In high-energy heavy-ion collisions, structures in the initial collision zone are a matter of intense investigation, both from theory and experimental points of views. A large number of models have been developed to represent the initial state of the collision including the Glauber model and color glass condensate (CGC), among others. Another important aspect of the study is to investigate proper observables that will be sensitive to the initial collision zone. In this work, we discuss a formalism to implement the spatial clusters at the partonic level in the string melting version of the ampt model for PbPb collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. These clusters are then propagated through the ampt hadronization scheme. Principal component analysis (PCA) has been used on the $\eta$, $\varphi$, and $p_T$ distributions of the produced charged particles and the eigenvalues have been compared before and after the implementation of the clustering. It is found that for all these three different distributions, all the prominent PCA modes show sensitivity to the clustering. A centrality dependent study has also been performed on those eigenvalues.

Currently the Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan is exploring a new region of the quantum chromodynamic phase diagram at large baryon densities that approaches nuclear astrophysics regimes. This provides an opportunity to study relativistic hydrodynamics in a regime where the net conserved charges of baryon number, strangeness, and electric charge play a role, which will significantly change the theoretical approach to simulating the baryon-dense quark-gluon plasma. Here we detail many of the important changes needed to adapt both initial conditions and the medium to baryon-rich matter. Then, we make baseline predictions (i.e., assuming a high-energy approach) for the elliptical flow and fluctuations based on extrapolating the physics at Large Hadron Collider and top RHIC energies to support future analyses of where and how the new baryon-dense physics causes these extrapolations to break down. First we compare eccentricities across beam energies, exploring their underlying assumptions; we find the extrapolated initial state is predicted to be nearly identical to that at AuAu $\sqrt{s_{NN}}=200$ GeV. Then we make exploratory predictions of the final flow harmonic based on linear $+$ cubic response. We discuss preliminary STAR results in order to determine the implications that they have for linear $+$ cubic response coefficients at the lowest beam energy of AuAu $\sqrt{s_{NN}}=7$ GeV.

Under the assumption that a quark-gluon plasma (QGP) droplet is produced and its evolution can be described by hydrodynamics in $p+A$ collisions, $\gamma$-triggered hadron spectra are studied within a next-to-leading-order perturbative QCD parton model with the medium-modified parton fragmentation functions. The initial conditions and space-time evolution of the small QGP droplet are provided by the superSONIC hydrodynamic model simulations and parton energy loss in such a medium is described by the high-twist (HT) approach. The range of scaled jet transport coefficient ${\widehat{q}}_0/T_0^3$ in this HT approach is extracted from single hadron suppression in $A+A$ collisions with similar initial medium temperature as in $p+A$ collisions. Numerical results for this scenario show that $\gamma$-hadron spectra at $p_{\mathrm{T}}^{\gamma }=12\text{–}40\mathrm{GeV}/c$ are suppressed by 5–15% in the most central 0–10% $p+\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. The suppression becomes weaker at higher transverse momentum of the $\gamma$ trigger. As a comparison, $\gamma$-hadron suppression in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ and 5.02 TeV is also predicted.

Background: The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). An azimuthal correlator called $R_{{\mathrm{\Psi }}_m}$ was proposed to measure the CME. By observing the same $R_{{\mathrm{\Psi }}_2}$ and $R_{{\mathrm{\Psi }}_3}$ (convex) distributions from A Multi-Phase Transport (ampt) model, by contrasting data and model as well as large and small systems and by event shape engineering (ESE), a recent preprint (arXiv:2006.04251v1) from STAR suggests that the $R_{{\mathrm{\Psi }}_m}$ observable is sensitive to the CME signal and relatively insensitive to backgrounds, and their $\text{Au}+\text{Au}$ data are inconsistent with known background contributions.

Purpose: We examine those claims by studying the robustness of the $R_{{\mathrm{\Psi }}_m}$ observable using ampt as well as toy model simulations. We compare $R_{{\mathrm{\Psi }}_m}$ to the more widely used $\mathrm{\Delta }\gamma$ azimuthal correlator to identify their commonalities and differences.

