We calculate the Gaussian radius parameters of the pion-emitting source in high-energy heavy-ion collisions, assuming a first-order phase transition from a thermalized quark-gluon plasma (QGP) to a gas of hadrons. Such a model leads to a very long-lived dissipative hadronic rescattering phase which dominates the properties of the two-pion correlation functions. The radii are found to depend only weakly on the thermalization time ${\tau }_i$, the critical temperature $T_c$ (and thus the latent heat), and the specific entropy of the QGP. The model calculations suggest a rapid increase of $R_{\mathrm{out}}/R_{\mathrm{side}}$ as a function of $K_T$ if a thermalized QGP were formed.

We have measured the cross section of the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction for $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=185.8\mathrm{}$, 134.7, and 111.7 keV using a radioactive ${}^7\mathrm{Be}$ target (132 mCi). Single and coincidence spectra of ${\beta }^{+}$ and $\alpha$ particles from ${}^8\mathrm{B}$ and ${}^8{\mathrm{Be}}^{*}$ decay, respectively, were measured using a large acceptance spectrometer. The zero energy $S$ factor inferred from these data is $18.5\pm 2.4\mathrm{eV}\mathrm{b}$ and a weighted mean value of $18.8\pm 1.7\mathrm{eV}\mathrm{b}$ (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies.

The Skyrme model is a classical field theory which has topological soliton solutions. These solitons are candidates for describing nuclei, with an identification between the numbers of solitons and nucleons. We have computed numerically, using two different minimization algorithms, minimum energy configurations for up to 22 solitons. We find, remarkably, that the solutions for seven or more solitons have nucleon density isosurfaces in the form of polyhedra made of hexagons and pentagons. Precisely these structures arise, though at the much larger molecular scale, in the chemistry of carbon shells, where they are known as fullerenes.

The nuclear magnetic dipole moment $\mu$ and electric quadrupole moment $Q$ of the $\beta$-emitting ${}^{16}\mathrm{N}(I^{\pi }{=2\mathrm{}}^{-}{,T}_{1/2}=7.13\mathrm{s})$ nucleus have been determined for the first time by detecting its $\beta$-NMR in a MgO crystal and $\beta$-NQR (nuclear quadrupole resonance) in a $\mathrm{TiO}{}_2$ crystal to be $|\mu |=(1.9859\pm 0.0011){\mu }_{\mathrm{N}}$ and $|Q|=(17.9\pm 1.7)\mathrm{mb}$, respectively. Although the prediction of $\mu$ given by the Hartree-Fock calculation agrees well with the experiment, an abnormally small effective charge for neutrons is required to account for the experimental $Q$.

We present evidence that numerically accurate quantum calculations employing modern internucleon forces do not reproduce the proton analyzing power, $A_y$, for $p-{}^3\mathrm{He}$ elastic scattering at low energies. These calculations underpredict new measured analyzing powers by approximately $30\%$ at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=1.20\mathrm{}\mathrm{MeV}$ and by 40% at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=1.69\mathrm{}\mathrm{MeV}$, an effect analogous to a well-known problem in $p-d$ and $n-d$ scattering. The calculations are performed using the complex Kohn variational principle and the (correlated) hyperspherical harmonics technique with full treatment of the Coulomb force. The inclusion of the three-nucleon interaction does not improve the agreement with the experimental data.

The energy and centrality dependence of the charged multiplicity per participant nucleon is shown to be able to differentiate between final state saturation and fixed scale perturbative QCD models of initial entropy production in high-energy heavy-ion collisions. The energy dependence is shown to test the nuclear enhancement of the minijet component of the initial conditions, while the centrality dependence provides a key test of whether gluon saturation is reached at RHIC energies. The HIJING model predicts that the rapidity density per participant increases with centrality, while the saturation model prediction is essentially independent of centrality.

We present results for the charged-particle multiplicity distribution at midrapidity in Au-Au collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$ measured with the PHENIX detector at RHIC. For the $5\%$ most central collisions we find ${\mathrm{dN}}_{\mathrm{ch}}/d{\eta }_{|\eta =0\mathrm{}}=622\mathrm{}\pm 1\left(\mathrm{stat}\right)\pm 41\left(\mathrm{syst}\right)$. The results, analyzed as a function of centrality, show a steady rise of the particle density per participating nucleon with centrality.

