The problem of nucleon resonances $N^{\prime }$ with masses below the $\Delta$ is considered. We derive bounds for the properties of such states. Some of these are new, while others improve upon existing limits. We discuss the nature of $N^{\prime }$ states, and their unitary partners, assuming that their existence can be verified.

The transfer reaction ${}^{94}\mathrm{Zr}(d,p){}^{95}\mathrm{Zr}$ has been studied to check the existence of a low-lying first excited level at $23\text{keV}$ in ${}^{95}\mathrm{Zr}$. This level—if it exists—might have significant influence on the branching of the astrophysical $s$ process at the branching nucleus ${}^{95}\mathrm{Zr}$. Our experimental spectra, measured with very good energy resolution, do not show any evidence for the existence of such a low-lying level. This is in agreement with experimental results from several reactions and contradicts the only claim for evidence of such a low-lying level which was also derived from ${}^{94}\mathrm{Zr}(d,p){}^{95}\mathrm{Zr}$ data, however with moderate resolution, but still the best of the previous experiments.

The width of the giant dipole resonance (GDR) at finite temperature $T$ in ${}^{120}\mathrm{Sn}$ is calculated within the phonon damping model including the neutron thermal pairing gap determined from the modified BCS theory. It is shown that the effect of thermal pairing causes a smaller GDR width at $T\lesssim 2\text{MeV}$ as compared to the one obtained by neglecting pairing. This improves significantly the agreement between theory and experiment, including the most recent data point at $T=1\text{MeV}$.

We present a theory of one-neutron halo breakup reactions within the framework of post-form distorted wave Born approximation wherein pure Coulomb, pure nuclear, and their interference terms are treated consistently in a single setup. This formalism is used to study the breakup of one-neutron halo nucleus ${}^{11}\mathrm{Be}$ on several targets of different masses. We investigate the role played by the pure Coulomb, pure nuclear, and the Coulomb-nuclear interference terms by calculating several reaction observables. The Coulomb-nuclear interference terms are found to be important for more exclusive observables.

The recent isotopic shift measurements for the chain of neon isotopes have revealed a rich structural information and very interesting anomalous behavior of the charge radii with neutron number. Here we study the systematics of the charge radii of neon isotopes within the relativistic mean field (RMF) framework. The pairing correlations are incorporated by simple constant gap approximation as well as self-consistently through the Bogoliubov transforms employing in the pairing channel the finite range Gogny-D1S or the density dependent zero range interaction. It is observed that the RMF in the axially deformed oscillator basis successfully explains the observed anomaly in the charge radii of neon isotopes.

The nuclear matrix elements $M^{0\nu }$ of the neutrinoless double-beta decay $\left(0\nu \beta \beta \right)$ are evaluated for ${}^{76}\mathrm{Ge},{}^{100}\mathrm{Mo},{}^{130}\mathrm{Te},$ and ${}^{136}\mathrm{Xe}$ within the renormalized quasiparticle random phase approximation (RQRPA) and the simple QRPA. Three sets of single particle level schemes are used, ranging in size from 9 to 23 orbits. When the strength of the particle-particle interaction is adjusted so that the $2\nu \beta \beta$ decay rate is correctly reproduced, the resulting $M^{0\nu }$ values become essentially independent of the size of the basis, and of the form of different realistic nucleon-nucleon potentials. Thus, one of the main reasons for variability of the calculated $M^{0\nu }$ within these methods is eliminated.

A Reggeized model for $\eta$ and ${\eta }^{\prime }$ photoproduction on the nucleon is presented. In this model, $t$-channel vector meson exchanges are described in terms of Regge trajectories to comply with the correct high energy behavior. We compare this Reggeized model with an isobar model ($\eta$-MAID), where the $t$-channel exchanges are described by $\rho$ and $\omega$ poles. Both models contain the same resonance contributions, and describe current $\gamma p\to \eta p$ data up to $E_{\gamma }^{\text{lab}}=2\text{GeV}$ quite well, but only the Reggeized model can be successfully extended to higher energies. For the $\gamma p\to {\eta }^{\prime }p$ reaction, the Reggeized model is found to be able to give a satisfactory description. For the differential cross section data from SAPHIR, we find that the observed linear forward rise in $\cos \theta$ near $E_{\gamma }^{\text{lab}}=1.6\text{GeV}$ can be well described by the interference of an $S_{11}$ resonance and the Regge trajectory exchanges without any need for an additional $P$-wave resonance.

