The geometry of the shears mechanism in nuclei is derived from the nuclear shell model. This is achieved by taking the limit of large angular momenta (classical limit) of shell-model matrix elements.

In a previous publication [Phys. Rev. Lett. 110, 112501 (2013)] we have proposed a generalization of the adiabatic model of $(d,p)$ reactions that allows the nonlocality of the nucleon optical potential to be included in a consistent way together with the deuteron breakup. In this model an effective local $d\text{−}A$ potential is constructed from local nucleon optical potentials taken at an energy shifted by $\sim 40$ MeV with respect to the widely used $E_d/2$ value, where $E_d$ is the deuteron incident energy. The effective $d\text{−}A$ potential is shallower than that traditionally used in the analysis of $(d,p)$ reactions within the adiabatic distorted wave approximation and this affects the calculated cross sections and the nuclear structure quantities obtained from their comparison with experimental data. In the present paper we give full derivation of the deuteron effective potential, consider its leading-order term within the local-energy approximation and discuss corrections to the leading-order term. The new method is applied to $(d,p)$ reactions on ${}^{16}$O, ${}^{36}$Ar, and ${}^{40}$Ca targets and the influence of the deviation from the $E_d/2$ rule on the calculated cross sections is quantified.

The first high-statistics cross sections for the reactions $\gamma p\to K^{*+}\Lambda$ and $\gamma p\to K^{*+}{\Sigma }^0$ were measured using the CLAS detector at photon energies between threshold and 3.9 GeV at the Thomas Jefferson National Accelerator Facility. Differential cross sections are presented over the full range of the center-of-mass angles, and then fitted to Legendre polynomials to extract the total cross section. Results for the $K^{*+}\Lambda$ final state are compared with two different calculations in an isobar and a Regge model, respectively. Theoretical calculations significantly underestimate the $K^{*+}\Lambda$ total cross sections between 2.1 and 2.6 GeV, but are in better agreement with present data at higher photon energies.

Applying the semirealistic $NN$ interactions that include a realistic tensor force to the Hartree-Fock calculations, we investigate tensor-force effects on the single-particle levels in Ca isotopes. The semirealistic interactions successfully describe the experimental difference between $\varepsilon \left(p1s_{1/2}\right)$ and $\varepsilon \left(p0d_{3/2}\right)$ (denoted by $\Delta {\varepsilon }_{13}$) both at ${}^{40}$Ca and ${}^{48}$Ca, confirming the importance of the tensor force. The tensor force plays a role in the $N$ dependence of $\Delta {\varepsilon }_{13}$ also in neutron-rich Ca nuclei. While the $p1s_{1/2}$–$p0d_{3/2}$ inversion is predicted in heavier Ca nuclei as in ${}^{48}$Ca, it takes place only for $N\ge 46$, delayed by the tensor force. We further investigate the possibility of proton bubble structure in Ar, which is suggested by the $p1s_{1/2}$–$p0d_{3/2}$ inversion in ${}^{48}$Ca and more neutron rich Ca nuclei, by using spherical Hartree-Fock-Bogolyubov calculations. Even with the inversion at ${}^{48}$Ca the pair correlation prohibits prominent bubble distribution in ${}^{46}$Ar. Bubble structure in Ar is unlikely also near the neutron drip line because of either unboundness or deformation. However, ${}^{34}$Si remains a candidate for proton bubble structure, owing to the large shell gap between $p1s_{1/2}$ and $p0d_{5/2}$.

We address the question of why so far most of the simulation approaches to find the energy of vanishing flow (EVF) in light systems have failed to reproduce the experimental data. By investigating systematically the dependence of the EVF on the initial setup of the nuclei in these approaches we find out that for light systems a small variation of this setup can create large differences in the EVF whereas for large systems the dependence is weak. These studies have been done with the isospin-dependent quantum molecular dynamics model.

The Born theory for bremsstrahlung from high-energy electrons colliding with extended (finite-mass) nuclei is reexamined. Higher-order effects are included into the Born approximation by making use of the weak-potential Sommerfeld-Maue prescription in an additional contribution to the transition amplitude. Predictions are made for the differential cross section (with respect to the photon degrees of freedom) and for the polarization correlations between the incoming electron and the emitted photon. It is found that at collision energies exceeding 20 MeV the cross section as well as the polarization correlations are strongly influenced by nuclear recoil and nuclear structure effects, particularly at backward photon angles. Numerical results are presented for bremsstrahlung from 10–100 MeV electrons colliding with protons, ${}^{19}$F and ${}^{89}$Y nuclei.

