A simple but useful guide for understanding the structure of light nuclei is presented. It is based on counting the number of interacting pairs in different spin-isospin ($S,T$) states for a given spatial symmetry and estimating the overall binding according to the sum of ${\sigma }_i·{\sigma }_j{\tau }_i·{\tau }_j$ expectation values, as suggested by one-pion exchange. Applied to s- and p-shell nuclei, this simple picture accounts for the relative stability of nuclei as A increases and as T changes across isobars, the saturation of nuclear binding in the p shell, and the tendency to form $d,t$, or α subclusters there. With allowance for pairwise tensor and spin-orbit forces, which are also generated or boosted by pion exchange, the model explains why mixing of different spatial symmetries in ground states increases as T increases across isobars and why, for states of the same spatial symmetry, the ones with greater S are lower in the spectrum. The ordering of some sd-shell intruder levels can also be understood. The success of this simple model supports the idea that one-pion exchange is the dominant force controlling the structure of light nuclei.

We construct an invariant basis for Compton scattering with two virtual photons (VVCS). The basis tensors are chosen to be gauge invariant and orthogonal to each other. The properties of the corresponding 18 invariant amplitudes are studied in detail. We consider the special case of elastic VVCS with the virtualities of the initial and final photons equal. The invariant basis for VVCS in this orthogonal form does not exist in the literature. We furthermore use this VVCS tensor for a calculation of the beam normal spin asymmetry in the forward kinematics. For this, we relate the invariant amplitudes to the helicity amplitudes of the VVCS reaction. The imaginary parts of the latter are related to the inclusive cross section by means of the optical theorem. We use the phenomenological value of the transverse cross section ${\sigma }_T~0.1$ mb and the Callan-Gross relation which relates the longitudinal cross section ${\sigma }_L$ to the transverse one. The result of the calculation agrees with an existing calculation, and predicts negative values of the asymmetry $B_n$ of order of 5 ppm in the energy range from 3 to 45 GeV and for very forward angles.

The incoherent transition strength of the exotic ${\mu }^{-}-e^{-}$ conversion in the ${}^{208}\mathrm{Pb}$ nucleus is investigated by utilizing the continuum random-phase-approximation method, appropriate for the evaluation of the rate that goes to the continuum of the nuclear spectrum. We find that the contribution of resonances lying high in the continuum is not negligible. Special attention is paid to the detailed study of the pronounced $1^{-}$ contribution that according to previous calculations, dominates the overall incoherent rate in about all the nuclear targets. The spurious center-of-mass admixture to the partial rate originating from the $1^{-}$ excitations is explored, and its elimination is performed by correcting properly the dipole operators. The results found this way show that the greatest portion of the total $1^{-}$ contribution to the incoherent rate is spurious.

We provide accurate assessments of the consequences of violations of self-consistency in Hartree-Fock-(HF) based random-phase approximation (RPA) calculations of the centroid energy $E_{\mathrm{cen}}$ of isoscalar and isovector giant resonances of multipolarities $L=0-3$ in a wide range of nuclei. This is done by carrying out highly accurate HF-RPA calculations neglecting the particle-hole (p-h) spin-orbit or Coulomb interaction in the RPA and comparing with the fully self-consistent HF-RPA results. We find that the shifts in the value of $E_{\mathrm{cen}}$ because of self-consistency violation associated with the spin-orbit and Coulomb interactions are comparable or larger than the current experimental errors in $E_{\mathrm{cen}}$.

We report results from an experiment measuring the semiinclusive reaction ${}^2\mathrm{H}$($e,e^{\text{'}}{p}_s$) in which the proton $p_s$ is moving at a large angle relative to the momentum transfer. If we assume that the proton was a spectator to the reaction taking place on the neutron in deuterium, the initial state of that neutron can be inferred. This method, known as spectator tagging, can be used to study electron scattering from high-momentum (off-shell) neutrons in deuterium. The data were taken with a 5.765 GeV electron beam on a deuterium target in Jefferson Laboratory's Hall B, using the CEBAF large acceptance spectrometer. A reduced cross section was extracted for different values of final state missing mass $W^{*}$, backward proton momentum ${\overrightarrow{p}}_s$, and momentum transfer $Q^2$. The data are compared to a simple plane wave impulse approximation (PWIA) spectator model. A strong enhancement in the data observed at transverse kinematics is not reproduced by the PWIA model. This enhancement can likely be associated with the contribution of final state interactions (FSI) that were not incorporated into the model. Within the framework of the simple spectator model, a “bound neutron structure function” $F_{2n}^{\text{eff}}$ was extracted as a function of $W^{*}$ and the scaling variable $x^{*}$ at extreme backward kinematics, where the effects of FSI appear to be smaller. For $p_s>0.4\mathrm{GeV}/c$, where the neutron is far off-shell, the model overestimates the value of $F_{2n}^{\text{eff}}$ in the region of $x^{*}$ between 0.25 and 0.6. A dependence of the bound neutron structure function on the neutron's “off-shell-ness” is one possible effect that can cause the observed deviation.

