The excited states of ${}^{187}\mathrm{Os}$ have been studied via ${}^{186}\mathrm{W}({}^4\mathrm{He},3n){}^{187}\mathrm{Os}$ reaction at a beam energy of 36 MeV. The $\gamma$ rays were detected using the Indian National Gamma Array at the Variable Energy Cyclotron Centre having seven Compton-suppressed clover high-purity germanium (HPGe) detectors and one low-energy photon spectrometer (LEPS) detector with a digital data acquisition system. The level scheme of ${}^{187}\mathrm{Os}$ has been extended substantially up to $\approx$3.86 MeV of excitation energy and $37/2\hslash$ of spin with the placement of more than 90 new $\gamma$ rays. All known bands have been extended and new band structures have been identified. The results show evidence of triaxial shapes for different configurations of ${}^{187}\mathrm{Os}$ and different manifestations of nonaxial shape have been observed in the same nucleus. A comparison of the observed band crossing frequency in ${}^{187}\mathrm{Os}$ with neighboring nuclei gives evidence of a deformed shell gap at $N=110$. The experimental results are well explained using total Routhian surface calculations.

The odd-mass ${}^{99–105}\mathrm{Pd}$ nuclei were studied via ${}^{90–96}\mathrm{Zr}({}^{12,13}\mathrm{C},\mathrm{xn}\gamma )$ fusion/evaporation reactions. The beam was provided by the IFIN-HH Tandem accelerator at energies of approximately 50 MeV. Emitted $\gamma$ rays were detected by the hybrid multidetector system RoSphere. The structure of the low-lying excited states in ${}^{99–105}\mathrm{Pd}$ and their gamma-decay pattern are discussed in the framework of the rigid triaxial rotor plus particle model, providing a reasonable description of the low-lying level energies, electromagnetic transition rates, and magnetic moments.

The internal transition decay and $\alpha$ decay of the $T_{1/2}=53.3\mathrm{ms}, 9/2^{-}$ isomeric state in the neutron-deficient isotope, ${}^{183}\mathrm{Tl}$, have been studied using the Resonance Ionization Laser Ion Source and the Windmill detection setup at the ISOLDE facility at CERN. Clean samples of ${}^{183m}\mathrm{Tl}$ were produced by selective laser ionization and subsequent mass separation. An internal transition cascade of 356.5–272.2 keV $\gamma$ rays has been identified. Multipolarities of these transitions have been determined by means of simultaneous $\gamma$-ray and conversion-electron spectroscopy. Improved data for the fine structure of the ${}^{183m}\mathrm{Tl}\to {}^{179}\mathrm{Au}$ decay were deduced. This involves a 6058 keV $\alpha$-decay transition, which populates a previously unknown state in ${}^{179}\mathrm{Au}$, that is tentatively assigned as a ($9/2^{-}$). It is interpreted as a coupling of the $1h_{9/2}$ proton-intruder with the excited $0^{+}$ state in the ${}^{178}\mathrm{Pt}$ core.

The reported transverse wobbling band in odd-mass ${}^{105}\mathrm{Pd}$ has been reinvestigated by the triaxial particle rotor model. Employing different parameter sets of moment of inertia (MOI), several calculated results could be in good agreement with the experimental data, which show distinct modes of rotational excitation, respectively. These modes are sensitive to the ratio between the MOI at intermediate and short axis. With the increase of this ratio, a wobble about the short axis of the total angular momentum is gradually changed to a wobble about the intermediate axis. In addition, it is exhibited that precession and tunneling are two aspects of the quantum wobbling motion. The tunneling aspect dominates in the yrare states of ${}^{105}\mathrm{Pd}$. The present results in ${}^{105}\mathrm{Pd}$ show the complexity of the transverse wobbling mode.

At top collider energies where baryon stopping is negligible, the initial state of heavy-ion collisions is overall charge neutral and predominantly composed of gluons. Nevertheless, there can also be significant local fluctuations of the baryon number, strangeness, and electric charge densities about zero, perturbatively corresponding to the production of quark/antiquark pairs. These previously ignored local charge fluctuations can permit the study of charge diffusion in the quark-gluon plasma (QGP), even at top collider energies. In this paper we present a new model denoted ICCING (initial conserved charges in nuclear geometry) which can reconstruct the initial conditions of conserved charges in the QGP by sampling a ($g\to q\overline{q}$) splitting probability over the initial energy density. We find that the new charge distributions generally differ from the bulk energy density; in particular, the strangeness distribution is significantly more eccentric than standard bulk observables and appears to be associated with the geometry of hot spots in the initial state. The new information provided by these conserved charges opens the door to studying a wealth of new charge- and flavor-dependent correlations in the initial state and ultimately the charge transport parameters of the QGP.

