This work presents a three-dimensional dynamical initialization model for relativistic heavy-ion collisions, implementing local energy-momentum conservation and baryon charge fluctuations at string junctions. Constraining parameters using experimental data from $p+p$ collisions at various collision energies, the model provides a very good description of the charged hadron and net proton rapidity distributions in $\mathrm{Au}+\mathrm{Au}$ collisions from 7.7 to 200 GeV and $\mathrm{Pb}+\mathrm{Pb}$ collisions at 8.77 and 17.3 GeV. We demonstrate the importance of fluctuations of baryon densities to string junctions for describing net-proton distributions at collision energies of 62.4 and 200 GeV. Including this improved baryon stopping description along with the requirement of strangeness neutrality also yields a good description of identified particle yields as functions of the collision energy above 7.7 GeV. We further study asymmetric $p+\mathrm{Al}$ and $(p,d,{}^3\mathrm{He})+\mathrm{Au}$ collisions at the top Relativistic Heavy-Ion Collider (RHIC) energy and $p+\mathrm{Pb}, \mathrm{Xe}+\mathrm{Xe}$, and $\mathrm{Pb}+\mathrm{Pb}$ collisions at Large Hadron Collider (LHC) energies. We identify the produced particle rapidity distributions in asymmetric collision systems as particularly useful for constraining models of the early-time longitudinal dynamics.

The linear-chain (LC) structure provides significant insights into quantum many-body systems with geometric configurations. In this study, $4\alpha +2n$ LC was assessed in ${}^{18}\mathrm{O}$. The excitation energies, moment of inertia, and $\alpha$- and ${}^9\mathrm{Be}$-decay widths of the LC states were predicted using antisymmetrized molecular dynamics. We predict that there are two $4\alpha$ LC bands, $K^{\pi }=0^{+}$ and $K^{\pi }=3^{-}$, which exhibit different decay properties. We demonstrate that the $K^{\pi }=3^{-}$ LC states can be verified by the head-on ${}^9\mathrm{Be}+{}^9\mathrm{Be}$ collision experiments because their states exhibited large decay widths in the ${}^9\mathrm{Be}+{}^9\mathrm{Be}$ channel.

We apply the dynamical generator coordinate method (DGCM) with a conjugate momentum to a nuclear collective excitation. To this end, we first discuss how to construct a numerically workable scheme of the DGCM for a general one-body operator. We then apply the DGCM to the quadrupole vibration of ${}^{16}\mathrm{O}$ using the Gogny D1S interaction. We show that both the ground state energy and the excitation energies are lowered as compared to the conventional GCM with the same number of basis functions. We also compute the sum rule values for the quadrupole and monopole operators, and show that the DGCM yields more consistent results than the conventional GCM to the values from the double commutator. These results imply that the conjugate momentum is an important and relevant degree of freedom in collective motions.

We present results of collisions of ${}^{90}\mathrm{Zr}+{}^{90}\mathrm{Zr}$ and ${}^{96}\mathrm{Zr}+{}^{96}\mathrm{Zr}$ obtained within time-dependent density functional theory (TDDFT) extended to superfluid systems, known as the time-dependent superfluid local density approximation (TDSLDA). We discuss qualitatively new features occurring in collisions of two superfluid nuclei at energies in the vicinity of the Coulomb barrier. We show that a solitonic excitation—an abrupt pairing phase distortion—reported previously [P. Magierski et al., Phys. Rev. Lett. 119, 042501 (2017)] increases the barrier for capture, generating effective repulsion between colliding nuclei. Moreover we demonstrate that pairing field leads to qualitatively different dynamics at the Coulomb barrier which manifests itself in a slower evolution of deformation towards a compact shape. Last but not least, we show that magnitude of pairing correlations can be dynamically enhanced after collision. We interpret it as a dynamically induced $\text{U}\left(1\right)$ symmetry breaking, which leads to large-amplitude oscillations of pairing field and bears similarity to the pairing Higgs mechanism.

The azimuthal variation of jet yields in heavy-ion collisions provides information about the path-length dependence of the energy loss experienced by partons passing through the hot, dense nuclear matter known as the quark–gluon plasma. This paper presents the azimuthal anisotropy coefficients $v_2, v_3$, and $v_4$ measured for jets in $\text{Pb}+\text{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV using the ATLAS detector at the LHC. The measurement uses data collected in 2015 and 2018, corresponding to an integrated luminosity of 2.2 ${\mathrm{nb}}^{-1}$. The $v_n$ values are measured as a function of the transverse momentum of the jets between 71 and 398 GeV and the event centrality. A nonzero value of $v_2$ is observed in all but the most central collisions. The value of $v_2$ is largest for jets with lower transverse momentum, with values up to 0.05 in mid-central collisions. A smaller, nonzero value of $v_3$ of approximately 0.01 is measured with no significant dependence on jet $p_{\mathrm{T}}$ or centrality, suggesting that fluctuations in the initial state play a small but distinct role in jet energy loss. No significant deviation of $v_4$ from zero is observed in the measured kinematic region.

