Background: Modern applications of nuclear time-dependent density functional theory (TDDFT) are often capable of providing quantitative description of heavy ion reactions. However, the structures of precompound (preequilibrium, prefission) states produced in heavy ion reactions are difficult to assess theoretically in TDDFT as the single-particle density alone is a weak indicator of shell structure and cluster states.

Purpose: We employ the time-dependent nucleon localization function (NLF) to reveal the structure of precompound states in nuclear reactions involving light and medium-mass ions. We primarily focus on spin saturated systems with $N=Z$. Furthermore, we study reactions with oxygen and carbon ions, for which some experimental evidence for $\alpha$ clustering in precompound states exists.

Method: We utilize the symmetry-free TDDFT approach with the Skyrme energy density functional UNEDF1 and compute the time-dependent NLFs to describe ${}^{16}\mathrm{O}$ + ${}^{16}\mathrm{O},{}^{40}\mathrm{Ca}$ + ${}^{16}\mathrm{O},{}^{40}\mathrm{Ca}$ + ${}^{40}\mathrm{Ca}$, and ${}^{16,18}\mathrm{O}$ + ${}^{12}\mathrm{C}$ collisions at energies above the Coulomb barrier.

Results: We show that NLFs reveal a variety of time-dependent modes involving cluster structures. For instance, the ${}^{16}\mathrm{O}$ + ${}^{16}\mathrm{O}$ collision results in a vibrational mode of a quasimolecular $\alpha \text{−}{}^{12}\mathrm{C}\text{−}{}^{12}\mathrm{C}\text{−}\alpha$ state. For heavier ions, a variety of cluster configurations are predicted. For the collision of ${}^{16,18}\mathrm{O}$ + ${}^{12}\mathrm{C}$, we showed that the precompound system has a tendency to form $\alpha$ clusters. This result supports the experimental findings that the presence of cluster structures in the projectile and target nuclei gives rise to strong entrance channel effects and enhanced $\alpha$ emission.

Conclusion: The time-dependent nucleon localization measure is a very good indicator of cluster structures in complex precompound states formed in heavy-ion fusion reactions. The localization reveals the presence of collective vibrations involving cluster structures, which dominate the initial dynamics of the fusing system.

Local chiral effective field theory interactions have recently been developed and used in the context of quantum Monte Carlo few- and many-body methods for nuclear physics. In this work, we go over detailed features of local chiral nucleon-nucleon interactions and examine their effect on properties of the deuteron, paying special attention to the perturbativeness of the expansion. We then turn to three-nucleon interactions, focusing on operator ambiguities and their interplay with regulator effects. We then discuss the nuclear Green's function Monte Carlo method, going over both wave-function correlations and approximations for the two- and three-body propagators. Following this, we present a range of results on light nuclei: Binding energies and distribution functions are contrasted and compared, starting from several different microscopic interactions.

The polarizations of $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ hyperons are important quantities in extracting the fluid vorticity of the strongly coupled quark gluon plasma and the magnitude of the magnetic field created in off-central heavy-ion collisions, through the spin-vorticity and spin-magnetic coupling. We computed the energy dependence of the global $\mathrm{\Lambda }$ polarization in off-central Au+Au collisions in the energy range $\sqrt{s_{NN}}=7.7–200$ GeV using a multiphase transport model. The observed polarizations with two different impact parameters agree quantitatively with recent STAR measurements. The energy dependence of the global $\mathrm{\Lambda }$ polarization is decomposed as energy dependence of the $\mathrm{\Lambda }$ distribution at hadronization and the space-time distribution of the fluid-vorticity field. The visualization of both the $\mathrm{\Lambda }$ distribution and the fluid-vorticity field show a smaller tilt at higher collisional energies, which indicates that the smaller global polarization at higher collisional energies is caused by a smaller angular momentum deposition at midrapidity.

The Compton scattering cross section from ${}^4\mathrm{He}$ has been measured with high statistical accuracy over a scattering angle range of ${40}^{\circ }-{159}^{\circ }$ using a quasimonoenergetic 61-MeV photon beam at the High Intensity Gamma-Ray Source. The data are interpreted using a phenomenological model sensitive to the dipole isoscalar electromagnetic polarizabilities (${\alpha }_s$ and ${\beta }_s$) of the nucleon. These data can be fit with the model using values of ${\alpha }_s$ and ${\beta }_s$ that are consistent with the currently accepted values. These data will serve as benchmarks of future calculations from effective field theories and lattice quantum chromodynamics.

