violation in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in this energy range.

Precollective nuclei, that is, those with E($4_1^{+}$)/E($2_1^{+}$)<2.0, are shown to evolve structurally in a very simple and universal way, in which E($4_1^{+}$) is linear against E($2_1^{+}$) with a slope of unity. A clue to this behavior is provided in terms of a seniority v=0 pair addition mode. Combined with recent studies of vibrator and rotor nuclei, this ‘‘seniority’’ regime gives a new tripartite global characterization of the evolution of nuclear structure.

A generic explanation for the recently observed anomalous crossing frequencies in odd proton rare earth nuclei is given. As an example, the proton 1/2[541] band in ${}_{}{}^{175}{}_{}{}^{}\mathrm{Ta}$ is discussed in detail by using the angular momentum projection theory. It is shown that the quadrupole pairing interaction is decisive in delaying the crossing point and the changes in crossing frequency along the isotope chain are due to the different neutron shell fillings.

We present new, non-Abelian solutions to the equations of motion which describe the collective excitations of a quark-gluon plasma at high temperature. These solutions correspond to spatially uniform color oscillations.

Gamma rays emitted from hot nuclei with mass around 115 and excitation energies between 350 and 500 MeV, formed in the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ + ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ reaction at 27 MeV/nucleon have been measured. The γ-ray yield from the decay of the giant dipole resonance in these nuclei remains constant over the excitation energy range studied. This quenching of the γ multiplicity cannot be explained by a continuous increase with temperature of the width of the resonance. Better agreement with the data is obtained by assuming a cutoff of γ emission from the resonance above an excitation energy of 250 MeV. The existing data do not show entrance channel effects.

We have measured a new electron scattering observable, the “fifth” structure function, ${\mathrm{f}}_{01}^{\prime }$, which is the imaginary part of the transverse-longitudinal interference response. Its observation requires a longitudinally polarized beam and coincident, out-of-plane particle detection. ${\mathrm{f}}_{01}^{\prime }$ arises from interference between reaction channels and provides an additional means for their disentanglement. In the quasielastic ${\mathrm{C}}^{12}$(e→,e′p) measurements reported here, ${\mathrm{f}}_{01}^{\prime }$ is driven by the interference of the direct knockout and rescattering amplitudes.

Two new features of superdeformed (SD) bands in the A≊190 region emerge from a study of ${}_{}{}^{194}{}_{}{}^{}\mathrm{Hg}$ with the Gammasphere detector array. A decrease of the dynamic moment of inertia is observed for rotational frequencies ħω≥0.4 MeV, confirming long standing expectations based on mean field calculations with pairing. Evidence for a small staggering in the SD transition energies is also observed, suggesting the presence of terms with fourfold symmetry in the SD Hamiltonian.

In weakly interacting quark-gluon plasmas diffusion of color is found to be much slower than the diffusion of spin and flavor because color is easily exchanged by the gluons in the very singular forward scattering processes. If the infrared divergence is cut off by a magnetic mass, ${\mathit{m}}_{\mathrm{mag}}$∼${\mathrm{\alpha }}_{\mathit{s}}$T, the color diffusion is ${\mathit{D}}_{\mathrm{color}}$∼[${\mathrm{\alpha }}_{\mathit{a}}$ln(1/${\mathrm{\alpha }}_{\mathit{s}}$)T${]}^{\mathrm{-}1}$, a factor ${\mathrm{\alpha }}_{\mathit{s}}$ smaller than spin and flavor diffusion. A similar effect is expected in electroweak plasmas above ${\mathit{M}}_{\mathit{W}}$ due to ${\mathit{W}}^{\pm }$ exchanges. The color conductivity in quark-gluon plasmas and the electrical conductivity in electroweak plasmas are correspondingly small in relativistic heavy ion collisions and the very early Universe.

The temperature dependence of the nucleon effective mass is calculated for the ${}_{}{}^{98}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{64}{}_{}{}^{}\mathrm{Zn}$, and ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$. In all three cases, the effective mass is found to decrease appreciably in the temperature interval 0–1 MeV. Such a dependence has consequences, among other things, on the level-density parameter and on the symmetry energy. In particular, the effect of the increased symmetry energy on the neutronization processes in collapsing stars is estimated. We find indication that the larger initial lepton fraction thus obtained may significantly help the subsequent supernova explosion.

