The mechanism of forward angle incoherent photoproduction of pseudoscalar mesons off nuclei is revisited via the time-dependent multicollisional Monte Carlo (MCMC) intranuclear cascade model. Our results—combined with recent developments to address coherent photoproduction—reproduce with good accuracy recent JLab data of ${\pi }^0$ photoproduction from carbon and lead at an average photon energy $k\sim 5.2$ GeV. For the case of $\eta$ photoproduction, our results for $k=9$ GeV suggest that future measurements to extract the $\eta \to \gamma \gamma$ decay width via the Primakoff method should be focused on light nuclei, where the disentanglement between the Coulomb and strong amplitudes is more easily achieved. The prospects to use heavy nuclei data to access the unknown $\eta N$ cross section in cold nuclear matter are also presented.

Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction $dd\to {}^4\mathrm{He}{\pi }^0{\pi }^0$ have been performed in the energy range 0.8–1.4 GeV covering thus the region of the Abashian-Booth-Crowe effect, which denotes a pronounced low-mass enhancement in the $\pi \pi$ invariant mass spectrum. The experiments were carried out with the WASA detector setup at the cooler synchrotron at Forshungszentrum Julich GmbH. Similar to the observation in the basic $pn\to d{\pi }^0{\pi }^0$ reaction, the data reveal a correlation between the ABC effect and a resonancelike energy dependence in the total cross section. The maximum occurs at $m=2.37$ GeV $+$ 2$m_N$, i.e., at the same position as in the basic reaction. The observed resonance width $\Gamma \approx 160$ MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a $pn$ resonance formation during the reaction process.

Lifetime measurements have been made in the neutron-deficient nucleus ${}^{109}$Te using the coincident recoil distance Doppler-shift method. The experimental $B\left(E2\right)$ values have been compared with state-of-the-art shell-model calculations using the monopole-corrected realistic charge-dependent Bonn nucleon-nucleon potential. Lifetimes in the $\nu h_{11/2}$ band are consistent with an interpretation based on the deformation driving properties of a single valence neutron outside of the even-even tellurium core and highlight the unexpected presence of collective behavior as the $N=50$ shell closure is approached. Lifetime measurements for the low-lying positive-parity states also appear to correlate well with shell-model calculations. In addition, a comparison with the proton-unbound nucleus ${}^{109}$I suggests that the presence of a single decoupled valence proton affects the total measured $B\left(E2\right)$ strengths in a manner that is not currently well understood.

The semimicroscopic algebraic cluster model (SACM) is applied to the systems ${}^{12}\mathrm{C}+\alpha$ $\to$ ${}^{16}$O, ${}^{14}\mathrm{C}+\alpha$ $\to$ ${}^{18}$O, ${}^{16}\mathrm{O}+\alpha$ $\to$ ${}^{20}$Ne, ${}^{18}\mathrm{C}+\alpha$ $\to$ ${}^{22}$Ne, and ${}^{20}\mathrm{Ne}+\alpha$ $\to$ ${}^{24}$Mg. The spectrum and some $E2$ values are fitted to experiment. Further $E2$ transition values as well as $E1$ and $M1$ transitions are calculated and compared to experiment. In addition, we list the spectroscopic factors of the states listed. These factors are predictions of the model and are of interest in current astrophysical studies.

Background: Quadrupole moments of excited nuclear states are important observables for geometrically interpreting nuclear structure in terms of deformed shapes, although data are scarce and sometimes ambiguous, in particular, in neutron-rich nuclides.

Purpose: A measurement was performed for determining the spectroscopic quadrupole moment of the $2_1^{+}$ state of ${}^{140}$Ba in order to clarify the character of quadrupole deformation (prolate or oblate) of the state in its yrast sequence of levels.

Method: We have utilized a new combined technique of lifetime measurement at REX-ISOLDE and MINIBALL using the Doppler-shift attenuation method (DSAM) and a reorientation analysis of Coulomb-excitation yields.

Results: On the basis of the new lifetime of $\tau \left(2_1^{+}\right)=10.4_{-0.8}^{+2.2}$ ps the electric quadrupole moment was determined to be $Q\left(2_1^{+}\right)=-0.52\left(34\right)$ $e$b, indicating a predominant prolate deformation.

Conclusions: This finding is in agreement with beyond-mean-field calculations using the Gogny D1S force and with results from the Monte Carlo shell-model approach.

