The modeling of nuclear $\gamma$-ray line emission induced by highly accelerated particles in astrophysical sites (e.g., solar flares, the gas and dust in the inner galaxy) and the comparison with observed emissions from these sites needs a comprehensive database of related production cross sections. The most important reactions of protons and $\alpha$ particles are those with abundant target elements like C, O, N, Ne, Mg, Si, and Fe at projectile energies extending from the reaction threshold to a few hundred MeV per nucleon. In this work, we have measured $\gamma$-ray production cross section excitation functions for 30, 42, 54, and 66 MeV proton beams accelerated onto ${}^{\mathrm{nat}}\mathrm{C}$, $\mathrm{C}+\mathrm{O}$ (Mylar), ${}^{\mathrm{nat}}\mathrm{Mg}, {}^{\mathrm{nat}}\mathrm{Si}$, and ${}^{56}\mathrm{Fe}$ targets of astrophysical interest at the Separated Sector Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with eight Compton suppressed high-purity (HPGe) clover detectors was used to record $\gamma$-ray line energy spectra. For known, intense lines previously reported experimental data measured up to $E_p\simeq 25$ MeV at the Washington and Orsay tandem accelerators were thus extended to higher proton energies. Our experimental data for the last three targets are reported here and discussed with respect to previous data and to the Murphy et al. compilation [Astrophys. J. Suppl. Ser. 183, 142 (2009)], as well as to the predictions of the nuclear reaction code talys. The overall agreement between theory and experiment obtained in first-approach calculations using default input parameters of talys has been appreciably improved by using modified optical model potential (OMP), level deformation, and level density parameters. The OMP parameters have been extracted from theoretical fits to available experimental elastic and inelastic nucleon scattering angular distribution data by means of the coupled-channels reaction code optman. Experimental data for several new $\gamma$-ray lines are also reported and discussed. The astrophysical implications of our results are emphasised.

Pion-induced reactions provide unique opportunities for an unambiguous description of baryonic resonances and their coupling channels by means of a partial-wave analysis. Using the secondary pion beam at SIS18, the two-pion production in the second resonance region has been investigated to unravel the role of the $N\left(1520\right){\frac{3}{2}}^{-}$

resonance in the intermediate $\rho$-meson production. Results on exclusive channels with one pion (${\pi }^{-}p$) and two pions (${\pi }^{+}{\pi }^{-}n$, ${\pi }^0{\pi }^{-}p$) in the final state measured in the ${\pi }^{-}\text{−}p$ reaction at four different pion beam momenta (0.650, 0.685, 0.733, and 0.786 GeV/$c$) are presented. The excitation function of the different partial waves and $\mathrm{\Delta }\pi$, $N\sigma$, and $N\rho$ isobar configurations is obtained, using the Bonn-Gatchina partial-wave analysis. The $N\left(1520\right){\frac{3}{2}}^{-}$ resonance is found to dominate the $N\rho$ final state with the branching ratio $\text{BR}=12.2\%\pm 1.9\%$.

Background: Weakly bound and unbound nuclei close to particle drip lines are laboratories of new nuclear structure physics at the extremes of neutron/proton excess. The comprehensive description of these systems requires an open quantum system framework that is capable of treating resonant and nonresonant many-body states on equal footing.

Purpose: In this work, we develop the complex-energy configuration interaction approach to describe binding energies and spectra of selected $5\le A\le 11$ nuclei.

Method: We employ the complex-energy Gamow shell model (GSM) assuming a rigid ${}^4\mathrm{He}$ core. The effective Hamiltonian, consisting of a core-nucleon Woods-Saxon potential and a simplified version of the Furutani-Horiuchi-Tamagaki interaction with the mass-dependent scaling, is optimized in the $sp$ space. To diagonalize the Hamiltonian matrix, we employ the Davidson method and the Density Matrix Renormalization Group technique.

Results: Our optimized GSM Hamiltonian offers a good reproduction of binding energies and spectra with the root-mean-square (rms) deviation from experiment of 160 keV. Since the model performs well when used to predict known excitations that have not been included in the fit, it can serve as a reliable tool to describe poorly known states. A case in point is our prediction for the pair of unbound mirror nuclei ${}^{10}\mathrm{Li}\text{−}{}^{10}\mathrm{N}$ in which a huge Thomas-Ehrman shift dramatically alters the pattern of low-energy excitations.

Conclusion: The new model will enable comprehensive studies of structure and reactions aspects of light drip-line nuclei.

