Background: The rapid neutron capture process is one of the main nucleosynthesis processes of elements heavier than Fe. Uncertainties in nuclear properties, such as masses, half-lives, and $\beta$-delayed neutron probabilities can cause orders of magnitude of variation within astrophysical $r$-process simulations. Presently, theoretical models are used to make global predictions of various nuclear properties for the thousands of nuclei required for these simulations, and measurements are required to benchmark these models, especially far from stability.

Purpose: $\beta$-decay strength distributions can be used to not only inform astrophysical $r$-process simulations, but also to provide a stringent test for theoretical calculations. The aim of this work is to provide accurate strength distributions for ${}^{69,71}\mathrm{Co}\beta$ decay.

Method: The technique of total absorption spectroscopy was used to measure the $\beta$ decay of ${}^{69,71}\mathrm{Co}$ for the first time at the National Superconducting Cyclotron Laboratory. The ions were implanted in a double-sided silicon strip detector at the center of the Summing NaI(Tl) detector and identified using standard particle identification methods. The response of the detection system to the $\beta$-decay electron and subsequent $\gamma$-ray radiation was fit to the observed experimental data using a ${\chi }^2$-minimization technique.

Results: $\beta$-feeding intensities and Gamow-Teller strength distributions were extracted from the fits of the experimental data. The $\beta$-decay intensities show that there is a large percentage of feeding to levels above 2 MeV, which have not been observed in previous studies. The resultant $\beta$-feeding intensities and Gamow-Teller strength distributions were compared to shell model and quasiparticle random phase approximation (QRPA) calculations.

Conclusions: Comparing experimentally determined $\beta$-decay strength distributions provides a test of models, which are commonly used for global $\beta$-decay properties for astrophysical calculations. This work highlights the importance of performing detailed comparisons of models to experimental data, particularly far from stability and as close to the $r$-process path as possible.

Thermodynamical properties of an interacting system of scalar bosons at finite temperatures are studied within the framework of a field-theoretical model containing the attractive and repulsive self-interaction terms. Self-consistency relations between the effective mass and the thermodynamic functions are derived in the mean-field approximation. We show that for a sufficiently strong attractive interaction a first-order phase transition develops in the system via the formation of a scalar condensate. An interesting prediction of this model is that the condensed phase appears within a finite temperature interval and is characterized by a constant scalar density of Bose particles.

Background: The density-constrained time-dependent Hartree-Fock method is currently a tool of choice to predict fusion cross sections. However, it does not include pairing correlations, which have been found recently to play an important role.

Purpose: To describe the fusion cross section with a method that includes the superfluidity and to understand the impact of pairing on both the fusion barrier and cross section.

Method: The density-constrained method is tested first on the following reactions without pairing, ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ and ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$. A new method is developed, the density-constrained time-dependent Hartree-Fock-Bogoliubov method. Using the Gogny-TDHFB code, it is applied to the reactions ${}^{20}\mathrm{O}+{}^{20}\mathrm{O}$ and ${}^{44}\mathrm{Ca}+{}^{44}\mathrm{Ca}$.

Results: The Gogny approach reproduces the experimental data well for reaction ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ and ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$. The DC-TDHFB method is coherent with the TDHFB fusion threshold. The effect of the phase-lock mechanism is shown for those reactions.

Conclusions: The DC-TDHFB method is a useful new tool to determine the fusion potential between superfluid systems and to deduce their fusion cross sections.