Using hadronic Lagrangians that include the interaction of pentaquark ${\Theta }^{+}$ baryon with $K$ and $N$, we evaluate the cross sections for its production from meson-proton, proton-proton, and photon-proton reactions near threshold. With empirical coupling constants and form factors, the predicted cross sections are about $1.5\text{mb}$ in kaon-proton reactions, $0.1\text{mb}$ in $\rho$-nucleon reactions, $0.05\text{mb}$ in pion-nucleon reactions, $20\mu \mathrm{b}$ in proton-proton reactions, and $40\text{nb}$ in photon-proton reactions.

The quasielastic scattering of muon neutrinos on oxygen 16 is studied for neutrino energies between $200\text{MeV}$ and $1\text{GeV}$ using a relativistic shell model. Final state interactions are included within the distorted wave impulse approximation, by means of a relativistic optical potential, with and without imaginary part, and of a relativistic mean field potential. For comparison with experimental data the inclusive charged-current quasielastic cross section for ${\nu }_{\mu }-{}^{12}\mathrm{C}$ scattering in the kinematical conditions of the LSND experiment at Los Alamos is also presented and briefly discussed.

We study the effect of virtual Coulomb breakup, commonly known as the dipole polarizability, of the deuteron projectile on the astrophysical fusion reaction ${}^3\mathrm{He}\left(d,p\right){}^4\mathrm{He}$. We use the adiabatic approximation to estimate the potential shift due to the $E1$ transition to the continuum states in the deuteron and compute the barrier penetrability in the WKB approximation. We find that the enhancement of the penetrability due to the deuteron breakup is too small to resolve the longstanding puzzle observed in laboratory measurements that the electron screening effect is surprisingly larger than theoretical prediction based on an atomic physics model. The effect of ${}^3\mathrm{He}$ breakup in the ${}^3\mathrm{He}\left(d,p\right){}^4\mathrm{He}$ reaction, as well as the ${}^7\mathrm{Li}$ breakup in the ${}^7\mathrm{Li}\left(p,\alpha \right){}^4\mathrm{He}$ reaction is also discussed.

We investigate $\eta$ electroproduction on nuclei for $Q^2=2.4$ and $3.6{\text{GeV}}^2$ in the framework of a coupled-channel Boltzmann-Uehling-Uhlenbeck transport model. We analyze the importance of final state interactions and side feeding and compare with findings drawn from $\eta$ photoproduction. It is shown that in contrast to photoproduction the influence of $\eta$’s stemming from secondary processes becomes important at high $Q^2$.

Since the existing calculations of the effective meson mass in nuclear medium involve approximations, it is important to examine whether they satisfy the general requirement of the equivalence theorem that the physical observables should be independent of the choice of field variables. We study here consequences of nucleon field transformations. As an illustrative case we consider the in-medium effective pion mass calculated for the s-wave pion-nucleon interaction in the linear-density approximation. We demonstrate that it is necessary to include the Born term explicitly in order that the effective pion mass should obey the equivalence theorem.

The optical potential approach for low-energy scattering of $\eta$ mesons on three-body nuclei is compared to an exact treatment of the $\eta 3N$ system using four-body scattering theory with separable interactions in $s$ waves only. The higher-order terms including the interaction of the struck nucleon with the surrounding nuclear medium and virtual target excitations in between successive $\eta$ scatterings are found to cause important corrections. Effects of final state interaction in $\eta$ photoproduction on ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$ are also studied and sizable contributions beyond the optical model approach are found.

High spin states in the ${}^{177}\mathrm{Hg}$ nucleus were populated by the ${}^{144}\mathrm{Sm}\left({}^{36}\mathrm{Ar},3\mathrm{n}\right){}^{177}\mathrm{Hg}$ reaction at a beam energy of $178\text{MeV}$. The emitted prompt $\gamma$ rays were detected with the Jurosphere $\gamma$-ray spectrometer, while the recoiling nuclei were identified using an active stopper at the focal plane of the gas-filled separator RITU. A quasi-rotational band that decays to an isomeric state with a half-life $t_{1∕2}=1.50\pm 0.15\mu \mathrm{s}$ and its subsequent $\gamma$ decay to the ground state of ${}^{177}\mathrm{Hg}$ have been observed for the first time. Based on the observed decays from this isomeric state, we suggest that the spin of the ground state of ${}^{177}\mathrm{Hg}$ is $J^{\pi }=7∕2^{-}$. In addition, a sequence of transitions that bypass this isomeric state has also been observed. Evidence for shape coexistence is presented. The properties of the observed states are discussed in terms of the systematics of the mercury nuclei in this transitional region.

