Magnetic dipole ($M1$) excitations constitute not only a fundamental mode of nucleonic transitions, but they are also relevant for nuclear astrophysics applications. We have established a theory framework for the description of $M1$ transitions based on the relativistic nuclear energy density functional. For this purpose, the relativistic quasiparticle random phase approximation (RQRPA) is established using density-dependent point coupling interaction DD-PC1, supplemented with the isovector-pseudovector interaction channel in order to study unnatural parity transitions. The introduced framework has been validated using the $M1$ sum rule for core-plus-two-nucleon systems, and employed in studies of the spin, orbital, isoscalar, and isovector $M1$ transition strengths that relate to the electromagnetic probe in magic nuclei ${}^{48}\mathrm{Ca}$ and ${}^{208}\mathrm{Pb}$ and open shell nuclei ${}^{42}\mathrm{Ca}$ and ${}^{50}\mathrm{Ti}$. In these systems, the isovector spin-flip $M1$ transition is dominant, mainly between one or two spin-orbit partner states. It is shown that pairing correlations have a significant impact on the centroid energy and major peak position of the $M1$ mode. The $M1$ excitations could provide an additional constraint to improve nuclear energy density functionals in the future studies.

We present a systematic study of the strange and multistrange particle production in Pb $+$ Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV based on paciae model simulations. Two different mechanisms, namely the single string structure variations and multiple string interactions, are implemented in the simulations. These modifications give rise to an enhancement of the string tension value involved in the Lund string fragmentation framework and generate more strange particles in the hadronic final state. By comparing the simulation results with the ALICE experimental data, it turns out that the inclusion of the variable effective string tension in the paciae model results in an improved agreement between theory and experiment on the strangeness production in Pb $+$ Pb collisions.

Global polarization of $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ is calculated based on the axial vortical effect (AVE). Simulations are performed within the three-fluid dynamics model. Equations of state with a deconfinement transition result in a good agreement with STAR data for both $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ polarization, in particular, with the $\mathrm{\Lambda }\text{−}\overline{\mathrm{\Lambda }}$ splitting. Suppression of the gravitational-anomaly contribution required for the data reproduction is in agreement with predictions of the QCD lattice simulations. Predictions for the global polarization in forthcoming experiments at lower collision energies are made. These forthcoming data will provide a critical test for the AVE and thermodynamic mechanisms of the polarization.

A particle with spin and magnetic-dipole moment can be trapped in certain suitable magnetic-field configurations only as long as its spin remains aligned with the field direction as it moves through the trap. Here, we extend earlier analyses of spin-flip probabilities, which lead to storage loss for ultracold neutrons, and present arguments indicating that some of the earlier results should be multiplied by a factor of two.

Background: The structure of the Hoyle state, a highly $\alpha$-clustered state at 7.65 MeV in ${}^{12}\mathrm{C}$, has long been the subject of debate. Understanding if the system comprises of three weakly interacting $\alpha$ particles in the $0s$ orbital, known as an $\alpha$-condensate state, is possible by studying the decay branches of the Hoyle state.

Purpose: The direct decay of the Hoyle state into three $\alpha$ particles, rather than through the ${}^8\mathrm{Be}$ ground state, can be identified by studying the energy partition of the three $\alpha$ particles arising from the decay. This paper provides details on the breakup mechanism of the Hoyle stating using a new experimental technique.

Method: By using $\beta$-delayed charged-particle spectroscopy of ${}^{12}\mathrm{N}$ using the Texas active target time-projection chamber, a high-sensitivity measurement of the direct $3\alpha$ decay ratio can be performed without contributions from pileup events.

Results: A Bayesian approach to understanding the contribution of the direct components via a likelihood function shows that the direct component is $<0.043\%$ at the 95% confidence level. This value is in agreement with several other studies, and, here, we can demonstrate that a small nonsequential component with a decay fraction of about ${10}^{-4}$ is most likely.

Conclusion: The measurement of the nonsequential component of the Hoyle state decay is performed in an almost medium-free reaction for the first time. The derived upper limit is in agreement with previous studies and demonstrates sensitivity to the absolute branching ratio. Further experimental studies would need to be combined with robust microscopic theoretical understanding of the decay dynamics to provide additional insight into the idea of the Hoyle state as an $\alpha$ condensate.

