We present a measurement of the pseudorapidity density of primary charged particles near midrapidity in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\hspace{0.5em}\mathrm{GeV}$ as a function of the number of participating nucleons. The pseudorapidity density, ${\mathrm{dN}}_{\mathrm{ch}}/d\eta {|}_{|\eta |<1\mathrm{}}/\left(\frac{1}{2}〈N_{\mathrm{part}}〉\right),$ rises from $2.87\pm 0.21$ in peripheral events $\left(〈N_{\mathrm{part}}〉\sim 83\right)$ to $3.45\pm 0.18$ in central events $\left(〈N_{\mathrm{part}}〉\sim 353\right),$ which is $53\pm 8\%$ higher than $p\overline{p}$ collisions at a similar center-of-mass energy. This is consistent with an additional contribution to charged particle production that scales with the number of binary nucleon-nucleon collisions ${(N}_{\mathrm{coll}}).\mathrm{}$

An improved version of a recently developed quark model approach to vector meson photoproduction is applied to the investigation of contributions of vector meson photoproduction to the Gerasimov-Drell-Hearn (GDH) sum rule. We find that the sum rule converges at a few GeV’s. Contributions to the proton channel are found to be small while to the neutron are relatively large.

Photon scattering experiments have been performed to investigate the structure of the two doubly magic nuclei ${}^{40,48}\mathrm{Ca}.$ The method is highly selective to induce low-order multipole transitions, i.e., $E1,$ $M1,$ and $E2\mathrm{}$ from the ground state. We determined the energies and spins of excited states and the absolute strengths of the $\gamma$ decays in a model independent way. We find the summed electric dipole strengths below 10 MeV to exhaust the energy weighted sum rule by 0.023 and 0.27 %, respectively. The summed electric quadrupole strengths are $\sum B\left(E2\mathrm{}\right)\mathrm{}\uparrow =332\mathrm{}{e}^2{\mathrm{fm}}^4$ and $407e^2{\mathrm{fm}}^4$ for ${}^{40}\mathrm{Ca}$ and ${}^{48}\mathrm{Ca},$ respectively. In order to explain the difference in the $E1\mathrm{}$ strengths of the two isotopes several theoretical models are discussed.

The giant resonance region from $8\mathrm{MeV}<E_x<55\mathrm{}\mathrm{MeV}$ in ${}^{28}\mathrm{Si}$ has been studied with inelastic scattering of 240 MeV α particles at small angles including 0°. Strength corresponding to $81\pm 10\%,$ $68\pm 9\%,$ and $15\pm 4\%$ of the isoscalar $E0,$ $E2,$ and $E1\mathrm{}$ sum rules, respectively, was identified with centroids of $21.25\pm 0.38\mathrm{MeV},$ $18.54\pm 0.25\mathrm{MeV},$ $19.15\pm 0.60\mathrm{MeV},$ and rms widths of $6.4\pm 0.6\mathrm{MeV},$ $4.7\pm 0.6\mathrm{MeV},$ and $6.9\pm 0.7\mathrm{MeV}.$ The mass dependence of the compression modulus of finite nuclei is shown to be reasonably well reproduced from $A=24\mathrm{}$ to 208 in relativistic mean field calculations with the NLC interaction having $K_{\mathrm{nm}}=225\mathrm{}\mathrm{MeV}$ and in nonrelativistic calculations with the RATP interaction having $K_{\mathrm{nm}}=240\mathrm{}\mathrm{MeV}.$

The effect of isospin breaking pion s-wave rescattering is included in elastic $\mathrm{NN}$ scattering at low energies using an interaction obtained from effective field theory. Although this mechanism gave a large contribution to charge symmetry breaking in $n\overrightarrow{p}d{\pi }^0,$ the effect is rather small in $\mathrm{pp}$ vs $\mathrm{nn}$ scattering parameters and in the ${}^3\mathrm{H}{-}^3\mathrm{He}$ binding energy difference. This smallness is caused by large cancellation of the up-down quark mass difference contribution and electromagnetic effects to the $\mathrm{np}$ mass difference.

The ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$ longitudinal and transverse response functions are determined from an analysis of the world data on quasielastic inclusive electron scattering. The corresponding Euclidean response functions are derived and compared to those calculated with Green’s function Monte Carlo methods, using realistic interactions and currents. Large contributions associated with two-body currents are found, particularly in the ${}^4\mathrm{He}$ transverse response, in agreement with data. The contributions of the two-body charge and current operators in the ${}^3\mathrm{He},$ ${}^4\mathrm{He},$ and ${}^6\mathrm{Li}$ response functions are also studied via sum-rule techniques. A semiquantitative explanation for the observed systematics in the excess of transverse quasielastic strength, as function of mass number and momentum transfer, is provided. Finally, a number of model studies with simplified interactions, currents, and wave functions are carried out to elucidate the role played, in the full calculation, by tensor interactions and correlations.

