Isospin quartets ($T=3/2$) and quintets ($T=2$) have been investigated for $A=15$ and $A=16$ nuclei, respectively. Data from an invariant-mass experiment, with a ${}^{17}\mathrm{Ne}$ beam, were reanalyzed and the $T=3/2$ and $T=2$ states in ${}^{15}\mathrm{O}$ and ${}^{16}\mathrm{F}$, associated with $p+{}^{14}\mathrm{N}$ and $2p+{}^{14}\mathrm{N}$ exit channels, respectively, were found. In some cases, $\gamma$-ray gating was used to tag on events that decay to the excited $0^{+}$, $T=1$ state in ${}^{14}\mathrm{N}$ rather than the ground state. With the new states, the lowest-energy $1/2^{+}$ and $5/2^{+}$ quartets for $A=15$ and the $0^{+}$ and $2^{+}$ quintets for $A=16$ are completed. In addition, members of these multiplets in ${}^{15}\mathrm{F}$ and ${}^{16}\mathrm{Ne}$ decaying to the $p+{}^{14}\mathrm{O}$ and $2p+{}^{14}\mathrm{O}$ channels are reevaluated by gating on events where the ${}^{14}\mathrm{O}$ fragment recoils perpendicular to beam axis in the parent reference frame. Such transverse-decay events have the best invariant-mass resolution. No evidence for deviations from a quadratic dependence of the mass on the isospin projection was found for the $A=15$ quartets. However for the $A=160^{+}$ and $2^{+}$ quintets, evidence for deviations were found.

The ${}^8\mathrm{B}+{}^{51}\mathrm{V}$ elastic scattering at $E_{\mathrm{lab}}=22$ MeV was measured using a ${}^8\mathrm{B}$ secondary beam produced and selected by the RIBRAS (Radioactive Ion Beams in Brasil) system. An elastic scattering angular distribution was obtained and analyzed within the optical model, using a Woods-Saxon form factor. A full continuum discretized coupled-channels calculation was performed to take into account the effect of the ${}^8\mathrm{B}\to {}^7\mathrm{Be}+p$ elastic breakup on the elastic scattering dynamics. The breakup and total reaction cross sections obtained from these analyses are also presented.

The harmonic flow coefficients of light nuclei and hypernuclei in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=3$ GeV are investigated using the Ultra-relativistic Quantum Molecular Dynamics transport model. For the equation of state we employ a density- and momentum-dependent potential from the chiral-mean-field model. Light nuclei and hypernuclei production is described at kinetic freeze-out via a coalescence mechanism or with a statistical multifragmentation calculation. The directed flow $v_1$ of $p$, $d$, $t$, ${}^3\mathrm{He}$, ${}^4\mathrm{He}$, as well as the $\mathrm{\Lambda }$, ${}_{\mathrm{\Lambda }}^3\mathrm{H}$, and ${}_{\mathrm{\Lambda }}^4\mathrm{H}$, is shown to approximately scale with mass number $A$ of the light cluster in both calculations. This is in agreement with the experimental results for the directed flow measured by STAR. Predictions for the directed and elliptic flow of (hyper)nuclei at further RHIC-FXT and FAIR energies show that the scaling properties should improve as the beam energy is increased.

Unraveling the internal structure of hadrons and nuclei in terms of the quarks and gluons of quantum chromodynamics is a central focus of current nuclear physics research. Directly observing gluonic states in the nucleus would be groundbreaking and is an objective of the future Electron-Ion Collider (EIC). Over 30 years ago, Jaffe and Manohar [R. L. Jaffe and A. Manohar, Phys. Lett. B 223, 218 (1989)] identified a new double-helicity flip structure function, directly sensitive to exotic gluons. They pointed out that this could be measured in inclusive high-energy electron scattering from a transversely polarized nuclear target with spin $I\ge 1$. Here, we identify the spin-3 nucleus boron-10 as a particularly interesting system to search for exotic gluons. Leveraging technical advances in atomic physics over the past decade, we outline an experimental scheme to directly optically pump a beam of stable boron atoms to polarize the nuclear spin. Technical challenges to realize a spin-polarized beam of boron-10 in the EIC are discussed. The proposed scheme will also polarize the ${}^{11}\mathrm{B}$ nucleus, which could significantly enhance the proton-boron fusion cross section.

