We argue that the event-by-event fluctuations of the ratio of positively charged over negatively charged pions provides a measurement of the number of rho and omega mesons right after hadronization. This finding can be utilized to put the hypothesis of chemical equilibration in relativistic heavy ion collisions to a test. The fluctuation may also serve as an indicator for new physics to be discovered in relativistic heavy-ion collisions.

We report a measurement of the spin-dependent total cross section ratios $\Delta {\sigma }_{\mathrm{T}}/{\sigma }_{\mathrm{tot}}$ and $\Delta {\sigma }_{\mathrm{L}}/{\sigma }_{\mathrm{tot}}$ of the $\mathrm{pp}\to \mathrm{pp}{\pi }^0$ reaction between 325 and 400 MeV. The experiment was carried out with a polarized internal target in a storage ring. Nonvertical beam polarization was obtained by the use of solenoidal spin rotators. Near threshold, the knowledge of both spin-dependent total cross sections is sufficient to deduce the strength of certain participating partial waves, free of any model.

Cross sections for the ${}^3\mathrm{He}\left({e,e}^{\prime }\mathrm{pp}\right)n$ reaction were measured at an energy transfer of 220 MeV and three-momentum transfers $q$ of 305, 375, and $445\mathrm{MeV}/c$. Results are presented as a function of $q$ and the final-state neutron momentum for slices in specific kinematic variables. At low neutron momenta, comparison of the data to results of continuum Faddeev calculations performed with the Bonn- $B$ nucleon-nucleon potential indicates a dominant role for two-proton knockout induced by a one-body hadronic current.

Comparative measurements of the lifetimes of yrast superdeformed (SD) states in ${}^{80–83}\mathrm{Sr}$, ${}^{83}\mathrm{Y}$, and ${}^{84}\mathrm{Zr}$ have been performed using the Doppler-shift attenuation method. Thus, the transition quadrupole moments ( $Q_t$) of these structures have been determined accurately. The yrast SD bands in ${}^{80–83}\mathrm{Sr}$ possess $Q_t\sim 3.5e\mathrm{b}$, while the ${}^{83}\mathrm{Y}$ and ${}^{84}\mathrm{Zr}$ cases display $Q_t=4.4\mathrm{}e\mathrm{b}$ and $5.6e\mathrm{b}$, respectively. Intruder orbital assignments based on these results demonstrate a previously unnoticed transition in the structure of the SD bands when the proton number changes from $Z=38\mathrm{}$ to $Z\ge 39$.

Predictions for electron induced proton knockout from $p_{1/2}$ and $p_{3/2}$ shells in ${}^{16}\mathrm{O}$ are presented using various approximations for the relativistic nucleonic current. Results for differential cross section, transverse-longitudinal response ( $R_{\mathrm{TL}}$), and left-right asymmetry $A_{\mathrm{TL}}$ are compared at $|Q^2|=0.8\mathrm{}(\mathrm{GeV}/c{)}^2$. We show that there are important dynamical and kinematical relativistic effects which can be tested by experiment.

Unresolved $\gamma$ rays of ${}^{114}\mathrm{Te}$ sorted into one- and two-dimensional spectra were studied. The reaction ${}^{64}\mathrm{Ni}(E_{\mathrm{beam}}=230\mathrm{}–270\mathrm{MeV}){+}^{54}\mathrm{Cr}$ was used and the $\gamma$ rays were detected with the EUROBALL array. The effective moment of inertia for the quasicontinuum was found to be almost constant for $I=(20–40)ħ$, in contrast with the decreasing behavior of the terminating yrast band. A comparative analysis with the nucleus ${}^{164}\mathrm{Yb}$ is presented and the results from a fluctuation analysis were compared with cranked shell model calculations. The comparison shows consistency in the scaling of the rotational damping width with mass number.