The PHENIX Collaboration presents a systematic study of inclusive ${\pi }^0$ production from $p+p, p+\mathrm{Al}, p+\mathrm{Au}, d+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{NN}}}=200\mathrm{GeV}$. Measurements were performed with different centrality selections as well as the total inelastic, 0–100%, selection for all collision systems. For 0–100% collisions, the nuclear-modification factors, $R_{xA}$, are consistent with unity for $p_T$ above $8\mathrm{GeV}/c$, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are similar for all systems for the same centrality class. It is shown that for high-$p_T\text{−}{\pi }^0$ production, the nucleons in the $d$ and ${}^3\mathrm{He}$ interact mostly independently with the Au nucleus and that the counterintuitive centrality dependence is likely due to a physical correlation between multiplicity and the presence of a hard scattering process. These observations disfavor models where parton energy loss has a significant contribution to nuclear modifications in small systems. Nuclear modifications at lower $p_T$ resemble the Cronin effect—an increase followed by a peak in central or inelastic collisions and a plateau in peripheral collisions. The peak height has a characteristic ordering by system size as $p+\mathrm{Au}>d+\mathrm{Au}>{}^3\mathrm{He}+\mathrm{Au}>p+\mathrm{Al}$. For collisions with Au ions, current calculations based on initial-state cold nuclear matter effects result in the opposite order, suggesting the presence of other contributions to nuclear modifications, in particular at lower $p_T$.

We explore the photoproduction mechanisms for charged and neutral pion pairs off a heavy nucleus at threshold. We calculate the production of charged pairs in the Coulomb field of the nucleus in the Born approximation using explicit expressions for the differential cross sections and their connection with the total cross section $\sigma (\gamma \gamma \to {\pi }^{+}{\pi }^{-})$. The production of $\sigma$ mesons at threshold and their subsequent decay into pions is an important mechanism and is investigated quantitatively in a framework that can be used for both charged and neutral pions. $\sigma$ mesons can be produced via electromagnetic (photon exchange) or strong ($\omega$ exchange) interactions. For neutral pions, another production mechanism consists of the two-step process where charged pions are produced first and then charge exchange into two neutral pions. Differential and total cross sections are computed for each production mechanism.

Light antinucleus yields are calculated in a multiphase transport model coupled with a dynamical coalescence model. The model is tuned to reproduce the transverse momentum and rapidity distributions of antiproton in $pp$ collisions at $\sqrt{\mathrm{s}}=7.7$ GeV to 7 TeV. By applying a widely used cosmic-ray propagation model, the antinucleus fluxes near the earth are estimated over a broad range of kinetic energies. Our result on the antideuteron flux is consistent with the calculations in the literature, while our upper limit on the antihelium-3 flux sits in-between calculations in the field that span an order of magnitude in its value. This study suggests that further accurate estimation of secondary antihelium-3 flux could be improved with more ground-based experiments and model simulations. Most importantly, our value of antinucleus background from hadronic source is far below the projected sensitivity of AMS-02 with five years of integration time, which supports the idea of searching for new physics by measurements of light antinuclei in upcoming decade.

Background: An assessment done under the auspices of the Organization for Economic Co-operation and Developement Nuclear Energy Agency (OECD-NEA) in 2007 suggested that the $\beta$ decays of many abundantly produced fission products in nuclear reactors may be incomplete. In this assessment, the fission product ${}^{98}\mathrm{Nb}$ was assigned the highest priority for study by total absorption spectroscopy due to its large cumulative fission branching fraction and because the $\beta$-decay data from several experiments are discrepant.

Purpose: To obtain the complete $\beta$-decay feeding pattern of ${}^{98}\mathrm{Nb}$ and determine the impact on the average $\gamma$ energy per ${}^{98}\mathrm{Nb}\beta$ decay and ${\overline{\nu }}_e$ emission calculations. The complete ${}^{98}\mathrm{Nb}$ $\beta$-decay feeding pattern includes ground-state to ground-state $\beta$ feeding and direct $\beta$ feeding to the $0^{+}$ first-excited state (both have no associated $\gamma$ rays), and the ground-state to excited-state $\beta$ transitions followed by $\gamma$ transitions to the ground state of the daughter nucleus, ${}^{98}\mathrm{Mo}$.

