Single- reference coupled-cluster theory is an accurate and affordable computational method for the nuclear many-body problem. For open-shell nuclei, the reference state typically breaks rotational invariance and angular momentum must be restored as a good quantum number. We perform angular-momentum projection after variation and employ the disentangled coupled-cluster formalism and a Hermitian approach. We compare our results with benchmarks for ${}^8\mathrm{Be}$ and ${}^{20}\mathrm{Ne}$ using a two-nucleon interaction from chiral effective field theory and for $pf$-shell nuclei within the traditional shell model. We compute the rotational band in the exotic nucleus ${}^{34}\mathrm{Mg}$ and find agreement with data.

Background: The predominant mass-asymmetric fission of actinide nuclides occurs mainly through the so-called standard I and standard II modes. Though understood to be caused by shape-dependent shell structures encountered between the fission barrier deformation and scission, the most relevant shell gaps are still not firmly established. The standard I mode had been associated with the spherical doubly magic ${}^{132}\mathrm{Sn}$, and thus the $Z=50$ proton shell, but recently it has been proposed that standard I and standard II are associated with quadrupole and octupole deformed gaps at $Z=52$ and 56, respectively.

Purpose: We investigate how the relative probabilities of the standard I and standard II modes vary with excitation energy near threshold, probing where the two modes bifurcate.

Methods: The Australian National University Heavy Ion Accelerator Facility and CUBE fission spectrometer have been used to measure fission mass distributions for the $p{+}^{232}\text{Th}$ reaction (forming ${}^{233}\mathrm{Pa}$) at closely spaced bombarding energy intervals from 6.5 to 28 MeV.

Results: A model-independent analysis of the energy dependence of the shape of the mass-asymmetric peak shows a strong dependence of the standard I and standard II relative probability on excitation energy near threshold.

Conclusions: The results are consistent with the standard II mode having a lower fission barrier than standard I in ${}^{233}\mathrm{Pa}$, with the latter increasing continually in relative probability above its barrier energy. It is concluded that multichance fission, in particular last chance fission, plays a strong role in determining the observed energy dependence of all fission modes.

Experimental cross sections for the ${}^4\mathrm{He}(e,e^{\prime }p)X$ reactions in the missing energy range from 0.017 to 0.022 GeV and up to a missing momentum of 0.632 GeV/$c$ at $x_B=1.24$ and $Q^2=2$ (GeV/${c)}^2$ are reported. The data are compared to relativistic distorted-wave impulse approximation calculations for the ${}^4\mathrm{He}(e,e^{\prime }p){}^3\mathrm{H}$ channel. Significantly more events are observed for $p_m\ge 0.45$ GeV/$c$ than are predicted by the theoretical model, and striking fluctuations in the ratio of data to the theoretical model around $p_m=0.3\mathrm{GeV}$/$c$ are possible signals of initial-state multinucleon correlations.

Background: Advancement in accelerator facilities has opened the door to dig deep to understand the interplay between nuclear reactions and structures. Although the influence of inelastic excitations on nuclear scattering and sub-barrier fusion is somewhat established, a clear understanding of nucleon transfer with a positive-$Q$ value is yet to achieve.

Purpose: The objective of this paper is to examine the role of the $2n$-transfer channel with a positive $Q$ value on sub-barrier fusion and back-angle quasielastic (QE) scattering in the ${}^{30}\mathrm{Si}+{}^{156}\mathrm{Gd}$ reaction. Furthermore, extraction of barrier distributions (BDs) from fusion and QE scattering to infer their shapes is also a prime goal.

Method: The excitation functions (EFs) of fusion and back-angle QE scattering have been measured over a wide range of incident beam energy around the Coulomb barrier using a recoil mass spectrometer. Furthermore, BDs have been extracted using the measured fusion and back-scattered QE data. The underlying findings have been analyzed within the framework of coupled-channel (CC) formalism using ccfull and ecc programs.

