Zr isotopes are important nuclides on the $s$-process path, and their neutron capture cross sections are of great significance for studying the evolution of heavy nuclei in the universe. In this work, the cross section of the ${}^{91}\mathrm{Zr}(n,\gamma ){}^{92}\mathrm{Zr}$ reaction was measured at the China Spallation Neutron Source (CSNS) Back-n platform from 0.82 keV to 229 keV, essentially covering the energy range of astrophysical interest. In the experiment, a high-purity germanium detector with excellent energy resolution was used, which allowed for the accurate identification of characteristic $\gamma$ rays emitted during ${}^{92}\mathrm{Zr}$'s de-excitation, thereby enabling precise measurement of the neutron capture cross section. Furthermore, the measurement yielded the Maxwellian-averaged cross section of $56.4\pm 5.0$ mb calculated at $kT=30$ keV.

In this work we introduce a worldline-based fermion Monte Carlo algorithm for studying few body quantum mechanics of self-interacting fermions in the Hamiltonian lattice formulation. Our motivation to construct the method comes from our interest in studying renormalization of chiral nuclear effective-field theory with lattice regularization. In particular we wish to apply our method to compute the lattice spacing dependence of local lattice interactions as we take the continuum limit of the lattice theory. Our algorithm can compute matrix elements of the operator $exp(-\beta H)$, where $H$ is the lattice Hamiltonian and $\beta$ is a free real parameter. These elements help us compute deep bound states that are well separated from scattering states even at values of $\beta$ which are not very large. Computing these bound-state energies accurately can help us study renormalization of the lattice theory. In addition to developing the algorithm, in this work we also introduce a finite-volume renormalization scheme for the lattice Hamiltonian of the leading pionless effective-field theory and show how it would work in the one- and two-body sectors.

We calculate neutron-neutron relative-energy distributions of $s$-wave two-neutron ($2n$) halo nuclei using halo effective field theory (halo EFT) at leading order. At this order these systems are described by the $2n$ separation energy, the neutron-core ($nc$) virtual-state energy, and the neutron-neutron ($nn$) scattering length. We focus on knockout reactions where the removal of the core is sudden, such that the final-state interactions are dominated by the $nn$ interaction. We consider the neutron relative-energy distribution for the nuclei ${}^{11}\mathrm{Li}$, ${}^{14}\mathrm{Be}$, ${}^{17}\mathrm{B}$, ${}^{19}\mathrm{B}$, and ${}^{22}\mathrm{C}$. We show that the ground-state neutron momentum distributions of all these nuclei stem from a single curve, which can be obtained by taking both the neutron-core and neutron-neutron interaction to the unitary limit. This universal description can be extended to the final distribution measured in experiment by including $nn$ final-state interactions via the approximate technique of enhancement factors. For all the nuclei considered we find good agreement between the full leading-order halo EFT calculation and the universal prediction obtained in this way. The universality of the ground-state momentum distribution in two-neutron Borromean halos can thus be tested by dividing the experimental results from sudden core knockout by the enhancement factor and comparing them to the unitary-limit prediction.

The ground-state decay width of the two-phonon $J^{\pi }=1^{-}$, 4742 keV state of ${}^{88}\mathrm{Sr}$ has been determined with the relative self-absorption method combined with a monoenergetic photon beam. This width is important to determine the decay transition strengths into the ground state and the one-phonon $2_1^{+}$ and $3_1^{-}$ levels which are required to verify the two-phonon character of the $J^{\pi }=1^{-}$ state. The experiment was performed at the High Intensity $\gamma$-ray Source ($\mathrm{HI}\gamma \mathrm{S}$) using a novel experimental approach to adapt the relative self-absorption method to monoenergetic photon beams. The result for the ground-state decay width is, thus, independent of any calibration standard and confirms the two-phonon character of the ${}^{88}\mathrm{Sr},J^{\pi }=1^{-}$, 4742 keV state within an improved uncertainty.