The statistical hadronization model successfully describes the yields of hadrons and light nuclei from central heavy-ion collisions over a wide range of energies. It is a simple and efficient phenomenological framework in which the relative yields for very high energy collisions are essentially determined by a single model parameter—the chemical freeze-out temperature. Recent measurements of yields of hadrons and light nuclei covering over nine orders of magnitudes from the ALICE collaboration at the Large Hadron Collider were described by the model with remarkable accuracy with a chemical freeze-out temperature of 156.5 $\pm$ 1.5 MeV. A key physical question is whether (at least to a good approximation) the freeze-out temperature can be understood, literally, as the temperature at which the various species of an equilibrated gas of hadrons (including resonances) and nuclei chemically freeze out, as the model assumes, or whether it successfully parametrizes the yield data for a different reason. This paper analyzes the yields of weakly bound light nuclei—the deuteron and the hypertriton—to probe this issue. Such nuclei are particularly sensitive to assumptions of the model because their binding energies are at a scale far below both typical hadronic scales and the freeze-out temperature. The analysis depends only on outputs of the statistical hadronization model, known hadronic properties and standard assumptions of kinetic theory while making no additional dynamical assumptions about the dynamics of heavy-ion collisions. The analysis indicates that a key assumption underlying the model—that hadrons (and nuclei), just prior to chemical freeze-out temperature, are in thermal equilibrium and are sufficiently dilute as to have particle distributions accurately described statistically by a nearly ideal gas of hadrons and nuclei with masses given by their free space values—appears to be inconsistent with the chemical freeze-out temperature output by the model, at least for these weakly bound nuclei. Implications of this analysis for the interpretation of parameters extracted from the model are discussed.

We study exclusive charmonium and bottomonium production in ultraperipheral heavy-ion collisions and electron-ion collisions within the dipole picture. We employ heavy quarkonium light-front wave functions obtained within the basis light-front quantization framework, which has some features of the light-front holographic QCD. We focus on comparison with measurements of exclusive charmonium and bottomonium production in ultraperipheral $pp$, $p\mathrm{Pb}$, and PbPb collisions at the CERN Large Hadron Collider and find reasonable agreement with the cross sections. We also discuss the coherent production cross-section ratios of excited states to the ground state for charmonium and bottomonium, which exhibit insensitivity to the dipole model parameters. We show that electron-ion collisions provide an opportunity for a quantitative study of heavy quarkonium structure.

The Majorana Collaboration is operating an array of high-purity Ge detectors to search for the neutrinoless double-$\beta$ decay of ${}^{76}\mathrm{Ge}$. The Majorana Demonstrator consists of 44.1 kg of Ge detectors (29.7 kg enriched to 88% in ${}^{76}\mathrm{Ge}$) split between two modules constructed from ultraclean materials. Both modules are contained in a low-background shield at the Sanford Underground Research Facility in Lead, South Dakota. We present updated results on the search for neutrinoless double-$\beta$ decay in ${}^{76}\mathrm{Ge}$ with $26.0\pm 0.5$ kg yr of enriched exposure. With the Demonstrator's energy resolution of 2.53 keV FWHM at $Q_{\beta \beta }$, which is the best among all neutrinoless double-$\beta$ decay experiments, we observe one event in the region of interest with 0.65 events expected from the estimated background, resulting in a lower limit on the ${}^{76}\mathrm{Ge}$ neutrinoless double-$\beta$ decay half-life of $2.7\times {10}^{25}$ yr [90% confidence level (CL)] with a median sensitivity of $4.8\times {10}^{25}$ yr (90% CL). Depending on the matrix elements used, a 90% CL upper limit on the effective Majorana neutrino mass in the range of 200–433 meV is obtained. The measured background in the configurations with full shielding and optimized grounding is $11.9\pm 2.0$ counts/(FWHM t yr).

The correlations of identical charged kaons were measured in $p$-Pb collisions at $\sqrt{s_{\mathit{NN}}}=5.02$ TeV by the ALICE experiment at the LHC. The femtoscopic invariant radii and correlation strengths were extracted from one-dimensional kaon correlation functions and were compared with those obtained in $pp$ and Pb-Pb collisions at $\sqrt{s}=7$ TeV and $\sqrt{s_{\mathit{NN}}}=2.76$ TeV, respectively. The presented results also complement the identical-pion femtoscopic data published by the ALICE collaboration. The extracted radii increase with increasing charged-particle multiplicity and decrease with increasing pair transverse momentum. At comparable multiplicities, the radii measured in $p$-Pb collisions are found to be close to those observed in $pp$ collisions. The obtained femtoscopic parameters are reproduced by the EPOS 3 hadronic interaction model and disfavor models with large initial size or strong collective expansion at low multiplicities.