A search for $\Sigma$ hypernuclear states in $p$-shell hypernuclei has been performed with the Moby Dick spectrometer and the low energy separated beam (LESB-2) at the Brookhaven Alternating Gradient Synchrotron (BNL AGS). Unlike some previously published reports, no narrow states have been observed for targets of ${}^6\mathrm{Li}$ and ${}^9\mathrm{Be}$ in $(K^{-},{\pi }^{\pm })$ reactions, either for bound state or continuum regions. Together with the previously reported $J=0\mathrm{}$, $T=1\mathrm{}/2$ bound state in ${}_{\Sigma }^4\mathrm{He}$, these results demonstrate the crucial role of isospin in $\Sigma$ hypernuclei.

The depopulation of the quasistable isomer in ${}^{180}\mathrm{Ta}$ with $J^{\pi }{=9\mathrm{}}^{-}$ at $E_x=75\mathrm{}\mathrm{keV}$ by resonant photoabsorption was investigated with intense bremsstrahlung. The results indicate a dramatic acceleration of the isomer decay to the short-lived $J^{\pi }{=1\mathrm{}}^{+}$ ground state under stellar $s$-process conditions. The consequences for a possible nucleosynthesis of nature's rarest isotope ${}^{180}\mathrm{Ta}$ within the $s$ process are discussed.

Estimates are made of the $\mathrm{dd}\to \alpha \gamma \gamma$ production cross sections in a model where each neutron-proton pair in the beam and target initiates an $\mathrm{np}\to d\gamma$ reaction. This approach, which successfully reproduces observables in two-pion production at intermediate energies, suggests that direct two-photon production could provide a very significant background to the measurement of the charge-symmetry-breaking (CSB) reaction $\mathrm{dd}\to \alpha {\pi }^0$. A nonvanishing CSB cross section has been reported which might be confused with such two-photon production under the given experimental conditions.

The deuteron magnetic and quadrupole moments are unambiguosly determined within the front-form Hamiltonian dynamics, by using a new current operator which fulfills Poincaré, parity, and time reversal covariance, together with Hermiticity and the continuity equation. For both quantities the usual disagreement between theoretical and experimental results is largely removed.

The space-time evolution of high-energy noncentral heavy-ion collisions is studied with relativistic hydrodynamics. The results are very sensitive to the equation of state (EoS). For an EoS with the QCD phase transition, an unusual matter distribution develops. Before freeze-out, two shells are formed which physically separate and leave a maximum in the center. We make specific predictions for the azimuthal dependence of the flow and for two-pion interferometry, contrasting our results with a resonance gas EoS.

The transmission of ultracold neutrons through natural Gd and isotopic enriched ${}^{157}\mathrm{Gd}$ samples has been measured. Absorption cross sections in the order of 100 Mb have been identified. Here one touches a region where fluctuations of the physical parameters influence the result and can cause a basic deviation from the exponential attenuation law and where a purely imaginary interaction potential exists within the sample.

Annihilation of 1.2 GeV antiprotons has been explored as a means to generate high thermal excitation in heavy nuclei (U, Au, Ho) and to observe their decay with a minimal contribution from dynamical distortion. Conventional fission and heavy residue formation are found to dominate the decay up to $E^{*}\approx 1000\mathrm{MeV}$. Both modes are increasingly accompanied by a modest emission of intermediate-mass fragments (up to 1 on average), but true multifragmentation is not observed. These features are in agreement with the predictions of the statistical model with no need for a fission delay ${\tau }_f>0.5\mathrm{}\times {10}^{-21\mathrm{}}\mathrm{s}$.

We propose a novel mechanism for disoriented chiral condensate (DCC) formation in a first-order chiral phase transition. In this case the effective potential for the chiral order parameter has a local minimum at $\Phi \sim 0$ in which the chiral field can be “trapped.” If the expansion is fast, a bubble of disoriented chiral field can emerge and decouple from the rest of the fireball. The bubble may overshoot the mixed phase and supercool until the barrier disappears, when the potential resembles that at $T=0\mathrm{}$. This situation corresponds to the initial condition realized in a “quench.” Thus, the subsequent alignment in the vacuum direction leads to strong amplification of low-momentum modes of the pion field. We propose that these DCCs could accompany the previously suggested baryon rapidity fluctuations.