The ($d,{}^2\mathrm{He}$) reaction in inverse kinematics has been developed for experiments with rare-isotope beams to constrain electron-capture rates needed for astrophysical simulations of processes in dense nuclear environments such as supernovae and neutron star crusts. The first experiment focused on the measurement of the ${}^{14}\mathrm{O}(d,{}^2\mathrm{He})$ and ${}^{13}\mathrm{N}(d,{}^2\mathrm{He})$ reactions in inverse kinematics, utilizing the active-target time-projection chamber placed in front of the S800 magnetic spectrograph. This work focuses on the experimental and analysis details, and presents the results for the ${}^{13}\mathrm{N}(d,{}^2\mathrm{He})$ reaction, which is important for constraining electron captures rates on ${}^{13}\mathrm{N}$ in the preexplosion convective phase of Type Ia supernova. The extracted Gamow-Teller transition strengths associated with electron capture on ${}^{13}\mathrm{N}$ are consistent with those previously obtained from the analog transitions from ${}^{13}\mathrm{C}$. The successful development of the ($d,{}^2\mathrm{He}$) reaction in inverse kinematics presents a novel opportunity for performing experiments aimed at constraining electron-capture rates in nuclei far from stability.

We study the evolution of the spin alignment of neutral $\rho$ mesons in a pion gas using spin kinetic or Boltzmann equations. The $\rho \pi \pi$ coupling is given by the chiral effective theory. The collision terms at the leading and next-to-leading order in spin Boltzmann equations are derived. The evolution of the spin density matrix of the neutral $\rho$ meson is simulated with different initial conditions. The numerical results show that the interaction of pions and neutral $\rho$ mesons creates very small spin alignment in the central rapidity region if there is no $\rho$ meson in the system at the initial time. Such a small spin alignment in the central rapidity region will decay rapidly toward zero in later time. If there are $\rho$ mesons with a sizable spin alignment at the initial time the spin alignment will also decrease rapidly. We studied the effect on ${\rho }_{00}$ from the elliptic flow of pions in the blast wave model. With vanishing spin alignment at the initial time, the deviation of ${\rho }_{00}$ from 1/3 is positive but very small. The effect of tensor polarizations of $\rho$ mesons on $\gamma$ correlator observables for CME has also been investigated.

We argue that measurements of forward neutrons from nuclear breakup in inclusive high energy photon-nucleus ($\gamma A$) scattering provide a novel way to study small-$x$ dynamics of QCD in heavy-ion ultraperipheral collisions (UPCs). Using models for hadronic fluctuations of the real photon and neutron emission in nuclear fragmentation, we calculate the distribution over the number of evaporation neutrons produced in $\gamma \text{Pb}$ collisions at the Large Hadron Collider. We show that it is correlated with the number of wounded nucleons (inelastic collisions) and, hence, can constrain the mechanism of nuclear shadowing and its $x$ dependence.

We investigate the neutrino elastic differential cross section (NDCS) and corresponding mean free path for neutral current scattering in the dense matter of a neutron star. A wide range of observed neutron star (NS) masses is considered, including the presence of $\mathrm{\Lambda }$, ${\mathrm{\Xi }}^{-}$, and ${\mathrm{\Xi }}^0$ hyperons in the heaviest stars. Their presence significantly decreases the total neutrino mean free path in the heavier stars.

Studies of exotic hadrons such as the ${\chi }_{c1}\left(3872\right)$ state provide crucial insights into the fundamental force governing the strong interaction dynamics, with an emerging frontier to investigate their production in high energy collisions where a partonic medium is present. The latest experimental measurements from the Large Hadron Collider show an intriguing evolution pattern of the ${\chi }_{c1}\left(3872\right)$-to-$\psi \left(2S\right)$ yield ratio from proton-proton collisions with increasing multiplicities toward proton-lead and lead-lead collisions. Here we propose a mechanism of medium-assisted enhancement for the ${\chi }_{c1}\left(3872\right)$ production, which competes with the more conventional absorption-induced suppression and results in a nonmonotonic trend from small to large colliding systems. Realistic simulations from this model offer a quantitative description of all available data. Predictions are made for the centrality dependence of this observable in PbPb collisions as well as for its system-size dependence from OO and ArAr to XeXe and PbPb collisions. In both cases, a nonmonotonic behavior emerges as the imprint of the competition between enhancement and suppression and can be readily tested by future data.

Recent experiments using advanced laser spectroscopy technique revealed that the charge radii of neutron-deficient gold (Au) isotopes exhibit significant changes in ground state deformation: odd-even shape staggering in the $N=98\text{–}100$ region and abrupt change of charge radii from $N=108$. In this study, we examine the abnormal evolution of the nuclear charge radii. To understand the nuclear structure underlying this phenomenon, we exploit the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc). The significant change in mean-squared charge radii ($\delta \langle r^2\rangle$) turns out to originate from nuclear shape transitions between prolate deformation and small oblate deformation due to the shape coexistence possibility. We elucidate the nuclear shape evolution by analyzing the evolution of occupation probability for single-particle states. In addition, the abrupt kink structure in the nuclear charge radius of lead (Pb) isotopes near the $N=126$ shell is also investigated and reproduced quite well.