Results: Fusion enhancement has been observed compared to those predicted from the one-dimensional barrier penetration model at sub-barrier energies. Fusion enhancement and QE EFs are explained by CC predictions considering the collective excitations among the colliding nuclei. The inclusion of $2n$ transfer and collective excitations in ccfull improves the fit to the experimental fusion data in a short span of energy window around the Coulomb barrier, whereas no significant effect has been observed at the sub-barrier region. However, no such effect of $2n$-pickup transfer has been observed from ecc model calculations. Thus, no firm conclusion can be made on the role of $2n$-pickup transfer with a positive $Q$ value in present measurements.

Conclusion: Fusion EFs have been successfully explained by the CC calculations using ccfull and ecc model codes. No significant effect of the $2n$-pickup channel with a positive $Q$ value was observed on sub-barrier fusion enhancement. However, QE EFs are reproduced by considering the collective excitations and $2n$-transfer channel couplings. Fusion and QE BDs are similar in shape within the experimental uncertainty. One-dimensional barrier parameters extracted from the measured data agree with the different theoretical models. Also, the present system obeys the systematic based on deformation values after transfer at the exit.

We perform a systematic study on the local and global spin polarization of $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ hyperons in relativistic heavy-ion collisions at beam energy scan energies via the ($3+1$)-dimensional CLVisc hydrodynamics model with a multiphase transport (AMPT) and simulating many accelerated strongly interacting hadron (SMASH) initial conditions. Following the quantum kinetic theory, we decompose the polarization vector as the parts induced by thermal vorticity, shear tensor and the spin Hall effect (SHE). We find that the polarization induced by the SHE and the total polarization strongly depends on the initial conditions. At $7.7\mathrm{GeV}$, the SHE gives a sizable contribution and even flips the sign of the local polarization along the beam direction for the AMPT initial condition, which is not observed for the SMASH initial condition. Meanwhile, the local polarization along the out-of-plane direction induced by the SHE with the AMPT initial condition does not always increase with decreasing collision energies. Next, we find that the polarization along the beam direction is sensitive to the baryon diffusion coefficient, but the local polarization along the out-of-plane direction is not. Our results for the global polarization of $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ agree well with the data of the STAR Collaboration. Interestingly, the global polarization of $\overline{\mathrm{\Lambda }}$ is not always larger than that of $\mathrm{\Lambda }$ due to various competing effects. Our findings are helpful for understanding the polarization phenomenon and the detailed structure of quark-gluon plasma in relativistic heavy-ion collisions.

Background: Theoretical approaches based on energy density functionals (EDF) are gaining in popularity due to their broad range of applicability. One of their key features is the proper treatment of symmetries of the nuclear interaction. It is because of this that EDF-based methods may provide another independent verification of foundations of the standard model, i.e., the assumption that hadronic structure of matter is indeed built upon three generations of quarks. However, such a study cannot be precisely performed without including very subtle isospin-symmetry-breaking (ISB) terms both in the long- and short-range part of the nuclear interaction. Only very recently, the latter part of ISB interaction has been successfully adapted to EDF to describe Nolen-Shiffer anomaly.

Purpose: The aim of the paper is to study the impact of the short-range ISB terms on isospin impurities in the wave functions of $T=1/2$ mirrors (${\alpha }_{\mathrm{ISB}}$) and the ISB corrections to their Fermi decays (${\delta }_{\mathrm{ISB}}$). The consequent purpose is to eventually lead the calculation towards evaluation of the $V_{\mathrm{ud}}$ matrix element of Cabbibo-Kobayashy-Maskawa (CKM) quark mixing matrix.

Methods: We use multireference density functional theory (MR-DFT) that conserves angular-momentum and properly treats isospin. Moreover, for the very first time, the functional includes both short- and long-range isospin-symmetry-breaking forces. Calculations are performed using three different variants of the ISB interaction: (i) involving only the Coulomb force, (ii) involving the Coulomb and leading-order (LO) contact isovector forces, and (iii) involving the Coulomb and next-to-leading-order (NLO) contact isovector forces. The evaluation of $V_{\mathrm{ud}}$ matrix element requires more subtle approach involving configuration mixing. For this reason, the calculation is performed with DFT-rooted no core configuration interaction (DFT-NCCI) model including above-mentioned ISB terms as well.