Background: Separable interactions have a long history in nuclear physics. In the last few years, separable expansions have been used to represent the optical potential between a nucleon (proton or neutron) and a target.

Purpose: We explore the nonlocal properties of these separable optical potentials as well as their convergence behavior.

Method: For a couple of cases, we use the generalized Ersnt-Shakin-Thaler scheme to generate separable interactions starting from local optical potentials. We study the variation of the interaction with energy range and rank.

Results: We find that, overall, the off-diagonal behavior of the converged separable interaction deviates from the Gaussian form assumed by Perey and Buck [F. Perey and B. Buck, Nucl. Phys. 32, 353 (1962)]. However, in the region surrounding the maximum depth the Gaussian form works quite well. Focusing on this region, we study potentials describing neutron elastic scattering on ${}^{16}\mathrm{O}$ and ${}^{48}\mathrm{Ca}$ for beam energies in the range of $E=10$–50 MeV and explore several measures of nonlocality of the separable interactions.

Conclusions: When the energy range considered for generating the separable interaction is $0\le E_{\mathrm{range}}\le 50$ MeV, the resulting nonlocality is large and target dependent. Contrarily, the nonlocality obtained including larger energy ranges in the separable procedure is independent of the target and other details of the original local potential. We find that, even when including in the expansion many support points with energy ranges $0\le E_{\mathrm{range}}\le 2400$ MeV, the resulting potential retains nonlocal behavior. Connections with microscopic optical potentials as well as other transformations used in the nucleon-nucleon domain are made.

We study the ternary fission of various even-even $\alpha$-structured parent nuclei with $12\le A\le 60$, such as ${}^{12}\mathrm{C}$, ${}^{16}\mathrm{O}$, ${}^{20}\mathrm{Ne}$, ${}^{24}\mathrm{Mg}$, ${}^{28}\mathrm{Si}$, ${}^{32}\mathrm{S}$, ${}^{36}\mathrm{Ar}$, ${}^{40}\mathrm{Ca}$, ${}^{44}\mathrm{Ti}$, ${}^{48}\mathrm{Cr}$, ${}^{52}\mathrm{Fe}$, ${}^{56}\mathrm{Ni}$, and ${}^{60}\mathrm{Zn}$, within a three-body decay approach. In the present study, we consider the three spherical ternary fission fragments with the lightest fragment $A_3$ at the middle of the other two main fission fragments, $A_1$ and $A_2$. The effects of hyperradius and the hypermomentum quantum number in the ternary fission potential energy barrier are also studied. Further, the total excitation energy and the ternary fission relative yields are calculated for the possible ternary fragmentation of each parent nuclei considered. From the results obtained, we find the emission of $\alpha$-structured ternary fragments is more favored than the other ternary fragment combinations.

Cascade solutions of the Boltzmann equation suffer from causality violation at high densities and/or scattering cross sections. Although the particle subdivision technique can reduce the causality violation, it alters event-by-event correlations and fluctuations and is also computationally expensive. Here we evaluate and then improve the accuracy of the ZPC parton cascade for elastic scatterings inside a box without using parton subdivision. We first test different collision schemes for the collision times and ordering time and find that the default collision scheme does not accurately describe the equilibrium momentum distribution at large opacities. We then find a specific collision scheme that can describe very accurately the equilibrium momentum distribution as well as the time evolution towards equilibrium, even at large opacities. We also calculate the shear viscosity and the $\eta /s$ ratio of the parton systems and confirm that the new collision scheme is more accurate. In addition, we use a novel parton subdivision method to obtain the “exact” evolution of the system. This subdivision method is valid for such box calculations and is so much more efficient than the standard subdivision method that we use a subdivision factor of ${10}^6$ in this study.

We study the propagation and diffusion of electric charge fluctuations in the Bjorken hydrodynamic model with both white and Catteneo noise using purely numerical methods. We show that a lattice of noise fluctuations is required to fully calculate the two-point correlators of charge. We introduce a numerical procedure to solve the stochastic differential equations that arise from the charge conservation equation on the lattice event by event. We explicitly identify the self-correlation term in the case of Catteneo noise and provide a physical interpretation. We provide a numerical recipe to remove this contribution from the full two-point correlators. Finally, we calculate the balance functions for charged hadrons. By limiting the speed of signal propagation, we observe the expected narrowing of the balance functions after removing the self-correlations.

