The experimental ratio of ${\psi }^{\prime }$ to $J/\psi$ is approximately a constant in $\mathrm{pA}$ collisions, but decreases as the transverse energy increases in nucleus-nucleus collisions. These peculiar features can be explained as arising from approximately the same $c\overline{c}$-baryon absorption cross section for ${\psi }^{\prime }$ and $J/\psi$ but greater disruption probabilities for ${\psi }^{\prime }$ than for $J/\psi$ due to the interaction of the $c\overline{c}$ system with soft particles produced in baryon-baryon collisions.

The SINDRUM II spectrometer at Paul Scherrer Institute is used in a search for coherent $\mu \to e$ conversion in muonic atoms. We report on a measurement on lead, which resulted in $\gamma ({\mu }^{-}\mathrm{Pb}\to e^{-}{\mathrm{Pb}}^{\mathrm{g}.\mathrm{s}.\mathrm{}})/\gamma \left({\mu }^{-}\mathrm{Pb}\mathrm{capture}\right)<4.6\mathrm{}\times {10}^{-11\mathrm{}}$ (90% C.L.). This upper limit improves on the previous value by an order of magnitude. Combined with the limit on titanium, it is interpreted in terms of phenomenological couplings between the lepton current and the isoscalar and isovector quark currents.

Differential cross sections have been measured near 0° for the dominant channels in the mirror reaction ${}^{13}$C${(}^{13}$N${,}^{13}$C${)}^{13}$N at $E/A=57\mathrm{}$ and 105 MeV. The cross sections of the peaks in the excitation spectrum are discussed in terms of Gamow-Teller and Fermi transition strength. The cross section per unit Gamow-Teller strength is found to be enhanced relative to that for unit Fermi strength when compared with previous results from $(p,n)$ reactions. The present work represents the first use of a mirror-symmetric projectile and target system in a charge-exchange reaction as well as the first application of the developing radioactive nuclear beam field to this area.

The thermodynamic properties of heated nuclear matter are explored using an exactly solvable canonical ensemble model. This model reduces to the results of an ideal Fermi gas at low temperatures. At higher temperatures, the fragmentation of the nuclear matter into clusters of nucleons leads to features that resemble a Bose gas. Some parallels of this model with the phenomena of Bose condensation and with percolation phenomena are discussed. A simple expression for the hadronic equation of state is obtained from the model.

We discuss the role of kaon-nucleon and nucleon-nucleon correlations in kaon condensation in dense matter. Correlations raise the threshold density for kaon condensation, possibly to densities higher than those encountered in stable neutron stars.

Alpha- and beta-decay studies of mass-separated Rn and At nuclei reveal the existence of a low-lying $0^{+}$ state in ${}_{}{}^{196,198,200,202}{}_{}{}^{}\mathrm{Po}$. The excited $0^{+}$ states are interpreted as proton-pair excitations across the $Z=82\mathrm{}$ shell gap leading to a deformed state, coexisting with the spherical ground state. It is shown that with decreasing neutron number the deformed configuration intrudes to lower excitation energy, increasingly mixing into the ground state.

The elastic electromagnetic form factors for the deuteron are calculated in the context of a one-boson-exchange model using the Gross or Spectator equation. The formalism is manifestly covariant and gauge invariant, and provides a very good representation of the data.

Multifragment disintegrations have been measured for central Au+Au collisions at $\frac{E}{A}=35\mathrm{}$ MeV. Fragment emission occurs predominantly at low center of mass energies of about $\frac{E}{A}\approx 5$ MeV, consistent with a Coulomb dominated breakup of a single source. Mean fragment multiplicities of $〈N_{\mathrm{IMF}}〉\approx 10.8$ are extracted after correction for the detection efficiency. The fragment charge distributions decrease much more gradually than expected from scaling laws recently applied to the extraction of critical exponents for the nuclear liquid-gas phase transition from nuclear collisions.

An interacting boson model sum rule for the strength of exciting the magnetic dipole scissors mode is used to relate this strength to the quadrupole deformation, resulting in a parameter-free description of the $M1\mathrm{}$ transition strength over the entire range of nuclei from Nd to W studied experimentally. Also, the experimentally established quadratic dependence on the quadrupole ground state deformation is quantitatively reproduced for nuclei up to Yb, but systematic deviations are predicted for heavier nuclei.

Secondary beams from fragmentation of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ have been produced with energies of $\mathrm{}(200-220)A$ MeV, separated with a fragment separator and injected into a storage-cooler ring for half-life measurements. The relative momentum spread $\frac{\Delta p}{p}\approx 1\times {10}^{-6\mathrm{}}$ (FWHM) which we achieved allowed us to resolve the ground and isomeric states of cooled ${}_{}{}^{52}{}_{}{}^{}\mathrm{Mn}$ and ${}_{}{}^{53}{}_{}{}^{}\mathrm{Fe}$ nuclei in the measured mass spectra. The circulating beams were fully ionized, which rendered it possible to measure pure ${\beta }^{+}$ branches for ${}_{}{}^{52g}{}_{}{}^{}\mathrm{Fe}$ and ${}_{}{}^{53g}{}_{}{}^{}\mathrm{Fe}$ and the sum of pure ${\beta }^{+}$ and $\gamma$ branches in the decay of the isomers ${}_{}{}^{52m}{}_{}{}^{}\mathrm{Mn}$ and ${}_{}{}^{53m}{}_{}{}^{}\mathrm{Fe}$.