Methods: We use ampt to simulate $\text{Au}+\text{Au}$, $p+\text{Au}$, and $d+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$, and study the responses of $R_{{\mathrm{\Psi }}_m}$ to anisotropic flow backgrounds in the model. We also use a toy model to simulate resonance flow background and input CME signal to investigate their effects in $R_{{\mathrm{\Psi }}_2}$. Additionally we use the toy model to perform an ESE analysis to compare with STAR data as well as predict the degree of sensitivity of $R_{{\mathrm{\Psi }}_2}$ to isobar collisions with the event statistics taken at RHIC.

Results: Our ampt results show that the $R_{{\mathrm{\Psi }}_2}$ in $\text{Au}+\text{Au}$ collisions is concave and apparently different from $R_{{\mathrm{\Psi }}_3}$, in contradiction to the findings in STAR's preprint, while the $R_{{\mathrm{\Psi }}_2}$ in $p+\text{Au}$ and $d+\text{Au}$ collisions are slightly concave. Our toy model ESE analysis indicates that the $R_{{\mathrm{\Psi }}_2}$ is sensitive to the event-by-event anisotropy $q_2$ as well as the elliptic flow parameter $v_2$. The toy model results further show that $R_{{\mathrm{\Psi }}_2}$ depends on both the CME signal and the flow backgrounds, similar to the $\mathrm{\Delta }\gamma$ observable. It is found that the $R_{{\mathrm{\Psi }}_2}$ and $\mathrm{\Delta }\gamma$ observables show similar sensitivities and centrality dependencies in isobar collisions.

Conclusions: Our ampt results contradict those from a recent preprint by STAR. Our toy model simulations demonstrate that $R_{{\mathrm{\Psi }}_2}$ is sensitive to both the CME signal and physics backgrounds. Toy model simulations of isobar collisions show similar centrality dependence and magnitudes for the relative $R_{{\mathrm{\Psi }}_2}$ strengths as well as the relative $\mathrm{\Delta }\gamma$ strengths. We conclude that $R_{{\mathrm{\Psi }}_2}$ and the inclusive $\mathrm{\Delta }\gamma$ are essentially the same.

Droplets of absolutely stable strange quark matter (strangelets) immersed in a lepton background may be the energetically preferred composition of strange star crusts and may also constitute the interior of a new class of stellar objects known as strangelet dwarfs. In this work we calculate the surface tension $\sigma$ and the curvature coefficient $\gamma$ of charged strangelets as a function of the baryon number density, the temperature, the chemical potential of trapped neutrinos, the strangelet size, the electric potential, and the electric charge at their boundary. Strange quark matter in chemical equilibrium and with global electric charge neutrality is described within the MIT bag model. We focus on three different astrophysical scenarios, namely, cold strange stars, protostrange stars, and postmerger strange stars, characterized by the temperature and the amount of neutrinos trapped in the system. Finite-size effects are implemented within the multiple reflection expansion framework. We find that $\sigma$ decreases significantly as the strangelet's boundary becomes more positively charged. This occurs because $\sigma$ is dominated by the contribution of $s$ quarks which are the most massive particles in the system. Negatively charged $s$-quarks are suppressed in strangelets with a large positive electric charge, diminishing their contribution to $\sigma$ and resulting in smaller values of the total surface tension. We also verify that the more extreme astrophysical scenarios, with higher temperatures and higher neutrino chemical potentials, allow higher positive values of the strangelet's electric charge at the boundary and consequently smaller values of $\sigma$. In contrast, $\gamma$ is strongly dominated by the density of light ($u$ and $d$) quarks and is quite independent of the charge-per-baryon ratio, the temperature and neutrino trapping. We discuss the relative importance of surface and curvature effects as well as some astrophysical consequences of these results.

Background: In the continuum-discretized coupled-channel method, a breakup cross section (BUX) is obtained as an admixture of several components of different channels in multichannel scattering.