Practically all serious calculations of exclusive particle production in ultrarelativistic nuclear or hadronic interactions are performed in the framework of Gribov-Regge theory or the eikonalized parton model scheme. It is the purpose of this paper to point out serious inconsistencies in the above-mentioned approaches. We demonstrate that requiring theoretical self-consistency reduces the freedom in modeling high-energy nuclear scattering enormously, and we introduce a fully self-consistent formulation of the multiple-scattering scheme in the framework of a Gribov-Regge–type effective theory. In addition, we develop new computational techniques which allow for the first time a satisfactory solution of the problem in the sense that calculations of observable quantities can be done strictly within a self-consistent formalism.

The double-beta $\beta \beta \left(2\nu \right)$-decay rate of ${}^{100}\mathrm{Mo}$ to the first excited $0^{+}$ state of ${}^{100}\mathrm{Ru}$ has been measured by a $\gamma -\gamma$ coincidence technique that uses two HPGe detectors to observe the two $\gamma$ rays ( $E_{\gamma 1}=590.76\mathrm{keV}$; $E_{\gamma 2}=539.53\mathrm{keV}$) from the ${}^{100}\mathrm{Ru}$ nucleus as it deexcites to the ground state via the $0^{+}\to 2^{+}\to 0^{+}$ sequence. Unlike all previous $\beta \beta$-decay experiments, this technique provides data which have a large signal-to-background ratio. After a 440-day measurement of a 1.05-kg isotopically enriched $\left(98.4\%\right)$ disk of ${}^{100}\mathrm{Mo}$, 22 detected coincidence events (with an estimated background of 2.5 events) yield a half-life of $\left[{5.9}_{-1.1\mathrm{}}^{+1.7\mathrm{}}\right(\mathrm{stat})\pm 0.6(\mathrm{syst}\left)\right]\times {10}^{20}$ years.

We discuss the scaling laws of both the charged fragments multiplicity $n$ fluctuations and the charge of the largest fragment $Z_{\max }$ fluctuations for $\mathrm{Xe}+\mathrm{Sn}$ collisions in the range of bombarding energies between $25A\mathrm{MeV}$ and $50A\mathrm{MeV}$. We show at $E_{\mathrm{lab}}\gtrsim 32\mathrm{MeV}/A$ the transition in the fluctuation regime of $Z_{\max }$ which is compatible with the transition from the ordered to disordered phase of excited nuclear matter. The size (charge) of the largest fragment is closely related to the order parameter characterizing this process.

The angular distributions of $\gamma$ rays from the ${}^{12}\mathrm{C}(\alpha ,\gamma {)}^{16}\mathrm{O}$ reaction have been measured at 20 energy points in the energy range $E_{\mathrm{cm}}=0.95\mathrm{}$ to 2.8 MeV. The sensitivity of the present experiment compared to previous direct investigations was raised by 1–2 orders of magnitude, by using an array of highly efficient ( $100\%$) Ge detectors shielded actively with BGOs, as well as high beam currents of up to $500\mu \mathrm{A}$ that were provided by the Stuttgart Dynamitron accelerator. The $S_{E1\mathrm{}}$ and $S_{E2\mathrm{}}$ factors deduced from the $\gamma$ angular distributions have been extrapolated to the range of helium burning temperatures applying the $R$-matrix method, which yielded $S_{E1\mathrm{}}^{300}=(76\pm 20)\mathrm{keV}\mathrm{b}$ and $S_{E2\mathrm{}}^{300}=(85\pm 30)\mathrm{keV}\mathrm{b}$.

Nucleon total reaction and neutron total cross sections to 300 MeV for ${}^{12}\mathrm{C}$ and ${}^{208}\mathrm{Pb}$, and for 65 MeV scattering spanning the mass range, are predicted using coordinate space optical potentials formed by full folding of effective nucleon-nucleon interactions with realistic nuclear ground state densities. Good to excellent agreement is found with existing data.

Multifragmentation of a “fused system” was observed for central collisions between 32 MeV/nucleon ${}^{129}\mathrm{Xe}$ and ${}^{\mathrm{nat}}\mathrm{Sn}$. Most of the resulting charged products were well identified due to the high performances of the INDRA $4\pi$ array. Experimental higher-order charge correlations for fragments show a weak but nonambiguous enhancement of events with nearly equal-sized fragments. Supported by dynamical calculations in which spinodal decomposition is simulated, this observed enhancement is interpreted as a “fossil” signal of spinodal instabilities in finite nuclear systems.