In this study, the nuclear level density (NLD) of superheavy even-even ${}^{266,268,270,272}\mathrm{Hs}$ nuclei was calculated using an accurate microscopic statistical approach that avoids common approximations. The approach employs a recursive partition-function method that uses realistic deformation-dependent single-particle level (SPL) spectra obtained from the deformed Woods-Saxon potential diagonalization as input. Calculations are performed at both the ground state and the saddle point (SP), which allows the detailed analysis of NLD behavior along the fission path and provides insight into the probability of survival of the synthesized superheavy Hs nuclei. The SPs were determined using the macroscopic-microscopic method and applying the imaginary water flow technique. The results are compared with those obtained using SPL schemes derived from self-consistent mean-field models and with the predictions of traditional Fermi gas models. The precise microscopic method used in this study provides a more realistic representation of NLD behavior in superheavy nuclei, which offers significant improvements over approximative methods.

Negative-parity medium- and high-spin structure of the nucleus ${}^{105}\mathrm{Pd}$ was studied through the ${}^{96}\mathrm{Zr}({}^{13}\mathrm{C},4n){}^{105}\mathrm{Pd}$ reaction at incident energies of 51 and 58 MeV, using the EUROBALL IV $\gamma$-ray spectrometer in conjunction with the DIAMANT charged particle array. New bands have been observed and the previously reported bands have been extended to higher energies and spins. Altogether six decoupled bands with $E2$ transitions and one strongly coupled band with $M1+E2$ transitions have been observed. The observed energy spectra and $B\left(M1\right)/B\left(E2\right)$ ratios are compared with results of quantum particle rotor model calculations. Based on these comparisons, quasiparticle configurations can be assigned to two newly observed decoupled bands as well as to the strongly coupled band. The previously emerged possible interpretation for the third decoupled band as a two-phonon wobbling excitation lacks support. The observations indicate possible $\gamma$-band nature for this band. The strongly coupled band, consistently with the absence of another observed strongly coupled band in this experiment, does not exhibit chirality.

Following our study of possible $K$ isomers in odd-even Md–Rg nuclei, here we continue with searching for three-quasiparticle $1\nu 2\pi$ and $3\nu$ isomer candidates in even-odd Fm–Cn nuclei. We use the same approach to calculate energies of different nuclear configurations using a microscopic-macroscopic model with the Woods-Saxon potential. We used two versions of pairing: the quasiparticle BCS method and particle number projection formalism. The optimal deformations for both ground states and high-$K$ configurations are determined through a four-dimensional energy minimization process. We point out the most promising candidates for high-$K$ isomers and compare them, where possible, with existing experimental data.

Background: Charge equilibration is a crucial phenomenon of nuclear dynamics observed in collisions of heavy nuclei characterized by varying neutron-to-proton ($N/Z$) ratios. This process involves equalizing the $N/Z$ ratios of fragments, which occurs at the initial stage of nuclear reaction.

Purpose: This work focuses on a theoretical investigation of the charge equilibration process that occurs during low-energy collisions of heavy nuclei, and on examining its impact on multinucleon transfer and fusion processes.

Method: A multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations [A. V. Karpov et al., Phys. Rev. C 96, 024618 (2017)] was employed in this work.

Results: A broad set of experimental data on multinucleon transfer products of the ${}^{40}\mathrm{Ca}, {}^{56}\mathrm{Fe}, {}^{58}\mathrm{Ni}, {}^{64}\mathrm{Ni}+{}^{208}\mathrm{Pb}$ reactions was analyzed within the dynamical model. The agreement of the calculated energy, atomic number, angular, and isotopic distributions of the reaction products with corresponding experimental data enabled us to refine the model parameters governing the time of nuclear neck evolution and the nucleon transfer rate. Based on this analysis, the mechanism and duration of 0.5 zs for the charge equilibration process were determined. An influence of $N/Z$ equilibration was observed on capture and fusion processes in the ${}^{40}\mathrm{Ca}, {}^{48}\mathrm{Ca}+{}^{208}\mathrm{Pb}$ reactions.

Conclusions: Equilibration of $N/Z$ ratios of fragments is primarily driven by the minimization of the potential energy of the system. This process predominantly occurs along an optimal path, and involves the redistribution of neutrons and protons between the fragments in opposite directions. The products formed in these multinucleon transfer channels exhibit increased cross sections. The decrease in the potential energy of the system during the charge equilibration leads to an enhancement of multinucleon transfer and fusion processes, which are particularly evident at energies below the potential barrier.