The level structure of ${}^{130}\mathrm{La}$ has been investigated using the ${}^{121}\mathrm{Sb}({}^{12}\mathrm{C}$, 3n) reaction with the ROSPHERE array at IFIN-HH, Bucharest. The level scheme was significantly extended with the observation of 45 new states and 100 new transitions. Several band structures have been identified and a clear connection with the lower-lying states has been established. A lifetime of $\tau =3.6\left(2\right)$ ns has been measured for the 346-keV $6^{-}$ state by the in-beam fast timing technique. The lifetimes of 18 high-spin states have been determined by applying the Doppler-shift attenuation method. The deformations derived from the experimental $B\left(E2\right)$ transition strengths indicate distinct coexisting shapes at high spins in ${}^{130}\mathrm{La}$. The experimental properties of both low- and high-spin states were compared with theoretical calculations performed in the frame of the two-quasiparticles-plus-rotor model. Two new negative-parity decoupled bands, with a deduced quadrupole deformation ${\beta }_2=0.150\left(15\right)$, were interpreted by coupling the proton in the 1/2[550] and 3/2[541] orbitals with the odd neutron occupying mainly the low-$\mathrm{\Omega }$ orbitals from the $d_{3/2}$ and $s_{1/2}$ states. A quadrupole deformation ${\beta }_2=0.220\left(17\right)$ was derived for a newly identified positive-parity decoupled band. This enhanced deformation was attributed to the involvement in the band configuration of the $\mathrm{\Omega }=1/2$ $(f_{7/2},h_{9/2})$ intruder neutron orbital. The multiparticle configuration $\pi g_{7/2}{\left(h_{11/2}\right)}^2\otimes \nu \left(h_{11/2}\right)$ was assigned to a high-spin negative-parity dipole band, based on the comparison of the experimental $B\left(M1\right)$ transition strengths with values calculated by applying the geometrical model of Dönau and Frauendorf.

Nuclear structure of ${}^{243}\mathrm{Fm}$, ${}^{245}\mathrm{Fm}$, and their daughter nuclei were investigated via detection of their radioactive decays, $\alpha$, $\gamma$, and spontaneous fission. Measured $\alpha$-decay energies, half-lives, and branching ratios improve the literature data significantly. A signature for detection of the hitherto unknown ${}^{235}\mathrm{Cm}$ was found in the $\alpha$-decay chains from ${}^{243}\mathrm{Fm}$. Two groups of $\alpha$ events with average energies of 6.69(2) MeV and 7.01(2) MeV and with a half-life of $T_{1/2}={300}_{-100}^{+250}$ s are suggested to originate from ${}^{235}\mathrm{Cm}$. Tentative decay schemes for ${}^{243}\mathrm{Fm}$, ${}^{239}\mathrm{Cf}$, ${}^{235}\mathrm{Cm}$, and ${}^{245}\mathrm{Fm}$, ${}^{241}\mathrm{Cf}$ isotopes are suggested based on the present experimental data. Systematical trends of single-particle states in $N=141$ isotones of $Z=92–98$ nuclei are discussed.

The relativistic point-coupling model is combined with the complex momentum representation with resonances considered by BCS approximation, which is called the RMFPC-CMR-BCS theory. The RMFPC-CMR-BCS theory can be used to explore exotic structures in nuclei. The resonant levels near the continuum threshold can be shown to play an important role in the formation of exotic phenomena. The Ce isotopes are taken as examples, and the energy and width are obtained for the bound states and resonant states in a clear shell structure. The occupation probabilities of valence nucleons in these orbits close to the Fermi surface are calculated, and the contributions of every orbit to the nuclear density distribution are compared. It is found that several resonant levels with low-angular momentum contribute fairly diffuse density distributions, which result in the appearance of halos and giant halos in the Ce isotopes close to the neutron drip line. ${}^{186–190}\mathrm{Ce}$ are suggested to be halo nuclei and ${}^{192–198}\mathrm{Ce}$ are suggested to be giant halo nuclei, which agrees the relativistic HFB calculations and is expected to be verified in experiment.