Measurements from the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC) can be used to study the properties of quark-gluon plasma. Systematic constraints on these properties must combine measurements from different collision systems and methodically account for experimental and theoretical uncertainties. Such studies require a vast number of costly numerical simulations. While computationally inexpensive surrogate models (“emulators”) can be used to efficiently approximate the predictions of heavy ion simulations across a broad range of model parameters, training a reliable emulator remains a computationally expensive task. We use transfer learning to map the parameter dependencies of one model emulator onto another, leveraging similarities between different simulations of heavy ion collisions. By limiting the need for large numbers of simulations to only one of the emulators, this technique reduces the numerical cost of comprehensive uncertainty quantification when studying multiple collision systems and exploring different models.

Using the ampt$+$music$+$urqmd hybrid model, we study the global and local spin polarizations of $\mathrm{\Lambda }$ hyperons as functions of the freeze-out temperature of the spin degree of freedom in the hadronic phase of Au$+$Au collisions at $\sqrt{s_{NN}}=19.6$ GeV. Including contributions from both the thermal vorticity and thermal shear of the hadronic matter, we find that with the spin freeze-out temperature dropping from the hadronization temperature of 160 MeV to 110 MeV at the kinetic freeze-out, both the global and local spin polarizations of $\mathrm{\Lambda }$ hyperons due to the thermal vorticity decrease by a factor of 2, while those due to the thermal shear decrease quickly and become negligibly small at 140 MeV. Our results thus suggest that it is important to take into account the evolution of the spin degree of freedom in the hadronic stage of relativistic heavy-ion collisions when theoretically predicted global and local $\mathrm{\Lambda }$ spin polarizations are compared with the experimental measurements.

Background: Heavy charged particles after nuclear muon capture are an important nuclear physics background to the muon-to-electron conversion experiments Mu2e and COMET, which will search for charged lepton flavor violation at an unprecedented level of sensitivity.

Purpose: The AlCap experiment aimed to measure the yield and energy spectra of protons, deuterons, tritons, and $\alpha$ particles emitted after the nuclear capture of muons stopped in Al, Si, and Ti in the low-energy range relevant for the muon-to-electron conversion experiments.

Methods: Individual charged particle types were identified in layered silicon detector packages and their initial energy distributions were unfolded from the observed energy spectra.

Results: The proton yields per muon capture were determined as $Y_p\left(\text{Al}\right)=26.64\left(28\text{stat.}\right)\left(77\text{syst.}\right)\times {10}^{-3}$ and $Y_p\left(\text{Ti}\right)=26.48\left(35\right)\left(80\right)\times {10}^{-3}$ in the energy range 3.5–20.0 MeV, and as $Y_p\left(\text{Si}\right)=52.5\left(6\right)\left(18\right)\times {10}^{-3}$ in the energy range 4.0–20.0 MeV. Detailed information on yields and energy spectra for all observed nuclei are presented in the paper.

Conclusions: The yields in the candidate muon stopping targets, Al and Ti, are approximately half of that in Si, which was used in the past to estimate this background. The reduced background allows for less shielding and a better energy resolution in these experiments. It is anticipated that the comprehensive information presented in this paper will stimulate modern theoretical calculations of the rare process of muon capture with charged particle emission and inform the design of future muon-to-electron conversion experiments.