Results: We compute isospin impurities and ISB corrections in $T=1/2$ mirrors ranging from $A=11$–47 with MR-DFT formalism. Next, we focus on the best measured $A=19$, 21, 35, and 37 mirror pairs, calculate the ISB corrections to their Fermi decays with DFT-rooted NCCI method and then extract $V_{\mathrm{ud}}$ matrix element. The final result shows that $V_{\mathrm{ud}}=0.9736\left(16\right)$, which (central value) is in a good agreement with the value assessed from the superallowed $0^{+}\to 0^{+}$ Fermi transitions and is only slightly above the value obtained using state-of-the-art shell model. Last but not least, we demonstrate the stability of our calculation.

Conclusions: The isovector short-range interaction surprisingly strongly influences the isospin impurities and ISB corrections in the $T=1/2$ mirrors as compared to the calculation where Coulomb interaction is the only source of the isospin-symmetry-breaking. Moreover, $V_{\mathrm{ud}}$ matrix element is sensitive to the short-range isovector terms in the interaction and can be successfully extracted within DFT-rooted approach that includes configuration mixing.

Causality is violated in the early stages of state-of-the-art heavy-ion hydrodynamic simulations. Such violations are present in up to 75% of the fluid cells in the initial time and only after 2–3 fm/$c$ of evolution do we find that $50\%$ of the fluid cells are definitely causal. Superluminal propagation reaches up to 15% the speed of light in some of the fluid cells. The inclusion of pre-equilibrium evolution significantly reduces the number of acausal cells. Our findings suggests that relativistic causality may place constraints on the available parameter space of heavy-ion collision simulations when factored into more thorough statistical analyses.

The isomeric state of ${}^{16}\mathrm{N}$ was studied using the ${}^{16}\mathrm{N}{}^{g,m}(d,{}^3\mathrm{He})$ proton-removal reactions at 11.8 MeV/u in inverse kinematics. The ${}^{16}\mathrm{N}$ beam, of which 24% was in the isomeric state, was produced using the Argonne Tandem-Linac Accelerator System (ATLAS) in-flight system and delivered to the Helical Orbit Spectrometer (HELIOS), which was used to analyze the ${}^3\mathrm{He}$ ions from the $(d,{}^3\mathrm{He})$ reactions. The simultaneous measurement of reactions on both the ground state and the isomeric states, reduced the systematic uncertainties from the experiment and in the analysis. A direct and reliable extraction of the relative spectroscopic factors was made based on a distorted-wave Born approximation approach. The experimental results suggest that the isomeric state of ${}^{16}\mathrm{N}$ is an excited neutron-halo state. The results can be understood through calculations using a Woods-Saxon potential model, which captures the effects of weak binding.

We explore the preparation of specific nuclear states on gate-based quantum hardware using variational algorithms. Large-scale classical diagonalizations of the nuclear shell model have reached sizes of ${10}^9–{10}^{10}$ basis states but are still severely limited by computational resources. Quantum computing can, in principle, solve such systems exactly with exponentially fewer resources than classical computing. Exact solutions for large systems require many qubits and large gate depth, but variational approaches can effectively limit the required gate depth. We use the unitary coupled cluster approach to construct approximations of the ground-state vectors, later to be used in dynamics calculations. The testing ground is the phenomenological shell model space, which allows us to mimic the complexity of the internucleon interactions. We find that often one needs to minimize over a large number of parameters, using a large number of entanglements that makes the application on existing hardware challenging. Prospects for rapid improvements with more capable hardware are, however, very encouraging.

Background: The ${}^8\mathrm{Li}(n,\gamma ){}^9\mathrm{Li}$ reaction plays a critical role in several reaction chains leading to the nucleosynthesis of $A>12$ nuclei. Due to unstable nature of ${}^8\mathrm{Li}$ and the unavailability of neutron targets, direct measurements of this reaction are exceedingly difficult. Only upper limits of this cross section, provided by the indirect experiments, have been obtained so far.

