The island of inversion is a region of neutron-rich nuclei around ${}^{31}\mathrm{Na}$ that are deformed in their ground states. In this region, less is known about the energy levels of odd-mass nuclei, how they evolve with increasing neutron numbers, and how they can be organized into rotational bands. We perform ab initio coupled-cluster calculations of spectra in odd-mass Ne, Na, and Mg nuclei based on an interaction of chiral effective field theory. Our results confirm some tentative spin and parity assignments, predict the structure of nuclei near the neutron dripline, and inform us about rotational bands in this region of the nuclear table.

We have implemented the $3+1$ dimensional CLVisc hydrodynamics model with TrENTo-3D initial conditions to investigate the spin polarization of $\mathrm{\Lambda }$ hyperons along the beam direction in $\mathrm{p}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=8.16$ TeV. Following our previous theoretical framework based on quantum kinetic theory, we consider three different scenarios: $\mathrm{\Lambda }$ equilibrium, $s$ quark equilibrium, and isothermal equilibrium scenarios. We have computed the second Fourier sine coefficients of spin polarization along the beam direction, denoted as $\langle P_{z}sin2({\varphi }_p-{\mathrm{\Psi }}_2)\rangle$, with ${\varphi }_p-{\mathrm{\Psi }}_2$ being the azimuthal angle relative to the second-order event plane ${\mathrm{\Psi }}_2$, as functions of multiplicity, transverse momentum, and pseudorapidity in the three scenarios. Additionally, we have also computed the spin polarization along the beam direction, $P_z$, as a function of the azimuthal angle. We find that the spin polarization induced by thermal vorticity always provides an opposite contribution compared to the shear-induced polarization in $\mathrm{p}+\mathrm{Pb}$ collisions. The total spin polarization computed by the current hydrodynamic model disagrees with the data measured by LHC-CMS experiments.

In relativistic heavy-ion collisions, the formation of a deconfined and thermalized state of partons, known as quark-gluon plasma (QGP), leads to enhanced production of strange hadrons in contrast to proton-proton ($pp$) collisions, which are taken as baseline. This observation is known as strangeness enhancement in heavy-ion collisions and is considered one of the important signatures that can signify the formation of QGP. However, in addition to strangeness enhancement, recent measurements hint at observing several heavy-ion-like features in high multiplicity $pp$ collisions at energies available at the CERN Large Hadron Collider. Alternatively, event shape observables, such as transverse spherocity, transverse sphericity, charged particle flattenicity, and relative transverse activity classifiers, can fundamentally separate hard interaction-dominated jetty events from soft isotropic events. These features of event shape observables can probe the observed heavy-ion-like features in $pp$ collisions with significantly reduced selection bias and can bring all collision systems on equal footing. In this article, we present an extensive summary of the strange particle ratios to pions as a function of different event classifiers using the PYTHIA 8 model with color reconnection and rope hadronization mechanisms to understand the microscopic origin of strangeness enhancement in $pp$ collisions and also prescribe the applicability of these event classifiers in the context of strangeness enhancement. Charged-particle flattenicity is found to be most suited for the study of strangeness enhancement, and it shows a quantitative enhancement similar to that seen for the analysis based on the number of multiparton interactions.

The pseudospin partner bands (labeled as bands 1 and 2) built on the configuration $\pi {(1g_{7/2},2d_{5/2})}^1$ in ${}^{133}\mathrm{Cs}$ have been studied within the core-quasiparticle-coupling model, utilizing deformation parameters calculated from the relativistic density functional theory. The calculated energy spectra and electromagnetic transition probability ratios $B\left(M1\right)/B\left(E2\right)$ agree well with experimental observations. An angular momentum coupling scheme relevant to these bands is deduced through investigations of the $g$ factors, the static quadrupole moments, the probability distributions of the core angular momentum, the valence particle configuration components, the angle between particle and core angular momenta, and the individual angular momentum components. It is revealed that bands 1 and 2 are primarily based the $1g_{7/2}$ and $2d_{5/2}$ orbitals, with their respective core angular momentum values $R$ approximately equal to $I-7/2$ and $I-5/2$, respectively. This results in a notable suppression of interband $B\left(M1\right)$ transitions from band 1 to band 2, consistent with the observed near-zero $B\left(M1\right)/B\left(E2\right)$ ratio.