Neutron-capture rate plays a crucial role in the rapid neutron-capture process (r-process) and nuclear mass is one of the most important inputs for the estimations of neutron-capture rates. In this work, we employ ten nuclear mass models, including macroscopic, macroscopic-microscopic, and microscopic models, to calculate the radiative neutron-capture rates for the nuclei relevant to the r-process at various temperatures $T={10}^5–{10}^{10}\mathrm{K}$. It is found that the differences in the predictions of neutron-capture rate using these mass models get larger when moving to the neutron-rich and superheavy regions, whereas they generally become smaller with the increase of temperature. Taking the nuclei on the $N=126$ r-process path as examples, we find that the uncertainties of neutron-capture rates at $T={10}^9\mathrm{K}$ range from about one to four orders of magnitude. The influence of the experimental mass errors on neutron-capture rates is investigated as well.

A study of low-energy incomplete fusion was done by the measurements of excitation functions of evaporation residues produced in the ${}^{16}\mathrm{O}+{}^{148}\mathrm{Nd}$ system at energies $\approx 4–7$ MeV/nucleon. The stacked foil activation technique using offline $\gamma$-ray spectrometry was employed. Significant enhancements were found in the measured cross sections from the theoretical predictions of pace-4 for the evaporation residues populated through $\alpha$-emission channels. This enhancement is attributed to incomplete fusion (ICF) of ${}^{16}\mathrm{O}$ with ${}^{148}\mathrm{Nd}$. The comparison of present work with literature data shows that the ICF probability increases exponentially with existing entrance channel parameters. The dependence of ICF dynamics on target deformation was investigated using deformation parameter (${\beta }_2^T$), deformation length (${\beta }_2^T{R}^T$) and neutron excess ${(N-Z)}^T$ of the target. The present analysis indicates that the ICF fraction rises exponentially with ${\beta }_2^T$, ${\beta }_2^T{R}^T$, and ${(N-Z)}^T$. These results show that the ICF fraction follows a systematic exponential pattern rather than a simple linear growth with various entrance channel parameters reported in the literature. However, this study also suggests that the ICF dynamics is strongly influenced by the structure of projectile along with that of the target. Further, the role of deformation parameters on incomplete-fusion dynamics was also investigated through the method of universal fusion function. Analysis of the present data indicates that the experimental fusion functions are suppressed with different factors depending on deformation of the target nuclei. These suppressions are removed by including incomplete-fusion cross sections in the fusion function calculations. The average value of experimental fusion functions deviates from the universal fusion function for deformed targets. However, the average value of the total fusion function for deformed targets shifts towards the average value of the universal fusion function. The present study shows that the effect of target deformation plays an important role in affecting the ICF dynamics, along with various entrance channel parameters for different systems.

To understand the low-energy incomplete fusion (ICF) reaction dynamics, the excitation function measurements of ${}^{12}\mathrm{C}+{}^{165}\mathrm{Ho}$ system has been performed in the energy region of ≈ 4–7 MeV/nucleon, by employing the stacked foil activation technique. The cross sections of the measured evaporation residues are compared with the theoretical predictions of statistical model code PACE4, which takes into account only the complete fusion (CF) reaction cross section. It is observed that residues populated via xn and pxn channels are in good agreement with the PACE4 predictions, implying that these residues are populated via CF process. However, in the case of α-emission channels a significant enhancement from the PACE4 predictions is observed even after the deduction of precursor contribution, which is accredited to ICF process. The projectile break-up probability is found to increase with increment in the incident projectile energy. Further, the dependence of incomplete fusion dynamics on entrance channel parameters like mass asymmetry, Coulomb effect ($Z_{\mathrm{P}}{Z}_{\mathrm{T}}$), and projectile $Q_{\alpha }$ value is systematically studied. The present results reveal that a single entrance channel parameter does not oversee the ICF reaction dynamics but have varying contributions depending upon the projectile-target combination. Moreover, the effect of projectile break-up on complete fusion cross section at energies above the Coulomb barrier is also studied. The suppression in fusion cross section is observed when compared with the universal fusion function.