Method: The complete $\beta$-decay intensities of ${}^{98}\mathrm{Nb}$ were measured with the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory (ORNL). The ${}^{98}\mathrm{Nb}$ was produced by the $\beta$ decay of mass 98 fission fragments at ORNL's On-Line Test Facility (OLTF) using proton-induced fission of ${}^{238}\mathrm{U}$.

Results: We find that changes to the current ENSDF assessment of ${}^{98}\mathrm{Nb}\beta$-decay intensity are required. We report improved uncertainties for the $\beta$-decay feeding values and report new $\beta$ feedings to high-energy levels in ${}^{98}\mathrm{Mo}$.

Conclusions: A more complete ${}^{98}\mathrm{Nb}\beta$-feeding pattern with improved accuracy and precision is offered. The impacts of the measured changes to the ${}^{98}\mathrm{Nb}\beta$-feeding pattern on both reactor decay heat calculations and predicted detection rates of reactor ${\overline{\nu }}_e$ are presented. The Modular Total Absorption Spectrometer measurements of ${}^{98}\mathrm{Nb}$ demonstrate the importance of reexamining and remeasuring complex $\beta$-decaying fission products with total absorption spectroscopy, including nuclei very near $\beta$ stability.

Methods for obtaining fusion cross section formulas are discussed, especially for those that take on an empirical form. A new expression starting with $\sigma \left(E\right)=\frac{1}{E}{\int }_{E_0}^E\left({\int }_{E_0}^{E^{\prime }}B\left(E^{″}\right)d{E}^{″}\right)d{E}^{\prime }$ has been explored. Here, $B\left(E\right)$ is a reasonable, assumed function of the barrier height distribution, $\frac{d^2\left(\sigma E\right)}{d{E}^2}$. The resulting analytic cross section formula reproduces very well the excitation functions for many light and heavy fusion systems across wide energy ranges, when $B\left(E\right)$ is assumed to be a multi-Gaussian function. This study offers an improved determination of the fusion barrier height distribution over other numerical techniques.

There has been much work in recent years pertaining to viability studies for the intranuclear observation of neutron-antineutron transformations. These studies begin first with the design and implementation of an event generator for the simulation of this rare process, where one hopes to retain as much of the underlying nuclear physics as possible in the initial state, and then studying how these effects may perturb the final-state observable particles for detector efficiency studies following simulated reconstruction. There have been several searches for intranuclear neutron-antineutron transformations, primarily utilizing the ${}_8{}^{16}\mathrm{O}$ nucleus, and completed within large underground water Cherenkov detectors such as Super-Kamiokande. The latest iteration of a generator is presented here for use in such an experiment. This generator includes several new features, including a new radial (position) annihilation probability distribution and related intranuclear suppression factor for ${}_8{}^{16}\mathrm{O}$, as well as a highly general, modern nuclear multifragmentation model with photonic de-excitations. The latter of these may allow for improved identification of the signal using large underground detectors such as Super-Kamiokande and the future Hyper-Kamiokande, potentially increasing the overall signal efficiencies of these rare searches. However, it should be noted that certain fast photonic de-excitations may be washed out by ${\pi }^0$ decays to photons. These new features implemented in these $\overline{n}{}_8{}^{15}\mathrm{O}$ simulations increase the overall physical realism of the model and are easily portable to other future searches such as to extranuclear $\overline{n}{}_6{}^{12}\mathrm{C}$ for the ESS NNBAR experiment, as well as intranuclear $\overline{n}{}_{18}{}^{39}\mathrm{Ar}$ used in DUNE.

By including the recently introduced thermal shear term that contributes to the spin-polarization vector at local equilibrium, we determine longitudinal polarization of $\mathrm{\Lambda }$ hyperons emitted from a hot and rotating hadronic medium using the thermal model with single freeze-out. In our analysis, we consider the RHIC top energies and use the model parameters which were determined in the earlier analyses of particle spectra and elliptic flow. We confirm that, unlike the previous calculations done by using only the thermal vorticity, the thermal shear term alone leads to the correct sign of the quadrupole structure of the longitudinal component of the polarization three-vector measured in experiments. However, we find almost complete cancellation between thermal shear and vorticity terms, which eventually leads to disagreement with the data. To clarify the role played by velocity and temperature gradient terms, we present a systematic analysis of different contributions to the longitudinal polarization. Finally, replacing the mass of $\mathrm{\Lambda }$ hyperon with its constituent strange quark mass in the polarization formula we achieve agreement with the data.