We present measurements of bulk properties of the matter produced in Au+Au collisions at $\sqrt{s_{NN}}=7.7,11.5,19.6,27$, and 39 GeV using identified hadrons (${\pi }^{\pm }$, $K^{\pm }$, $p$, and $\overline{p}$) from the STAR experiment in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). Midrapidity ($\left|y\right|<0.1$) results for multiplicity densities $dN/dy$, average transverse momenta $\langle p_T\rangle$, and particle ratios are presented. The chemical and kinetic freeze-out dynamics at these energies are discussed and presented as a function of collision centrality and energy. These results constitute the systematic measurements of bulk properties of matter formed in heavy-ion collisions over a broad range of energy (or baryon chemical potential) at RHIC.

Non-zero-range interactions are often incorporated into mean field theories through gradient terms. Here, a formalism is developed to incorporate such terms into hydrodynamics. These terms alter expressions for the entropy, chemical potential, temperature, and the stress-energy tensor. The formalism respects local conservation of energy, charge, and entropy. The formalism leads to static solutions where the temperature, chemical potential, and hydrodynamic acceleration all vanish, even when the density profile might be nonuniform. Profiles for a phase boundary and for correlation functions are calculated to illustrate the gradient modifications for various thermodynamic quantities. Also, for hydrodynamic calculations that add thermal noise to generate density-density correlations of the desired strength, an additional noise term is derived so that, at equilibrium, correlations are generated with both the correct size and length scale.

Background: Exotic nuclei, particularly those near the drip lines, are at the core of one of the fundamental questions driving nuclear structure and astrophysics today: What are the limits of nuclear binding? Exotic nuclei play a critical role in both informing theoretical models as well as in our understanding of the origin of the heavy elements.

Purpose: Our aim is to refine existing mass models through the training of an artificial neural network that will mitigate the large model discrepancies far away from stability.

Methods: The basic paradigm of our two-pronged approach is an existing mass model that captures as much as possible of the underlying physics followed by the implementation of a Bayesian neural network (BNN) refinement to account for the missing physics. Bayesian inference is employed to determine the parameters of the neural network so that model predictions may be accompanied by theoretical uncertainties.

Results: Despite the undeniable quality of the mass models adopted in this work, we observe a significant improvement (of about 40%) after the BNN refinement is implemented. Indeed, in the specific case of the Duflo-Zuker mass formula, we find that the rms deviation relative to experiment is reduced from ${\sigma }_{\mathrm{rms}}=0.503$ MeV to ${\sigma }_{\mathrm{rms}}=0.286$ MeV. These newly refined mass tables are used to map the neutron drip lines (or rather “drip bands”) and to study a few critical $r$-process nuclei.

Conclusions: The BNN approach is highly successful in refining the predictions of existing mass models. In particular, the large discrepancy displayed by the original “bare” models in regions where experimental data are unavailable is considerably quenched after the BNN refinement. This lends credence to our approach and has motivated us to publish refined mass tables that we trust will be helpful for future astrophysical applications.

We calculate the three-hole-line contributions to the binding energy of symmetric nuclear matter in the Brueckner-Bethe-Goldstone expansion using various modern nucleon-nucleon potentials of high precision. The relation with the correlation parameter $\kappa =\rho V_{\mathrm{core}}$ is examined. In all cases the three-hole-line contributions turn out to be sufficiently small, but no satisfactory saturation is obtained. This means that three-nucleon forces are essential for all considered potentials.

Chiral effective field theory (EFT) predictions are necessarily truncated at some order in the EFT expansion, which induces an error that must be quantified for robust statistical comparisons to experiment. In previous work, a Bayesian model for truncation errors of perturbative expansions was adapted to EFTs. The model yields posterior probability distribution functions (pdfs) for these errors based on expectations of naturalness encoded in Bayesian priors and the observed order-by-order convergence pattern of the EFT. A first application was made to chiral EFT for neutron-proton scattering using the semilocal potentials of Epelbaum, Krebs, and Meißner (EKM). Here we extend this application to consider a larger set of regulator parameters, energies, and observables as a general example of a statistical approach to truncation errors. The Bayesian approach allows for statistical validations of the assumptions and enables the calculation of posterior pdfs for the EFT breakdown scale. The statistical model is validated for EKM potentials whose convergence behavior is not distorted by regulator artifacts. For these cases, the posterior for the breakdown scale is consistent with EKM assumptions.