Purpose: In this work, we use the Gamow shell model (GSM) in the coupled-channel representation (GSM-CC) to study the properties of ${}^9\mathrm{Li}$ and the radiative capture reaction ${}^8\mathrm{Li}(n,\gamma ){}^9\mathrm{Li}$.

Method: GSM-CC is a theoretical framework allowing for the description of both nuclear structure and reaction cross sections. In GSM-CC calculations, a translationally invariant Hamiltonian is used with a finite-range two-body interaction tuned to reproduce the low-energy spectra of ${}^{8,9}\mathrm{Li}$. The reaction channels are built by coupling wave functions of the ground state $2_1^{+}$, the first-excited state $1_1^{+}$, and the first resonance state $3_1^{+}$ in ${}^8\mathrm{Li}$ with the neutron wave function of the projectile in different partial waves. In the calculation of ${}^8\mathrm{Li}(n,\gamma ){}^9\mathrm{Li}$ cross section, all relevant $E1$, $M1$, and $E2$ transitions from the initial continuum states to the final bound states ${3/2}_1^{-}$, ${1/2}_1^{-}$ and the resonance ${5/2}_1^{-}$ of ${}^9\mathrm{Li}$ are included.

Results: The GSM-CC approach reproduces the experimental low-energy spectrum, neutron emission threshold, and spectroscopic factors in ${}^9\mathrm{Li}$. The calculated reaction rate is consistent with the experimental upper limit of the reaction rate obtained in the indirect measurements at stellar energies.

Conclusion: The GSM-CC calculations suggest that the ${}^8\mathrm{Li}(n,\gamma ){}^9\mathrm{Li}$ reaction does not reduce significantly heavy-element production via the main chain ${}^7\mathrm{Li}(n,\gamma ){}^8\mathrm{Li}(\alpha ,n){}^{11}\mathrm{B}(n,\gamma ){}^{12}\mathrm{B}\left({\beta }^{+}\right){}^{12}\mathrm{C}$. Major contribution to the calculated cross section is given by the direct $E1$ transition to the ground state of ${}^8\mathrm{Li}$. The contribution of excited states to the reaction rate does not exceed $\approx 20$% of the total reaction rate.

Elastic scattering, total reaction, and fusion cross sections of the systems ${}^9\mathrm{Be}+{}^{208}\mathrm{Pb}$ and ${}^9\mathrm{Be}+{}^{197}\mathrm{Au}$ at near-barrier energies, are coherently analyzed into two theoretical contexts. In a phenomenological approach, a BDM3Y1 interaction is used in an optical model potential analysis of the elastic-scattering data and the energy dependence of the potential is mapped around the Coulomb barrier. In a second approach, the elastic scattering is investigated within a four body framework by using the continuum-discretized coupled-channels method. In both scenarios, total reaction cross sections are determined and compared with phenomenological predictions. Moreover, an effective potential is obtained and in a one barrier penetration model analysis, the fusion excitation function is determined and compared with experimental data, further validating our analysis.

Neutron captures and delayed decays of reaction products are common sources of backgrounds in ultrarare event searches. In this work, we studied ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$ reactions induced by $\alpha$ particles emitted within the calibration sources of the Majorana Demonstrator. These sources are thorium-based calibration standards enclosed in carbon-rich materials. The reaction rate was estimated by using the 6129-keV $\gamma$ rays emitted from the excited ${}^{16}\mathrm{O}$ states that are populated when the incoming $\alpha$ particles exceed the reaction $Q$ value. Thanks to the excellent energy performance of the Demonstrator's germanium detectors, these characteristic photons can be clearly observed in the calibration data. Facilitated by Geant4 simulations, a comparison between the observed 6129-keV photon rates and predictions by a talys-based software was performed. The measurements and predictions were found to be consistent, albeit with large statistical uncertainties. This agreement provides support for background projections from $(\alpha ,n)$ reactions in future double-beta decay search efforts.

