At the Cooler Synchrotron COSY/Jülich spin-correlation parameters in elastic proton-proton ($pp$) scattering have been measured with a 2.11 GeV polarized proton beam and a polarized hydrogen atomic beam target. We report results for $A_{NN}$, $A_{SS}$, and $A_{SL}$ for c.m. scattering angles between $30°$ and $90°$. Our data on $A_{SS}$—the first measurement of this observable above 800 MeV—clearly disagrees with predictions of available $pp$ scattering phase-shift solutions while $A_{NN}$ and $A_{SL}$ are reproduced reasonably well. We show that in the direct reconstruction of the scattering amplitudes from the body of available $pp$ elastic scattering data at 2.1 GeV the number of possible solutions is considerably reduced.

Correlations of decays above and below isomeric states in the normally deformed minimum of ${}^{192}\mathrm{P}\mathrm{b}$ have been used to identify discrete transitions in the decay of the superdeformed (SD) band. The data establish the absolute excitation energy of the lowest observed SD level as 4.425 MeV. Extrapolation to the bandhead indicates that the excitation energy of the superdeformed well in ${}^{192}\mathrm{P}\mathrm{b}$ is 0.5 MeV lower than in the heavier isotope ${}^{194}\mathrm{P}\mathrm{b}$. The results confirm the trend to decreasing excitation energy with decreasing neutron number predicted by both a macroscopic Strutinsky method approach and microscopic mean field calculations.

The concept of a mean first passage time is used to study the time lapse over which a fissioning system may emit light particles. The influence of the “transient” and “saddle to scission times” on this emission are critically examined. It is argued that within the limits of Kramers’s picture of fission no enhancement over that given by his rate formula needs to be considered.

We calculate the production of high-energy photons from Compton scattering and annihilation of a quark jet passing through a quark gluon plasma produced in a relativistic heavy ion collision. The contributions are large and reflect the momentum distribution of the jets and the initial conditions of the plasma.

We present results of the first calculation of the double differential cross section for the ${}^{208}\mathrm{P}\mathrm{b}({}^8\mathrm{B},{}^7\mathrm{B}\mathrm{e}p){}^{208}\mathrm{P}\mathrm{b}$ Coulomb breakup reaction which treats the postdecay acceleration of the ejectiles within a genuine three-body approach. From this we conclude that, in order to minimize postdecay Coulomb acceleration effects, experiments should be performed at as small as possible scattering angles, not too low ${}^7\mathrm{B}\mathrm{e}-p$ relative energies, and high incident energy.

Landau theory of phase transitions is applied to quadrupole shapes of rotating atomic nuclei within the interacting boson model (IBM) with cranking. It is shown that the coherent-state method must be generalized to allow for non-Hermitian quadrupole tensors of the coherent-state coefficients, which results in important modifications of the cranking shape-phase diagram compared to previous non-IBM studies of rotating nuclei. The parameter space has two surfaces of the first-order phase transitions and a curve of the second-order phase transition at their intersection. The phase structure of the cranked IBM closely resembles systems with competing superconducting and normal phases.

We present ratios of the numbers of charged antihadrons to hadrons (pions, kaons, and protons) in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$ as a function of rapidity in the range $y=0–3$. While the ratios at midrapidity are approaching unity, the $K^{-}/K^{+}$ and $\overline{p}/p$ ratios decrease significantly at forward rapidities. An interpretation of the results within the statistical model indicates a reduction of the baryon chemical potential from ${\mu }_B\approx 130\mathrm{M}\mathrm{e}\mathrm{V}$ at $y=3$ to ${\mu }_B\approx 25\mathrm{M}\mathrm{e}\mathrm{V}$ at $y=0$.

In heavy ion reactions at energies around $(1–2)A\mathrm{G}\mathrm{e}\mathrm{V}$ the measured $K^{-}$ yields appear rather high as compared to $pp$ collisions as shown by the KaoS Collaboration. Employing quantum molecular dynamics simulations, we show that this is caused by the fact that the dominant production channel is not $BB\to BB{K}^{+}{K}^{-}$ but the mesonic $\Lambda (\Sigma )\pi \to K^{-}B$ reaction. Because the $\Lambda$ ($\Sigma$) stem from the reaction $BB\to \Lambda (\Sigma )K^{+}B$, the $K^{+}$ and the $K^{-}$ yield are strongly correlated, i.e., the $K^{-}/K^{+}$ ratio occurs to be nearly independent of the impact parameter as found experimentally. The final $K^{-}$ yield is strongly influenced by the $K^{+}N$ [due to their production via the $\Lambda (\Sigma )$] but very little by the $K^{-}N$ potential.

We examine the current status of the extraction of the rate of partonic energy loss in nuclei from $A$-dependent data. The advantages and difficulties of using the Drell-Yan process to measure the energy loss of a parton traversing a cold nuclear medium are discussed. The prospects of using relatively low energy proton beams for a definitive measurement of partonic energy loss are presented.

We argue that the distribution of hadrons near the longitudinal light cone in central high-energy $pA$ collisions is computable in weak coupling QCD. This is because the density of gluons per unit transverse area in the dense target at saturation provides an intrinsic semihard momentum scale, $Q_s$. We predict that the longitudinal distribution of (anti)baryons and mesons steepens with increasing energy and atomic number of the target and that the transverse momentum distribution broadens. We show that the evolution of high moments of the longitudinal net baryon distribution with $Q_s$ is determined by the anomalous dimension ${\gamma }_{qq}$.