A simplified, though realistic, model describing two receding and accelerating fission fragments, due to their mutual Coulomb repulsion, shows that fission fragments share excitation energy well after they ceased to exchange nucleons. This mechanism leads to a lower total kinetic energy of the fission fragments, particularly if the pygmy resonances in the fission fragments are excited. Even though the emphasis here is on fission, similar arguments apply to fragments in heavy-ion reactions.

In order to investigate the interplay between nuclear structure (shell closure) and dynamics, fission fragment mass distributions have been measured for reactions ${}^{35,37}\mathrm{Cl}+{}^{206,208}\mathrm{Pb}$. These reactions have similar entrance channel parameters except for the number of closed shell configuration in the entrance channel. Fission fragment mass distributions have been measured for these reactions in the energy region close to the Coulomb barrier. No mass-angle correlation was observed in any of the four reactions, indicating the absence of fast quasifission (QF), but mass distributions were wider than that of compound nucleus (CN) fission, which indicates the presence of slow QF. With comparable fissility and deformation values, extra stability against QF was observed for reactions which have more closed shell configurations in the entrance channel. Mass-angle distributions of these reactions do not follow the systematics with respect to mean fissility. A new systematics has been obtained by considering quadrupole deformation of the heavy reaction partner along with the fissility, which explains the absence of mass-angle correlation in the presently measured reactions.

Two-particle correlations based on the multiplicity of selected isobars are found to be sensitive to the parametrization of the fragments' binding energies and the breakup volume assumed in the model calculations. The properties of these correlations have been examined in the framework of the statistical multifragmentation model as a function of the breakup temperature. The model calculations suggest that the maxima of these correlation functions occur at well-separated temperatures as the breakup volumes used in the model vary from 3 to 6 times that at normal density. These volumes are within the range assumed in most statistical calculations and supported by experiments. Besides their position, the height and width of the maxima are also found to be sensitive to the parametrization of the fragments' binding energy. The magnitude of all these effects also depends on the isobars considered in the correlations. We found that, due to an interplay between the symmetry energy and the volume dependent terms of the Helmholtz free energy, in the case of nearly symmetric sources, correlations involving light mirror nuclei seem to enhance these effects. We suggest that the proposed correlation functions could be used to extract information on the fragments' energies and on the breakup volume of nuclear sources.

Recently, a hint for dibaryon $N\mathrm{\Delta }\left(D_{21}\right)$ was observed at the Wide Angle Shower Apparatus at the cooler synchrotron at Forschungszentrum Julich, GmbH (WASA-at-COSY) with a mass of about $30\pm 10$ MeV below the $N\mathrm{\Delta }$ threshold. It has a relatively small binding energy compared with $d^{*}\left(2380\right)$ and a width close to the width of the $\mathrm{\Delta }$ baryon, which suggests that it may be a dibaryon in a molecular state picture. In this work, we study the possible $S$-wave molecular states from the $N\mathrm{\Delta }$ interaction within the quasipotential Bethe-Salpeter approach. The interaction is described by exchanging $\pi , \rho$, and $\omega$ mesons. With reasonable parameters, a $D_{21}$ bound state can be produced from the interaction. The results also suggest that there may exist two more possible $D_{12}$ and $D_{22}$ states with smaller binding energies. The $\pi$ exchange is found to play the most important role to bind two baryons to form the molecular states. An experimental search for possible $N\mathrm{\Delta }\left(D_{12}\right)$ and $N\mathrm{\Delta }\left(D_{22}\right)$ states will be helpful for understanding the hint of the dibaryon $N\mathrm{\Delta }\left(D_{21}\right)$.

Lifetimes of low-lying yrast states in ${}^{162}\mathrm{Er}$ are measured using the electronic $\gamma \text{−}\gamma$ fast-timing technique. Excited states were populated in a ${}^{154}\mathrm{Sm}({}^{12}\mathrm{C},4n){}^{162}\mathrm{Er}$ fusion-evaporation reaction and $\gamma$ rays were detected in a combined setup of high purity germanium and ${\mathrm{LaBr}}_3$(Ce) scintillation detectors. The lifetimes of the $4_1^{+}$ and $6_1^{+}$ states are determined for the first time and the lifetimes of the $2_1^{+}$ and $7^{-}$ states are remeasured with higher precision. Reduced transition probabilities are extracted and well reproduced by theoretical calculations in the framework of the confined $\beta$ soft model and the interacting boson model.