Purpose: Our goal is to propose an approximate way of decomposing the discretized BUX into components of each channel. This approximation is referred to as the “probability separation (P separation).”

Method: As an example, we consider ${}^{11}\mathrm{Be}$ scattering by using the three-body model with core excitation (${}^{10}\mathrm{Be}+n+T$, where $T$ is a target). The structural part is constructed by the particle-rotor model and the reaction part is described by the distorted-wave Born approximation.

Results: The validity of the P separation is tested by comparing with the exact calculation. The approximate way reproduces the exact BUXs well regardless of the configurations and/or the resonance positions of ${}^{11}\mathrm{Be}$.

Conclusion: The method proposed here can be an alternative approach for decomposing discretized BUXs into components in four- or five-body scattering where the strict decomposition is hard to perform.

The nuclear reaction study with weakly bound heavy nuclei is an enduring open question due to the scarcity of experimental data. In view of this, an experiment has been performed to study the fusion dynamics of weakly bound ${}^6\mathrm{Li}$ projectile in ${}^6\mathrm{Li}+{}^{89}\mathrm{Y}$ reaction at energies slightly above the Coulomb barrier. The off-beam $\gamma$-spectroscopic technique has been used to measure the cross sections of populated residues in ${}^6\mathrm{Li}+{}^{89}\mathrm{Y}$ reaction, and the data are analyzed using equilibrium and pre-equilibrium models in the framework of the empire3.2.2 code. It has been found that complete fusion (CF) and incomplete fusion (ICF) of ${}^6\mathrm{Li}$ play a substantial role in producing the residues. Subsequently, the ICF cross section, which is a model-dependent quantity, has been extracted. The strength of incomplete fusion has been deduced and compared with the existing data from ${}^7\mathrm{Li}+{}^{89}\mathrm{Y}$ reaction. The ICF strength is found to be higher for ${}^6\mathrm{Li}+{}^{89}\mathrm{Y}$ as compared with the ${}^7\mathrm{Li}+{}^{89}\mathrm{Y}$ system, which possibly indicates the role of the projectile's structure on the ICF occurrence probability. The occurrence of ICF below a critical angular momentum is also anticipated for both ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$ interaction with ${}^{89}\mathrm{Y}$.

We study the $\mathrm{\Lambda }$ hypernuclei of C and B isotopes by the Hartree-Fock model with Skyrme-type nucleon-nucleon and $\mathrm{\Lambda }$-nucleon interactions. The calculated $\mathrm{\Lambda }$ binding energies agree well with the available experiment data. We found halo structure in the $\mathrm{\Lambda }1p$ state with extended wave functions beyond the nuclear surface in the light C and B isotopes. We also found the enhanced electric-dipole transition between $\mathrm{\Lambda }1p$ and $1s$ states, which could be the evidence for this hyperon halo structure.

A ${}^{160}\mathrm{Gd}$ beam was accelerated to an energy of 1000 MeV and, separately, bombarded thick targets of ${}^{154}\mathrm{Sm}$ and ${}^{164}\mathrm{Dy}$ in order to observe neutron-rich, rare-earth nuclei via deep-inelastic collision processes. Gammasphere was utilized to observe $\gamma$-ray emissions. Many new states and transitions were observed in ${}^{160}\mathrm{Gd}$ as a result of so-called unsafe Coulomb excitation. The ground-state band in ${}^{160}\mathrm{Gd}$ has been extended to $I^{\pi }={20}^{+}$ and a rotational band based on the $K^{\pi }=4^{+}$ state, previously associated with a hexadecapole vibration, was observed up to ${18}^{+}$. The quasiparticle configuration of the $K^{\pi }=4^{+}$ band has been determined, and its unusual alignment behavior may result from a possible quenching of static neutron pairing. In addition, the band based on the [523]5/2 quasineutron orbital in ${}^{161}\mathrm{Gd}$ was extended from $11/2^{-}$ to $33/2^{-}$ and also displays the same unusual alignment behavior.