The spherical to prolate deformed shape transition is studied in the framework of the interacting boson IBA-2 model by using a one-parameter Hamiltonian. Excitation energies and $B\left(E2\right)$ reduced transition strengths of the ground-state, quasi-$\beta$, and quasi-$\gamma$ bands are considered. Particular attention is payed to effects related to the finite boson number. Structural changes are investigated taking also into account the wave functions of the relevant states. The IBA-2 and X(5) predictions are compared to the experimental data on ${}^{150}$Nd, considered one of the best examples of an X(5)-like nucleus. The analysis of potential energy surfaces of ${}^{144-156}$Nd, carried out in the framework of the IBA-2 model, provides further information on the structure of the Nd chain and the identification of the phase transition critical point.

Calculations in ab initio no-core configuration interaction (NCCI) approaches, such as the no-core shell model or no-core full configuration methods, have conventionally been carried out using the harmonic-oscillator many-body basis. However, the rapid falloff (Gaussian asymptotics) of the oscillator functions at large radius makes them poorly suited for the description of the asymptotic properties of the nuclear wave function. We establish the foundations for carrying out NCCI calculations with an alternative many-body basis built from Coulomb-Sturmian functions. These provide a complete, discrete set of functions with a realistic exponential falloff. We present illustrative NCCI calculations for ${}^6\mathrm{Li}$ with a Coulomb-Sturmian basis and investigate the center-of-mass separation and spurious excitations.

Cross sections for the ${}^{174}$Hf($n,2n$)${}^{173}$Hf and ${}^{176}$Hf($n,2n$)${}^{175}$Hf reactions have been measured on the 5.5-MV Van de Graaff tandem accelerator of National Centre for Scientific Research “Demokritos” in Athens, in the neutron energy region from 8.8 to 11.0 MeV, using the activation technique. An experimental method to account for the contamination of the ${}^{176}$Hf($n,2n$) reaction by the ${}^{174}$Hf($n,\gamma$) reaction activated by the parasitic neutrons of the beam is presented. Statistical model calculations have also been performed using the nuclear-reaction codes empire-ii and talys. The results and effects of the nuclear input parameters as well as pre-equilibrium emission are discussed in detail.

We compute the photon production of a QCD plasma at leading order in the strong-coupling with a finite baryon chemical potential. Our approach starts from the real-time formalism of finite-temperature field theory. We identify the class of diagrams contributing at leading order when a finite chemical potential is added and resum them to perform a full treatment of the Landau-Pomeranchuk-Migdal effect similar to the one performed by Arnold, Moore, and Yaffe [J. High Energy Phys. 11 (2001) 057] at zero chemical potential. Our results show that the contribution of $2\mapsto 3$ and $3\mapsto 2$ processes grows as the chemical potential grows.

We have studied the form dependence of fits to $\pi N$ elastic scattering data, based on a Chew-Mandelstam $K$-matrix formalism. Extracted partial-wave amplitudes and resonances characterized by $T$-matrix poles are compared in fits generated with and without explicit Chew-Mandelstam $K$-matrix poles. Diagonalization of the $S$-matrix yields the eigenphase representation. While the eigenphases can vary significantly for the different parametrizations, the locations of most $T$-matrix poles are relatively stable. We also find the partial-wave amplitudes for $\pi N$ elastic scattering to be quite stable. By turning on and off the explicit Chew-Mandelstam pole contributions, we are able to determine how the $T$-matrix poles are generated in this approach.

We study the transition form factors of the pesudoscalar mesons ($\pi ,\eta$, and ${\eta }^{\prime }$) as functions of the momentum transfer $Q^2$ within the light-front quark model. We compare our results with the recent experimental data by CELLO, CLEO, BaBar and Belle collaborations. By considering the possible uncertainties from the quark masses, we illustrate that our predicted form factors can fit with all the data, including those at the large $Q^2$ regions.

A set of $B\left(E2\right)$ values for the low-lying excited states in the radioactive isotope ${}^{109}$Sn were deduced from a Coulomb excitation experiment. The 2.87-MeV/$u$ radioactive beam was produced at the REX-ISOLDE facility at CERN and was incident on a secondary ${}^{58}$Ni target. The $B\left(E2\right)$ values were determined using the known $2^{+}\to 0^{+}$ reduced transition probability in ${}^{58}$Ni as normalization with the semiclassical Coulomb excitation code gosia2. The transition probabilities are compared to shell-model calculations based on a realistic nucleon-nucleon interaction and the predictions of a simple core-excitation model. This measurement represents the first determination of multiple $B\left(E2\right)$ values in a light Sn nucleus using the Coulomb excitation technique with low-energy radioactive beams. The results provide constraints for the single-neutron states relative to ${}^{100}$Sn and also indicate the importance of both single-neutron and collective excitations in the light Sn isotopes.