A new framework for computing the similarity renormalization group (SRG) evolution of three-nucleon forces (3NF) in momentum representation is presented. The use of antisymmetric three-particle hyperspherical momentum states ensures unitary evolutions within certain basis truncations, much like antisymmetric harmonic oscillator SRG evolutions. Additionally, in each partial wave the ${\mathit{T}}_{\mathrm{rel}}$-SRG regulator is exactly represented, similar to recent 3NF momentum representation evolutions. Unitary equivalence is demonstrated for the triton using several chiral two- plus three-nucleon interactions. This method allows for a clean visualization of the evolution of the three-nucleon forces, which manifests the SRG decoupling pattern and low-momentum universality.

Background: The major challenge for nuclear theory is to describe and predict global properties and collective modes of atomic nuclei. Of particular interest is the response of the nucleus to a time-dependent external field that impacts the low-energy multipole and $\beta$-decay strength, as well as individual nuclear excitations.

Purpose: We propose a method to compute low-lying collective modes in deformed nuclei within the finite-amplitude method (FAM) based on the quasiparticle random-phase approximation (QRPA). By using the analytic property of the response function, we find the QRPA amplitudes by computing the residua of the FAM amplitudes by means of a contour integration around the QRPA poles in a complex frequency plane.

Methods: We use superfluid nuclear density functional theory with Skyrme energy density functionals, the FAM-QRPA approach, and the conventional matrix formulation of the QRPA.

Results: We demonstrate that the complex-energy FAM-QRPA method reproduces low-lying collective states obtained within the conventional matrix formulation of the QRPA theory. Illustrative calculations are performed for the isoscalar monopole strength in deformed ${}^{24}$Mg and for low-lying $K=0$ quadrupole vibrational modes of deformed Yb and Er isotopes.

Conclusions: The proposed FAM-QRPA approach, in addition to providing a quick estimate of various strength functions, allows one to efficiently calculate the individual QRPA amplitudes of the low-lying collective modes in spherical and deformed nuclei throughout the entire nuclear landscape, in particular shape-vibrational and pairing-vibrational modes and $\beta$-decay rates. It can also be employed in microscopic approaches to large-amplitude nuclear collective motion based on the adiabatic self-consistent collective coordinate method.

The action of the long-range residual force on the expectation value of observables in the nuclear ground states is evaluated by finding optimal values for the coefficients of the canonical transformation which connects the phonon vacuum state with the (quasi)particle ground state. After estimating the improvements over the predictions of the independent-particle approximation we compare the ground-state wave functions, obtained using the presented approach, with those obtained using the conventional random phase approximation (RPA) and its extended version. The problem with overbinding of the nuclear ground state calculated using the RPA is shown to be removed if one sticks to the prescriptions of the present approach. The reason being that the latter conforms to the original variational formulation. Calculations are performed within the two-level Lipkin-Meshkov-Glick model in which we present results for the ground and first excited state energies as well as for the ground-state particle occupation numbers.

We present a study of the average transverse momentum ($p_t$) fluctuations and $p_t$ correlations for charged particles produced in Cu+Cu collisions at midrapidity for $\sqrt{s_{NN}}=$ 62.4 and 200 GeV. These results are compared with those published for Au+Au collisions at the same energies, to explore the system size dependence. In addition to the collision energy and system size dependence, the $p_t$ correlation results have been studied as functions of the collision centralities, the ranges in $p_t$, the pseudorapidity $\eta$, and the azimuthal angle $\varphi$. The square root of the measured $p_t$ correlations when scaled by mean $p_t$ is found to be independent of both colliding beam energy and system size studied. Transport-based model calculations are found to have a better quantitative agreement with the measurements compared to models which incorporate only jetlike correlations.

We study the shear and bulk viscosities of partonic and hadronic matter as functions of temperature $T$ within the parton-hadron-string dynamics (PHSD) off-shell transport approach. Dynamical hadronic and partonic systems in equilibrium are studied by the PHSD simulations in a finite box with periodic boundary conditions. The ratio of the shear viscosity to entropy density $\eta \left(T\right)/s\left(T\right)$ from PHSD shows a minimum (with a value of about $0.1$) close to the critical temperature $T_c$, while it approaches the perturbative QCD limit at higher temperatures in line with lattice QCD (lQCD) results. For $T<T_c$, i.e., in the hadronic phase, the ratio $\eta /s$ rises fast with decreasing temperature due to a strong decrease of the entropy density $s$ in the hadronic phase at decreasing $T$. Within statistics, we obtain practically the same results in the Kubo formalism and in the relaxation time approximation. The bulk viscosity $\zeta \left(T\right)$—evaluated in the relaxation time approach—is found to strongly depend on the effects of mean fields (or potentials) in the partonic phase. We find a significant rise of the ratio $\zeta \left(T\right)/s\left(T\right)$ in the vicinity of the critical temperature $T_c$, when consistently including the scalar mean-field from PHSD, which is also in agreement with that from lQCD calculations. Furthermore, we present the results for the ratio $(\eta +3\zeta /4)/s$, which is found to depend nontrivially on temperature and to generally agree with the lQCD calculations as well. Within the PHSD calculations, the strong maximum of $\zeta \left(T\right)/\eta \left(T\right)$ close to $T_c$ has to be attributed to mean-field (or potential) effects that in PHSD are encoded in the temperature dependence of the quasiparticle masses, which is related to the infrared enhancement of the resummed (effective) coupling $g\left(T\right)$.