A first measurement of longitudinal as well as transverse spin correlation coefficients for the reaction $\overrightarrow{p}\overrightarrow{p}\to \mathrm{pn}{\pi }^{+}$ is made using a polarized proton target and a polarized proton beam. We report kinematically complete measurements for this reaction at 325-, 350-, 375-, and 400-MeV beam energies. The spin correlation coefficients $A_{\mathrm{xx}}{+A}_{\mathrm{yy}},$ $A_{\mathrm{xx}}-A_{\mathrm{yy}},$ $A_{\mathrm{zz}},$ and $A_{\mathrm{xz}}$ and the analyzing power $A_y,$ as well as angular distributions for $\sigma \left({\theta }_{\pi }\right)$ and the polarization observables $A_{\mathrm{ij}}\left({\theta }_{\pi }\right),$ are extracted. Partial wave cross sections for dominant transition channels are obtained from a partial-wave analysis that included transitions with final-state angular momenta of $l<~1.$ The measurements of the $\overrightarrow{p}\overrightarrow{p}\to \mathrm{pn}{\pi }^{+}$ polarization observables are compared with the predictions from the Jülich meson exchange model. The agreement is very good at 325 MeV, but it deteriorates increasingly for the higher energies. At all energies agreement with the model is better than for the reaction $\overrightarrow{p}\overrightarrow{p}\to \mathrm{pp}{\pi }^0.$

Lifetimes and $\gamma \gamma$ coincidences for low-spin states of the odd-odd nucleus ${}^{50}\mathrm{Mn}$ were measured in the ${}^{40}\mathrm{Ca}{(}^{12}\mathrm{C}{,np)}^{50}\mathrm{Mn}$ fusion-evaporation reaction at 27 MeV beam energy at the ESTU-tandem accelerator at Yale. The excitation energy of the $J^{\pi }{=5\mathrm{}}^{+}$ isomer is established for the first time from high-resolution $\gamma$-ray spectroscopy. Comparison to simulations of the Doppler-shift attenuation processes as functions of the level lifetimes enables us to extract lifetime information for five states. The measurement of $B\left(M1\mathrm{}\right)\mathrm{}$ values agrees with the previous assignments of quasideuteron configurations in ${}^{50}\mathrm{Mn}$ done on the basis of $E2/M1\mathrm{}$-multipole mixing ratios and $\gamma$-branching ratios. The observations verify the predictions of an earlier full $\mathrm{pf}$-shell model calculation for ${}^{50}\mathrm{Mn}.$

The decay of on-line mass-separated ${}^{98}\mathrm{Rb}$ to ${}^{98}\mathrm{Sr}$ is studied by $\gamma$ spectroscopy. The revised decay scheme adds further evidence of the coexistence of very different shapes in ${}^{98}\mathrm{Sr}.$ A set of levels is proposed to originate from particle-hole pair excitations across the $Z=40\mathrm{}$ spherical gap in analogy with ${}^{96}\mathrm{Sr}.$ A deformed $K=3\mathrm{}$ band with probable even parity is built on a 7.1-ns isomer at 1838 keV. It is interpreted as a two-quasineutron excitation in accordance with a quantum Monte Carlo pairing calculation based on a deformed shell model. Configurations of the calculated lowest-lying two-quasiparticle levels confirm the importance of the [404]9/2 neutron orbital at the largest deformations in the neutron-rich $A\simeq 100$ region.

A generalized $M1\mathrm{}$ sum rule for orbital magnetic dipole strength from excited symmetric states to mixed-symmetry states is considered within the proton-neutron interacting boson model of even-even nuclei. Analytic expressions for the dominant terms in the $B\left(M1\mathrm{}\right)\mathrm{}$ transition rates from the $2_{1,2}^{+}$ states are derived in the U(5) and SO(6) dynamic symmetry limits of the model, and the applicability of a sum rule approach is examined at and between these limits. Lastly, the sum rule is applied to the new data on mixed-symmetry states of ${}^{94}\mathrm{Mo}$ and a quadrupole d-boson ratio $n_d{(0\mathrm{}}_1^{+}{)/n}_d{(2\mathrm{}}_2^{+})\approx 0.6$ is obtained in a largely parameter-independent way.

The quadrupole moment of the ${11}^{-}$ isomer in ${}^{194}\mathrm{Pb}$ has been determined as $|Q_s|=4.48\mathrm{}\left(86\right)e\mathrm{b}$ via a new extension of the level mixing spectroscopy technique (LEMS). The new analysis technique allows one to take into account the influence of the electric quadrupole and the magnetic dipole interactions of two subsequent isomers on the angular distribution of the lower lying $\gamma$-ray transitions. For each isomeric state the ratio of its quadrupole interaction frequency to its magnetic moment can be extracted from this double perturbation analysis, thus allowing to deduce their quadrupole moments provided that the electric field gradient and the magnetic moments are known.

The standard relativistic mean-field model is extended by including dynamical effects that arise in the coupling of single-nucleon motion to collective surface vibrations. A phenomenological scheme, based on a linear ansatz for the energy dependence of the scalar and vector components of the nucleon self-energy for states close to the Fermi surface, allows a simultaneous description of binding energies, radii, deformations, and single-nucleon spectra in a self-consistent relativistic framework. The model is applied to the spherical doubly closed-shell nuclei ${}^{132}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}.$

Muon capture and neutrino scattering cross sections in ${}^{12}\mathrm{C},$ ${}^{14}\mathrm{N},$ and ${}^{16}\mathrm{O}$ are calculated within a large shell-model basis. The effects of quenching of the isovector strength on these quantities are studied.