Beam-recoil transferred polarizations for the exclusive electroproduction of $K^{+}\mathrm{\Lambda }$ and $K^{+}{\mathrm{\Sigma }}^0$ final states from an unpolarized proton target have been measured using the CLAS12 spectrometer at Jefferson Laboratory. The measurements at beam energies of 6.535 and 7.546 GeV span the range of four-momentum transfer $Q^2$ from 0.3 to 4.5 ${\mathrm{GeV}}^2$ and invariant energy $W$ from 1.6 to 2.4 GeV, while covering the full center-of-mass angular range of the $K^{+}$. These new data extend the existing hyperon polarization data from CLAS in a similar kinematic range but from a significantly larger dataset. They represent an important addition to the world data, allowing for better exploration of the reaction mechanism in strangeness production processes, for further understanding of the spectrum and structure of excited nucleon states, and for improved insight into the strong interaction in the regime of nonperturbative dynamics.

A standard method to detect thermal neutrons is the nuclear interaction ${}^3\mathrm{He}{(\mathrm{n},\mathrm{p})}^3\mathrm{H}$. The spin dependence of this interaction is also the basis of a neutron spin-polarization filter using nuclear polarized ${}^3\mathrm{He}$. We consider the corresponding interaction for neutrons placed in an intrinsic orbital angular momentum (OAM) state. We derive the relative polarization-dependent absorption cross sections for neutrons in an $L=1$ OAM state. The absorption of those neutrons results in compound states $J^{\pi }=0^{-}$, $1^{-}$, and $2^{-}$. Varying the three available polarizations tests that an OAM neutron has been absorbed and probes which decay states are physically possible. We describe the energetically likely excited states of ${}^4\mathrm{He}$ after absorption, taking account of the odd parity of the compound state. This provides a definitive method for detecting neutron OAM states and suggests that intrinsic OAM states offer the possibility to observe new physics, including anomalous cross sections and new channels of radioactive decay.

Background: Two recent studies of the evolution of the isoscalar giant monopole resonance (ISGMR) within the calcium isotope chain report conflicting results. One study suggests that the monopole resonance energy, and thus the incompressibility of the nucleus, $K_A$, increase with mass, which implies that $K_{\tau }$, the asymmetry term in the nuclear incompressibility, has a positive value. The other study reports a weak decreasing trend of the energy moments, resulting in a generally accepted negative value for $K_{\tau }$. Differences in the observed trends have been attributed to the use of different techniques to account for instrumental background and the physical continuum.

Purpose: An independent measurement of the ISGMR in the Ca isotope chain is provided to gain a better understanding of the origin of possible systematic trends.

Methods: Inelastically scattering of 196 MeV $\alpha$ particles were observed at small scattering angles, including $0^{\circ }$, for a range of calcium targets (${}^{40,42,44,48}\mathrm{Ca}$). The scattered $\alpha$ particles were momentum analyzed in the K600 magnetic spectrometer at iThemba LABS, South Africa. Monopole strengths spanning an excitation-energy range between 9.5 and 25.5 MeV were obtained using the difference-of-spectra (DoS) technique, adjusted to allow corrections for the variation of the angular shape of the sum of the $L>0$ multipoles as a function of excitation energy, and compared with previous results that employed the multipole-decomposition analysis (MDA) techniques.

Results: The structure of the $E0$ strength distributions of ${}^{40,42,44}\mathrm{Ca}$ agrees well with the results from the previous measurement that support a weak decreasing trend of the energy moments, while no two datasets agree in the case of ${}^{48}\mathrm{Ca}$. Despite the variation in the structural character of $E0$ strength distribution from different studies, we find for all datasets that the moment ratios, calculated from the ISGMR strength in the excitation-energy range that covers the resonance peak, display at best only a weak systematic sensitivity to a mass increase.

Conclusion: Different trends observed in the nuclear incompressibility are caused by contributions to the $E0$ strength outside of the region covering the resonance peak, and in particular for high excitation energies. While procedures exist to identify and subtract instrumental background, more work is required to characterize and subtract continuum background contributions at high excitation energies.

Elastic scattering measurements were performed for the proton drip-line nucleus ${}^{13}\mathrm{O}$ (with $S_p=1.512$ MeV) and its partner mirror nucleus ${}^{13}\mathrm{B}$ (with $S_n=4.878$ MeV) projectiles on a ${}^{208}\mathrm{Pb}$ target at intermediate energies, namely $E_{\mathrm{lab}}=413$ and 254 MeV, respectively. These secondary radioactive ion beams were produced at the Radioactive Ion Beam Line in Lanzhou (RIBLL), Heavy-Ion Research Facility in Lanzhou (HIRFL). The elastic scattering angular distributions for these projectiles show a typical Fresnel diffraction peak at forward angles. Optical model analyses of the angular distributions, using double-folding and global potentials, were performed and different densities for these projectiles were probed.