Charge radii are one of the most fundamental properties of atomic nuclei characterizing their charge distributions. Though the general trend as a function of the mass number is well described by the $A^{1/3}$ rule, some fine structure, such as the evolution along the calcium isotopic chain and the corresponding odd-even staggerings, are notoriously difficult to describe both in density functional theories and ab initio methods. In this work, we propose a novel ansatz to describe the charge radii of calcium isotopes by adding a correction term, proportional to the number of Cooper pairs and determined by the BCS amplitudes and a single parameter, to the charge radii calculated in the relativistic mean field model with the pairing interaction treated with the BCS method. It is shown that the new ansatz yields results consistent with data not only for calcium isotopes, but also for 10 other isotopic chains, including oxygen, neon, magnesium, chromium, nickel, germanium, zirconium, cadmium, tin, and lead. It is quite remarkable that this ansatz with a single parameter can describe nuclear charge radii throughout the periodic table, particularly the odd-even staggerings and parabolic behavior.

The slowest reaction in the CNO cycle ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$ has been studied by populating the $E_p^{\mathrm{lab}}=278$ keV ($E_{\mathrm{c}.\mathrm{m}.}^r=259$ keV) proton capture resonant state of ${}^{15}\mathrm{O}$ at 7556 keV. The strength of the resonance ($\omega \gamma$) has been determined from the experimental data. The level lifetime of the subthreshold resonant state at $E_x=6792$ keV, as well as the lifetimes of the 5181 keV and 6172 keV states, have been measured using the Doppler shift attenuation method (DSAM). The structural properties of the nucleus ${}^{15}\mathrm{O}$, such as the level energies, transition strengths, level lifetimes, and spectroscopic factors, have been calculated theoretically by using the large basis shell model, which agrees reasonably well with the present as well as the previous experimental data.

The configuration interaction methods are powerful tools for exploring various properties of nuclei. However, in practice, it is often necessary to truncate the model space and then to extrapolate the results to very large model space to obtain the best estimations of the exact eigenvalues under a given nuclear interaction. In this study, a nonparametric extrapolation method based on constrained Gaussian processes for configuration interaction methods is presented. The proposed method has many advantages: (i) applicability to small data sets such as results of ab initio methods, (ii) flexibility to incorporate constraints, which are guided by physics, into the extrapolation model, (iii) providing predictions with quantified extrapolation uncertainty, etc. An application to the extrapolation problem of ground-state energies in the full configuration interaction method is discussed as an example.

We have studied the isoscalar giant quadruple resonance (ISGQR) and the isovector giant dipole resonance (IVGDR) in ${}^{208}\mathrm{Pb}$ based on an improved isospin-dependent Boltzmann-Uehling-Uhlenbeck transport approach using an improved isospin- and momentum-dependent interaction. With the isoscalar nucleon effective mass and the nucleon-nucleon cross section which reproduces respectively the excitation energy and the width of the ISGQR strength function, the slope parameter of the symmetry energy and the neutron-proton effective-mass splitting are constrained respectively within $36<L<62$ MeV and $0.08\delta <(m_{n0}^{*}-m_{p0}^{*})/m<0.42\delta$, by comparing the resulting centroid energy of the IVGDR and the electric-dipole polarizability with the experimental data. It is found that nucleon-nucleon collisions have considerable effects on the resulting electric-dipole polarizability, which needs to be measured more accurately in order to pin down isovector nuclear interactions.

Excitation of the isomer ${}^{229m}\mathrm{Th}$ with energy 8.3 eV in the electron bridge (EB) via continuous electron spectrum is treated as a two-step process. At first an outer atomic electron absorbs the laser photon and leaves the atom, afterwards it returns to the atom transferring its energy to the nucleus. This EB transition is described in the framework of strict scattering theory for the atomic-nuclear system with two overlapping resonances. The derived EB cross section differs in some details from the results of P. V. Borisyuk et al. [Phys. Rev. C 100, 044306 (2019)].

A search for $\alpha$ decay of naturally occurring osmium isotopes to the lowest excited levels of daughter nuclei has been performed by using an ultra-low-background broad-energy germanium $\gamma$ detector with a volume of 112 ${\mathrm{cm}}^3$ and an ultrapure osmium sample with a mass of 118 g at the Gran Sasso National Laboratory of the INFN (Italy). The isotopic composition of the osmium sample has been measured with high precision using negative thermal ionization mass spectrometry. After 15851 h of data taking with the $\gamma$ detector, no effect has been detected, and lower limits on the $\alpha$ decays were set at level of $lim{T}_{1/2}\approx {10}^{15}–{10}^{19}$ yr. The limits for the $\alpha$ decays of ${}^{184}\mathrm{Os}$ and ${}^{186}\mathrm{Os}$ to the first excited levels of daughter nuclei, $T_{1/2}\left({}^{184}\mathrm{Os}\right)\ge 6.8\times {10}^{15}$ yr and $T_{1/2}\left({}^{186}\mathrm{Os}\right)\ge 3.3\times {10}^{17}$ yr (at 90% C.L.), exceed the present theoretical estimates of the decays' half-lives. For ${}^{189}\mathrm{Os}$ and ${}^{192}\mathrm{Os}$ also decays to the ground states of the daughter nuclei were searched for due to the instability of the daughter nuclides relative to $\beta$ decay.