We present a general systematic formalism for describing dynamics of fluctuations in an arbitrary relativistic hydrodynamic flow, including their feedback (known as long-time hydrodynamic tails). The fluctuations are described by two-point equal-time correlation functions. We introduce a definition of equal time in a situation where the local rest frame is determined by the local flow velocity and a method of taking derivatives and Wigner transforms of such equal-time correlation functions, which we call confluent. We find that not only do the equations for confluent Wigner functions resemble kinetic equations but also the kinetic equation for phonons propagating on an arbitrary background nontrivially matches the equations for Wigner functions, including relativistic inertial and Coriolis forces due to acceleration and vorticity of the flow. We also describe the procedure of renormalization of short-distance singularities which eliminates cutoff dependence, allowing efficient numerical implementation of these equations.

In the present work, the effect of proton-neutron interaction and its different components, i.e., central, spin-orbit, and tensor force, on proton shell-structure of odd-$A$ Sc, F, and Li isotopes is studied within the nuclear shell model framework. It has been observed that the central force possesses strong-orbital node $\left(nl\right)$ and weak-spin $\left(j\right)$ dependency, and plays a key role in producing changes in proton shell-structure. The integrated effect of proton shell-structure and proton single-particle strength in building the level structure of ${}^{49,53,55}\mathrm{Sc}$, ${}^{23,25}\mathrm{F}$, and ${}^9\mathrm{Li}$ isotopes are also discussed. Proton single-particle strength in the level structure of above-mentioned nuclei is studied using proton-transfer spectroscopic factors. It has been particularly discerned that the low energy of the ${\frac{3}{2}}_1^{-}$ state of ${}^{55}\mathrm{Sc}$ is caused by the weakening of the $N=34$ semimagic gap, the high energy of the ${\frac{1}{2}}_1^{+}$ state of ${}^{23}\mathrm{F}$ is originated from an increase in the energy gap between orbitals $\pi 1s_{1/2}$ and $\pi 0d_{5/2}$ at $N=14$, and the high energy of the ${\frac{1}{2}}_1^{-}$ state of ${}^9\mathrm{Li}$ is originated from the large energy gap between $\pi 0p_{1/2}$ and $\pi 0p_{3/2}$ orbitals which remained nearly constant from ${}^5\mathrm{Li}$ to ${}^9\mathrm{Li}$.

The pairing properties of the neutrinoless double-$\beta$ decay candidate ${}^{116}\mathrm{Cd}$ have been investigated. Measurements of the two-neutron removal reactions on isotopes of ${}^{114,116}\mathrm{Cd}$ have been made in order to identify $0^{+}$ strength in the residual nuclei up to $\approx 3$ MeV. No significant $L=0$ strength has been found in excited states indicating that the Bardeen-Cooper-Schrieffer (BCS) approximation is a reasonable basis to describe the neutrons in the ground state. This approximation avoids complications in calculations of double-$\beta$ decay matrix elements that use the quasiparticle random-phase approximation (QRPA) techniques. However this is not the case for the protons, where pair vibrations are prevalent and the BCS approximation is no longer valid, complicating the use of traditional QRPA techniques for this system as a whole.

Background: Studies of low-energy fusion of light nuclei are important in astrophysical modeling, with small variations in reaction rates having a large impact on nucleosynthesis yields. Due to the lack of experimental data at astrophysical energies, extrapolation and microscopic methods are needed to model fusion probabilities.

Purpose: To investigate deep sub-barrier ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion cross sections and establish trends for the $S$ factor.

Method: Microscopic methods based on static Hartree-Fock and time-dependent Hartree-Fock (TDHF) mean-field theory are used to obtain ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ ion-ion fusion potentials. Fusion cross sections and astrophysical $S$ factors are then calculated using the incoming wave boundary condition method.