A simple and efficient method to treat nuclear pairing correlations within a simple Hartree-Fock–plus-BCS description is proposed and discussed. It relies on the fact that the intensity of pairing correlations depends crucially on level densities around the Fermi surface $\left[\rho \left(e_F\right)\right]$ and that any fitting of nuclear energies as functions of the nucleon numbers is akin to a semiclassical average, smoothing out their quantal structure. A particular attention has been paid to two points generally ignored in previous similar approaches. One is a correction advocated by P. Möller and J. R. Nix [Nucl. Phys. A 536, 20 (1992)] taking into account the fact that the data included into the fit correspond to $\rho \left(e_F\right)$ values systematically lower than average. The second is due to a systematic overestimation of the proton single particle (sp) level density at the Fermi surface resulting from the local Slater approximation of the Coulomb exchange terms in use in most microscopic descriptions. Our approach is validated by the agreement with data of corresponding calculated moments of inertia of well and rigidly deformed rare-earth nuclei, evaluated according to the Inglis-Belyaev ansatz with some crude Thouless-Valatin corrections. Indeed, the agreement found is at least of the same quality as that resulting from a specific fit of the pairing intensities to these particular pieces of data. While this approach is currently limited to the very simple seniority force pairing treatment, it may serve as a starting point to define pairing residual interactions from averaged odd-even mass differences data, using merely average sp level densities associated with the calculated canonical basis.

The low energy of the isomeric state of the radionuclide thorium-229 (${}^{229}\mathrm{Th}$) makes it highly promising for applications in fundamental physics, precision metrology, and quantum technologies. The direct access to the isomer state from the ground state has attracted significant attention. Here, we propose a tabletop approach utilizing the scanning tunneling microscope technique to induce excitation of a single ${}^{229}\mathrm{Th}$ nucleus. With achievable parameters, the isomeric excitation rate is advantageous over existing methods, allowing the excitation and control of ${}^{229}\mathrm{Th}$ on the single-nucleus level. It offers the unique potential of exciting and detecting subsequent $\gamma$ decay from a single nucleus, providing a new direction for future experimental investigation of the ${}^{229}\mathrm{Th}$ isomeric state.

For many fission products, the $\gamma$ rays emitted following $\beta$ decay provide an easily detectable signature that can be used to identify their quantities and distributions in a sample. As a result, $\gamma$-ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the $\gamma$-ray intensities is available. In many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. In this paper, we present high-precision results for the absolute $\gamma$-ray emission intensities for the most intense transitions in the $\beta$ decays of ${}^{144}\mathrm{Ce}$ and ${}^{147}\mathrm{Nd}$. We measured these intensities to $\lesssim 1\%$ accuracy by producing radiopure samples with fission-product beams at CARIBU and detecting the emitted radiation with a $4\pi \beta$ counter and a meticulously efficiency-calibrated high purity germanium detector at Texas A&M University.

Neutron-rich nuclei are attracting significant attention due to vital roles in the nucleosynthesis processes of the universe. The shell evolution which breaks or creates magic numbers in some instances leads to shape coexistence that frequently serves as a portal to the islands of inversion (IOI). ${}^{74}\mathrm{Zn}$ was suggested as a northern extension of the $N=40$ IOI across $Z=28$, and a new IOI around $N=50$ ($Z=20$–28) had also been predicted. We have performed ab initio calculations for even-even Zn isotopes and $N=50$ ($Z>28$) isotones located in the north of the $N=40$ and 50 IOIs. With a chiral two- plus three-nucleon force, the shell-model valence-space effective Hamiltonian is derived using the many-body perturbation theory named $\widehat{\mathrm{Q}}$-box folded diagrams, and the effective operators of electromagnetic transitions are obtained using similar $\widehat{\mathrm{\Theta }}$-box folded diagrams. The calculations reproduce experimental excitation energies and electric qudrupole transition strengths of excited states of the nuclei, showing a collectivity of ${}^{70\text{−}78}\mathrm{Zn}$ isotopes and a noncollectivity of the $N=50$ ($Z>28$) isotones.