The properties of toroidal hyperheavy even-even nuclei and the role of toroidal shell structure are extensively studied within covariant density functional theory. The general trends in the evolution of toroidal shapes in the $Z\approx 130\text{–}180$ region of the nuclear chart are established for the first time. These nuclei are stable with respect to breathing deformations. The most compact fat toroidal nuclei are located in the $Z\approx 136,N\approx 206$ region of the nuclear chart, but thin toroidal nuclei become dominant with increasing proton number and toward proton and neutron drip lines. The roles of toroidal shell structure, its regularity, supershell structure, and shell gaps as well as the role of different groups of the pairs of the orbitals in its formation are investigated in detail. The lowest in energy solutions at axial symmetry are characterized either by large shell gaps or low density of the single-particle states in the vicinity of the Fermi level in at least one of the subsystems (proton or neutron). Related quantum shell effects are expected to act against the instabilities in breathing and sausage deformations for these subsystems. The investigation with a large set of covariant energy density functionals reveals that substantial proton $Z=154$ and 186 and neutron $N=228$, 308, and 406 spherical shell gaps exist in all functionals. The nuclei in the vicinity of the combination of these particle numbers form the islands of stability of spherical hyperheavy nuclei. The study suggests that the $N=210$ toroidal shell gap plays a substantial role in the stabilization of fat toroidal nuclei.

The spontaneous fission (SF) analysis of even mass ${}^{242-260}\mathrm{Fm}$ isotopes is carried out using a preformed cluster model based on quantum mechanical fragmentation theory. The deformation effects are included up to the quadrupole (${\beta }_2$) deformed nuclei with optimum orientations (${\theta }_i^{\mathrm{opt}.}$) leading to hot-compact (side-to-side) and cold-elongated (tip-to-tip) configurations. The spherical and hot-compact deformed configurations of decay fragments result in the symmetric fragment mass distributions for Fm isotopes; however, the symmetric peak gets sharper with an increase in the neutron ($N$) number of the parent nucleus. In the case of cold orientations, a transition from two-peaked (asymmetric fission) to three-peaked (multimodal fission) mass distribution is observed with an increase in the mass number of Fm. The SF half-lives ($T_{1/2}^{\mathrm{SF}}$) are calculated using the neck-length parameter ($\mathrm{\Delta }R$) for ${}^{242-260}\mathrm{Fm}$ isotopes and compared with the experimental data. Besides this, the induced fission of Fm isotopes is studied within the dynamical cluster-decay model. The energy dependence of fission fragment mass distributions and the isotopic dependence is analyzed at energy range $E^{*}=5$–42 MeV. In addition, the role of temperature-dependent deformations in the fission dynamics is also explored.

We present a scattering model for nuclei with similar masses. In this three-body model, the projectile has a $\mathrm{core}+\mathrm{valence}$ structure, whereas the target is identical to the core nucleus. The three-body wave functions must be symmetrized for the exchange of the cores. This property gives rise to nonlocal potentials, which are computed without approximation. The present model is an extension of the continuum discretized coupled channel formalism, with an additional treatment of core exchange. We solve the coupled-channel system, including nonlocal terms, by the $R$-matrix method using Lagrange functions. This model is applied to the ${}^{13}\mathrm{C}+{}^{12}\mathrm{C}$, ${}^{13}\mathrm{N}+{}^{12}\mathrm{C}$, and ${}^{16}\mathrm{O}+{}^{12}\mathrm{C}$ systems. Experimental scattering cross sections are fairly well reproduced without any parameter fitting. The backward-angle enhancement of the elastic cross sections is due to the nonlocal potential. We discuss in more detail the various nonlocal contributions and present effective local potentials.