Results: Both density-constrained frozen Hartree-Fock (DCFHF) and density-constrained TDHF (DC-TDHF) predict a rising $S$ factor at low energies, with DC-TDHF predicting a slight damping in the deep sub-barrier region ($\approx 1$ MeV). Comparison between DC-TDHF calculations and maximum experimental cross sections in the resonance peaks are good. However, the discrepancy in experimental low-energy results inhibits interpretation of the trend.

Conclusions: Using the fully microscopic DCFHF and DC-TDHF methods, no $S$ factor maximum is observed in the ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ fusion reaction. In addition, no extreme sub-barrier hindrance is predicted at low energies. The development of a microscopic theory of fusion including resonance effects, as well as further experiments at lower energies must be done before the deep sub-barrier behavior of the reaction can be established.

Ultraperipheral collisions (UPCs) of relativistic ions are an important tool for studying photoproduction at high energies. Vector-meson photoproduction is an important tool for nuclear structure measurements and other applications. A future electron-ion collider (EIC) will allow additional studies, using virtual photons with a wide range of $Q^2$. We propose a significant expansion of the UPC and EIC photoproduction physics programs to include charged final states which may be produced via Reggeon exchange. We consider two examples: $a_2^{+}\left(1320\right)$, which is a conventional $q\overline{q}$ meson, and the exotic $Z_c^{+}\left(4430\right)$ state (modeled here as a tetraquark). The $Z_c^{+}\left(4430\right)$ cross section depends on its internal structure, so photoproduction can test whether the $Z_c^{+}\left(4430\right)$ is a tetraquark or other exotic object. We calculate the rates and kinematic distributions for $\gamma p\to X^{+}n$ in $pA$ UPCs and $ep$ collisions at an EIC and in UPCs. The rates are large enough for detailed studies of these final states. Because the cross section for Reggeon exchange is largest near threshold, the final-state rapidity distribution depends on the beam energies. At high-energy colliders like the proposed LHeC or $pA$ collisions at the Large Hadron Collider, the final states are produced at far forward rapidities. For lower energy colliders, the systems are produced closer to midrapidity, within reach of central detectors.

We report studies of charge-independent (CI) and charge-dependent (CD) two-particle differential-number correlation functions, ${\mathrm{R}}_2\left(\mathrm{\Delta }\eta ,\mathrm{\Delta }\phi \right)$, and transverse momentum (${\mathit{p}}_{\mathrm{T}}$) correlation functions, ${\mathrm{P}}_2\left(\mathrm{\Delta }\eta ,\mathrm{\Delta }\phi \right)$, of charged particles in $\sqrt{\mathit{s}}=2.76\mathrm{TeV}$ pp collisions with the PYTHIA and HERWIG models. Model predictions are presented for inclusive charged hadrons ($h^{\pm }$), as well as pions (${\pi }^{\pm }$), kaons (${\mathrm{K}}^{\pm }$), and (anti-)protons ($\overline{\mathrm{p}}$/p) in the ranges $0.2<{\mathit{p}}_{\mathrm{T}}\le 2.0\mathrm{GeV}/\mathit{c}$, $2.0<{\mathit{p}}_{\mathrm{T}}\le 5.0\mathrm{GeV}/\mathit{c}$, and $5.0<{\mathit{p}}_{\mathrm{T}}\le 30.0\mathrm{GeV}/\mathit{c}$, with full azimuthal coverage in the range $\left|\eta \right|<1.0$. We compare the model predictions for the strength and shape of the ${\mathrm{R}}_2$ and ${\mathrm{P}}_2$ correlators as these pertain to recent measurements by the ALICE collaboration. The ${\mathrm{R}}_2$ and ${\mathrm{P}}_2$ correlation functions estimated with PYTHIA and HERWIG exhibit qualitatively similar near-side and away-side correlation structures but feature important differences. Our analysis indicates that comparative studies of ${\mathrm{R}}_2$ and ${\mathrm{P}}_2$ correlation functions would provide valuable insight towards the understanding of particle production in pp collisions, and by extension, should also be useful in studies of heavy-ion collisions. Comparison of the $\mathrm{\Delta }\eta$ dependence of ${\mathrm{R}}_2$ and ${\mathrm{P}}_2$ could contribute, in particular, to a better understanding and modeling of the angular ordering of particles produced by hadronization in jets, as well as a better description of jet fragmentation functions of identified species at low momentum fraction $\left(z\right)$.