Precise measurements of the deuteron vector analyzing power ${\mathrm{A}}_y^d$ and the tensor analyzing power A${}_{\mathit{yy}}$ of the ${}^1\mathrm{H}$ $(\overrightarrow{d},\gamma )$${}^3\mathrm{He}$ capture reaction have been performed at deuteron energies of 29 MeV and 45 MeV. The data have been compared to theoretical state-of-the-art calculations available today. Due to the large sensitivity of polarization observables and the precision of the data light could be shed on small effects present in the dynamics of the reaction.

Double-differential cross sections are reported for light-ion (p, d, t, ${}^3\mathrm{He}$, and α) production in oxygen induced by 96 MeV neutrons. Energy spectra are measured at eight laboratory angles from 20° to 160° in steps of 20°. Procedures for data taking and data reduction are presented. Deduced energy-differential and production cross sections are reported. Experimental cross sections are compared to theoretical reaction model calculations and experimental data at lower neutron energies in the literature. The measured proton data agree reasonably well with the results of the model calculations, whereas the agreement for the other particles is less convincing. The measured production cross sections for protons, deuterons, tritons, and α particles support the trends suggested by data at lower energies.

The semiclassical approach is one of the fundamental tools used to investigate and analyze heavy ion reaction processes. We show in this contribution that the evolution of the motion that emerges from the knowledge of the semiclassical amplitudes for the reaction channels as a function of time cannot be taken as a reliable representation for an actual wave function of the intrinsic states.

Excitation functions were measured for the reactions ${}^{\mathrm{nat}}$Pt(${}^3\mathrm{He}$$,\mathit{xn}$)${}^{195}\mathrm{Hg}$${}^{m,g},{}^{\mathrm{nat}}$Pt(${}^3\mathrm{He}$$,\mathit{xn}$)${}^{197}\mathrm{Hg}$${}^{m,g},{}^{\mathrm{nat}}$Pt(${}^3\mathrm{He}$$,x$)${}^{196}\mathrm{Au}$${}^{m,g}$, and ${}^{\mathrm{nat}}$Pt$(\alpha ,\mathit{xn}$)${}^{197}\mathrm{Hg}$${}^{m,g}$ over the energy range of 18–35 MeV for ${}^3\mathrm{He}$ particles and 17–26 MeV for α particles. The reactions ${}^{197}\mathrm{Au}$$(p,n$)${}^{197}\mathrm{Hg}$${}^{m,g}$ were also investigated over the proton energy range of 6–20 MeV. The three projectiles were produced at the Jülich variable-energy compact cyclotron (CV 28). Use was made of the activation technique in combination with conventional high-resolution as well as low-energy HPGe-detector γ-ray spectroscopy. For most of the reactions, the present measurements provide the first consistent sets of data. From the available experimental data, isomeric cross-section ratios were determined for the above-mentioned reactions. Nuclear model calculations using the code STAPRE, which employs the Hauser-Feshbach (statistical model) and exciton model (precompound effects) formalisms, were undertaken to describe the formation of both the isomeric and the ground states of the products. The calculations were compared with the results of the EMPIRE-II code. The excitation functions of the (${}^3\mathrm{He}$$,\mathit{xn})$ and $(\alpha ,\mathit{xn})$ processes are described well by the theory. In the case of (${}^3\mathrm{He}$$,\mathrm{pxn})$ reactions, however, considerable deviations were observed between the experiment and the theory, presumably due to strong contributions from direct interactions. A description of the isomeric cross-section ratio by the model was possible only with a very low value of $\eta$, i.e., the ${\Theta }_{\mathrm{eff}}/{\Theta }_{\mathrm{rig}}$ ratio. A mass dependence of $\eta$ is proposed.

We study the mechanism of the associated Λ-kaon and Σ-kaon production in nucleon-nucleon collisions over an extended range of near-threshold beam energies within an effective Lagrangian model, to understand the new data on $\mathit{pp}\to p\Lambda K^{+}$ and $\mathit{pp}\to p{\Sigma }^0{K}^{+}$ reactions published recently by the COSY-11 Collaboration. In this theory, the hyperon production proceeds via the excitation of $N^{*}(1650),N^{*}(1710)$, and $N^{*}(1720)$ baryonic resonances. Interplay of the relative contributions of various resonances to the cross sections is discussed as a function of the beam energy over a larger near threshold energy domain. Predictions of our model are given for the total cross sections of $\mathit{pp}\to p{\Sigma }^{+}{K}^0,\mathit{pp}\to n{\Sigma }^{+}{K}^{+}$, and $\mathit{pn}\to n\Lambda K^{+}$ reactions.

Short range correlations are introduced using the unitary correlation method in a relativistic approach to the equation of state of the infinite nuclear matter in the framework of the Hartree-Fock approximation. It is shown that the correlations give rise to an extra node in the ground state wave function in the nucleons, contrary to what happens in nonrelativistic calculations with a hard core. The effect of the correlations on the ground state properties of nuclear and neutron matter is studied. The nucleon effective mass and equation of state (EOS) are very sensitive to short range correlations. In particular, if the pion contact term is neglected, a softening of the EOS is predicted. Correlations have also an important effect on the neutron matter EOS which presents no binding but only a very shallow minimum, contrary to the Walcka model.