The influence of background states with increasing level of complexity on the strength distribution of the isoscalar and isovector giant quadrupole resonance in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ is studied. It is found that the background characteristics, typical for chaotic systems, strongly affect the fluctuation properties of the strength distribution. In particular, the small components of the wave function obey a scaling law analogous to self-organized systems at the critical state. This appears to be consistent with the Porter-Thomas distribution of the transition strength.

The complete hyperfine spectrum in the optical transition 5${\mathit{d}}^2$6${\mathit{s}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_2$→5d6${\mathit{s}}^2$6p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ of ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}_{}^{\mathrm{m}2\mathrm{}}{}_{}{}^{}$ was recorded by collinear laser spectroscopy using nanogram amounts of samples. The quadrupole moment and isomer shift were determined for the first time as well as a precise value and the sign of the magnetic dipole moment. The change in nuclear mean-square charge radius between the isomeric state ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}_{}^{\mathrm{m}2\mathrm{}}{}_{}{}^{}$ and the ground state ${}_{}{}^{178}{}_{}{}^{}\mathrm{Hf}_{}^{\mathit{g}}{}_{}{}^{}$ was evaluated as δ〈${\mathit{r}}^2$${\mathrm{〉}}^{178.178\mathrm{m}2}$=-0.059(9) ${\mathrm{fm}}^2$. From the hyperfine A and B factors the magnetic moment ${\mathrm{\mu }}_{\mathit{I}}^{178\mathrm{m}2}$=+8.16(4) nuclear magnetons and the spectroscopic quadrupole moment ${\mathit{Q}}_{\mathit{s}}^{178\mathrm{m}2}$=+6.00(7) b were were extracted.

The effect of the coupling to a resonant state in one of the partners of a heavy-ion fusion reaction on the fusion cross section is discussed. We conclude that the width of the resonance could either enhance or hinder the fusion, depending on the relative importance of the spreading to escape widths. General comments on the fusion of neutron-rich nuclei are made.

The nuclear dependence for 800 GeV/c proton production of neutron D mesons has been measured near ${\mathit{x}}_{\mathit{F}}$=0 in Experiment 789 at Fermilab. D mesons from beryllium and gold targets were detected with a pair spectrometer and a silicon vertex detector via their decay D→Kπ. No nuclear dependence is found, with a measured α=1.02±0.03±0.02. The measured differential cross section, dσ/${\mathit{dx}}_{\mathit{F}}$, for neutral-D-meson production at 〈${\mathit{x}}_{\mathit{F}}$〉=0.031 is 58±3±7 μb/nucleon. The integrated cross section obtained by extrapolation of the measured cross section to all ${\mathit{x}}_{\mathit{F}}$ is 17.7±0.9±3.4 μb/nucleon and is consistent with previous measurements.

The interferometric analysis of meson correlations provides a measure of the average phase space density of the mesons in the final state. This quantity is a useful indicator of the statistical properties of the system, and it can be extracted with a minimum of model assumptions. Values obtained from recent measurements are consistent with the thermal value, but do not rule out superradiance effects.

Classical and quantum mechanical results are reported for the single particle motion in a harmonic oscillator potential which is characterized by a quadrupole deformation and an additional octupole deformation. The chaotic character of the motion is strongly dependent on the quadrupole deformation in that for a prolate deformation virtually no chaos is discernible while for the oblate case the motion shows strong chaos when the octupole term is turned on.

Alpha particles from the dissociation of ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ on Al and Au targets have been observed at 5° in the laboratory for beam energies near 65 MeV/nucleon. Coincident γ rays were observed by an array of ${\mathrm{BaF}}_2$ scintillators that surrounded the target, subtending 90% of the solid angle. In all cases at least half of the observed events were accompanied by γ rays, presumably from excitation of the target via nuclear processes. For ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ incident on the Au target, the data permit an approximate separation into nuclear and Coulomb processes; the latter are in qualitative agreement with theoretical predictions.