The beam energy scan (BES) program at the BNL Relativistic Heavy Ion Collider (RHIC) was extended to energies below $\sqrt{s_{NN}}=7.7$ GeV in 2015 by successful implementation of the fixed-target mode of operation in the STAR (Solenoidal Tracker At RHIC) experiment. In this mode, ions circulate in one ring of the collider and interact with a stationary target at the entrance of the STAR time projection chamber. The first results for $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=4.5$ GeV are presented, demonstrating good performance of all the relevant detector subsystems in fixed-target mode. Results presented here include directed and elliptic flow of identified hadrons, and radii from pion femtoscopy. The latter, together with recent HADES results, reveal a long-sought peak structure that may be caused by the system evolving through a first-order phase transition from quark-gluon plasma to the hadronic phase. Directed and elliptic flow for pions are presented for the first time at this beam energy. Pion and proton elliptic flow show behavior which hints at constituent quark scaling, and demonstrate that a definitive conclusion will be achievable using the full statistics of the ongoing second phase of BES (BES-II). In particular, BES-II to date has recorded fixed-target data sets with two orders of magnitude more events at each of nine energies between $\sqrt{s_{NN}}=3.0$ and 7.7 GeV.

Newly observed decay schemes of the nuclei ${}^{137}\mathrm{Sb}$ and ${}^{138}\mathrm{Sb}$ are reported. The neutron-rich Sb isotopes were produced by the in-flight fragmentation of a ${}^{238}\mathrm{U}$ primary beam with an energy of 345 MeV/nucleon. Several new excited states of ${}^{137}\mathrm{Te}$ with tentatively assigned spin-parities of $(5/2^{-})$, $(9/2^{-})$, and $(7/2)$ have been established which play an important role in the evolution of neutron levels beyond $N=82$. The study of the $\beta$ decay of ${}^{138}\mathrm{Sb}$ led to a considerable extension of the level scheme of ${}^{138}\mathrm{Te}$ including the identification of several nonyrast states. The structure of ${}^{137}\mathrm{Te}$ and ${}^{138}\mathrm{Te}$ is discussed on the basis of large-scale shell-model calculations performed using two different effective interactions.

A quark-meson coupling model based on the quark model proposed by Bogoliubov for the description of the quark dynamics is developed and applied to the description of neutron stars. Starting from a SU(3) symmetry approach, it is shown that this symmetry has to be broken in order to satisfy the constraints set by the hypernuclei and by neutron stars. The model is able to describe observations such as two-solar-mass stars or the radius of canonical neutron stars within the uncertainties presently accepted. If the optical potentials for $\mathrm{\Lambda }$ and $\mathrm{\Xi }$ hyperons in symmetric nuclear matter at saturation obtained from laboratory measurements of hypernuclei properties are imposed, the model predicts no strangeness inside neutron stars.

The study of the CNO cycle involves the examination of the proton radiative capture, or the $(p,\gamma )$ reactions below 2 MeV. The astrophysical $\mathcal{S}$ factor characterizing the $(p,\gamma )$ reaction is usually reduced to the electric dipole transition $E1$ from the scattering state to the bound state. In this work, the partial scattering and the single-particle bound wave functions in the reduced matrix element of the transition are obtained from the single self-consistent mean-field potential deduced from the Skyrme Hartree-Fock calculation. The astrophysical $\mathcal{S}$ factors of the $(p,\gamma )$ reactions in the CNO cycle were successfully reproduced. The self-consistent Hartree-Fock calculation from the discrete to the continuum is a promising approach for the microscopic analysis of the nucleon-induced reactions in nuclear astrophysics.

Energy dependence of fission observables is a key issue for wide nuclear applications. We studied real-time fission dynamics from low-energy to high excitations in the compound nucleus ${}^{240}\mathrm{Pu}$ with the time-dependent Hartree-Fock $+$ BCS approach. It is shown that the evolution time of the later phase of fission towards scission is considerably lengthened at finite temperature. As the role of dynamical pairing is vanishing at high excitations, the random transition between single-particle levels around the Fermi surface to mimic thermal fluctuations is indispensable to drive fission. The obtained fission yields and total kinetic energies with fluctuations can be divided into two asymmetric scission channels, namely, S1 and S2, which explain well experimental results and give microscopic support to the Brosa model. With increasing fluctuations, the S2 channel takes over the S1 channel and the spreading fission observables are obtained.