We study the production of pions, kaons, and (anti)protons using a multiphase transport (AMPT) model in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=$ 7.7, 27, and 200 GeV. We present the centrality and energy dependence of various bulk observables such as invariant yields as a function of transverse momentum $p_T$, particle yields $dN/dy$, average transverse momentum $\langle p_T\rangle$, and various particle ratios, and compare them with experimental data. Both default and string melting (SM) versions of the AMPT model are used with three different sets of initial conditions. We observe that neither the default nor the SM version of the model could consistently describe the centrality dependence of all observables at the above energies with any one set of initial conditions. The energy dependence behavior of the experimental observables for 0–5% central collisions is in general better described by the default AMPT model using the modified hijing parameters for Lund string fragmentation and 3 mb parton scattering cross section. In addition, the kaon production as well as the $K/\pi$ ratio at 7.7 GeV are underpredicted by the AMPT model.

The measurements of particle multiplicity distributions have generated considerable interest in understanding the fluctuations of conserved quantum numbers in the quantum chromodynamics (QCD) hadronization regime, in particular near a possible critical point and near the chemical freeze-out. Net-protons and net-kaons have been used as proxies for the net-baryon number and net-strangeness, respectively. We report the measurement of efficiency- and centrality-bin width-corrected cumulant ratios ($C_2/C_1$, $C_3/C_2$) of net-$\mathrm{\Lambda }$ distributions, in the context of both strangeness and baryon number conservation, as a function of collision energy, centrality, and rapidity. The results are for $\text{Au}+\text{Au}$ collisions at five beam energies ($\sqrt{s_{NN}}=19.6$, 27, 39, 62.4, and 200 GeV) recorded with the Solenoidal Tracker at RHIC (STAR). We compare our results to the Poisson and negative binomial (NBD) expectations, as well as to ultrarelativistic quantum molecular dynamics (UrQMD) and hadron resonance gas (HRG) model predictions. Both NBD and Poisson baselines agree with data within the statistical and systematic uncertainties. UrQMD describes the measured net-$\mathrm{\Lambda }{C}_1$ and $C_3$ at 200 GeV reasonably well but deviates from $C_2$, and the deviation increases as a function of collision energy. The ratios of the measured cumulants show no features of critical fluctuations. The chemical freeze-out temperatures extracted from a recent HRG calculation, which was successfully used to describe the net-proton, net-kaon, and net-charge data, indicate $\mathrm{\Lambda }$ freeze-out conditions similar to those of kaons. However, large deviations are found when comparing with temperatures obtained from net-proton fluctuations. The net-$\mathrm{\Lambda }$ cumulants show a weak but finite dependence on the rapidity coverage in the acceptance of the detector, which can be attributed to quantum number conservation.

A general procedure for obtaining frame-independent three-dimensional light-front coordinate-space wave functions is introduced. The third spatial coordinate $\tilde{z}$ is the boost and Lorentz frame-independent coordinate conjugate to the light-front momentum coordinate $x=\frac{k^{+}}{P^{+}}$ which appears in the momentum-space light-front wave functions underlying generalized parton distributions, structure functions, distribution amplitudes, form factors, and other hadronic observables. These causal light-front coordinate-space wave functions are used to derive a general expression for the quark distribution function of hadrons as an integral over the frame-independent longitudinal distance (the Ioffe time) between virtual-photon absorption and emission appearing in the forward virtual photon-hadron Compton scattering amplitude. Specific examples using models derived from light-front holographic QCD show that the spatial extent of the proton eigenfunction in the longitudinal direction can have a very large extent in $\tilde{z}$.

Background: Cross sections for the formation of superheavy elements (SHE) by heavy ion fusion are suppressed by the competing quasifission process. This results in a fissionlike decay after capture but before formation of a compact compound nucleus. Fast quasifission is evident from very mass-asymmetric fission, focused in angle. In contrast, slow quasifission shows no significant mass-angle correlation, and a mass distribution peaked at symmetry. However, it shows angular distributions more anisotropic than those calculated for fission following fusion. Following fusion, low excitation energies should increase SHE survival through reduced competition from fission. However, in reactions with deformed actinide target nuclei, subbarrier fusion is highly suppressed by both fast and slow quasifission.

