Background: The possibility that an unconventional depletion (referred to as a “bubble”) occurs in the center of the charge density distribution of certain nuclei due to a purely quantum mechanical effect has attracted theoretical and experimental attention in recent years. Based on a mean-field rationale, a correlation between the occurrence of such a semibubble and an anomalously weak splitting between low angular-momentum spin-orbit partners has been further conjectured. Energy density functional and valence-space shell model calculations have been performed to identify and characterize the best candidates, among which ${}^{34}\mathrm{Si}$ appears as a particularly interesting case. While the experimental determination of the charge density distribution of the unstable ${}^{34}\mathrm{Si}$ is currently out of reach, $(d,p)$ experiments on this nucleus have been performed recently to test the correlation between the presence of a bubble and an anomalously weak $1/2^{-}\text{−}3/2^{-}$ splitting in the spectrum of ${}^{35}\mathrm{Si}$ as compared to ${}^{37}\mathrm{S}$.

Purpose: We study the potential bubble structure of ${}^{34}\mathrm{Si}$ on the basis of the state-of-the-art ab initio self-consistent Green's function many-body method.

Methods: We perform the first ab initio calculations of ${}^{34}\mathrm{Si}$ and ${}^{36}\mathrm{S}$. In addition to binding energies, the first observables of interest are the charge density distribution and the charge root-mean-square radius for which experimental data exist in ${}^{36}\mathrm{S}$. The next observable of interest is the low-lying spectroscopy of ${}^{35}\mathrm{Si}$ and ${}^{37}\mathrm{S}$ obtained from $(d,p)$ experiments along with the spectroscopy of ${}^{33}\mathrm{Al}$ and ${}^{35}\mathrm{P}$ obtained from knock-out experiments. The interpretation in terms of the evolution of the underlying shell structure is also provided. The study is repeated using several chiral effective field theory Hamiltonians as a way to test the robustness of the results with respect to input internucleon interactions. The convergence of the results with respect to the truncation of the many-body expansion, i.e., with respect to the many-body correlations included in the calculation, is studied in detail. We eventually compare our predictions to state-of-the-art multireference energy density functional and shell model calculations.

Results: The prediction regarding the (non)existence of the bubble structure in ${}^{34}\mathrm{Si}$ varies significantly with the nuclear Hamiltonian used. However, demanding that the experimental charge density distribution and the root-mean-square radius of ${}^{36}\mathrm{S}$ be well reproduced, along with ${}^{34}\mathrm{Si}$ and ${}^{36}\mathrm{S}$ binding energies, only leaves the ${\mathrm{NNLO}}_{\text{sat}}$ Hamiltonian as a serious candidate to perform this prediction. In this context, a bubble structure, whose fingerprint should be visible in an electron scattering experiment of ${}^{34}\mathrm{Si}$, is predicted. Furthermore, a clear correlation is established between the occurrence of the bubble structure and the weakening of the $1/2^{-}\text{−}3/2^{-}$ splitting in the spectrum of ${}^{35}\mathrm{Si}$ as compared to ${}^{37}\mathrm{S}$.

Conclusions: The occurrence of a bubble structure in the charge distribution of ${}^{34}\mathrm{Si}$ is convincingly established on the basis of state-of-the-art ab initio calculations. This prediction will have to be reexamined in the future when improved chiral nuclear Hamiltonians are constructed. On the experimental side, present results act as a strong motivation to measure the charge density distribution of ${}^{34}\mathrm{Si}$ in future electron scattering experiments on unstable nuclei. In the meantime, it is of interest to perform one-neutron removal on ${}^{34}\mathrm{Si}$ and ${}^{36}\mathrm{S}$ in order to further test our theoretical spectral strength distributions over a wide energy range.