The chiral soliton lattice (CSL), which has been studied in condensed-matter systems such as chiral magnets, arises as a parity-violating topological soliton. In hadron physics, various attempts have also been made to apply the idea of the CSL to baryonic matter. In this work, we explore the CSL effects on baryonic matter based on the skyrmion crystal approach by putting the CSL into the skyrmion crystal lattice. This system can be viewed as “medium-in-medium,” where the hybrid system is constructed from skyrmions and the CSL within the mean field approximation. In this hybrid approach, it turns out that massless modes such as phonons are by accident invisible, though they should be present. It is found that the CSL causes an inverse catalysis for the topology change in dense baryonic matter. Furthermore, we observe that the CSL makes the single-baryon shape deformed to be higher-intensity objects with a definite frequency, which leads to the enhancement of baryon energy. Above the critical frequency of the CSL, the CSL structure goes away from the skyrmion crystal. Of interest is that in a high-density region, the CSL goes away due to the topology change in the baryonic matter. What we find here might deepen our understanding of dense-matter systems as well as compact stars.

In 2008 the Jefferson Laboratory $F_{\pi }$ Collaboration released results for the pion electromagnetic form factor, which they extracted from pion electroproduction data. The measured values for the pion form factor are model dependent, and require the use of the Vanderhaeghen, Guidal, and Laget Regge model for their extraction. While agreement between this model and data is impressive, the theoretical implementation of gauge invariance is less satisfying. We would like to establish how well the extracted form factor corresponds to the true form factor. To do this, we use a simple toy model, which imposes gauge invariance in a more theoretically satisfying way. The model form factor is extracted from our model cross section using the method employed by the $F_{\pi }$ Collaboration to extract the experimental pion form factor. We conclude that the reconstructed model form factor is a reasonable representation of the true model form factor for the kinematics chosen, although we note that the extracted form factor is smaller than the true form factor. This suggests that current extracted values of the pion form factor may be overestimated.

We exploit the many-body self-consistent Green's function method to analyze finite-temperature properties of infinite nuclear matter and to explore the behavior of the thermal index used to simulate thermal effects in equations of state for astrophysical applications. We show how the thermal index is both density and temperature dependent, unlike often considered, and we provide an error estimate based on our ab initio calculations. The inclusion of three-body forces is found to be critical for the density dependence of the thermal index. We also compare our results to a parametrization in terms of the density dependence of the nucleon effective mass. Our findings point to possible shortcomings of predictions made for the gravitational-wave signal from neutron-star merger simulations with a constant thermal index.

We calculate the $p$-wave contribution to the proton-proton fusion $S$ factor and its energy derivative in pionless effective-field theory (EFT) up to next-to-leading order. The leading contributions are given by a recoil piece from the Gamow-Teller and Fermi operators and from relativistic $1/m$ suppressed weak interaction operators. We obtain the value of $(2.5\pm 0.3)\times {10}^{-28}\mathrm{MeV}{\mathrm{fm}}^2$ for the $S$ factor and $(2.2\pm 0.2)\times {10}^{-26}{\mathrm{fm}}^2$ for its energy derivative at threshold. These are smaller than the results of a prior study that employed chiral EFT by several orders of magnitude. We conclude that, contrary to what has been previously reported, the $p$-wave contribution does not need to be considered in a high-precision determination of the $S$ factor at astrophysical energies. Combined with the chiral EFT calculation of Acharya et al. [Phys. Lett. B 760, 584 (2016)] for the $s$-wave channel, this gives a total threshold $S$ factor of $S\left(0\right)=(4.{047}_{-0.032}^{+0.024})\times {10}^{-23}\mathrm{MeV}{\mathrm{fm}}^2$.