We examine Cr isotopes at the drip line, where surface effects related to the existence of a weakly bound $s_{1/2}$ state are known to be important and tightly connected with the pairing phenomenon (antihalo effect). For these weakly bound isotopes, we evaluate the ground state to ground state two-neutron transfer probabilities within a mean-field-based approach. An important part of the discussion is devoted to the analysis of several procedures that can be employed to constrain the parameters of a phenomenological pairing interaction. The parameters are first adjusted to reproduce the experimental gaps evaluated with the five-point formula. This choice has, however, some consequences on the evolution of the pairing correlations along the isotopic chains and, in particular, at shell closures. Other procedures are then followed (adjustment on a theoretical pairing gap at mid-shell and on the two-neutron separation energies). For the transfer probabilities, we discuss the effects associated with different choices of the spatial localization of the pairing interaction. We indicate that the analysis of pair-transfer reactions for such cases (where the last bound state is a low-$l$ state in a weakly bound nucleus) may improve our understanding of two aspects: the spatial distribution of pairing correlations in nuclei and the general problem of the persistence of pairing at the drip lines.

Background: The recent Jefferson Laboratory data for the nuclear transparency in ${\rho }^0$ electroproduction have the potential to settle the scale for the onset of color transparency (CT) in vector meson production.

Purpose: To compare the data to calculations in a relativistic and quantum-mechanical Glauber model and to investigate whether they are in accordance with results including color transparency given that the computation of $\rho$-nucleus attenuations is subject to some uncertainties.

Method: We compute the nuclear transparencies in a multiple-scattering Glauber model and account for effects stemming from color transparency, from $\rho$-meson decay, and from short-range correlations (SRC) in the final-state interactions (FSI).

Results: The robustness of the model is tested by comparing the mass dependence and the hard-scale dependence of the $A(e,e^{\prime }p)$ nuclear transparencies with the data. The hard-scale dependence of the $(e,e^{\prime }{\rho }^0)$ nuclear transparencies for ${}^{12}$C and ${}^{56}$Fe are only moderately affected by SRC and by ${\rho }^0$ decay.

Conclusions: The RMSGA calculations confirm the onset of CT at four-momentum transfers of a few (GeV/$c$)${}^2$ in $\rho$ meson electroproduction data. A more precise determination of the scale for the onset of CT is hampered by the lack of precise input in the FSI and $\rho$-meson decay calculations.

Configuration-constrained potential-energy-surface calculations with reflection asymmetry show enhanced octupole correlations in the $K^{\pi }=6^{-}$ states with configuration $\nu 5/2^{+}\left[633\right]\otimes \nu 7/2^{-}\left[743\right]$ in $N=142,144$ isotones, where a 33.5-$\mu$s isomer has been observed in ${}^{234}$U. High-$K$ isomeric states in other nuclei around ${}^{240}$Pu are calculated to have reflection-symmetric deformations with excitation energies, in agreement with available data.

Equilibration of $N/Z$ in binary breakup of an excited and transiently deformed projectile-like fragment (PLF${}^{*}$), produced in peripheral collisions of ${}^{64}\mathrm{Zn}+{}^{27}$Al, ${}^{64}$Zn, ${}^{209}$Bi at $E/A=45$ MeV, is examined. The composition of emitted light fragments ($3\le Z\le 6$) changes with the decay angle of the PLF${}^{*}$. The most neutron-rich fragments observed are associated with a small rotation angle. A clear target dependence is observed with the largest initial $N/Z$ correlated with the heavy, neutron-rich target. Using the rotation angle as a clock, we deduce that $N/Z$ equilibration persists for times as long as 3–4 zs ($1\mathrm{zs}=1\times {10}^{-21}$ s $=300$ fm$/c$). The rate of $N/Z$ equilibration is found to depend on the initial neutron gradient within the PLF${}^{*}$.

Angular distributions of ${}^{16}\mathrm{O}+{}^{16}$O elastic scattering at energies that range from 124 to 1120 MeV have been analyzed in the framework of the double folding (DF) optical model. Based upon the α-cluster structure of the ${}^{16}$O nucleus, two different versions of the real DF optical potential have been generated by using three effective α-α, α-nucleon ($N$) and nucleon-nucleon ($\mathit{NN}$) interactions. A microscopic optical potential built upon the M3Y effective $\mathit{NN}$ interaction and the matter density distribution of the ${}^{16}$O nucleus has also been extracted. The obtained real potentials, in conjunction with phenomenological squared Woods-Saxon imaginary parts, have successfully reproduced seven sets of elastic-scattering data. No renormalization of the real folded α-cluster potentials is required to fit the data. The energy dependence of the extracted real and imaginary volume integrals and total reaction cross section has also been investigated.