Quasifission and fusion-fission represent the two most likely reaction outcomes to occur postcapture in collisions leading to superheavy nuclei. As such, understanding these mechanisms and how they relate to one another is key to understanding the intricate dynamics that drive the formation (or dissociation) of the nascent compound nuclei formed in fusion reactions. This understanding directly translates to a more informed picture of suitable reaction partners and can provide vital information for experimental efforts to study the physics and chemistry of superheavy elements. In this work we report results from time-dependent simulations of ${}^{48}\mathrm{Ca} + {}^{238}\mathrm{U}$ and ${}^{50}\mathrm{Ti} + {}^{236}\mathrm{Th}$ reactions at incident energies just above the Coulomb barrier with a focus on the quasifission process that prevent the formation of a fully equilibrated ${}^{286}\mathrm{Cn}$ compound nucleus. We study these reactions systematically and consider a wide range of initial configurations to extract a robust estimate of primary fragment yields for the quasifission process. Multiple preferred exit channels are observed, with both spherical and deformed shell effects in the heavy and light fragments driving contributions to the production yields depending on the initial configuration of the system. Orientation effects of the deformed actinide targets are found to be a primary driver of which exit channels are populated. Furthermore, the impact of moving away from a doubly magic projectile is explored with implications towards the reactions considered for current and future superheavy searches.

It has recently been shown that extremely strong electric fields can be created in central collisions of heavy ions, due to which the Schwinger effect can be significant. A direct analog of the electric field in hydrodynamics is the acceleration of the medium. Using the parton-hadron-string dynamics framework we model the Au-Au collisions at intermediate collision energies $\sqrt{s_{NN}}=4.5–11.5\mathrm{GeV}$ and obtain the spatial distribution of acceleration at different time moments. The present study demonstrates that extremely high acceleration of the order of 1 GeV may be generated in both central and noncentral collisions, and that the distribution exhibits a core-corona structure. Consequently, in contrast to the case with an electric field, the Unruh effect is expected to be significant. It is demonstrated that for the confined phase the temperature is less than the Unruh temperature. Conversely, in the deconfined phase, the relationship is inverse. The obtained results thus support the prediction about the existence of states with $T<T_U$ at the early stages of the collision and the associated complementary description of thermalization in terms of the novel phase transition at the Unruh temperature.

Very recently, the two-photon decay width of the ${\eta }_b$ meson was computed with lattice QCD methods. This decay has not yet been measured. The knowledge of this width allows for the calculation of the ${\eta }_b$ production cross section through photon-photon interactions in ultraperipheral (UPC) $Pb\text{−}Pb$ collisions. In this work we present this calculation, which is the first application of the lattice result. Since UPCs are gaining increasing attention of the heavy-ion community, we take the opportunity to perform a comprehensive study of the different ways of defining ultraperipheral collisions and of the different ways to treat the equivalent photon flux.

We investigate the magnetic properties of quarkyonic matter, which naturally bridges nuclear and quark matter at intermediate densities relevant to neutron-star cores. We extend the quarkyonic model to include spin polarization, where nucleons near the Fermi surface can be polarized while quarks in the deep Fermi sea remain unpolarized due to strong Pauli blocking. After including neutron interactions with spin-dependent terms, we find that quarkyonic matter can develop ferromagnetic instabilities at low densities, characterized by negative magnetic susceptibility. This ferromagnetic behavior occurs in pure neutron matter, independent of proton contributions, and results from the competition between attractive spin-dependent interactions and kinetic energy costs. The system returns to paramagnetic behavior at higher densities when Pauli pressure dominates. Our results demonstrate that the splitting of Fermi momenta of quarkyonic matter produces fundamentally different magnetic responses compared to conventional nuclear matter, with important implications for neutron-star magnetism and magnetar physics.