We extend the cascade-exciton model (CEM), and the Los Alamos version of the quark-gluon string model (LAQGSM), event generators of the Monte Carlo $N$-particle transport code version 6 (MCNP6), to describe production of energetic light fragments (LF) heavier than ${}^4\mathrm{He}$ from various nuclear reactions induced by particles and nuclei at energies up to about 1 TeV/nucleon. In these models, energetic LF can be produced via Fermi breakup, preequilibrium emission, and coalescence of cascade particles. Initially, we study several variations of the Fermi breakup model and choose the best option for these models. Then, we extend the modified exciton model (MEM) used by these codes to account for a possibility of multiple emission of up to 66 types of particles and LF (up to ${}^{28}\mathrm{Mg})$ at the preequilibrium stage of reactions. Then, we expand the coalescence model to allow coalescence of LF from nucleons emitted at the intranuclear cascade stage of reactions and from lighter clusters, up to fragments with mass numbers $A\le 7$, in the case of CEM, and $A\le 12$, in the case of LAQGSM. Next, we modify MCNP6 to allow calculating and outputting spectra of LF and heavier products with arbitrary mass and charge numbers. The improved version of CEM is implemented into MCNP6. Finally, we test the improved versions of CEM, LAQGSM, and MCNP6 on a variety of measured nuclear reactions. The modified codes give an improved description of energetic LF from particle- and nucleus-induced reactions; showing a good agreement with a variety of available experimental data. They have an improved predictive power compared to the previous versions and can be used as reliable tools in simulating applications involving such types of reactions.

We extend our recent study of chiral magnetic effect in relativistic heavy ion collisions based on an anomalous transport model by including also the chiral vortical effect. We find that although vorticities in the chirally restored quark matter, which result from the large angular momentum in noncentral collisions, can generate an axial charge dipole moment in the transverse plane of a heavy ion collision, it does not produce a difference in the eccentricities of negatively and positively charged particles. As a result, including the chiral vortical effect alone cannot lead to a splitting between the elliptic flows of negatively and positively charged particles. On the other hand, negatively and positively charged particles do develop a splitting in their elliptic flows if the effect due to a strong and long-lived magnetic field is also included. However, to have a positive slope in the dependence of the elliptic flow splitting on the charge asymmetry of the quark matter, as seen in experiments, requires the neglect of the effect of the Lorentz force. In this case, an elliptic flow splitting appears even at vanishing charge asymmetry.

The high spin excited states of ${}^{169}\mathrm{Tm}_{}$ have been studied via the ${}^{169}\mathrm{Tm}_{}$(${}^{32}\mathrm{S}_{}$, ${}^{32}\mathrm{S}^{\prime }$)${}^{169}{\mathrm{Tm}}^{*}_{}$ reaction at a beam energy of 164 MeV. The $\gamma$ rays were detected using an array of 19 Compton-suppressed clover HPGe detectors. The band based on the $\left[411\right]1/2^{+}$ Nilsson orbital has been extended to observe the band crossing for the first time in this nucleus. A sharp backbending, similar to ${}^{165}\mathrm{Tm}_{}$, is observed in this nucleus which is in complete contrast with its immediate neighbor ${}^{167}\mathrm{Tm}_{}$. The data were interpreted in the cranked shell model approach by calculating the total Routhian surfaces, crossing frequencies, and the interaction strengths for these nuclei which are in excellent agreement with the experimental data. It is suggested that the $N=98$ deformed shell gap has larger effect in determining the nature of alignment than its shape driving effect.

Spin-orbit splitting is an essential ingredient for our understanding of the shell structure in nuclei. One of the most important advantages of relativistic mean-field (RMF) models in nuclear physics is the fact that the large spin-orbit (SO) potential emerges automatically from the inclusion of Lorentz-scalar and -vector potentials in the Dirac equation. It is therefore of great importance to compare the results of such models with experimental data. We investigate the size of $2p$ and $1f$ splittings for the isotone chain ${}^{40}\mathrm{Ca}$, ${}^{38}\mathrm{Ar}$, ${}^{36}\mathrm{S}$, and ${}^{34}\mathrm{Si}$ in the framework of various relativistic and nonrelativistic density functionals. They are compared with the results of nonrelativistic models and with recent experimental data.