We calculate the coherent charmonium photoproduction in the photon energy domain where the coherence and formation lengths exceed the average internucleon distance in nuclei but are comparable to the nuclear radii. In this kinematical regime we use the generalized vector dominance model (GVDM) adjusted to account for the physics of bound charmonium states and for the color screening phenomenon. We find significant oscillations in the energy dependence of the total and forward photoproduction cross sections due to the oscillating behavior of the longitudinal nuclear form factor. Within the GVDM these oscillations are strongly modified by the nondiagonal rescatterings of the charmonium. We demonstrate how to employ the oscillating behavior of the photoproduction cross sections off nuclear targets to determine the elementary charmonium photoproduction amplitudes and the genuine charmonium-nucleon cross sections in the forthcoming SLAC E160 experiment.

Elliptic flow of charm hadrons is investigated based on the quark coalescence model. Due to the large difference between the charm quark and light quark masses, hadrons containing both light and charm quarks show a qualitatively different $v_2\left(p_{\perp }\right)$ from hadrons containing only light quarks. Simple relations are proposed to infer quark elliptic flow from those of hadrons. The effects of the finite momentum spread of hadron wave functions are also studied, and are found to be small for charm hadrons.

We investigate the influence of possible in-medium modifications of the $S_{11}\left(1535\right)$ in $\eta$ photoproduction in nuclei. Besides Fermi motion, Pauli blocking, and binding effects also collisional broadening is accounted for. The in-medium width is obtained from a realistic resonance-hole model. Results on $\eta$ photoproduction are obtained from a semiclassical Boltzmann-Uehling-Uhlenbeck transport model and compared with data. We find that calculations including a momentum dependent nucleon and resonance potential are in agreement with the recent KEK data. In contrast, collisional broadening has only little influence.

It is shown that most of the available data on the $pp\to pp\eta$ reaction, including the invariant mass distributions in the $pp\to pp\eta$ reaction recently measured at COSY, can be understood in terms of the partial-wave amplitudes involving final $pp$ $S$ and $P$ states and the $\eta$ meson $s$ wave. This finding, together with the fact that results within a meson–exchange model are especially sensitive to the details of the excitation mechanism of the $S_{11}\left(1535\right)$ resonance, demonstrates the possibility of investigating the properties of this resonance in $NN$ collisions. The spin correlation function $C_{xx}$ is shown to disentangle the $S$- and $P$-wave contributions. It is also argued that spin correlations may be used to help constrain the contributions of the amplitudes corresponding to the final $pp$ ${}^3{P}_0$ and ${}^3{P}_2$ states.

Electric dipole transitions between $3_1^{-}$ octupole-phonon states and one-phonon $2_{1,\mathrm{ms}}^{+}$ mixed-symmetry states of ${}^{92}\mathrm{Zr},$ ${}^{94}\mathrm{Mo},$ ${}^{96}\mathrm{Ru},$ and ${}^{142}\mathrm{Ce}$ are observed and provide the first evidence for F-vector $E1\mathrm{}$ transitions in nuclei. For effective boson models of the nuclear valence shell, F spin is the analog of isospin in the shell model. The $3_1^{-}\to 2_{1,\mathrm{ms}}^{+}$ $E1\mathrm{}$ transitions are stronger than those of the $2_1^{+}$ state. The effective $E1\mathrm{}$ operator in the sdf-interacting boson model-2 is concluded to have F-vector character, in analogy with the well-known isovector character of the $E1\mathrm{}$ operator in microscopic models.

Decay properties of multiphonon quadrupole vibrational states and intruder structures in ${}^{116}\mathrm{Cd}$ have been examined with the ${(n,n}^{\prime }\gamma )$ reaction. γ-ray excitation functions, angular distributions, and $\gamma -\gamma$ coincidences have been measured. Lifetimes of many levels were determined with the Doppler-shift attenuation method, exposing the degree of collectivity of the intruder structure and the three-phonon states. In combination with other recent results, this new information reveals that the intruder picture is well supported in the Cd nuclei. However, a puzzle not present in the lighter Cd nuclei emerges in ${}^{116}\mathrm{Cd};$ strong configuration mixing between intruder and multiphonon vibrational excitations cannot describe the observed decays of the lowest $0^{+}$ excited states.