In this work we provide a model-independent experimental evaluation of the degree of isospin equilibration taking place in ${}^{58,64}\mathrm{Ni}+{}^{58,64}\mathrm{Ni}$ collisions at 32 MeV/nucleon across varying reaction centralities. This result has been obtained by combining the complementary information provided by two different datasets, sharing common characteristics. The first dataset has been acquired with the INDRA setup and has been used to implement a model-independent reconstruction of the impact parameter. The second dataset has been acquired in the first experimental campaign of the coupled INDRA-FAZIA apparatus at GANIL. The neutron-to-proton content of the quasiprojectile remnant measured by FAZIA has been employed as isospin observable. The effect of isospin diffusion has been evidenced by means of the isospin transport ratio, reported as a function of the impact parameter of the collision. The evolution toward isospin equilibration from semiperipheral to more central collisions is clearly extracted. This experimental result, expanding our previous works [Phys. Rev. C 106, 024603 (2022) and Phys. Rev. C 108, 054611 (2023)], can be compared with the predictions of any transport model, and can thus be used to set constraints on the behavior of the symmetry energy term of the nuclear Equation of State at sub- to saturation densities.

We investigate the electromagnetic form factors of protons in proton-nucleus scattering by analyzing experimental cross-sections of accompanying bremsstrahlung photons. A novel bremsstrahlung model for proton-nucleus scattering is developed, with a primary focus on previously unconsidered incoherent bremsstrahlung. In the analysis we select experimental bremsstrahlung data from $p+{}^{197}\mathrm{Au}$ scattering at a proton beam energy of 190 MeV obtained by the TAPS collaboration. Our findings are as follows: (1) The inclusion of incoherent emission in our calculations improves significantly the agreement with experimental data. Notably, the contribution of incoherent bremsstrahlung is substantially larger than that of coherent bremsstrahlung. (2) Incorporating form factors of the scattered proton enhances agreement with experimental data compared to calculations that do not include form factors alongside coherent and incoherent contributions. (3) The model exhibits high sensitivity in studying the form factors of the scattered proton. This presents a novel opportunity to investigate the internal structure of protons under the influence of nuclear forces in nuclear scattering.

The preformation factor quantifies the probability of $\alpha$ particles preforming on the surface of the parent nucleus in decay theory and is closely related to the study of $\alpha$ clustering structure. In this work, a multilayer perceptron and autoencoder ($\mathrm{MLP}+\mathrm{AE}$) hybrid neural network method is introduced to extract preformation factors within the generalized liquid drop model and experimental data. A $\mathcal{K}$-fold cross validation method is also adopted. The accuracy of the preformation factor calculated by this improved neural network is comparable to the results of the empirical formula. $\mathrm{MLP}+\mathrm{AE}$ can effectively capture the linear relationship between the logarithm of the preformation factor (${\text{log}}_{10}{P}_{\alpha }^{\text{exp}}$) and the square root of the ratio of the decay energy ($Q_{\alpha }^{-1/2}$), further verifying that Geiger-Nuttall law can deal with preformation factor. The extracted preformation probability of isotope and isotone chains show different trends near the magic number, and in addition, an odd-even staggering effect appears. This means that the preformation factors are affected by closed shells and unpaired nucleons. Therefore the preformation factors can provide nuclear structure information. Furthermore, for 41 new nuclides, the half-lives introduced with the preformation factors reproduce the experimental values as expected. Finally, the preformation factors and $\alpha$-decay half-lives of $Z=119$ and 120 superheavy nuclei are predicted.

Background: The dynamics of sub-barrier fusion between two heavy nuclei can be comprehended to a great extent within the coupled-channels formalism. However, the role of nucleon transfer channels on fusion remains ambiguous.

Purpose: This work aims to address some of the open questions about the influence of neutron transfer on fusion, e.g., relative importance of inelastic excitations and neutron transfer channels, role of deformation of the nuclei in the intermediate partition, number of positive $Q$-value neutron transfer channels which may affect the fusion dynamics, etc.

Method: Fusion excitation functions were measured for the systems ${}^{28}\mathrm{Si}+{}^{140,142}\mathrm{Ce}$ around the interaction barrier. The barrier height distributions were derived by the conventional double-differential recipe and a Gaussian-analytic method. Theoretical investigations by two different approaches were carried out to unravel the effects of positive $Q$-value neutron transfer channels on fusion dynamics.