Sulphur isotopic ratio measurements may help to establish the astrophysical sites in which certain presolar grains were formed. Nova model predictions of the ${}^{34}\mathrm{S}/{}^{32}\mathrm{S}$ ratio are, however, unreliable due to the lack of an experimental ${}^{34}\mathrm{S}(p,\gamma ){}^{35}\mathrm{Cl}$ reaction rate. To this end, we have measured the ${}^{34}\mathrm{S}({}^3\mathrm{He},d){}^{35}\mathrm{Cl}$ reaction at 20 MeV using a high resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. Twenty-two levels over 6.2 MeV $<E_x\left({}^{35}\mathrm{Cl}\right)<7.4$ MeV were identified, ten of which were previously unobserved. Proton-transfer spectroscopic factors have been measured for the first time over the energy range relevant for novae. With this new spectroscopic information a new ${}^{34}\mathrm{S}(p,\gamma ){}^{35}\mathrm{Cl}$ reaction rate has been determined using a Monte Carlo method. Hydrodynamic nova model calculations have been performed using this new reaction rate. These models show that remaining uncertainties in the ${}^{34}\mathrm{S}(p,\gamma )$ rate affect nucleosynthesis predictions by less than a factor of 1.4, and predict a ${}^{34}\mathrm{S}/{}^{32}\mathrm{S}$ isotopic ratio of 0.014–0.017. Since recent type II supernova models predict ${}^{34}\mathrm{S}/{}^{32}\mathrm{S}=0.026-0.053$, the ${}^{34}\mathrm{S}/{}^{32}\mathrm{S}$ isotopic ratio may be used, in conjunction with other isotopic signatures, to distinguish presolar grains from oxygen-neon nova and type II supernova origin. Our results address a key nuclear physics uncertainty on which recent considerations discounting the nova origin of several grains depend.

We searched for the bound state of the neutron-rich $\mathrm{\Lambda }$-hypernucleus ${}_{\mathrm{\Lambda }}{}^6\mathrm{H}$, using the ${}^6\mathrm{Li}({\pi }^{-},K^{+})X$ double charge-exchange reaction at a ${\pi }^{-}$ beam momentum of $1.2\mathrm{GeV}/c$ at J-PARC. A total of $1.4\times {10}^{12}{\pi }^{-}$ was driven onto a ${}^6\mathrm{Li}$ target of 3.5-$\mathrm{g}/{\mathrm{cm}}^2$ thickness. No event was observed below the bound threshold, i.e., the mass of ${}_{\mathrm{\Lambda }}{}^4\mathrm{H}+2n$, in the missing-mass spectrum of the ${}^6\mathrm{Li}({\pi }^{-},K^{+})X$ reaction in the $2^{\circ }<{\theta }_{\pi K}<{20}^{\circ }$ angular range. Furthermore, no event was found up to $2.8\mathrm{MeV}/c^2$ above the bound threshold. We obtained the double-differential cross section spectra of the ${}^6\mathrm{Li}({\pi }^{-},K^{+})X$ reaction in the angular range of $2^{\circ }<{\theta }_{\pi K}<{14}^{\circ }$. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the ${}_{\mathrm{\Lambda }}{}^6\mathrm{H}$ hypernucleus bound state. In addition, not only the bound state region, but also the $\mathrm{\Lambda }$ continuum region and part of the ${\mathrm{\Sigma }}^{-}$ quasifree production region of the ${}^6\mathrm{Li}({\pi }^{-},K^{+}$) reaction were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the ${\mathrm{\Sigma }}^{-}$-nucleus optical potential for ${\mathrm{\Sigma }}^{-}-{}^5\mathrm{He}$ through spectrum shape analysis.

The $g$ factor of the first $2^{+}$ state of radioactive ${}^{136}\mathrm{Te}$ with two valence protons and two valence neutrons beyond double-magic ${}^{132}\mathrm{Sn}$ has been measured by the recoil in vacuum (RIV) method. The lifetime of this state is an order of magnitude longer than the lifetimes of excited states recently measured by the RIV method in Sn and Te isotopes, requiring a new evaluation of the free-ion hyperfine interactions and methodology used to determine the $g$ factor. The calibration data are reported and the analysis procedures are described in detail. The resultant $g$ factor has a similar magnitude to the $g$ factors of other nuclei with an equal number of valence protons and neutrons in the major shell. However, an unexpected trend is found in the $g$ factors of the $N=84$ isotones, which decrease from ${}^{136}\mathrm{Te}$ to ${}^{144}\mathrm{Nd}$. Shell model calculations with interactions derived from the CD Bonn potential show good agreement with the $g$ factors and $E2$ transition rates of $2^{+}$ states around ${}^{132}\mathrm{Sn}$, confirming earlier indications that ${}^{132}\mathrm{Sn}$ is a good doubly magic core.