We present and discuss a systematic calculation, based on two-loop chiral perturbation theory, of the pion-nuclear $s$-wave optical potential. A proper treatment of the explicit energy dependence of the off-shell pion self-energy together with (electromagnetic) gauge invariance of the Klein-Gordon equation turns out to be crucial. Accurate data for the binding energies and widths of the $1s$ and $2p$ levels in pionic ${}^{205}\mathrm{P}\mathrm{b}$ and ${}^{207}\mathrm{P}\mathrm{b}$ are well reproduced without need for a notorious “missing repulsion” in the pion-nuclear $s$-wave optical potential. The connection with the in-medium change of the pion decay constant is clarified.

Experimental search for the superheavy ${}^7\mathrm{H}$ isotope was performed in the reaction $p({}^8\mathrm{H}\mathrm{e},pp){}^7\mathrm{H}$ with the ${}^8\mathrm{H}\mathrm{e}$ beam at $61.3A\mathrm{M}\mathrm{e}\mathrm{V}$. The evidence for existence of the ${}^7\mathrm{H}$ state near the $t+4n$ threshold was obtained. In the same experiment, the $p({}^8\mathrm{H}\mathrm{e},t)$ reaction populating the ground and excited $2^{+}$ state of ${}^6\mathrm{H}\mathrm{e}$ was investigated. The obtained results argue on a specific structure of the ${}^8\mathrm{H}\mathrm{e}$ ground state containing the ${}^6\mathrm{H}\mathrm{e}$ subsystem in the excited $2^{+}$ state with a large weight.

A new isomeric $0^{+}$ state was identified as the first excited state in the self-conjugate ($N=Z$) nucleus ${}^{\mathrm{72}}\mathrm{K}\mathrm{r}$. By combining for the first time conversion-electron and gamma-ray spectroscopy with the production of metastable states in high-energy fragmentation, the electric-monopole decay of the new isomer to the ground state was established. The new $0^{+}$ state is understood as the band head of the known prolate rotational structure, which strongly supports the interpretation that ${}^{\mathrm{72}}\mathrm{K}\mathrm{r}$ is one of the rare nuclei having an oblate-deformed ground state. This observation gives in fact the first evidence for a shape isomer in a $N=Z$ nucleus.

Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudorapidity range and full azimuth in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ and $p+p$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. The small-angle correlations observed in $p+p$ collisions and at all centralities of $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions are characteristic of hard-scattering processes previously observed in high-energy collisions. A strong back-to-back correlation exists for $p+p$ and peripheral $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$. In contrast, the back-to-back correlations are reduced considerably in the most central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

We calculate the production of high energy photons from Compton and annihilation processes as well as fragmentation off quarks in the parton cascade model. The multiple scattering of partons is seen to lead to a substantial production of high energy photons, which rises further when parton multiplication due to final state radiation is included. The photon yield is found to be directly proportional to the number of hard collisions and thus provides valuable information on the preequilibrium reaction dynamics.

The tensor analyzing power components $T_{20}$ and $T_{21}$ have been measured in elastic electron-deuteron scattering at the 2 GeV electron storage ring VEPP-3, Novosibirsk, in a four-momentum transfer range from 8.4 to $21.6{\mathrm{f}\mathrm{m}}^{-2}$. A new polarized internal gas target with an intense cryogenic atomic beam source was used. The new data determine the deuteron form factors $G_C$ and $G_Q$ in an important range of momentum transfer where the first node of the deuteron monopole charge form factor is located. The new results are compared with previous data and with some theoretical predictions.

For the first time a high-precision proton-deuteron bremsstrahlung experiment has been performed in which all the different exit channels have been distinguished separately. High-precision cross sections and analyzing powers in one of the outgoing channels, namely, the coherent bremsstrahlung with a proton and a deuteron in the final state, are presented at 190 MeV incoming proton beam energy and are compared to calculations based on the low-energy theorem. The results of the calculations vary considerably calling for a fully microscopic calculation. However, using a recipe including the initial- and final-state interactions, the predictions come close to the data.

The reaction rate of the stellar reaction ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$, which is currently considered to be the main neutron source for the slow ($s$) process at low energies, has been rederived using the direct $\alpha$-transfer reaction ${}^{13}\mathrm{C}({}^6\mathrm{L}\mathrm{i},d){}^{17}\mathrm{O}$ leading to the subthreshold state at 6.356 MeV in ${}^{17}\mathrm{O}$. The contribution of the subthreshold state is found to be much smaller than the currently accepted predictions for the main neutron source of the $s$ process, indicating less of a role of this reaction as the neutron source for the $s$-process scenario in low-mass stars at the asymptotic giant branch.

Exclusive coherent and incoherent electroproduction of the ${\rho }^0$ meson from ${}^{\mathrm{1}}\mathrm{H}$ and ${}^{\mathrm{14}}\mathrm{N}$ targets has been studied at the HERMES experiment as a function of coherence length ($l_c$), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon ($-Q^2$). The ratio of ${}^{\mathrm{14}}\mathrm{N}$ to ${}^{\mathrm{1}}\mathrm{H}$ cross sections per nucleon, called nuclear transparency, was found to increase (decrease) with increasing $l_c$ for coherent (incoherent) ${\rho }^0$ electroproduction. For fixed $l_c$, a rise of nuclear transparency with $Q^2$ is observed for both coherent and incoherent ${\rho }^0$ production, which is in agreement with theoretical calculations of color transparency.

It is shown that a very simple three-body monopole term can solve practically all the spectroscopic problems—in the $p$, $sd$, and $pf$ shells—that were hitherto assumed to need drastic revisions of the realistic potentials.