Results: Enhancement of sub-barrier fusion cross sections for ${}^{28}\mathrm{Si}+{}^{140}\mathrm{Ce}$, with two positive $Q$-value neutron pickup channels, is quite well reproduced by the theory. A marginal influence of neutron transfer on fusion is observed. Reasonably good reproduction of the barrier distribution is achieved for this system. In contrast, the measured excitation function for ${}^{28}\mathrm{Si}+{}^{142}\mathrm{Ce}$, with six positive $Q$-value neutron pickup channels, is not adequately accounted for within the coupled-channels framework, though the semiempirical coupled-channels model offers a better agreement with the experimental data. Nevertheless, the barrier distribution for this system cannot be satisfactorily reproduced by either model.

Conclusions: A much stronger influence of neutron transfer channels is inferred in ${}^{28}\mathrm{Si}+{}^{142}\mathrm{Ce}$ compared to ${}^{28}\mathrm{Si}+{}^{140}\mathrm{Ce}$. Mismatch between experimental results and theoretical predictions in case of ${}^{28}\mathrm{Si}+{}^{142}\mathrm{Ce}$ points to the limitations of existing coupled-channels approaches to interpret the influence of neutron transfer channels on fusion dynamics comprehensively.

Background: ${}^6\mathrm{Li}$ is usually treated as an $\alpha +p+n$ three-body system, and the validity of this picture is important for understanding ${}^6\mathrm{Li}$ reactions. The ($p,2p$) reaction is a powerful method to study the structure of valence nucleons in ${}^6\mathrm{Li}$. Recently, the new experimental data of the ${}^6\mathrm{Li}(p,2p){}^5\mathrm{He}$ reaction have been obtained and should be analyzed.

Purpose: We investigate the ${}^6\mathrm{Li}(p,2p){}^5\mathrm{He}$ reaction using the $\alpha +p+n$ three-body wave function of ${}^6\mathrm{Li}$ and study the validity of this model.

Methods: We calculate the ${}^6\mathrm{Li}$ wave function by using the Gaussian expansion method, and the function is used to obtain the relative wave function between $p$ and ${}^5\mathrm{He}$. We combine the relative wave function with the distorted wave impulse approximation.

Results: Our results reproduce the experimental data of the triple differential cross section within about a 10% difference in the absolute values, and contributions from both $p$- and $s$-wave states of ${}^5\mathrm{He}$ in ${}^6\mathrm{Li}$ are found to be important.

Conclusions: We can qualitatively understand the ${}^6\mathrm{Li}(p,2p){}^5\mathrm{He}$ reaction by describing ${}^6\mathrm{Li}$ with the three-body model. Contribution from the $s$-wave component is important in reproducing the experimental data in the zero recoil-momentum region.

Photoproduction of charged pions pairs off protons is studied within the invariant masses of the final state hadrons from 1.6 to 2.4 GeV at the Thomas Jefferson National Accelerator Facility with the CLAS detector. The total and differential cross sections and spin-density matrix elements are presented for the isobars $p{\rho }^0\left(770\right), \mathrm{\Delta }{\left(1232\right)}^{++}{\pi }^{-}$, and $\mathrm{\Delta }{\left(1232\right)}^0{\pi }^{+}$. The data are included in the Bonn-Gatchina coupled-channel analysis and provide the information necessary to determine the branching fractions of $N\rho \left(770\right)$ decays for most known $N^{*}$ and ${\mathrm{\Delta }}^{*}$ resonances. For the first time, the $N\rho$ branching ratios are obtained here from an event-based likelihood to $\gamma p\to {\pi }^{+}{\pi }^{-}p$.

We systematically probe different parametrizations of the attractive nuclear force based on real gas models to construct the nuclear matter equation of state. In each of the cases, the repulsion between nucleons is treated in the framework of excluded volume, and interaction parameters are fitted to the empirical properties of the nuclear ground state. We calculate the critical temperature $T_c$ and critical particle number density $n_c$, and find that they are strongly correlated. Both are also correlated with the incompressibility $K_0$ in the nuclear ground state. We also include a quarkyonic matter phase in the quasiparticle description and investigate the relationships among $K_0$, transition density to the quarkyonic phase, $n_{\mathrm{tr}}$, and corresponding peak in the speed of sound, $v_{s,\max }^2$. At each density, the quark fraction is found by minimizing the energy density. We find that both $n_{\mathrm{tr}}$ and $v_{s,\max }^2$ are negatively correlated with $K_0, n_c$, and $T_c$.