The fission excitation functions for 14 compound nuclei covering a mass range from $A=186\mathrm{} \mathrm{to} 213$ are shown to scale exactly according to the transition state prediction once shell effects are accounted for. The extracted shell effects correlate closely with those obtained from the ground state masses. No effects of transient times longer than 3 × ${10}^{-20\mathrm{}}$ sec are visible. Pairing effects are noticeable at excitation energies at few MeV above the barrier.

Two-neutron relative-momentum correlation functions have been measured in the 130 MeV ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$ reaction. Differences in the longitudinal and transverse correlation functions, observed for the first time for neutrons, allow an independent determination of the spatial extent and the time scale for decay of the ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ compound nucleus. A comparison with theoretical calculations indicates a radius of 4.4±0.3 fm and an average neutron emission time scale of 1100 ± 100 fm/c for ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ at 100 MeV excitation energy. Correlation functions selected by cuts on the total momentum of the neutron pair give a quantitative characterization of the cooling of a compound nucleus.

We propose a new strategy for the experimental search of the QCD phase transition in heavy ion collisions: One may tune collision energy to the point where the lifetime of the fireball is the longest. Using hydrodynamical description of space-time evolution and assuming Landau-like initial conditions, we show that this longest lifetime corresponds to the initial energy density being at the "softest point" (where the pressure to energy density ratio reaches its minimum), ${\epsilon }_i\approx 1.5$ GeV/${\mathrm{fm}}^3$ for our choice of equation of state. The plasma lifetime is effectively increased by about a factor of 3. We suggest distinct changes in various observables which may help to locate the softest point.

Using a relativistic transport model for the expansion stage of S + Au collisions at 200 GeV/nucleon, we show that the recently observed enhancement of low-mass dileptons by the CERES Collaboration can be explained by the decrease of vector meson masses in hot and dense hadronic matter.

Measurements of the forward and the transverse energy in 158 GeV per nucleon ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ + Pb collisions are presented. A total transverse energy of about 1 TeV is created in central collisions. An energy density of about 3 GeV/${\mathrm{fm}}^3$ is estimated for near head-on collisions. Only statistical fluctuations are seen in the ratio of electromagnetic to hadronic transverse energy.

A new decay scheme between Gamow-Teller (GT) resonances and isobaric analog states (IAS) by magnetic dipole transitions is studied. The sum rule of $M1\mathrm{}$ transitions between IAS and GT states is found to be significantly enhanced compared to the non-energy-weighted sum rule of the parent state. Calculated enhancement factors can be as large as ∼2.5 for ${}_{}{}^{48}{}_{}{}^{}\mathrm{Sc}$ and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Nb}$, and 1.5 for ${}_{}{}^{208}{}_{}{}^{}\mathrm{Bi}$. Transition strengths between specific states are calculated in the Tamm-Dancoff approximation. The interest of measuring $M1\mathrm{}$ transitions between IAS and GT states to obtain information on the spin-isospin response in finite nuclei is stressed.

We have measured the yields of antiprotons in Au + Au interactions in the rapidity range $1.2<y<\mathrm{}2.8\mathrm{}$ as a function of centrality using a beam line spectrometer. The shapes of the invariant multiplicity distributions at $p_t=0\mathrm{}$ are used to explore the dynamics of antiproton production and annihilation.

We demonstrate that $\Delta I=4\mathrm{}$ bifurcation can arise from the projected shell model without introducing explicitly either a $Y_{44}$ deformation or an $I^4$ term in the Hamiltonian. If band mixing through the usual two-body Hamiltonian is dominated by a single two-band mixture near the yrast line, a clear staggering can appear. Detailed investigation shows that this staggering is associated with interference effects in the rotation from intrinsic to laboratory coordinate systems.

We have made high statistics measurements of tritium beta decay to set a limit on the mass of the electron antineutrino. The measurements used a windowless gaseous source of molecular tritium and a high resolution toroidal field magnetic spectrometer. We calibrate the system using conversion electrons from the decay of ${}^{83m}\mathrm{Kr}$. The best fit value for the neutrino mass squared is significantly negative. An anomalous structure in the beta decay spectrum in the last 55 eV closest to the end point causes this result.

The interaction cross sections $\left({\sigma }_I\right)$ of ${}^A\mathrm{Na}$ isotopes $(A=20\mathrm{}–23,25–32)$ on a carbon target have been measured at $950A\mathrm{MeV}$. The effective root-mean-square matter radii of these isotopes were deduced from ${\sigma }_I$ by a Glauber-type calculation. By combining the isotope-shift data with the present data the radii of neutrons have been compared with those of protons for the first time along a chain of stable and unstable isotopes. A monotonic increase in the neutron skin thickness has been observed as the neutron number increases in Na isotopes.