The cross section of the ${}^{23}\mathrm{Na}(p,\gamma ){}^{24}\mathrm{Mg}$ reaction is dominated by direct capture at low energies relevant for stellar burning. Such cross sections can be constrained using spectroscopic factors ($C^{2}S$) or asymptotic normalization coefficients from transfer reactions. In this work, the ${}^{23}\mathrm{Na}({}^3\mathrm{He},d){}^{24}\mathrm{Mg}$ reaction was measured at $E_{\text{lab}}=21$ MeV to extract spectroscopic factors for ${}^{24}\mathrm{Mg}$ states with excitation energies in $E_x=7–12\mathrm{MeV}$ using the Enge split-pole spectrograph at the Triangle Universities Nuclear Laboratory. A new nonresonant astrophysical $S$ factor and the direct capture reaction rate for the ${}^{23}\mathrm{Na}(p,\gamma )$ reaction are calculated and presented based on this measurement. The new rate at $T<0.04$ GK is $43\%$ smaller than in previous studies. Rigorous treatments of uncertainties are presented using a Bayesian Markov Chain Monte Carlo (MCMC) method. Sources of uncertainties for computing the direct capture cross section are also discussed in detail.

Rotational structures in ${}^{249}\mathrm{Md}$ have been observed for the first time. One set of states forms a pair of strongly coupled bands with relatively strong E2 transitions and no identifiable M1 transitions between the two signature partners. Another set of states suggests a decoupled sequence of E2 transitions. These bands are assigned as based on the $7/2^{-}\left[514\right]$ and on the favored signature of the $1/2^{-}\left[521\right]$ Nilsson level, respectively. Based on previous decay studies, these levels are thought to be the ground state and first excited state of ${}^{249}\mathrm{Md}$, which also agrees with theoretical predictions.

Background: Phase transitions of matter under changes of external environment such as temperature and magnetic field have attracted great interests to various quantum many-body systems. Several phase transitions must have occurred in neutron stars as well such as transitions from normal to superfluid and superconducting phases and crust formation. While the temperature of a protoneutron star is as high as 10 MeV ($\approx {10}^{11}\mathrm{K}$) or higher, which are above critical temperatures for the emergence of superfluidity and crust formation, it cools rapidly down to 0.1 keV ($\approx {10}^6\mathrm{K}$) already after hundreds of years. While ordinary neutron stars have surface magnetic field strength of around ${10}^{12}\mathrm{G}$, those having higher magnetic field strength of ${10}^{14–15}\mathrm{G}$ or higher, so-called magnetars, have been observed. To uncover detailed evolution of neutron stars from their birth to later years, it is desired to develop fully microscopic approaches that take into account effects of superfluidity and superconductivity, finite temperature and magnetic field, on the same footing.

Purpose: The main purpose of this work is twofold: (1) to extend the formalism of the fully self-consistent superfluid nuclear band theory, developed in our previous work [K. Yoshimura and K. Sekizawa, Phys. Rev. C 109, 065804 (2024)], for finite-temperature and finite-magnetic-field systems, and (2) to explore possible phase transitions of nuclear matter by varying temperature and magnetic field.

Methods: We employ the superfluid band theory which is based on the Kohn-Sham density functional theory for superfluid systems with a local treatment of paring, known as superfluid local density approximation, subjected to the Bloch boundary conditions. We assume periodic spatial variation along $z$ direction with uniform distribution along $xy$ direction, allowing us to describe the slab phase as well as uniform nuclear matter. The finite-temperature extension is achieved in a similar manner as a finite-temperature Hartree-Fock-Bogoliubov calculation. Magnetic field effects are introduced taking into account both the Landau levels formation of relativistic electrons and the couplings of the magnetic field with nucleons' magnetic moments.

Results: We have performed superfluid band theory calculations for the slab phase of neutron star matter at $n_B=0.04,0.05,0.06$, and $0.07{\mathrm{fm}}^{-3}$ under various sets of temperature and magnetic field. From the results without magnetic field ($B=0$), we find that the superfluidity of neutrons disappears at around $k_{B}T=0.6–0.9\mathrm{MeV}$, and “melting” of nuclear slabs, that is, a structural change into the uniform matter, takes place at around $k_{B}T=2.5–4.5\mathrm{MeV}$. By turning on the magnetic field, we find that protons' spin gets polarized at around $B={10}^{16}\mathrm{G}$, whereas neutrons' spin is kept unpolarized on average up to around $B={10}^{17}\mathrm{G}$. Intriguingly, our microscopic calculations reveal that neutrons' spin is actually polarized locally inside and outside of the slab already at $B\approx {10}^{16}\mathrm{G}$, while keeping the system unpolarized in total. We show that the local polarization of neutrons' spin is caused by an interplay of ${}^1{S}_0$ pairing among neutrons and spin-dependent interactions between neutron and protons.