Octupole correlations in the low-energy collective states of neutron-rich nuclei with the neutron number $N\approx 56$ are studied within the interacting boson model (IBM) that is based on the nuclear density-functional theory. The constrained self-consistent mean-field (SCMF) calculations using a universal energy density functional and a pairing interaction provide the potential-energy surfaces in terms of the axially symmetric quadrupole and octupole deformations for the even-even nuclei ${}^{86–94}\mathrm{Se}, {}^{88–96}\mathrm{Kr}, {}^{90–98}\mathrm{Sr}, {}^{92–100}\mathrm{Zr}$, and ${}^{94–102}\mathrm{Mo}$. The SCMF energy surface is then mapped onto the energy expectation value of a version of the IBM in the boson condensate state, which consists of the neutron and proton monopole $s$, quadrupole $d$, and octupole $f$ bosons. This procedure determines the strength parameters of the IBM Hamiltonian, which is used to compute relevant spectroscopic properties. At the SCMF level, no octupole deformed ground state is obtained, while the energy surface is generally soft in the octupole deformation at $N\approx 56$. The predicted negative-parity yrast bands with the bandhead state $3_1^{-}$ weakly depend on $N$ and become lowest in energy at $N=56$ in each of the considered isotopic chains. The model further predicts finite electric octupole transition rates between the lowest negative- and the positive-parity ground-state bands.

The neutron energy-dependent angular distribution of $\gamma$ rays from the ${}^{117}\mathrm{Sn}(n,\gamma )$ reaction was measured with germanium detectors and a pulsed neutron beam. The angular distribution was clearly observed in $\gamma$-ray emissions with an energy of 9327 keV which corresponds to the transition from a neutron resonance of ${}^{117}\mathrm{Sn}+n$ to the ground state of ${}^{118}\mathrm{Sn}$. The angular distribution causes an angular-dependent asymmetric resonance shape. An asymmetry $A_{\mathrm{LH}}$ was defined as $(N_{\mathrm{L}}-N_{\mathrm{H}})/(N_{\mathrm{L}}+N_{\mathrm{H}})$, where $N_{\mathrm{L}}$ and $N_{\mathrm{H}}$ are integrated values for lower- and higher-energy regions of a neutron resonance, respectively. We found that the $A_{\mathrm{LH}}$ has the angular dependence of $(Acos{\theta }_{\gamma }+B)$, where ${\theta }_{\gamma }$ is the $\gamma$-ray emission angle with respect to the incident neutron momentum, with $A=0.394\pm 0.073$ and $B=0.118\pm 0.029$ in the 1.33 eV $p$-wave resonance.

In this work, the causality and stability of a first-order relativistic dissipative hydrodynamic theory, that redefines the hydrodynamic fields from a first principles microscopic estimation, are analyzed. A generic approach of gradient expansion for solving the relativistic transport equation is adopted using the Chapman-Enskog iterative method. Next, the momentum dependent relaxation time approximation is employed to quantify the collision term for analytical estimation of the field correction coefficients from kinetic theory. In the linear regime, in the local rest frame the dispersion relations are observed to produce a causal propagating mode. However, the acausality and instability reappear when a boosted background is considered for linear analysis. These facts point out relevant aspects regarding the methodology of extracting the causal and stable first-order hydrodynamics from kinetic theory and indicate the appropriate approach to construct a valid first-order theory with proper justification.

The poorly known crustal equation of state plays a critical role in many observational phenomena associated with a neutron star. Using semiclassical Monte Carlo simulations, we explore the possible configurations of the inner edge of the neutron star crust for a variety of baryon densities and proton fractions. Applying the Kirkwood-Buff theory to these two-component systems, we observe how the isothermal compressibility reaches a maximum when isolated nonsymmetric (or quasispherical) clusters are formed in an extremely dilute neutron gas. To determine the neutron fraction, we suggest a geometrical model based on the behavior of the proton-neutron pair correlation function. Accordingly, the equation of state of the inner crust is calculated, illustrating that the nuclear energy in $\beta$ equilibrium follows a power-law behavior with baryon density. As a possible astrophysical outcome of this study, our results could help refine the mass-radius relation. Finally, our results pave the way towards further investigations of the impact of the proton-neutron pair correlation function on transport properties within the neutron star crust.