Isospin-equilibrating weak processes, called “Urca” processes, are of fundamental importance in astrophysical environments like (proto-)neutron stars, neutron star mergers, and supernovae. In these environments, matter can reach high temperatures of tens of MeVs and be subject to large magnetic fields. We thus investigate Urca rates at different temperatures and field strengths by performing the full temperature and magnetic-fielddependent rate integrals for different equations of state. We find that the magnetic fields play an important role at temperatures of a few MeV, especially close to or below the direct Urca threshold, which is softened by the magnetic field. At higher temperatures, the effect of the magnetic fields can be overshadowed by the thermal effects. We observe that the magnetic field influences the neutron decay rates more strongly than the electron-capture rates, leading to a shift in the flavor equilibrium.

Machine learning offers a powerful framework for validating and predicting atomic mass. We compare three improved neural network methods for representation and extrapolation for atomic mass prediction. The powerful method, adopting a macroscopic-microscopic approach and treating complex nuclear effects as output labels, achieves superior accuracy in AME2020, yielding a much lower root-mean-square deviation of 0.122 MeV in the test set, significantly lower than alternative methods. It also exhibits a better extrapolation performance when predicting AME2020 from AME2016 with a root-mean-square deviation of 0.191 MeV. We further conduct sensitivity analyses against the model inputs to verify interpretable alignment beyond statistical metrics. Incorporating theoretical predictions of magic numbers and masses, our fully connected neural networks reproduce key nuclear phenomena including nucleon pairing correlation and magic number effects. The extrapolation capability of the framework is discussed and the accuracy of predicting new mass measurements for isotope chains has also been tested.

We perform Bayesian model calibration of two-nucleon $\left(NN\right)$ low-energy constants (LECs) appearing in an $NN$ interaction based on pionless effective field theory $\left(\cancel{\pi }\mathrm{EFT}\right)$. The calibration is carried out for potentials constructed using naive dimensional analysis in $NN$ relative momenta $\left(p\right)$ up to next-to-leading order $[\mathrm{NLO},O\left(p^2\right)]$ and next-to-next-to-next-to-leading order $[\mathrm{N}3\mathrm{LO},O\left(p^4\right)]$. We consider two classes of $\cancel{\pi }\mathrm{EFT}$ potential: one that acts in all partial waves and another that is dominated by $s$-wave physics. The two classes produce broadly similar results for calibrations to $NN$ data up to $E_{\mathrm{lab}}=5$ MeV. Our analysis accounts for the correlated uncertainties that arise from the truncation of the $\cancel{\pi }\mathrm{EFT}$. We simultaneously estimate both the EFT LECs and the parameters that quantify the truncation error. This permits quantitative estimates of the $\cancel{\pi }\mathrm{EFT}$ breakdown scale, ${\mathrm{\Lambda }}_b$: the 95% intervals are ${\mathrm{\Lambda }}_b\in [50.11,63.03]$ MeV at NLO and ${\mathrm{\Lambda }}_b\in [72.27,88.54]$ MeV at N3LO. Invoking naive dimensional analysis for the $NN$ potential therefore does not lead to consistent results across orders in $\cancel{\pi }\mathrm{EFT}$. This exemplifies the possible use of Bayesian tools to identify inconsistencies in a proposed EFT power counting.

The origin of the large angular momenta observed for fission fragments is still a question under discussion. To address this, we study isomeric yield ratios (IYRs), i.e., the relative population of two or more long-lived metastable states with different spins, of fission products. We report on IYRs of 17 isotopes produced in the 28-MeV $\alpha$-induced fission of ${}^{232}\mathrm{Th}$ at the IGISOL facility of the University of Jyväskylä. The fissioning nuclei in this reaction are ${}^{233,234,235}\mathrm{U}^{*}$. We compare our data to IYRs from thermal neutron-induced fission of ${}^{233}\mathrm{U}$ and ${}^{235}\mathrm{U}$, and we observe statistically significant larger IYRs in the ${}^{232}\mathrm{Th}$($\alpha$, $f$) reaction, where the average compound nucleus (CN) spin is 7.7 $\hslash$, than in ${}^{233,235}\mathrm{U}$($n_{\mathrm{th}}$, $f$), with average spins of 2.6 and 3.6 $\hslash$, respectively. To assess the influence of the excitation energy, we study literature data of IYRs from photon-induced fission reactions, and find that, within current uncertainties, the IYRs indicate no dependency of the CN excitation energy. We conclude that the different IYRs seem to be due to the different CN spins alone. This would imply that the fission fragment angular momentum only partly comes from the fission process itself and is, in addition, influenced by the angular momentum present in the CN.