Nuclear resonance fluorescence (NRF), a process by which a nucleus is excited by absorption of a specific quantum of energy and then deexcites via the emission of one or more $\gamma$ rays, may be applied to nondestructively measure the isotopic composition of a sample. NRF excitations in ${}^{240}$Pu were identified in the energy range of 2.1 to 2.8 MeV using a 3-MeV bremsstrahlung source. Utilizing high-purity germanium detectors at backward angles, nine resonances in ${}^{240}$Pu were identified in this energy range. The measured integrated cross sections range from 29 to 104 eV b. These resonances are of interest to nuclear structure physics and provide unique signatures for the assay of ${}^{240}$Pu content for nuclear forensics, nuclear safeguards, and counterterrorism applications.

We discuss the dependence of $J/\psi$ production on the charged particle multiplicity in proton-proton collisions at CERN Large Hadron Collider (LHC) energies. We show that, in the framework of parton saturation or string interaction models, the hard $J/\psi$ production exhibits a significant growth with the multiplicity, which is stronger than linear in the high density domain. This departure from linearity, that should affect any hard observable, applies for high multiplicity proton-proton collisions in the central rapidity region and is a consequence of the parton saturation or the strong interaction among color ropes that take place at LHC energies. Our assumption, the existence of coherence effects present in proton-proton collisions at high energy, can also be checked by studying the particular shape of the probability distribution associated to the $J/\psi$ production. Predictions for the forthcoming $p$Pb collisions at LHC energies are presented.

We calculate the nucleon self-energies in nuclear matter in the QCD sum rules approach, taking into account the contributions of the four-quark condensates. We analyze the dependence of the results on the model employed for the calculation of the condensates and demonstrate that the relativistic character of the models is important. The condensates are calculated with inclusion of the most important terms beyond the gas approximation. This corresponds to inclusion of the two-body nucleon forces and of the most important three-body forces. The results are consistent with the convergence of the operator product expansion. The density dependence of the nucleon self-energies is obtained. The results are consistent with those obtained by the standard nuclear physics methods, thus inspiring further development of the approach.

We derive corrections to the ground-state energies and radii of atomic nuclei that result from the limitations of finite oscillator spaces.

We present the first predictions for the widths of resonance states in a so-far unobserved exotic isotope beyond the proton dripline, ${}^{21}$Al. For this purpose we employ mirror symmetry between the widths of low-lying resonance states and the asymptotic normalization coefficients (ANC) of their mirror analogs. The latter are extracted from a recently measured peripheral reaction ${}^{20}$O($d$,$p$)${}^{21}$O while the positions of resonances are estimated within a microscopic cluster model and a two-body potential model. We have found that ${}^{21}$Al should have two low-lying states decaying into the ${}^{20}$Mg+$p$ channel and three states at higher energy, built on the 2${}^{+}$ core excited state and decaying into the ${}^{20}$Mg(2${}^{+})+p$ channel. The widths of all these states are much smaller than their energies, which makes experimental spectroscopic studies of this isotope beyond the proton dripline possible.

When the long-wavelength approximation is not performed, extensions of the Siegert theorem can take various forms. An alternative expression is derived for the electric multipole fields, which is inspired by earlier works on photonuclear reactions. It is applied to the Siegert transformation of electric transition operators for single photon emission. In the particular case of isospin forbidden $E1$ transitions, which can be useful for some important radiative capture reactions, an approximation of this electric transition operator is established and discussed.

We have used a potential model, together with information from ${}^{13}$Be, to compute expected energies and widths for the first two positive-parity states of ${}^{13}$F. Results are (all in MeV) $E_p$ = 2.30 and 4.94 (or 5.26), width ∼0.6 and 0.3 (or 0.4), for $1/2^{+}$ and $5/2^{+}$, respectively.

High-spin states in the odd-odd ${}^{128}$I have been studied experimentally using the ${}^{124}$Sn(${}^7$Li, 3n$\gamma$)${}^{128}$I reaction at beam energies of 28 and 32 MeV. A level scheme built on the known $T_{1/2}=175$ ns, ($6^{-})$ isomer has been established. The low-lying states in the level scheme have been proposed to be associated with the $\pi d_{5/2}\otimes \nu h_{11/2}$ and $\pi g_{7/2}\otimes \nu h_{11/2}$ two-quasiparticle excitations. The strongly populated negative-parity states, forming a bandlike structure, have been assigned to be based on the $\pi g_{7/2}\otimes \nu h_{11/2}$ configuration. The $\pi h_{11/2}\otimes \nu h_{11/2}$ multiplet $9^{+}$, ${10}^{+}$, and ${11}^{+}$ members have been identified according to the systematics of the corresponding level structures observed in the lighter odd-odd iodine isotopes. The two-quasiparticle configuration assignments are supported by the nucleon pair approximation and empirical shell-model calculations.