An extension of the atomic mass surface in the region $A\approx 100$ was performed via measurements of the ${}^{100-102}\mathrm{Sr}$ and ${}^{100-102}\mathrm{Rb}$ masses with the ion-trap spectrometer ISOLTRAP at CERN-ISOLDE, including the first direct mass determination of ${}^{102}\mathrm{Sr}$ and ${}^{101,102}\mathrm{Rb}$. These measurements confirm the continuation of the region of deformation with the increase of neutron number, at least as far as $N=65$. To interpret the deformation in the strontium isotopic chain and to determine whether an onset of deformation is present in heavier krypton isotopes, a comparison is made between the experimental values and mean-field and beyond mean-field results available in the literature. To complete this comparison Hartree-Fock-Bogoliubov calculations for even and odd isotopes were performed, illustrating the competition of nuclear shapes in the region.

Predictions and comparisons of hadronic flow observables for Pb+Pb collisions at 2.76 and 5.02 TeV are presented using a hydrodynamics + hadronic cascade hybrid approach. Initial conditions are generated via a new formulation of the IP-Glasma model and then evolved using relativistic viscous hydrodynamics and finally fed into transport cascade in the hadronic phase. The results of this work show excellent agreement with the recent charged hadron anisotropic flow measurements from the ALICE Collaboration of Pb+Pb collisions at 5.02 TeV. Event-by-event distributions of charged hadron $v_n$, flow event-plane correlations, and flow factorization breaking ratios are compared with existing measurements at 2.76 TeV, and are predicted at 5.02 TeV. Further predictions of identified hadron observables (for both light and multistrange hadrons), such as $p_T$-spectra and anisotropic flow coefficients, are presented.

We report on the calculation of Gamow-Teller and double-$\beta$ decay properties for nuclei around ${}^{132}\mathrm{Sn}$ within the framework of the realistic shell model. The effective shell-model Hamiltonian and Gamow-Teller transition operator are derived by way of many-body perturbation theory, without resorting to the empirical effective quenching factor for the Gamow-Teller operator. The results are then compared with the available experimental data, in order to establish the reliability of our approach. This is a mandatory step before we apply the same methodology, in forthcoming studies, to the calculation of the neutrinoless double-$\beta$ decay nuclear matrix elements for nuclei that are currently considered among the best candidates for the detection of this process.

Measurement of $M$, the total multiplicity, for central collision between comparable mass heavy ions can provide a signature for first-order phase transition. The derivative of $M$ with respect to $E^{*}/A$, where $E^{*}$ is the excitation energy in the center of mass and $A$ is the total mass of the dissociating system, is expected to go through maximum as a function of $E^{*}$. Theoretical modeling shows that this is the energy where the specific heat $C_v$ maximizes, which typically happens at the first-order phase transition. The measurement of total $M$ is probably feasible in more than one laboratory.