The excitation of the dynamical dipole mode was explored in the formation of a heavy composite system with mass $A\simeq$ 190, by investigating its fission channel. The composite system was produced through the charge asymmetric reaction, ${}^{40}\mathrm{Ca} + {}^{152}\mathrm{Sm}$, and the nearly charge symmetric one, ${}^{48}\mathrm{Ca} +{}^{144}\mathrm{Sm}$, at $E_{\text{lab}}$ = 11 and 10.1 MeV/nucleon, respectively. High-energy $\gamma$ rays and light charged particles were detected in coincidence with the two fission fragments by means of the MEDEA multidetector array coupled to two parallel plate avalanche counters. The kinetic energy spectra of the light charged particles measured at different angles were used to infer the average excitation energy, the average mass, and the average charge of the produced nuclei whereas the time of flight and the emission angle of the fragments were employed to reconstruct the fission dynamics. The study of the $\gamma$-ray spectra and angular distributions for the selected fission events, allowed us to establish (i) the excitation of the giant dipole resonance in the composite system of both reactions and (ii) the excitation of the dynamical dipole mode in the dinucleus of the charge asymmetric reaction by isolating its prompt $\gamma$ radiation through the difference technique. The present results on the dynamical dipole mode were compared with the experimental findings for the evaporation channel of the ${}^{40}\mathrm{Ca} + {}^{152}\mathrm{Sm}$ reaction and moreover with calculations based on a collective bremsstrahlung analysis of the reaction dynamics. Interesting hints connecting the dynamical dipole $\gamma$ radiation with the superheavy element quest are given.

State-of-the-art hydrodynamic models of heavy-ion collisions have considerable theoretical model uncertainties in the description of the very early prehydrodynamic stage. We add a new computational module, ${\mathrm{K}}_{\mathrm{T}}$Iso, that describes the prehydrodynamic evolution kinetically, based on the relativistic Boltzmann equation with collisions treated in the isotropization time approximation. As a novelty, ${\mathrm{K}}_{\mathrm{T}}$Iso allows for the inclusion and evolution of initial-state momentum anisotropies. To maintain computational efficiency ${\mathrm{K}}_{\mathrm{T}}$Iso assumes strict longitudinal boost invariance and allows collisions to isotropize only the transverse momenta. We use it to explore the sensitivity of hadronic observables measured in relativistic heavy-ion collisions to initial-state momentum anisotropies and microscopic scattering during the prehydrodynamic stage.

One of the biggest questions in nuclear astrophysics is understanding where the elements come from and how they are made. This work focuses on the $p$ process, a nucleosynthesis process that consists of a series of photodisintegration reactions responsible for producing stable isotopes on the proton-rich side of stability. These nuclei, known as the $p$ nuclei, cannot be made through the well-known neutron-capture processes. Currently $p$-process models rely heavily on theory to provide the relevant reaction rates to predict the final $p$-nuclei abundances and more experimental data is needed. The present work reports on an experiment performed with the SuN detector at the National Superconducting Cyclotron Laboratory, NSCL, at Michigan State University using the ReA facility to measure the ${}^{84}\mathrm{Kr}(p,\gamma ){}^{85}\mathrm{Rb}$ reaction cross section in inverse kinematics. The reverse ${}^{85}\mathrm{Rb}(\gamma ,p){}^{84}\mathrm{Kr}$ reaction is a branching point in the $p$-process reaction network that was highlighted as an important reaction in sensitivity studies in the production of the ${}^{78}\mathrm{Kr}$ $p$ nucleus. A new hydrogen gas target was designed and fabricated and a new analysis technique for background subtraction and efficiency calculations of the detector were developed. The experimental cross section is compared to standard statistical model calculations using the non-smoker and talys codes.