Purpose: To investigate the threshold for quasifission by investigating signatures of slow quasifission in both fission angular and mass distributions, as a function of beam energy with respect to the capture barrier, for the projectiles ${}^9\mathrm{Be}$, ${}^{12}\mathrm{C},$ and ${}^{16}\mathrm{O}$ that form the neighboring compound nuclei ${}^{258,260}\mathrm{No}$.

Methods: Fission mass and angular distributions have been measured from below to above-barrier energies using the kinematic coincidence method for the reactions ${}^9\mathrm{Be}+{}^{249}\mathrm{Cf}$, ${}^{12}\mathrm{C}+{}^{248}\mathrm{Cm}$, and ${}^{16}\mathrm{O}+{}^{244}\mathrm{Pu}$. Fission following transfer reactions can significantly contaminate fission events that follow capture, and must be rejected. Existing methods to reject transfer-induced fission have been refined to allow quantitative subtraction of the transfer fission component.

Results: The capture-fission mass-angle distributions show no evidence for fast quasifission, as might be expected. However, measured fission fragment angular anisotropies are larger than transition state model (TSM) calculations for fusion fission. The deviations increase with larger projectile charge and for bombarding energies below the mean capture barrier energy. Even for the ${}^9\mathrm{Be}+{}^{249}\mathrm{Cf}$ reaction, the subbarrier angular anisotropy significantly exceeds the TSM calculation. Fission mass distributions measured at the same excitation energies also show a consistent dependence on the projectile charge.

Conclusions: New refined analysis techniques have been developed to enable reliable separation of fission following capture from sequential fission following transfer reactions. For fission following capture at above-barrier energies, the ${}^9\mathrm{Be}$ angular anisotropies are close to the TSM predictions, supporting the validity of TSM calculations of fusion-fission for such heavy elements. At subbarrier energies the angular anisotropy data indicate a component of slow quasifission even for ${}^9\mathrm{Be}$, and a probability that increases rapidly with projectile charge. It is concluded that the probability of slow quasifission changes smoothly with projectile charge, having no sharp threshold.

Background: Dust grains condensed in the outflows of presolar classical novae should have been present in the protosolar nebula. Candidates for such presolar nova grains have been found in primitive meteorites and can in principle be identified by their isotopic ratios, but the ratios predicted by state-of-the-art one-dimensional hydrodynamic models are uncertain due to nuclear-physics uncertainties.

Purpose: To theoretically calculate the thermonuclear rates and uncertainties of the ${}^{34}\mathrm{S}(p,\gamma ){}^{35}\mathrm{Cl}$ and ${}^{34g,m}\mathrm{Cl}(p,\gamma ){}^{35}\mathrm{Ar}$ reactions and investigate their impacts on the predicted ${}^{34}\mathrm{S}/{}^{32}\mathrm{S}$ isotopic ratio for presolar nova grains.

Method: A shell-model approach in a ($0+1$) $\hslash \omega$ model space was used to calculate the properties of resonances in the ${}^{34}\mathrm{S}(p,\gamma ){}^{35}\mathrm{Cl}$ and ${}^{34g,m}\mathrm{Cl}(p,\gamma ){}^{35}\mathrm{Ar}$ reactions and their thermonuclear rates. Uncertainties were estimated using a Monte Carlo method. The implications of these rates and their uncertainties on sulfur isotopic nova yields were investigated using a postprocessing nucleosynthesis code. The rates for transitions from the ground state of ${}^{34}\mathrm{Cl}$ as well as from the isomeric first excited state of ${}^{34}\mathrm{Cl}$ were explicitly calculated.

Results: At energies in the resonance region near the proton-emission threshold, many negative-parity states appear. Energies, spectroscopic factors, and proton-decay widths are reported. The resulting thermonuclear rates are compared with previous determinations.

Conclusions: The shell-model calculations alone are sufficient to constrain the variation of the ${}^{34}\mathrm{S}/{}^{32}\mathrm{S}$ ratios to within about 30%. Uncertainties associated with other reactions must also be considered, but in general we find that the ${}^{34}\mathrm{S}/{}^{32}\mathrm{S}$ ratios are not a robust diagnostic to clearly identify presolar grains made from nova ejecta.