Yrast and near-yrast levels up to spin values in excess of $I=30\hslash$ have been delineated in the doubly magic ${}^{208}\mathrm{Pb}$ nucleus following deep-inelastic reactions involving ${}^{208}\mathrm{Pb}$ targets and, mostly, 430-MeV ${}^{48}\mathrm{Ca}$ and 1440-MeV ${}^{208}\mathrm{Pb}$ beams. The level scheme was established up to an excitation energy of 16.4 MeV, based on multifold γ-ray coincidence relationships measured with the Gammasphere array. Below the well-known, 0.5-μs ${10}^{+}$ isomer, ten new transitions were added to earlier work. The delineation of the higher parts of the level sequence benefited from analyses involving a number of prompt- and delayed-coincidence conditions. Three new isomeric states were established along the yrast line with $I^{\pi }={20}^{-}$ (10 342 keV), ${23}^{+}$ (11 361 keV), and ${28}^{-}$ (13 675 keV), and respective half-lives of 22(3), 12.7(2), and 60(6) ns. Gamma transitions were also identified preceding in time the ${28}^{-}$ isomer; however, only a few could be placed in the level scheme and no firm spin-parity quantum numbers could be proposed. In contrast, for most states below this ${28}^{-}$ isomer, firm spin-parity values were assigned, based on total electron-conversion coefficients, deduced for low-energy $(<500\mathrm{keV})$ transitions from γ-intensity balances, and on measured γ-ray angular distributions. The latter also enabled the quantitative determination of mixing ratios. The transition probabilities extracted for all isomeric transitions in ${}^{208}\mathrm{Pb}$ have been reviewed and discussed in terms of the intrinsic structure of the initial and final levels involved. Particular emphasis was placed on the many observed $E3$ transitions as they often exhibit significant enhancements in strength [of the order of tens of Weisskopf units (W.u.)] comparable to the one seen for the neutron ${\mathrm{j}}_{15/2}\to {\mathrm{g}}_{9/2}$ $E3$ transition in ${}^{209}\mathrm{Pb}$. In this context, the enhancement of the 725-keV $E3$ transition (56 W.u.) associated with the decay of the highest-lying ${28}^{-}$ isomer observed in this work remains particularly challenging to explain. Large-scale shell-model calculations were performed with two approaches, a first one where the 1, 2, and 3 particle-hole excitations do not mix with one another, and another more complex one, in which such mixing takes place. The calculated levels were compared with the data and a general agreement is observed for most of the ${}^{208}\mathrm{Pb}$ level scheme. At the highest spins and energies, however, the correspondence between theory and experiment is less satisfactory and the experimental yrast line appears to be more regular than the calculated one. This regularity is notable when the level energies are plotted versus the $I(I+1)$ product and the observed, nearly linear, behavior was considered within a simple “rotational” interpretation. Within this approximate picture, the extracted moment of inertia suggests that only the 76 valence nucleons participate in the “rotation” and that the ${}^{132}\mathrm{Sn}$ spherical core remains inert.

We study the nuclear modifications of full jets and their structures in relativistic heavy-ion collisions, including the effect of hydrodynamic medium response to jet quenching. To study the evolutions of the full jet shower and the traversed medium with energy and momentum exchanges between them, we formulate a coupled jet-fluid model consisting of a set of jet transport equations and relativistic hydrodynamics equations with source terms. In our model, the full jet shower interacts with the medium and gets modified via collisional and radiative processes during the propagation. Meanwhile, the energy and momentum are deposited from the jet shower to the medium and then evolve with the medium hydrodynamically. The full jet defined by a cone size in the final state includes the jet shower and the particles produced from jet-induced flow. We apply our model to calculate the full jet energy loss and the nuclear modifications of jet rate and shape in Pb+Pb collisions at $2.76A\mathrm{TeV}$. It is found that the inclusion of jet-induced flow contribution leads to stronger jet-cone size dependence for jet energy loss and jet suppression. Jet-induced flow also has a significant contribution to jet shape function and dominates at large angles away from the jet axis.

Recent measurements at the Large Hadron Collider involve the correlation of different azimuthal flow harmonics $v_n$. These new observables add constraints to theoretical models and probe aspects of the system that are independent of traditional single-harmonic measurements such as two-particle and multiparticle cumulants $v_n\left\{m\right\}$. Many of these new observables have not yet been measured at the Relativistic Heavy Ion Collider (RHIC), leaving an opportunity to make predictions as a test of models across energies. We make predictions using NeXSPheRIO, a hydrodynamical model which has accurately reproduced a large set of single-harmonic correlations in a large range of transverse momenta and centralities at RHIC. Our predictions thus provide an important baseline for comparison to correlations of flow harmonics, which contain nontrivial information about the initial state as well as quark-gluon plasma transport properties. We also point out significant biases that can appear when using wide centrality bins and nontrivial event weighting, necessitating care in performing experimental analyses and in comparing theoretical calculations to these measurements.

By combining microscopically calculated level densities with the Metropolis walk method, we develop a consistent framework for treating the energy and angular-momentum dependence of the nuclear shape evolution in the fission process. For each nucleus under consideration, the level density is calculated microscopically for each of more than five million shapes with a recently developed combinatorial method. The method employs the same single-particle levels as those used for the extraction of the pairing and shell contributions to the macroscopic-microscopic potential-energy surface. Containing no new parameters, the treatment is suitable for elucidating the energy dependence of the dynamics of warm nuclei on pairing and shell effects. It is illustrated for the fission fragment mass distribution for several uranium and plutonium isotopes of particular interest.