The A-dependence of models for the attenuation of hadron production in semi-inclusive deep-inelastic scattering on a nucleus is investigated for realistic matter distributions. It is shown that the dependence for a pure partonic (absorption) mechanism is more complicated than a simple $A^{2/3}$ ($A^{1/3}$) behavior, commonly found when using rectangular or Gaussian distributions, but that the A-dependence may still be indicative for the dominant mechanism of hadronization.

We use two-body potentials derived from a constituent quark cluster model to analyze the bound-state problem of the $\Sigma \mathit{NN}$ system. The observables of the two-body subsystems, NN and $\Sigma N$, are well reproduced. We do not find $\Sigma \mathit{NN}$ bound states, but there are two attractive channels with a resonance close above the three-body threshold. These channels are the $(I,J)=(1,1/2)$ and $(0,1/2)$, their quantum numbers, widths and energy ordering consistent with the recently reported strange tribaryons from the ${}^4\mathrm{He}$$(K_{\mathrm{stopped}}^{-},N)$ reactions in the KEK PS E471 experiment.

Results are presented from a search for the decays $D^0\to {\text{K}}^{-}{\pi }^{+}$ and ${\overline{\text{D}}}^0\to {\text{K}}^{+}{\pi }^{-}$ in a sample of $3.8\times {10}^6$ central Pb-Pb events collected with a beam energy of 158A GeV by NA49 at the CERN SPS. No signal is observed. An upper limit on ${\text{D}}^0$ production is derived and compared to predictions from several models.

A fit of the experimental data to the total cross section of the process $\gamma \gamma \to {\pi }^{+}{\pi }^{-}$ in the energy region from threshold to 2500 MeV has been carried out using dispersion relations with subtractions for the invariant amplitudes, where the dipole and the quadrupole polarizabilities of the charged pion are free parameters. As a result, the sum and the difference of the electric and magnetic dipole and quadrupole polarizabilities of the charged pion have been found: $({\alpha }_1+{\beta }_1){}_{{\pi }^{\pm }}=(0.{18}_{-0.02}^{+0.11})\times {10}^{-4}{\mathrm{fm}}^3,({\alpha }_1-{\beta }_1){}_{{\pi }^{\pm }}=(13.0_{-1.9}^{+2.6})\times {10}^{-4}{\mathrm{fm}}^3,({\alpha }_2+{\beta }_2){}_{{\pi }^{\pm }}=(0.133\pm 0.015)\times {10}^{-4}{\mathrm{fm}}^5,({\alpha }_2-{\beta }_2){}_{{\pi }^{\pm }}=(25.0_{-0.3}^{+0.8})\times {10}^{-4}{\mathrm{fm}}^5$. These values agree with the dispersion sum rule predictions. The value found for the difference of the dipole polarizabilities is consistent with the results obtained from scattering of high energy ${\pi }^{-}$ mesons off the Coulomb field of heavy nuclei [Yu. M. Antipov et al., Phys. Lett. B121, 445 (1983)] and from radiative ${\pi }^{+}$ photoproduction from the proton at MAMI [J. Ahrens et al., Eur. Phys. J. A 23, 113 (2005)], whereas it is at variance with the recent calculations in the framework of chiral perturbation theory.

A general analysis of the sensitivities of neutron β-decay experiments to manifestations of possible interaction beyond the standard model is carried out. In a consistent fashion, we take into account all known radiative and recoil corrections arising in the standard model. This provides a description of angular correlations in neutron decay in terms of one parameter, which is accurate to the level of $~{10}^{-5}$. Based on this general expression, we present an analysis of the sensitivities to new physics for selected neutron decay experiments. We emphasize that the usual parametrization of experiments in terms of the tree-level coefficients $a,A$, and B is inadequate when the experimental sensitivities are at the same or higher level relative to the size of the corrections to the tree-level description.

The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

The odd-odd fp-shell nucleus ${}^{52}\mathrm{Sc}$ was investigated using in-beam γ-ray spectroscopy following secondary fragmentation of a ${}^{55}\mathrm{V}$ and ${}^{57}\mathrm{Cr}$ cocktail beam. Aside from the known γ-ray transition at 674(5) keV, a new decay at $E_{\gamma }=212(3)$ keV was observed. It is attributed to the depopulation of a low-lying excited level. This new state is discussed in the framework of shell-model calculations with the GXPF1, GXPF1A, and KB3G effective interactions. These calculations are found to be fairly robust for the low-lying level scheme of ${}^{52}\mathrm{Sc}$ irrespective of the choice of the effective interaction. In addition, the frequency of spin values predicted by the shell model is successfully modeled by a spin distribution formulated in a statistical approach with an empirical, energy-independent spin-cutoff parameter.

The low-lying decay scheme of ${}^{150}\mathrm{Sm}$ is studied through the (n,γ) reaction. Precise energies as well as lifetimes measured with the gamma-ray-induced Doppler technique provide important structural information. A comparison with the predictions of interacting boson model calculations confirms that this nucleus is very close to the phase transition between spherical and quadrupole axial symmetric shapes, lying just prior to the critical point on the spherical side of the transition.