High-precision ${}^1\mathrm{H}\left({e,e}^{\prime }p\right){\pi }^0$ measurements at $Q^2=0.126\mathrm{}(\mathrm{GeV}/c{)}^2$ are reported, which allow the determination of quadrupole amplitudes in the ${\gamma }^{*}N\to \Delta$ transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole ( $I=3/2\mathrm{}$) amplitude ratios, $R_{\mathrm{SM}}=(-6.5\mathrm{}\pm {0.2}_{\mathrm{stat}+\mathrm{sys}}\pm {2.5}_{\mathrm{mod}})\%$ and $R_{\mathrm{EM}}=(-2.1\mathrm{}\pm {0.2}_{\mathrm{stat}+\mathrm{sys}}\pm {2.0}_{\mathrm{mod}})\%$, are dominated by model error. Previous $R_{\mathrm{SM}}$ and $R_{\mathrm{EM}}$ results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account.

Laser cooling and atomic trapping techniques have been employed to confine polarized ${}^{82}\mathrm{Rb}$ atoms ( $T_{1/2}=75\mathrm{}\mathrm{s}$) in a magnetic time-orbiting-potential (TOP) trap. We have observed the parity-violating correlation between the emitted positron momentum and the parent nuclear spin as a continuous function of angle and positron energy for this pure Gamow-Teller (GT) transition. These proof-of-principle measurements demonstrate the utility of exploring fundamental symmetries in a TOP trap and the steps required to improve sensitivity in the search for physics beyond the standard model.

The excitation of the giant dipole resonance induced by fusion reaction is studied with $N/Z$ asymmetry in the entrance channel. The time dependent Hartree-Fock solution exhibits a strong dipole vibration which can be associated with a giant vibration along the main axis of the deformed compound nucleus. This dipole motion appears to be nonlinearly coupled to the shape oscillation, leading to a strong modulation of its frequency. These phenomena can be detected in the gamma-ray emission from hot compound nuclei.

We present measurements of the recoil proton polarization for the $d(\overrightarrow{\gamma },\overrightarrow{p})n$ reaction at ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=90\mathrm{}°$ for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization $p_y$ vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer $C_x$ does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the $d(\gamma ,p)n$ cross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime.

We argue that the observed antiproton production in heavy-ion collisions at CERN-SPS energies can be understood if (contrary to most sequential scattering approaches) the backward direction in the process $p\overline{p}\leftrightarrow \overline{n}\pi$ (with $\overline{n}=5\mathrm{}–6$) is consistently accounted for within a thermal framework. Employing the standard picture of subsequent chemical and thermal freezeout, which induces an oversaturation of pion number with associated chemical potentials of ${\mu }_{\pi }\simeq 60–80\mathrm{MeV}$, enhances the backward reaction substantially. The resulting rates turn out to be large enough to maintain an antiproton abundance at thermal freezeout in accordance with the measured $\overline{p}/p$ ratio in $\mathrm{Pb}\left(158A\mathrm{GeV}\right)+\mathrm{Pb}$ collisions.

The linear polarization of $\gamma$ rays between excited and yrast superdeformed (SD) states in ${}^{190}\mathrm{Hg}$ was measured using the four-element CLOVER detectors of the EUROBALL IV $\gamma$-ray spectrometer. This measurement shows in a model-independent way that the interband transitions which compete with the highly collective in-band quadrupole transitions are largely enhanced electric dipoles. Not only do these results represent the first measurement of the multipolarity of transitions between different SD states, but they also provide strong evidence for the interpretation of the structures in the SD minimum of the $A\sim 190$ region in terms of octupole excitations.

A kinematically complete measurement was made of the Coulomb dissociation of ${}^8\mathrm{B}$ nuclei on a Pb target at 83 MeV/nucleon. The cross section was measured at low relative energies in order to infer the astrophysical S factor for the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction. A first-order perturbation theory analysis including $E1\mathrm{}$, $E2\mathrm{}$, and $M1\mathrm{}$ transitions was employed to extract the $E1\mathrm{}$ strength relevant to neutrino-producing reactions in the solar interior. By fitting the measured cross section from $E_{\mathrm{rel}}=130\mathrm{}$ to 400 keV, we find $S_{17}\left(0\right){=17.8\mathrm{}}_{-1.2\mathrm{}}^{+1.4\mathrm{}}\mathrm{eV}\mathrm{b}$.