Background: Experiments designed to study rare processes, such as neutrinoless double-$\beta$ decay ($0\nu \beta \beta$), are crucial tests for physics beyond the standard model. These experiments rely on reducing the intrinsic radioactive background to unprecedented levels, while adequately shielding the detectors from external sources of radioactivity.

Purpose: The purpose of this work is focused on understanding the background rates from neutron interactions in Cu shielding in regions around the $Q$ values of many candidate $0\nu \beta \beta$ decay isotopes, as well as providing data for benchmarking Monte Carlo simulations of background events.

Methods: Using the broad-spectrum neutron beam at Los Alamos Neutron Science Center, we have measured $\gamma$ rays emitted from inelastic neutron scattering on ${}^{\text{nat}}$Cu.

Results: We extracted the level cross sections from the $\gamma$-production cross section for 46 energy levels in ${}^{\text{nat}}$Cu. These level cross sections were compared with the available experimental data, as well as the ENDF/B-VII evaluation for discrete levels.

Conclusions: For energy levels above 2 MeV we found significant discrepancies between the suggested level cross sections for both nuclei and our data. We found reasonable agreement between our measurement and the ENDF/B-VII evaluation for the total neutron inelastic cross section in ${}^{63}$Cu. Our measurement of the total neutron inelastic scattering cross section in ${}^{65}$Cu was 30$\%$ lower than the ENDF/B-VII evaluations, which we attribute to unobserved transitions in ${}^{65}$Cu. Furthermore, we found that the implementation of the ENDF/B-VII evaluation in simulations did not properly model the decay properties of the nucleus to the degree necessary for estimating backgrounds in rear-event searches. Finally, we examined the potential implications of our measurements on $0\nu \beta \beta$ measurements and found that many of the commonly studied $0\nu \beta \beta$ isotopes had $Q$ values below the cutoff for ENDF/B-VII evaluated discrete levels in either Cu nucleus.

The nucleon form factors in free space are usually thought to be modified when a nucleon is bound in a nucleus or immersed in a nuclear medium. We investigate effects of the density-dependent axial and weak-vector form factors on the electroneutrino (${\nu }_e$) and anti-electroneutrino $\left({\overline{\nu }}_e\right)$ reactions with incident energy $E_{\nu }\le$ 80 MeV via neutral current (NC) for a nucleon in a nuclear medium or ${}^{12}$C. For the density-dependent form factors, we exploit the quark-meson-coupling (QMC) model, and apply them to the ${\nu }_e$ and ${\overline{\nu }}_e$ induced reactions by NC. About 12$\%$ decrease of the total cross section by the ${\nu }_e$ reaction on the nucleon is obtained at normal density, $\rho ={\rho }_0\sim 0.15{\mathrm{fm}}^{-3}$, as well as about 18$\%$ reduction of the total ${\nu }_e$ cross section on ${}^{12}$C, by the modification of the weak form factors of the bound nucleon. However, similarly to the charged current reaction, effects of the nucleon property change in the ${\overline{\nu }}_e$ reaction reduce significantly the cross sections about 30$\%$ for the nucleon in matter and ${}^{12}$C cases. Such a large asymmetry in the ${\overline{\nu }}_e$ cross sections is addressed to originate from the different helicities of ${\overline{\nu }}_e$ and ${\nu }_e$.

Recent results for the β decay of ${}^{17}$B, together with a simple model, allow an estimate of the ($sd$)${}^4$ component in ${}^{16}$C(g.s.). The result is about 0.02, a small number.

The $pp\to pp{K}^{+}{K}^{-}$ reaction was measured below the $\varphi$ threshold at a beam energy of 2.568 GeV using the COSY-ANKE magnetic spectrometer. By assuming that the four-body phase space is distorted only by the product of two-body final-state interactions, fits to a variety of one-dimensional distributions permit the evaluation of differential and total cross sections. The shapes of the distributions in the $Kp$ and $Kpp$ invariant masses are reproduced only if the $K^{-}p$ interaction is even stronger than that found at higher energy. The cusp effect in the $K^{+}{K}^{-}$ distribution at the $K^0{\overline{K}}^0$ threshold is much more clear and some evidence is also found for coupling between the $K^{-}p$ and ${\overline{K}}^{0}n$ channels. However, the energy dependence of the total cross section cannot be reproduced by considering only a simple product of such pairwise final-state interactions.