Proton-rich nuclei beyond the proton drip line exhibit unique phenomena, such as the Thomas-Ehrman shift (TES), providing valuable insights into nuclear stability and isospin symmetry breaking. The discovery of the lightest new isotope, ${}^{21}\mathrm{Al}$, situated beyond the proton drip line, was recently reported in the experiment. In this study, we employ the Gamow shell model (GSM) to explore the TES in mirror pairs ${}^{21}\mathrm{Al}/{}^{21}\mathrm{O}$, focusing on how this phenomenon affects the energy levels of these nuclei. Our calculations describe the ground state energies and reveal significant TES with large mirror energy differences in the excited mirror $1/2^{+}$ states in ${}^{21}\mathrm{Al}/{}^{21}\mathrm{O}$. The large mirror energy difference is primarily due to the significant occupation of weakly bound or unbound $s_{1/2}$ orbitals, resulting in the extended radial density distributions, and variations in Coulomb energy and nuclear interaction contributions between the mirror states. Additionally, the low-lying states of ${}^{21}\mathrm{Al}$ are also calculated with the GSM in coupled-channel (GSM-CC) representation, Furthermore, we also predict the cross section of ${}^{20}\mathrm{Mg}$($p,p$) scattering, which serves as another candidate approach to study the unbound structure of ${}^{21}\mathrm{Al}$ in the experiment, offering a theoretical framework for studying the structure and reaction dynamics of ${}^{21}\mathrm{Al}$ in future experiments.

The potential for two-quasiparticle wobbling modes in even-even nuclei is investigated through a combined approach of microscopic adiabatic and configuration-fixed constrained relativistic density functional theory (RDFT) and fully quantal particle rotor model (PRM) calculations for isotope chains ${}^{124–134}\mathrm{Ba}$, ${}^{122–138}\mathrm{Nd}$, ${}^{122–132}\mathrm{Xe}$, and ${}^{122–136}\mathrm{Ce}$. The RDFT calculations reveal the existence of multiple nuclear states characterized by optimal triaxial deformations and high-$j$ particle configurations, particularly the $\pi h_{11/2}^2$ and $\nu h_{11/2}^2$ configurations. These configurations enable the establishment of wobbling modes in these isotopes. A detailed examination of the resulting energy spectra, electromagnetic transition probabilities, and angular momentum geometry is further performed in the framework of PRM. The results indicate the potential for an extended region with wobbling modes in even-even nuclei in the mass region of $A\approx 130$.

Using the dinuclear system model, the influence of driving potentials and thresholds of particle emission from a compound nucleus on the formation of evaporation residues is studied in complete fusion reactions. The experimental maximum production cross sections and excitation functions of evaporation residues in the $xn$, $pxn$, and $\alpha xn$ channels of complete fusion reactions leading to compound nuclei with atomic numbers $Z_{\mathrm{CN}}$ = 84, 90, and 92 are well described and several predictions are made.

The energy and centrality dependence of the kaon resonance ratio $(K^{*0}+{\overline{K}}^{*0})/(K^{+}+K^{-})$ is explored in the RHIC-BES and CBM-FAIR energy regime. To this aim, the ultrarelativistic quantum molecular dynamics model is employed to simulate reconstructable $K^{*}$ resonances in $\mathrm{Au}+\mathrm{Au}$ and $p+p$ collisions from $\sqrt{s_{NN}}=3–39$ GeV. We obtain a good description of the resonance yields and mean transverse momenta over the whole investigated energy range. The decrease of the $K^{*}/K$ ratio with increasing centrality is in line with the available experimental data. We also observe the experimenatlly measured increase in $\langle p_{\text{T}}\rangle$ with increasing centrality which is interpreted as a lower reconstruction probability of low-$p_{\text{T}}{K}^{*}$ due to the $p_{\text{T}}$ dependent absorption of the decay daughter hadrons. We conclude that the observed suppression of reconstructable $K^{*}$ resonances provides a strong sign of an extended hadronic rescattering stage at all investigated energies. Its duration increases from peripheral to central reactions as expected. Following a method, suggested by the STAR experiment, a lower bound on the duration of the hadronic stage is extracted using the $K^{*}/K$ ratios at chemical and kinetic freeze-out. The resulting lifetimes are in good agreement with the experimental data, but shorter than the actual lifetime of the hadronic phase in the transport simulations.