Background: Heavy-ion induced two-nucleon transfer reactions are powerful tools to reveal peculiar aspects of the atomic nucleus, such as pairing correlations, single-particle and collective degrees of freedom, and more. Also, these processes are in competition with the direct meson exchange in the double charge exchange reactions, which have recently attracted great interest due to their possible connection to neutrinoless double-β decay. In this framework, the exploration of two-nucleon transfer reactions in the ${}^{20}\mathrm{Ne}+{}^{116}\mathrm{Cd}$ collision at energies above the Coulomb barrier is particularly relevant since the ${}^{116}\mathrm{Cd}$ nucleus is a candidate for the double-β decay.

Purpose: We want to analyze selected transitions to low-lying $0^{+}$ and $2^{+}$ states of the residual nuclei in the ${}^{116}\mathrm{Cd}$(${}^{20}\mathrm{Ne},{}^{22}\mathrm{Ne}$)${}^{114}\mathrm{Cd}$ two-neutron pickup and ${}^{116}\mathrm{Cd}$(${}^{20}\mathrm{Ne},{}^{18}\mathrm{O}$)${}^{118}\mathrm{Sn}$ two-proton stripping reactions at 306 MeV incident energy and determine the role of the couplings with inelastic transitions.

Methods: We measured the excitation energy spectra and absolute cross sections for the two reactions using the MAGNEX large acceptance magnetic spectrometer to detect the ejectiles. We performed direct coupled reaction channels and sequential distorted wave Born approximation calculations using the double folding São Paulo potential to model the initial and final state interactions. The spectroscopic amplitudes for two- and single-particle transitions were derived by different nuclear structure approaches: microscopic large-scale shell model, interacting boson model-2 and quasiparticle random phase approximation.

Results: The calculations are able to reproduce the experimental cross sections for both two-neutron and two-proton transfer reactions. The role of couplings with the inelastic channels are found to be important in the two-proton transfer case. A competition between the direct and the sequential process is found in the reaction mechanism. For the two-proton transfer case, the inclusion of the $1g_{7/2}$ and $2d_{5/2}$ orbitals in the model space is crucial.

Conclusions: The approach presented here, combination of nuclear structure and reaction mechanism ingredients, is a very promising tool for the analysis of two-neutron and two-proton transfer reactions between heavy nuclei.

Isospin transport ratio is a powerful method to estimate the neutron-proton (n-p) equilibration in heavy-ion collisions, and extensively used to obtain information on the asy-stiffness of the nuclear equation of state. In fact such a ratio is expected to bypass any perturbations introducing a linear transformation of the chosen observable. In particular, it is supposed to overcome contributions due to emission, either of dynamical or statistical nature, from the primary fragments formed during the collisions. In this paper we explore the validity of this assumption, looking at the quasiprojectile n-p ratio ($N/Z$) in peripheral and semiperipheral events for $\mathrm{Ca}+\mathrm{Ca}$ reactions at $35\mathrm{MeV}/\mathrm{nucleon}$, simulated via the antisymmetrized molecular dynamics transport model, coupled to different statistical decay codes. The statistical de-excitation of the primary fragments introduces a linear transformation at relatively high excitation energies (above $2\mathrm{MeV}/\mathrm{nucleon}$) when the residue approaches the evaporation attractor line, while some effect is produced at lower excitation energies due to the occurrence of some nonlinearities. As for fast emissions after the end of the projectile-target interaction it is shown that they introduce a nonlinear transformation too.