High-spin states of ${}^{67}\mathrm{Ga}$ have been studied via the ${}^{58}\mathrm{Ni}({}^{12}\mathrm{C},$ $3p){}^{67}\mathrm{Ga}$ fusion-evaporation reaction at a beam energy of 50.4 MeV. Three negative-parity bands and three positive-parity bands in ${}^{67}\mathrm{Ga}$ are established. The observation of one new $E3$ transition linking the positive-parity $\pi 1g_{9/2}$ band and negative-parity $\pi 2p_{3/2}$ band provides evidence of octupole correlations in ${}^{67}\mathrm{Ga}$. The characteristics of octupole correlations in the ${}^{67}\mathrm{Ga}$ are discussed in terms of the reflection-asymmetric triaxial particle rotor model and microscopic relativistic mean field $+$ Bardeen-Cooper-Schrieffer model.

Background: Quasifission reactions occur in fully damped heavy-ion collisions without the formation of an equilibrated compound nucleus, leading to the formation of fragments with properties similar to those in fission reactions. In particular, similar shell effects are expected to affect fragment formation in both fission and quasifission. Experimentally, the role of shell effects in quasifission is still debated, and further theoretical predictions are needed.

Purpose: We aim to investigate quasifission dynamics in different reactions forming the same compound nucleus and to search for possible signatures of shell effects in fragment formation.

Methods: ${}^{50}\mathrm{Ca}+{}^{176}\mathrm{Yb}$ and ${}^{96}\mathrm{Zr}+{}^{130}\mathrm{Sn}$ quasifission reactions are simulated with the time-dependent Hartree-Fock code sky3d near the Coulomb barrier. Evolutions of the quadrupole ($Q_{20}$) and octupole ($Q_{30}$) moments are interpreted in terms of features of the potential energy surface (PES) of the ${}^{226}\mathrm{Th}$ compound nucleus.

Results: Both reactions encounter quasifission. In ${}^{50}\mathrm{Ca}+{}^{176}\mathrm{Yb}$, it only occurs at finite angular momenta. In the more symmetric ${}^{96}\mathrm{Zr}+{}^{130}\mathrm{Sn}$ reaction with stronger Coulomb repulsion in the entrance channel, quasifission also occurs in central collisions. In agreement with earlier predictions, ${}^{50}\mathrm{Ca}+{}^{176}\mathrm{Yb}$ encounters partial mass equilibration that is stopped when the heavy fragment reaches $Z\approx 54$ protons, as in the asymmetric fission mode of ${}^{226}\mathrm{Th}$. Interestingly, ${}^{96}\mathrm{Zr}+{}^{130}\mathrm{Sn}$ encounters an “inverse quasifission” (multinucleon transfer increasing the mass asymmetry between the fragments) also leading to fragments similar to those in asymmetric fission. In both systems, quasifission trajectories in the $\left(Q_{20}\text{−}{Q}_{30}\right)$ plane are found close to the asymmetric fission valley of the ${}^{226}\mathrm{Th}$ PES.

Conclusions: The observation of an inverse quasifission that goes against expectations from a simple liquid drop picture suggests that shell effects have an influence in quasifission. In addition, the similarity between fragments formed in asymmetric fission and quasifission supports the idea that the same shell effects are at play in both mechanisms. In particular, these were recently attributed to octupole deformed shell effects in $Z=52–56$ fragments. Interpreting quasifission dynamics with PESs used in fission is naturally limited by the fact that these PESs are usually computed with axial symmetry, no angular momentum, and no excitation energy, thus motivating future developments of PESs for quasifission.

