A model of mesons which is based on the QCD Hamiltonian in Coulomb gauge is presented. The model relies on a novel quasiparticle basis to improve the reliability of the Fock space expansion. It is also relativistic, yields chiral pions, and is tightly constrained by QCD (quark masses are the only parameters). Applications to hidden flavor mesons yield results comparable to phenomenological constituent quark models while revealing the limitations of such models.

A sum rule method is formulated, based on the shell model, for the evaluation of single-particle energies. It is shown that the triplet-even component of the $NN$ interaction plays an important role for a change of single-particle energy spectra, leading to a rapid decrease of the energy gap at $N=8$, when protons are successively removed from $Z=8$ to $Z=2$.

The cross section for production of $\varphi$ mesons in proton-nucleus reactions is calculated as a function of the target mass. The decay width of the $\varphi$ meson is affected by the change of the masses of the $\varphi$, $K^{+}$, and $K^{-}$ mesons in the medium. A strong attractive $K^{-}$ potential leads to a measurable change of the behavior of the cross section as a function of the target mass. Comparison between the kaon and electron decay modes is made.

We analyze the elastic scattering of protons on a ${}^{4}n$ system. This was used as part of the detection technique of a recent experiment [F. M. Marqués et al. Phys. Rev. C 65, 044006 (2002)] to search for the ${}^{4}n$ (tetraneutron) as a bound particle. We show that it is unlikely that this process alone could yield the events reported in F. M. Marqués et al., [Phys. Rev. C 65, 044006 (2002)], unless the ${}^{4}n$ has an anomalously large backward elastic scattering amplitude.

Gluon exchange currents can explain the decrease of the ratio ${\mu }_p{G}_E^p∕G_M^p$ for four-momentum transfer beyond $Q^2\sim 1{\text{GeV}}^2$. The $\text{SU}\left(6\right)$ breaking induced by gluonic currents predicts furthermore that the ratio of neutron to proton magnetic form factors ${\mu }_p{G}_M^n∕{\mu }_n{G}_M^p$ falls with increasing $Q^2$. We find that the experimental data are consistent with our expectations of an almost linear decrease of the ratio ${\mu }_p{G}_M^n∕{\mu }_n{G}_M^p$ with increasing $Q^2$.

On the basis of relativistic mean field calculations, we demonstrate that the spin-orbit splitting of $p_{3∕2}$ and $p_{1∕2}$ neutron orbits depends sensitively on the magnitude of the proton density near the center of the nucleus, and in particular on the occupation of $s_{1∕2}$ proton orbits. We focus on two exotic nuclei, ${}^{46}\mathrm{Ar}$ and ${}^{206}\mathrm{Hg}$, in which the presence of a pair of $s_{1∕2}$ proton holes would cause the spin-orbit splitting between the $p_{3∕2}$ and $p_{1∕2}$ neutron orbits near the Fermi surface to be much smaller than in the nearby doubly magic nuclei ${}^{48}\mathrm{Ca}$ and ${}^{208}\mathrm{Pb}$. We also explore how partial occupancy of the $s_{1∕2}$ proton orbits affects this quenching. We note that these two exotic nuclei depart from the long-standing paradigm of a central potential proportional to the ground state baryon density and a spin-orbit potential proportional to the derivative of the central potential.

The ${}^{19}\mathrm{Ne}\left(p,\gamma \right){}^{20}\mathrm{Na}$ reaction is part of the chain of reactions linking the hot-CNO cycles and the rp-process in hydrodynamic hydrogen and helium burning. The resonance strength of the $448\text{keV}$ level has been measured in the recoil separator ARES. An upper limit of $15\text{meV}$ ($90\%$ C.L.) has been obtained. This result slightly restricts a prior determination using different methods.

High-spin states in ${}^{185}\mathrm{Os}$ have been studied using the ${}^{176}\mathrm{Yb}\left({}^{13}\mathrm{C},4n\right)$ reaction at a beam energy of $65\text{MeV}$. Previously known one-quasiparticle bands have been extended to higher spins. New high-$K$ bands based on three-quasiparticle excitation have been identified. Nilsson configurations are assigned based on the $g$ factors deduced from $M1∕E2$ branching ratios within the bands. In addition, a new isomer at $5007\text{keV}$ has been found with a half-life of $18\left(2\right)\text{ns}$. The hindrance in decays of the high-$K$ intrinsic states are discussed in terms of the $\gamma$ tunneling model where the low-$K$ and high-$K$ states interact through triaxial shape fluctuation.