Conclusions: We have demonstrated validity and usefulness of the fully self-consistent superfluid nuclear band theory for describing neutron star matter under arbitrary temperature and magnetic field. Critical temperatures and magnetic fields have been predicted for (1) superfluid to normal transition, (2) crust formation, and (3) spin polarization, under conditions relevant to realistic neutron star environments.

In effective field theory, physical quantities, in particular observables, are expressed as a power series in terms of a small expansion parameter. For nonperturbative systems, for instance, nuclear physics, this requires the nonperturbative treatment of at least part of the interaction (or the potential, if one is dealing with a nonrelativistic system), while the rest of the interaction is included as perturbations. This is not entirely trivial and, as a consequence, different interpretations on how to treat these systems have appeared. A practical approach is to expand the effective potential, where this potential is later fully iterated in the Schrödinger equation for obtaining amplitudes and observables. The expectation is that this will lead to observables that will have an implicit power-counting expansion. Here, I explicitly check whether the amplitudes (when expanded according to the counting) are actually following the same power counting as the potential. It happens that reality does not necessarily conform to expectations, and the amplitudes will sometimes violate the power counting with which the potential has been expanded. A more formal approach is to formulate the expansion directly in terms of amplitudes and observables, which is the original aim of the effective field theory idea. Yet this second approach is technically complicated. I explore here the possibility of constructing potentials that, when fully iterated, will make sure that amplitudes are indeed expansible in terms of a small expansion parameter.

Measurements of fission fragment mass distributions provide valuable insights into the properties of fissioning systems and the dynamics of the fission process. Preneutron emission distributions, essential for fission fragment evaporation codes like $\mathtt{CGMF}$, are extracted from distributions that are always measured after neutron emission, as the timescale of the emission of prompt fission neutrons is too short for direct measurement before the emission. However, obtaining accurate preneutron emission distributions requires methods that eliminate the effects of mass resolution and detector efficiency. We propose a deblurring technique based on the Richardson-Lucy (RL) algorithm, commonly used in optics for image restoration, to correct for these experimental effects. The RL algorithm uses the measured mass distributions and a transfer matrix to perform iterative deconvolution. The advantage of this method over others is that it does not assume any predefined shape such as a sum of Gaussians, as in $\mathtt{CGMF}$, for the distributions. In this paper, we apply the algorithm to the fission fragment mass distributions measured in the spontaneous fission of ${}^{252}\mathrm{Cf}$ to extract preneutron emission fission fragment mass distributions. The results from deblurring are then used as inputs to $\mathtt{CGMF}$, and we compare the $\mathtt{CGMF}$ results obtained using deblurring inputs with the default $\mathtt{CGMF}$ results.

We investigate the statistical properties of neutron-induced nuclear reactions on ${}^{238}\mathrm{U}$ using the GOE-$S$-matrix model, in which the Gaussian orthogonal ensemble (GOE) is embedded into the scattering ($S$) matrix. The GOE-$S$-matrix model does not require any experimental values of the average level spacing $D$ and average decay width $\langle \mathrm{\Gamma }\rangle$ with their statistical distributions, but the model is fully characterized by the channel transmission coefficients used in the Hauser-Feshbach theory. We demonstrate that the obtained compound-nucleus decay-width distribution resembles the $\chi$-squared distribution with the degree of freedom greater than unity. This approach enables us to generate fluctuating cross sections while preserving requisite unitarity and accounting for interference between resonances. By comparing the calculated cross-section distribution with that from $R$-matrix theory, we demonstrate a smooth transition from the resolved resonance region to the continuum region.

Jet reconstruction in an ultrarelativistic heavy-ion collision suffers from a notoriously large, fluctuating thermal background. Traditional background‐subtraction methods struggle to remove this soft background while preserving the jet's hard substructure. In this Letter, we present DeepSub, a machine-learning-based approach for full-event background‐subtraction. DeepSub utilizes a model based on Swin Transformer layers to denoise jet images and disentangle hard jets from the heavy-ion background. DeepSub significantly outperforms existing subtraction techniques by reproducing key jet observables such as jet $p_{\mathrm{T}}$ and mass, and substructure observables such as girth and the energy correlation function, at the subpercent to percent level. As such, DeepSub paves the way for precision heavy-ion measurements in hitherto inaccessible kinematic regimes.