We show that kaonic nuclei can be produced by the ( $K^{-},p$) and ( $K^{-},n$) reactions. The reactions are shown to have cross sections experimentally measurable. The observation of kaonic nuclei gives a kaon-nucleus potential which answers the question as to the existence of kaon condensation in dense nuclear matter, especially in neutron stars.

We investigate the possibilities of the formation of even-even superheavy nuclei in the cold fusion reactions ${}^{207}{\mathrm{Pb}}_{125}(\mathrm{HI},1n)$. We reproduce the measured cross sections of the reactions ${}^{207}{\mathrm{Pb}}_{125}{(}^{50}{\mathrm{Ti}}_{28},1n{)}^{256}{\mathrm{Rf}}_{152}$, ${}^{207}{\mathrm{Pb}}_{125}{(}^{54}{\mathrm{Cr}}_{30},1n{)}^{260}{\mathrm{Sg}}_{154}$, and ${}^{207}{\mathrm{Pb}}_{125}{(}^{58}{\mathrm{Fe}}_{32},1n{)}^{264}{\mathrm{Hs}}_{156}$ within a factor of 2.9 on average. We predict the optimal bombarding energies and the formation cross sections of even-even superheavy nuclei with $Z=110\mathrm{}–120$.

Recent experiments indicate that the behavior exhibited by the ratios $E_{1^{+}}/M_{1^{+}}$ and $S_{1^{+}}/M_{1^{+}}$ of the ${\gamma }^{*}N\leftrightarrow \Delta$ transition remains small and negative for $Q^2\le 4.0{\mathrm{GeV}}^2$. It implies that perturbative QCD is still not applicable at these momentum transfers. We show that these data can be explained in a dynamical model for electromagnetic production of pions, together with a simple scaling assumption for the bare ${\gamma }^{*}N\Delta$ form factors. Within our model we find that the bare $\Delta$ is almost spherical and the electric $E2\mathrm{}$ and Coulomb $C2\mathrm{}$ quadrupole excitations of the physical $\Delta$ are nearly saturated by the pion cloud contribution in $Q^2\le 4.0{\mathrm{GeV}}^2$.

A precision measurement of spin transfer in $\mathrm{pp}$ elastic scattering at 197.8 MeV has been completed recently at the Indiana University Cyclotron Facility. The new data span a kinematic regime chosen specifically to maximize sensitivity to the neutral $\pi \mathrm{NN}$ coupling constant. Our results provide strong support for modern potential models of the $\mathrm{NN}$ interaction in which a relatively weak pion coupling ( $g_0^2\approx 13.6$, $f_0^2\approx 0.075$) is employed, but disagree significantly with predictions of older models in which $g_0^2\approx 14.4$. Calculations in a one-boson-exchange framework indicate that most of these latter differences can be removed by reducing $g_0^2$ from 14.4 to 13.6 in these models.

We have performed large-scale shell-model calculations of the half-lives and neutron-branching probabilities of the $r$-process waiting-point nuclei at the magic neutron number $N=82\mathrm{}$. We find good agreement with the measured half-lives of ${}^{129}\mathrm{Ag}$ and ${}^{130}\mathrm{Cd}$. Our shell-model half-lives are noticeably shorter than those currently adopted in $r$ process simulations. Our calculation suggests that ${}^{130}\mathrm{Cd}$ is not produced in $\beta$-flow equilibrium with the other $N=82\mathrm{}$ isotones on the $r$-process path.

We calculate the nuclear enhancement in the angular distribution of Drell-Yan pairs produced in proton-nucleus reactions. Nuclear effects are encoded in universal twist-4 parton correlation functions. We find that the Lam-Tung relation for the angular coefficients of the lepton-pair distribution holds for the double-hard, but not for the soft-hard, contribution. We also predict that nuclear enhancement effects at the Relativistic Heavy Ion Collider energies can be large.