The dependence of the half-lives for proton emission from deformed nuclei is studied for the different single particle potentials known in the literature, that describe standard nuclear structure properties. As an example, ground state and isomeric decays of ${}^{131}\mathrm{Eu}$ and ${}^{141}\mathrm{Ho}$ will be considered, since they are well deformed exotic nuclei for which the experimental data are very precise. In order to reproduce the experimental decay rates and properties of the decaying deformed nuclei, the interactions must have the spin-orbit term treated as deformed and a large radius parameter, $r_0\approx 1.24-1.275\hspace{0.5em}\mathrm{fm}.$ Most parts of the parameterizations are in this limit, and reproduce the decay widths, with the correct deformation, in a range of values within experimental uncertainties. The Becchetti-Greenlees [15] one is an exception, with $r_0=1.17\mathrm{}\hspace{0.5em}\mathrm{fm},$ and is unable to reproduce the data.

Extrapolation of the results of some optical model (OM) study of the $\alpha$-nucleus elastic scattering at incident energies up to 700 MeV implies that the $\alpha$-nucleus potential becomes repulsive above 910 MeV. To check this assumption, a detailed OM analysis of the elastic $\alpha {+}^{12}$C and $\alpha {+}^{40}$Ca scattering data at the incident energy of 1370 MeV has been performed using different forms of the optical potential. A realistic pattern of the near-side/far-side interference, required to reproduce the diffractive minima in the measured elastic cross sections, strongly suggests that the corresponding optical potentials are still attractive. The folding model prediction for the $\alpha {+}^{12}$C and $\alpha {+}^{40}$Ca optical potentials using the impulse approximation has been considered. This approximation, which uses the t-matrix parametrization of free nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ interaction as the model input, was found to be inadequate to give a good account of the data. Consequently, the medium modifications of the $\mathrm{NN}$ interaction remain important at this energy. In addition, similar failure of a density dependent $\mathrm{NN}$ interaction (CDM3Y6), which works quite well at lower energies, stresses the need for a more appropriate effective $\mathrm{NN}$ interaction in this energy region.

Electron-capture delayed fission was observed in 37-s ${}^{244}\mathrm{Es}$ produced via the ${}^{237}\mathrm{Np}{(}^{12}\mathrm{C}{,5n)}^{244}\mathrm{Es}$ reaction at 81 MeV (on target) with a production cross section of $0.31\pm 0.12\mu \mathrm{b}.$ The kinetic energies of coincident fission fragments were measured with our rotating wheel detection system and the average pre-neutron-emission total kinetic energy of the fragments was found to be $186\pm 19\mathrm{MeV}.$ The mass-yield distribution of the fission fragments is predominantly asymmetric. Based on the ratio of the number of fission events to the measured number of α decays from the electron-capture daughter ${}^{244}\mathrm{Cf}$ (100% α branch), the probability of delayed fission was determined to be $(1.2\mathrm{}\pm 0.4)\times {10}^{-4}.$ This value for the delayed fission probability fits the experimentally observed trend of increasing delayed fission probability with increasing Q value for electron capture.

We show, under general assumptions which are well satisfied in relativistic heavy-ion collisions, that the geometric relation of centrality c to the impact parameter b, namely, $c\simeq \pi b^2/{\sigma }_{\mathrm{inel}},$ holds to a very high accuracy for all but most peripheral collisions. More precisely, if $c\left(N\right)\mathrm{}$ is the centrality of events with a multiplicity higer than N, then b is the value of the impact parameter for which the average multiplicity $\mathrm{n̄}\mathrm{}\left(b\right)\mathrm{}$ is equal to N. The corrections to this geometric formula are of the order $\left(\Delta n\right(b)/\mathrm{n̄}{\mathrm{}\left(b\right))}^2,$ where $\Delta n\left(b\right)\mathrm{}$ is the width of the multiplicity distribution at a given value of b; hence they are very small. In other words, the centrality effectively measures the impact parameter.

We have studied possible formation of $\Theta$ vacua states in heavy ion collisions. Random phases of the chiral fields were evolved in a finite temperature potential, incorporating the breaking of $U_A\mathrm{}\left(1\right)\mathrm{}$ symmetry. Initial random phases very quickly settle into oscillation around the values dictated by the potential. The simulation study indicate that an initial $\Theta =0\mathrm{}$ state do not evolve into a $\Theta \ne 0$ state. However, an initial $\Theta \ne 0$ state, if formed in heavy ion collision, can survive, as a coherent superposition of a number of modes.

The dependence of the multiplicity on the number of collisions and the transverse momentum distribution for central and peripheral Au-Au collisions are studied in the model of percolation of strings relative to the experimental conditions at RHIC. The comparison with the first RHIC data shows a good agreement.