High-spin states of ${}^{95}\mathrm{Ru}$ have been populated using the ${}^{35}\mathrm{Cl}+{}^{64}\mathrm{Zn}$ reaction at a beam energy of $135\text{MeV}$. In a recoil-distance Doppler-shift experiment, the lifetimes or lifetime limits of 26 high-spin states have been measured, giving information on a total of 49 reduced transition strengths. The results are compared with shell-model calculations with different model spaces and residual interactions. Several families of states with defined proton and neutron seniorities are proposed. The $M1$ strengths in the negative-parity yrast sequence show a pronounced staggering which is reproduced by the shell-model calculations.

The polarization of protons emitted in $\left(p,2p\right)$ reactions has been measured for three kinds of targets at $1\text{GeV}$. The values of the polarization that we obtain are significantly smaller than the values predicted using the nucleon-nucleon (NN) interaction in free space, and the discrepancy between the two is seen to increase monotonically as a function of the effective mean density, which is defined as a measure of the sensitivity of a reaction to density-dependent terms of the interaction. The experimental data are also compared with a model calculation that includes a relativistic effect, and it is found that inclusion of this effect is able to account for about half of the density-dependent discrepancy between the experimental results and the values predicted with the free space NN interaction. These results, in conjunction with the previous results at $392\text{MeV}$, indicate that this discrepancy is not caused by a contribution of multistep processes and provide further evidence that there exists a medium effect.

A high statistics measurement of the $pp\to pp\eta$ reaction at an excess energy of $Q=15.5\text{MeV}$ has been performed at the internal beam facility COSY-11. The stochastically cooled proton beam and the used detection system allowed to determine the momenta of the outgoing protons with a precision of $4\text{MeV}∕c\left(\sigma \right)$ in the center-of-mass frame. The determination of the four-momentum vectors of both outgoing protons allowed to derive the complete kinematical information of the $\eta pp$ system. An unexpectedly large enhancement of the occupation density in the kinematical regions of low proton-$\eta$ relative momenta is observed. A description taking the proton-proton and the $\eta$-proton interaction into account and assuming an on-shell incoherent pairwise interaction among the produced particles fails to explain this strong effect. Its understanding will require a rigorous three-body approach to the $pp\eta$ system and the precise determination of contributions from higher partial waves. We also present an invariant mass spectrum of the proton-proton system determined at $Q=4.5\text{MeV}$. Interestingly, the enhancement at large relative momenta between protons is visible also at such a small excess energy. In contrast to all other determined angular distributions, the orientation of the emission plane with respect to the beam direction is extracted to be anisotropic.

We study the influence of the nucleon spectral function on $\eta$ photoproduction and electroproduction on nuclei. Besides kinematical effects due to ground state correlations, also a modification of the $S_{11}\left(1535\right)$ decay width is taken into account, which is caused by the possible decay into nucleons with mass smaller than the pole mass in the medium. Hence, resonances with masses below the free $N\eta$ threshold can contribute to $\eta$ production.

The effect of vacuum fluctuations on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization. The effect of the baryon Dirac sea is seen to modify hadronic properties and in contrast to a calculation in mean-field approximation it is seen to give rise to a significant drop of the vector meson masses in hot and dense matter. This effect is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation, where the baryon self-energy is modified due to interactions with both the nonstrange $\left(\sigma \right)$ and the strange $\left(\zeta \right)$ scalar fields.

Transverse momentum spectra and yields of hadrons are measured by the PHENIX collaboration in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=130\text{GeV}$ at the Relativistic Heavy Ion Collider. The time-of-flight resolution allows identification of pions to transverse momenta of $2\text{GeV}∕c$ and protons and antiprotons to $4\text{GeV}∕c$. The yield of pions rises approximately linearly with the number of nucleons participating in the collision, while the number of kaons, protons, and antiprotons increases more rapidly. The shape of the momentum distribution changes between peripheral and central collisions. Simultaneous analysis of all the $p_T$ spectra indicates radial collective expansion, consistent with predictions of hydrodynamic models. Hydrodynamic analysis of the spectra shows that the expansion velocity increases with collision centrality and collision energy. This expansion boosts the particle momenta, causing the yield from soft processes to exceed that for hard to large transverse momentum, perhaps as large as $3\text{GeV}∕c$.