The formation of $\alpha$ particles on nuclear surfaces has remained a fundamental problem since the dawn of nuclear physics. This $\alpha$-particle formation strongly affects the $\alpha$-decay lifetimes of heavy and superheavy elements, level scheme of light nuclei, and synthesis of elements in stars. However, despite its importance, the $\alpha$-particle formation in medium-mass nuclei is seldom investigated. Based on the ${}^{48}\mathrm{Ti}(p,p\alpha ){}^{44}\mathrm{Ca}$ reaction analysis, this study reports that $\alpha$-particle formation in the medium-mass ${}^{48}\mathrm{Ti}$ nucleus is pronounced more compared to that expected through mean-field approximations. Moreover, the estimated average distance between the $\alpha$ particle and residue equals approximately 4.5 fm. This result poses a challenge to describe the four nucleon correlations using microscopic nuclear models.

Predictions are made for the global polarization of $\mathrm{\Lambda }$ hyperons in $\mathrm{Au}+\mathrm{Au}$ collisions at moderately relativistic collision energies, 2.4 $\le \sqrt{s_{NN}}\le$ 11 GeV. These are based on the thermodynamic approach to the global polarization incorporated into the model of the three-fluid dynamics. Centrality dependence of the polarization is studied. It is predicted that the polarization reaches a maximum or a plateau (depending on the equation of state and centrality) at $\sqrt{s_{NN}}\approx$ 3 GeV. It is found that the global polarization increases with increasing width of the rapidity window around the midrapidity.

Mass measurements of the nuclides ${}^{69}\mathrm{As},{}^{70,71}\mathrm{Se}$, and ${}^{71}\mathrm{Br}$, produced via fragmentation of a ${}^{124}\mathrm{Xe}$ primary beam at the Fragment Separator (FRS) at GSI, have been performed with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher with an unprecedented mass resolving power of almost $1000000$. Such high resolving power is the only way to achieve accurate results and resolve overlapping peaks of short-lived exotic nuclei, whose total number of accumulated events is always limited. For the nuclide ${}^{69}\mathrm{As}$, this is the first direct mass measurement. A mass uncertainty of 22 keV was achieved with only ten events. For the nuclide ${}^{70}\mathrm{Se}$, a mass uncertainty of 2.6 keV was obtained, corresponding to a relative accuracy of $\delta m/m=4.0\times {10}^{-8}$, with less than 500 events. The masses of the nuclides ${}^{71}\mathrm{Se}$ and ${}^{71}\mathrm{Br}$ have been measured with an uncertainty of 23 and 16 keV, respectively. Our results for the nuclides ${}^{70,71}\mathrm{Se}$ and ${}^{71}\mathrm{Br}$ are in good agreement with the 2016 Atomic Mass Evaluation, and our result for the nuclide ${}^{69}\mathrm{As}$ resolves the discrepancy between the previous indirect measurements. We measured also the mass of the molecule ${}^{14}\mathrm{N}{}^{15}\mathrm{N}{}^{40}\mathrm{Ar}$ ($A=69$) with a relative accuracy of $\delta m/m=1.7\times {10}^{-8}$, the highest yet achieved with an MR-TOF-MS. Our results show that the measured restrengthening of the proton-neutron interaction ($\delta V_{pn}$) for odd-odd nuclei along the $N=Z$ line above $Z=29$ (recently extended to $Z=37$) is hardly evident at the $N-Z=2$ line, and not evident at the $N-Z=4$ line. Nevertheless, detailed structure of $\delta V_{pn}$ along the $N-Z=2$ and $N-Z=4$ lines, confirmed by our mass measurements, may provide a hint regarding the ongoing $\approx 500$ keV discrepancy in the mass value of the nuclide ${}^{70}\mathrm{Br}$, which prevents including it in the world average of $Ft$ value for superallowed $0^{+}\to 0^{+} \beta$ decays. The reported work sets the stage for mass measurements with the FRS Ion Catcher of nuclei at and beyond the $N=Z$ line in the same region of the nuclear chart, including the nuclide ${}^{70}\mathrm{Br}$.