The availability of realistic potential energy landscapes in restricted deformation space is the prerequisite starting point for modeling several nuclear properties and reactions, namely large-amplitude phenomena. The achievement of a macroscopic-microscopic approach, employing an innovative four-dimensional (4D) nuclear shape parametrization based on a Fourier expansion, and a realistic potential-energy prescription, is presented. A systematic analysis of the 4D deformation energy landscapes over an extended region of the nuclear chart from Pt to Pu is performed, searching for fission valleys, as well as exotic ground and metastable states. The significance of the approach for predicting mass partitioning in low-energy fission is demonstrated. The ability of the model to address shape-driven effects, like stable octupole and very elongated isomeric configurations, is discussed, too. The proposed approach constitutes an efficient framework for an extended model of fission dynamics over a wide range of fissioning mass, excitation energy, and angular momentum.

The Dalitz decays $\eta \to e^{+}{e}^{-}\gamma$ and $\omega \to {\pi }^0{e}^{+}{e}^{-}$ have been measured in the $\gamma p\to \eta p$ and $\gamma p\to \omega p$ reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron. The value obtained for the slope parameter of the electromagnetic transition form factor of $\eta , {\mathrm{\Lambda }}_{\eta }^{-2}=(1.97\pm 0.{11}_{\mathrm{tot}}){\mathrm{GeV}}^{-2}$, is in good agreement with previous measurements of the $\eta \to e^{+}{e}^{-}\gamma$ and $\eta \to {\mu }^{+}{\mu }^{-}\gamma$ decays. The uncertainty obtained in the value of ${\mathrm{\Lambda }}_{\eta }^{-2}$ is lower than in previous results based on the $\eta \to e^{+}{e}^{-}\gamma$ decay. The value obtained for the $\omega$ slope parameter, ${\mathrm{\Lambda }}_{\omega {\pi }^0}^{-2}=(1.99\pm 0.{21}_{\mathrm{tot}}){\mathrm{GeV}}^{-2}$, is somewhat lower than previous measurements based on $\omega \to {\pi }^0{\mu }^{+}{\mu }^{-}$, but the results for the $\omega$ transition form factor are in better agreement with theoretical calculations, compared to earlier experiments.

We analyze the spin flip loss for ultracold neutrons in magnetic bottles of the type used in experiments aiming at a precise measurement of the neutron lifetime, extending the one-dimensional field model used previously by Steyerl et al. [Phys. Rev. C 86, 065501 (2012)] to two dimensions for cylindrical multipole fields. We also develop a general analysis applicable to three dimensions. Here we apply it to multipole fields and to the bowl-type field configuration used for the Los Alamos $\mathrm{UCN}\tau$ experiment. In all cases considered the spin flip loss calculated exceeds the Majorana estimate by many orders of magnitude but can be suppressed sufficiently by applying a holding field of appropriate magnitude to allow high-precision neutron lifetime measurements, provided other possible sources of systematic error are under control.

An experiment using the electronic $\gamma -\gamma$ fast-timing technique was performed to measure lifetimes of the yrast states in ${}^{170}\mathrm{Yb}$. The lifetime of the yrast $2^{+}$ state was determined using the slope method. The value of $\tau =2.33\left(3\right)$ ns is in good agreement with the lifetimes measured using other techniques. The lifetimes of the first $4^{+}$ and $6^{+}$ states are determined using the generalized centroid difference method. The derived $B\left(E2\right)$ values are compared to calculations done using the confined beta soft model and show good agreement with the experimental values. These calculations were extended to the isotonic chain $N=100$ around ${}^{170}\mathrm{Yb}$ and show a good quantitative description of the collectivity observed along it.

The boson-fermion interaction in the interacting boson-fermion model-2 (IBFM-2) is derived in a systematic and general form from a quadrupole-quadrupole force using several nondegenerate levels. The boson-fermion quadrupole operator employed is obtained from the boson-fermion image of the one nucleon transfer operator which in turn can be calculated following two alternative schemes: the Otsuka-Arima-Iachello and generalized Holstein-Primakoff schemes. Four different terms (two quadrupole and two exchange) were obtained. Application of the new expressions to a single-$j$ model is studied and analyzed.