A study of the nucleon mean-field potential in nuclear matter (NM) is done within an extended Hartree-Fock (HF) formalism, using the CDM3Y6 density dependent version of the M3Y interaction which is associated with the nuclear incompressibility $K\simeq 252$ MeV. The momentum dependence of nucleon optical potential (OP) in NM at the saturation density ${\rho }_0$ is shown to be due mainly to its exchange term up to $k\approx 2{\mathrm{fm}}^{-1}$, so that the Pauli nonlocality is expected to be the main origin of the nucleon effective mass at low momenta. Because nucleons in neutron-rich NM at $\rho \approx {\rho }_0$ are either weakly bound or unbound by the in-medium nucleon-nucleon interaction, the determination of the effective mass of nucleon scattered on targets with neutron excess at low energies should be of interest for the mean-field studies of neutron star matter. For this purpose, the folding model is used to calculate the nonlocal nucleon OP for the optical model analysis of elastic nucleon scattering on ${}^{40,48}\mathrm{Ca}, {}^{90}\mathrm{Zr}$, and ${}^{208}\mathrm{Pb}$ targets at energies $E<50$ MeV, to probe the model reliability and validate the Wentzel-Kramers-Brillouin (WKB) local approximation to obtain the local folded nucleon OP. The nucleon effective mass $m^{*}$ is then carefully deduced from the momentum dependence of the local folded nucleon OP which results from the Pauli nonlocality of the exchange term. The obtained $m^{*}$ values agree well with the nucleon effective mass given by the extended HF calculation of the single-particle potential in asymmetric NM. The neutron-proton effective mass splitting determined at $\rho \approx {\rho }_0$ from the central strength of the real folded nucleon OP for ${}^{48}\mathrm{Ca}, {}^{90}\mathrm{Zr}$, and ${}^{208}\mathrm{Pb}$ targets has been found to depend linearly on the neutron-proton asymmetry parameter as $m_{n-p}^{*}\approx (0.167\pm 0.018)\delta$, in a good agreement with the recent empirical constraints.

We study bottom quark energy loss via the nuclear modification factor ($R_{AA}$) and elliptic flow ($v_2$) of nonprompt $D^0$ and $J/\psi$ in relativistic heavy-ion collisions at the Large Hadron Collider (LHC). The space-time profile of quark-gluon plasma is obtained from the clvisc hydrodynamics simulation, the dynamical evolution of heavy quarks inside the color deconfined QCD medium is simulated using a linear Boltzmann transport model that combines Yukawa and string potentials of heavy-quark-medium interactions, the hadronization of heavy quarks is performed using a hybrid coalescence-fragmentation model, and the decay of $B$ mesons is simulated via pythia. Using this numerical framework, we calculate the transverse momentum ($p_{\mathrm{T}}$) dependent $R_{AA}$ and $v_2$ of direct $D$ mesons, $B$ mesons, and nonprompt $D^0$ and $J/\psi$ from $B$ meson decay in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ TeV. We find the mass hierarchy of the nuclear modification of prompt $D$ and $B$ mesons depends on their $p_{\mathrm{T}}$. Both $R_{AA}$ and $v_2$ of heavy flavor particles show strong $p_{\mathrm{T}}$ and centrality dependences due to the interplay between parton energy loss, medium geometry and flow, and hadronization of heavy quarks. Nonprompt $D^0$ and $J/\psi$ share similar patterns of $R_{AA}$ and $v_2$ to $B$ mesons except for a $p_{\mathrm{T}}$ shift during the decay processes. Therefore, future more precise measurements on nonprompt $D^0$ and $J/\psi$ can help further pin down the bottom quark dynamics inside the quark-gluon plasma.

We have investigated the influence of the Coriolis force on the electrical conductivity of hadronic matter formed in relativistic nuclear collisions, employing the hadron resonance gas model. A rotating matter in the peripheral heavy-ion collisions can be expected from the initial stage of quark matter to late-stage hadronic matter. Present work is focused on rotating hadronic matter, whose medium constituents—hadron resonances—can face a nonzero Coriolis force, which can influence the hadronic flow or conductivity. We estimate this conductivity tensor by using the relativistic Boltzmann transport equation. In the absence of Coriolis force, an isotropic conductivity tensor for hadronic matter is expected. However, our study finds that the presence of Coriolis force can generate an anisotropic conductivity tensor with three main conductivity components—parallel, perpendicular, and Hall—similarly to the effect of Lorentz force at a finite magnetic field. Our study has indicated that a noticeable anisotropy of conductivity tensor can be found within the phenomenological range of angular velocity $\mathrm{\Omega }=0.001$–0.02 GeV and hadronic scattering radius $a=0.2$–2 fm.

Large-scale shell-model calculations have been performed to study the nuclear structure properties of Hg isotopes with mass varying from $A=193$ to $A=200$. The shell-model calculations are carried out in the $50\le Z\le 82$ and $82\le N\le 126$ model space using monopole-based truncation. We present detailed studies on low-energy excitation spectra, energy systematics, and collective properties of Hg isotopes, such as reduced transition probabilities, quadrupole, and magnetic moments along the isotopic chain. The evolution of wave function configurations with spin is analyzed in the case of even-$A$ Hg isotopes. The shell-model results are in reasonable agreement with the experimental data and predictions are made where experimental data are unavailable. The shapes of Hg isotopes are also investigated through the energy-surface plots.