The cross section for ${ϴ}^{+}$ production from the reaction $\gamma p\to {\pi }^{+}{K}^{-}{ϴ}^{+}$, which was observed in the CLAS experiment at the Jefferson National Laboratory, is evaluated in a hadronic model that includes couplings of ${ϴ}^{+}$ to both $KN$ and $K^{*}N$. With their coupling constants determined from the empirical $\pi NN\left(1710\right)$ and $\rho NN\left(1710\right)$ coupling constants using the SU(3) symmetry, the cross section for this reaction has been evaluated by taking ${ϴ}^{+}$ to have spin 1∕2 and isospin 0 but either positive or negative parity. We find that if ${ϴ}^{+}$ has positive parity as predicted by the chiral soliton model and the correlated quark model, the cross section is $50–110\text{nb}$, depending on the value of the $K^{*}Nϴ$ coupling. The cross section is reduced by more than a factor of 10 if ${ϴ}^{+}$ has negative parity as given by lattice QCD studies and the uncorrelated quark model. For both parities, the differential cross section peaks at small negative four-momentum transfer when the reaction is dominated by the $t$-channel kaon-exchange diagram that involves only the coupling of ${ϴ}^{+}$ to $KN$. After decreasing with increasing negative four-momentum transfer, the differential cross section increases again when the $u$-channel contribution due to intermediate ${ϴ}^{+}$ propagation becomes important at large negative four-momentum transfer.

Recent polarization transfer measurements of the proton electromagnetic form factors yield very different results from previous Rosenbluth extractions. This inconsistency implies uncertainties in our knowledge of the form factors and raises questions about how to best combine data from these two techniques. If the discrepancy is due to missing corrections to the cross section data, as has been suggested, then the true form factors, related to the proton structure, differ from the form factors that parametrize the deviation from point scattering, and different applications will require the use of different form factors. We present two extractions of the form factors: a global fit to the world’s cross section data, and a combined extraction from polarization transfer and cross section data. The former provides a parametrization of the elastic electron-proton cross section. The latter provides a consistent extraction of the underlying form factors, under the assumption that missing terms in the radiative correction explain the difference between the cross section and polarization transfer results.

The structure of ${}^{10}\mathrm{Be}$ has been investigated by inelastic scattering to states above the breakup threshold using the reaction ${}^{12}\mathrm{C}\left({}^{10}\mathrm{Be},{}^{10}\mathrm{Be}^{*}\to {}^6\mathrm{He}+{}^4\mathrm{He}\right){}^{12}\mathrm{C}$ at $E_{\mathit{beam}}=302\text{MeV}$. Excited states in ${}^{10}\mathrm{Be}$ were observed at $9.6\pm 0.1$ and $10.2\pm 0.1\text{MeV}$. No evidence was observed for the population of the $4^{+}$ member of the ground-state band of ${}^{10}\mathrm{Be}$ indicating the shell-model-like structure of the ground state. In addition, the decay of ${}^8\mathrm{Be}$, ${}^{10}\mathrm{B}$, and ${}^{11}\mathrm{B}$, populated in the two-neutron, proton pickup, breakup and $1p$ pickup reactions, was reconstructed through the detection of coincident ${}^4\mathrm{He}+{}^4\mathrm{He}$, ${}^4\mathrm{He}+{}^6\mathrm{Li}$, and ${}^4\mathrm{He}+{}^7\mathrm{Li}$ particles. Cross sections for the formation of the ${}^8\mathrm{Be}$, ${}^9\mathrm{Be}$, ${}^{10}\mathrm{B}$, and ${}^{11}\mathrm{B}$ were also deduced. Contrary to expectations, the two-neutron removal results in the production of ${}^8\mathrm{Be}$ predominantly $\left(80\%\right)$ in the first excited $\left(2^{+}\right)$ state. This suggests that dynamical excitations play an important role in the neutron removal process.

We investigate the use of an operatorial basis in a self-consistent theory of large amplitude collective motion. For the example of the pairing-plus-quadrupole model, which has been studied previously at equilibrium, we show that a small set of carefully chosen state-dependent basis operators is sufficient to approximate the exact solution of the problem accurately. This approximation is used to study the interplay of quadrupole and pairing degrees of freedom along the collective path for realistic examples. We show how this leads to a viable calculational scheme for studying nuclear structure, and discuss the surprising role of pairing collapse.

An excitation function for resonance elastic scattering of $\alpha$ particles on ${}^{18}\mathrm{O}$ and ${}^{18}\mathrm{Ne}$ was measured using the method of inverse geometry with a very thick target. Spectroscopic information was obtained for 23 levels in the excitation energy region from 11.9 to $13.7\text{MeV}$ in ${}^{22}\mathrm{Ne}$. Twelve of them are new. General features of $\alpha$-cluster bands in ${}^{22}\mathrm{Ne}$ are analyzed in the framework of the potential model with a deep potential well. Predictions for the ${11}^{-}$ level in ${}^{22}\mathrm{Ne}$, as well as for the isotopic shift of the cluster levels in ${}^{22}\mathrm{Mg}$, are given. Evidence is presented that new perspectives on the study of nuclear structure and nuclear spectroscopy can be obtained in complimentary measurements of $\alpha$-cluster states in mirror $N\ne Z$ nuclei.