I discuss the elliptic flows of $\psi \left(2S\right)$ with different production mechanisms in $\sqrt{s_{NN}}=2.76$ TeV Pb-Pb collisions. If the final $\psi \left(2S\right)\mathrm{s}$ are mainly from the recombination of uncorrelated charm and anticharm quarks at $T\approx T_c$, charm and anticharm quarks will carry large collective flows of the bulk medium, which will be inherited by the regenerated $\psi \left(2S\right)\mathrm{s}$. This indicates a larger elliptic flow of $\psi \left(2S\right)$ than that of $J/\psi$ which can be regenerated at $T\ge T_c$, $v_2^{\psi \left(2S\right)}>v_2^{J/\psi }$. However, if the final $\psi \left(2S\right)\mathrm{s}$ are mainly from the transitions of $J/\psi \to \psi \left(2S\right)$ caused by the color screening of quark-gluon plasma its elliptic flow should be close to the elliptic flow of $J/\psi$, $v_2^{\psi \left(2S\right)}\sim v_2^{J/\psi }$. Therefore, $\psi \left(2S\right)$ elliptic flow is a sensitive probe for its production mechanisms in relativistic heavy ion collisions.

We study the Kondo effect for ${\overline{D}}_s$ and ${\overline{D}}_s^{*}$ mesons as impurity particles in nuclear matter. The spin-exchange interaction between the ${\overline{D}}_s$ or ${\overline{D}}_s^{*}$ meson and the nucleon induces the enhancement of the effective coupling in the low-energy scattering in the infrared region, whose energy scale of singularity is given by the Kondo scale. We investigate the Kondo scale in the renormalization group equation at nucleon one-loop level. We furthermore study the ground state with the Kondo effect in the mean-field approach, and present that the Kondo scale is related to the mixing strength between the ${\overline{D}}_s$ or ${\overline{D}}_s^{*}$ meson and the nucleon in nuclear matter. We show the spectral function of the impurity when the Kondo effect occurs.

Background: Knowledge of nucleon structure is today ever more of a precision science, with heightened theoretical and experimental activity expected in coming years. At the same time, a persistent gap lingers between theoretical approaches grounded in Euclidean methods (e.g., lattice QCD, Dyson-Schwinger equations [DSEs]) as opposed to traditional Minkowski field theories (such as light-front constituent quark models).

Purpose: Seeking to bridge these complementary world views, we explore the potential of a Euclidean constituent quark model (ECQM). This formalism enables us to study the gluonic dressing of the quark-level axial-vector vertex, which we undertake as a test of the framework.

Method: To access its indispensable elements with a minimum of inessential detail, we develop our ECQM using the simplified quark $+$ scalar diquark picture of the nucleon. We construct a hyperspherical formalism involving polynomial expansions of diquark propagators to marry our ECQM with the results of Bethe-Salpeter equation (BSE) analyses, and constrain model parameters by fitting electromagnetic form factor data.

Results: From this formalism, we define and compute a new quantity—the Euclidean density function (EDF)—an object that characterizes the nucleon's various charge distributions as functions of the quark's Euclidean momentum. Applying this technology and incorporating information from BSE analyses, we find the quenched dressing effect on the proton's axial-singlet charge to be small in magnitude and consistent with zero, while use of recent determinations of unquenched BSEs results in a large suppression.

Conclusions: The quark $+$ scalar diquark ECQM is a step toward a realistic quark model in Euclidean space, and needs additional refinements. The substantial effect we obtain for the impact on the axial-singlet charge of the unquenched dressed vertex compared to the quenched demands further investigation.

Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive ${\pi }^{+}$ electroproduction reaction ${\gamma }^{*}p\to n{\pi }^{+}$. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic range covered is $1.1<W<3$ GeV and $1<Q^2<6{\mathrm{GeV}}^2$. Results were obtained for about 6000 bins in $W, Q^2, cos\left({\theta }^{*}\right)$, and ${\varphi }^{*}$. Except at forward angles, very large target-spin asymmetries are observed over the entire $W$ region. Reasonable agreement is found with phenomenological fits to previous data for $W<1.6$ GeV, but very large differences are seen at higher values of $W$. A generalized parton distributions (GPD)-based model is in poor agreement with the data. When combined with cross-sectional measurements, the present results provide powerful constraints on nucleon resonance amplitudes at moderate and large values of $Q^2$, for resonances with masses as high as 2.4 GeV.

Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive ${\pi }^0$ electroproduction reaction ${\gamma }^{*}p\to p{\pi }^0$, expanding an analysis of the ${\gamma }^{*}p\to n{\pi }^{+}$ reaction from the same experiment. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic ranges covered are $1.1<W<3$ GeV and $1<Q^2<6 {\mathrm{GeV}}^2$. Results were obtained for about 5700 bins in $W, Q^2, cos\left({\theta }^{*}\right)$, and ${\varphi }^{*}$. The beam-target asymmetries were found to generally be greater than zero, with relatively modest ${\varphi }^{*}$ dependence. The target asymmetries exhibit very strong ${\varphi }^{*}$ dependence, with a change in sign occurring between results at low $W$ and high $W$, in contrast to ${\pi }^{+}$ electroproduction. Reasonable agreement is found with phenomenological fits to previous data for $W<1.6$ GeV, but significant differences are seen at higher $W$. When combined with cross-sectional measurements, as well as ${\pi }^{+}$ observables, the present results will provide powerful constraints on nucleon resonance amplitudes at moderate and large values of $Q^2$, for resonances with masses as high as 2.4 GeV.

A new empirical parametrization is developed for calculating the fragment cross sections in projectile fragmentation reactions at high energies ($>100$ MeV/nucleon). The new parametrization, FRACS, consists of two main parts, i.e., the mass yield and the isobaric distribution, on the basis of previous parametrizations. The formalism for the mass yield is improved to describe the target and the projectile energy dependences observed in measured fragmentation cross sections. The parametrization of the isobaric distribution is also modified to reproduce recent experimental data. Furthermore, an additional term is proposed and first implemented in the FRACS parametrization to account for the evident odd-even staggering effect observed in many experimental cross sections. Comparisons with extensive cross sections measured in various fragmentation reactions reveal that FRACS is in much better agreement with experimental data and can reproduce measured cross sections in most cases within a factor of 1.84, which is a much smaller rms deviation as compared to that of the recent parametrization EPAX3.

Background: Formation of the compound nucleus (CN) is highly suppressed by quasifission in heavy-ion collisions involving massive nuclei. Though considerable progress has been made in the understanding of fusion-fission and quasifission, the exact dependence of fusion probability on various entrance channel variables is not completely clear, which is very important for the synthesis of new heavy and superheavy elements.

Purpose: To study the interplay between fusion and quasifission in reactions forming CN in the boundary region where the fusion probability starts to deviate from unity.

Methods: Fusion evaporation residue cross sections were measured for the ${}^{28,30}\mathrm{Si}+{}^{180}\mathrm{Hf}$ reactions using the Hybrid Recoil Mass Analyser at IUAC, New Delhi. Experimental data were compared with data from other reactions forming the same CN or isotopes of the CN. Theoretical calculations were performed using the dinuclear system and statistical models.

Results: Reduced evaporation residue cross sections were observed for the reactions studied compared with the asymmetric reaction forming the same CN, indicating fusion suppression in more symmetric systems. The observations are consistent with fission fragment measurements performed in the same or similar systems. Larger ER cross sections are observed with increase in mass in the isotopic chain of the CN.

Conclusions: Fusion probability varies significantly with the entrance channels in reactions forming the same CN. While complete fusion occurs for the ${}^{16}\mathrm{O}+{}^{194}\mathrm{Pt}$ reaction, the fusion probability drops to approximately $60–70\%$ for the ${}^{30}\mathrm{Si}+{}^{180}\mathrm{Hf}$ and less than $20\%$ for the ${}^{50}\mathrm{Ti}+{}^{160}\mathrm{Gd}$ reactions, respectively, forming the same CN at similar excitation energies.