We introduce a new framework for studying clustering and for calculating $\alpha$ partial widths using ab initio wave functions. We demonstrate the formalism for ${}^{20}\mathrm{Ne}$, by calculating the overlap between the ${}^{16}\mathrm{O}+\alpha$ cluster configuration and states in ${}^{20}\mathrm{Ne}$ computed in the $abinitio$ symmetry-adapted no-core shell model. We present spectroscopic amplitudes and spectroscopic factors, and compare those to no-core symplectic shell-model results in larger model spaces, to gain insight into the underlying physics that drives $\alpha$ clustering. Specifically, we report on the $\alpha$ partial width of the lowest $1^{-}$ resonance in ${}^{20}\mathrm{Ne}$, which is found to be in good agreement with experiment. We also present first no-core shell-model estimates for asymptotic normalization coefficients for the ground state, as well as for the first excited $4^{+}$ state in ${}^{20}\mathrm{Ne}$ that lies in a close proximity to the $\alpha {+}^{16}\mathrm{O}$ threshold. This outcome highlights the importance of correlations for developing cluster structures and for describing $\alpha$ widths. The widths can then be used to calculate $\alpha$-capture reaction rates for narrow resonances of interest to astrophysics. We explore the reaction rate for the $\alpha$-capture reaction ${}^{16}\mathrm{O}{(\alpha ,\gamma )}^{20}\mathrm{Ne}$ at astrophysically relevant temperatures and determine its impact on simulated x-ray burst abundances.

We present a perturbative quantum chromodynamics based model for vacuum and in-medium hadronization. The effects of induced energy loss and nuclear absorption have been included. The main objective is the determination of the relative contribution of these mechanisms to the multiplicity ratio observable, measured in semi-inclusive deep-inelastic scattering off deuterium and nuclear targets. This is directly related to the determination of the production length, $Lp$, necessary for a quark to turn into a prehadron. We compare our results with HERMES data for multiplicity ratio and $p_t$ broadening, and show that the description of the whole data set, keeping the model parameters fixed, puts strong constrains on $Lp$. Contrary to induced-energy-loss based models, we find an important contribution from nuclear absorption at HERMES energies. Finally, we discuss some consequences of our study for the CERN Large Hadron Collider physics, and we present the model predictions for the future Electron-Ion Collider (EIC) experiment.

In the outer core of a neutron star (NS) quantum liquids are thought to exist during most of the observable stellar lifetime. These liquids are characterized by two different, density-dependent superfluid (SF) condensation critical temperatures associated with neutrons and protons. A possibility that cannot be excluded in the state-of-the-art astrophysics, and that warrants examination, is a spatial overlap of the SF and superconducting (SC) domains. Partial overlap would imply that there is a layer where both critical temperatures are equal. In vicinity of this layer the Ginzburg-Landau (GL) effective field theory is valid. In this paper, an effective field theory for a proton superconductor (SC) interacting with a neutron SF, both with scalar order parameters, is developed and applied to the surface energy (SE) of a magnetized SC body. Essentially, the SE studied here differs from the nuclear SE: here, the proton SF density decays to zero while the total proton density is constant across the surface. Interactions between the condensates are parametrized phenomenologically and their effects determined from calculations of a planar SE as the ranges of parameters are varied. The critical GL parameter ${\kappa }_c$ which renders the SE equal to zero is found analytically by noting that in a system with vanishing SE the thermodynamic critical MF (magnetic field) is equivalent to the upper critical MF. In the case of weak coupling, ${\kappa }_c$ is shown to be a linear function of SF-SF density-density coupling, in agreement with the earlier results based on asymptotic intervortex interactions. Numerical simulations corroborate my analytical predictions. Coupling due to the mixed term arising from a scalar product of gradients of the SF densities, which had been considered in the earlier literature, is seen to have practically no effect on the superconductivity type. However, this coupling does produce a frozen wave packet of the SF neutron density localized at the surface. It is shown that the leading contribution from the gradient coupling arises from a novel mixed quantum pressure term, but still does not affect the planar SE. The present calculations provide an initial map of superconductivity types in the phenomenological effective field theory and will serve as a landmark for future studies, which require microscopic calculations of the coupling parameters introduced here phenomenologically.

We study the impact of fission on the production and destruction of translead nuclei during the $r$-process nucleosynthesis occurring in neutron-star mergers. Abundance patterns and rates of nuclear energy production are obtained for different ejecta conditions using three sets of stellar reaction rates, one of which is based on microscopic and consistent calculations of nuclear masses, fission barriers, and collective inertias. We show that the accumulation of fissioning material during the $r$ process can strongly affect the free neutron abundance after the $r$-process freeze-out. This leads to a significant impact on the abundances of heavy nuclei that undergo $\alpha$ decay or spontaneous fission, affecting the radioactive energy production by the ejecta at timescales relevant for kilonova emission.