The efficiency of the slow neutron-capture process in massive stars is strongly influenced by neutron-capture reactions on light elements. At low metallicity, ${}^{16}\mathrm{O}$ is an important neutron absorber, but the effectiveness of ${}^{16}\mathrm{O}$ as a light-element neutron poison is modified by competition between subsequent ${}^{17}\mathrm{O}(\alpha ,n){}^{20}\mathrm{Ne}$ and ${}^{17}\mathrm{O}(\alpha ,\gamma ){}^{21}\mathrm{Ne}$ reactions. The strengths of key ${}^{17}\mathrm{O}(\alpha ,\gamma ){}^{21}\mathrm{Ne}$ resonances within the Gamow window for core helium burning in massive stars are not well constrained by experiment. This work presents more precise measurements of resonances in the energy range $E_{\mathrm{c}.\mathrm{m}.}=612\text{–}1319$ keV. We extract resonance strengths of $\omega {\gamma }_{638}=4.85\pm 0.79\mu \mathrm{eV}$, $\omega {\gamma }_{721}=13.1_{-2.4}^{+3.2}\mu \mathrm{eV}$, $\omega {\gamma }_{814}=7.72\pm 0.55\mathrm{meV}$, and $\omega {\gamma }_{1318}=136\pm 13\mathrm{meV}$, for resonances at $E_{\mathrm{c}.\mathrm{m}.}=638$, 721, 814, and 1318 keV, respectively. We also report an upper limit for the 612 keV resonance of $\omega \gamma <140$ neV ($95\%$ c.l.), which effectively rules out any significant contribution from this resonance to the reaction rate. From this work, a new ${}^{17}\mathrm{O}(\alpha ,\gamma ){}^{21}\mathrm{Ne}$ thermonuclear reaction rate is calculated and compared to the literature. The effect of present uncertainties in the ${}^{17}\mathrm{O}(\alpha ,\gamma ){}^{21}\mathrm{Ne}$ reaction rate on weak $s$-process yields are then explored using postprocessing calculations based on a rotating $20M_{\odot }$ low-metallicity massive star. The resulting ${}^{17}\mathrm{O}(\alpha ,\gamma ){}^{21}\mathrm{Ne}$ reaction rate is lower with respect to the preexisting literature and found to enhance weak $s$-process yields in rotating massive star models.

Meaningful predictions for electric quadrupole ($E2$) observables from ab initio nuclear theory are necessary, if the ab initio description of collective correlations is to be confronted with experiment, as well as to provide predictive power for unknown $E2$ observables. However, converged results for $E2$ observables are notoriously challenging to obtain in ab initio no-core configuration interaction approaches. Matrix elements of the $E2$ operator are sensitive to the large-distance tails of the nuclear wave function, which converge slowly in an oscillator basis expansion. Similar convergence challenges beset ab initio prediction of the nuclear charge radius. We demonstrate that the convergence patterns of the $E2$ and radius observables are strongly correlated, and that meaningful predictions for the absolute scale of $E2$ observables may be made by calibrating to the experimentally known ground-state charge radius. We illustrate by providing robust ab initio predictions for several $E2$ transition strengths and quadrupole moments in $p$-shell nuclei, in cases where experimental results are available for comparison.

Ab initio calculations of nuclear masses, binding energy, and $\alpha$-decay half-lives are intractable for heavy nucleus because of the curse of dimensionality in many-body quantum simulations as proton number ($N$) and neutron number ($Z$) grow. We take advantage of the powerful nonlinear transformation and feature representation ability of deep neural network (DNN) to predict the nuclear masses and $\alpha$-decay half-lives. For nuclear binding energy prediction problem we achieve standard deviation $\sigma =0.263$ MeV on 10-fold cross validation on 2149 nuclei. Word-vectors which are high-dimensional representation of nuclei from the hidden layers of mass-regression DNN help us to calculate $\alpha$-decay half-lives. For this task, we get $\sigma =0.797$ on 100 times 10-fold cross validation on 350 nuclei on ${\text{log}}_{10}{T}_{1/2}$ and $\sigma =0.731$ on 486 nuclei. DNN is also used to reduce the residual of three-parameter Gamow formula on 159 even-even nuclei, from 0.3627 to 0.2297 on ${\text{log}}_{10}{T}_{1/2}$, using 100 times 10-fold cross validation. We find physical a priori such as shell structure, magic numbers and augmented inputs inspired by finite-range droplet model are important for this small data regression task.