We investigate vortex solutions in the Ginzburg-Landau theory for neutron ${}^{3}P_2$ superfluids relevant for neutron star cores in which neutron pairs possess the total angular momentum $J=2$ with spin triplet and $P$ wave, in the presence of the magnetic field parallel to the angular momentum of vortices. The ground state is known to be in the uniaxial nematic (UN) phase in the absence of magnetic field, while it is in the $D_2$ ($D_4$) biaxial nematic (BN) phase in the presence of the magnetic field below (above) the critical value. We find that a singly quantized vortex always splits into two half-quantized non-Abelian vortices connected by soliton(s) as a vortex molecule with any strength of the magnetic field. In the UN phase, two half-quantized vortices with ferromagnetic cores are connected by a linear soliton with the $D_4$ BN order. In the $D_2$ ($D_4$) BN phase, two half-quantized vortices with cyclic cores are connected by three linear solitons with the $D_4$ ($D_2$) BN order. The energy of the vortex molecule monotonically increases and the distance between the two half-quantized vortices decreases with the magnetic field increases, except for a discontinuously increasing jump of the distance at the critical magnetic field. We also construct an isolated half-quantized non-Abelian vortex in the $D_4$ BN phase.

The NASA telescope NICER has recently measured x-ray emissions from the heaviest of the precisely known two-solar mass neutron stars, PSR J0740 $+$ 6620. Analysis of the data [Astrophys. J. Lett. 918, L28 (2021), Astrophys. J. Lett. 918, L27 (2021)] suggests that PSR J0740 $+$ 6620 has a radius in the range of $R_{2.0}\approx (11.4–16.1)\text{km}$ at the $68\%$ credibility level. In this article, we study the implications of this analysis for the sound speed in the high-density inner cores by using recent chiral effective field theory ($\chi \mathrm{EFT}$) calculations of the equation of state at next-to-next-to-next-to-leading order to describe outer regions of the star at modest density. We find that the lower bound on the maximum speed of sound in the inner core, $min\left\{c_{s,\max }^2\right\}$, increases rapidly with the radius of massive neutron stars. If $\chi \mathrm{EFT}$ remains an efficient expansion for nuclear interactions up to about twice the nuclear saturation density, $R_{2.0}⩾13$ km requires $min\left\{c_{s,\max }^2\right\}⩾0.562$ and 0.442 at the 68% and 95% credibility level, respectively.

The accuracy of atomic theory calculations limits the extraction of nuclear charge radii from isotope shift measurements of odd-proton nuclei. For Na isotopes, though precise spectroscopic measurements have existed for more than half a century, calculations by different methods offer a wide range of values. Here, we present accurate atomic calculations to reliably extract the Na charge radii. By combining experimental matter radii with nuclear coupled-cluster calculations based on nucleon-nucleon and three-nucleon forces, we constrain the parameters obtained from the atomic calculations. Therefore, this study guides atomic theory and highlights the importance of using accurate atomic and nuclear computations in our understanding of the size of light nuclei.

The properties of the ${}^{216}\mathrm{Rn}$ nucleus have been investigated using $\alpha \text{−}{}^{212}\mathrm{Po}$ and ${}^8\mathrm{Be}\text{−}{}^{208}\mathrm{Pb}$ systems with each interacting via a cluster model local interaction, and with a three-body $\alpha \text{−}\alpha \text{−}{}^{208}\mathrm{Pb}$ system within the coupled-channel formalism. The energies, transition probabilities, and cluster decay half-lives are compared with available experimental data. The two-body configurations are found to yield similar results, in fair agreement with the existing experimental data. The three-body system yields energy spectra and wave functions whose lowest energy states provides satisfactory and better description of the nucleus.

The excited states of ${}^{78}\mathrm{Se}$ were populated using the ${}^{76}\mathrm{Ge}(\alpha ,2n)$ fusion evaporation reaction. The deexcited gamma rays were detected using the Indian National Gamma Array (INGA) spectrometer comprising clover and low-energy photon spectrometer (LEPS) detectors. The ground state band of ${}^{78}\mathrm{Se}$ has been extended up to $E_x$ = 8.5 MeV and $J$ = $16\hslash$; this excitation regime is very close to the $\pi \left(1g_{9/2}^2\right)$ crossing frequency. Several newly observed in-band and intraband transitions belonging to the other bands of ${}^{78}\mathrm{Se}$ have also been placed in the level scheme based on their coincidence relationships. From the newly identified $E1$ transitions, an enhancement in the $B\left(E1\right)$/$B\left(E2\right)$ values with spin has been observed which indicates the onset of octupole correlations in the band structure built on the $3^{-}$, 2508-keV state. Persistence of triaxial shape up to the highest observed spin of the ground state band has been observed and the feature of successive $1g_{9/2}^2$ quasiparticle alignments due to protons and neutrons has been unveiled. The consequences arising due to the occurrence of the neutron $1g_{9/2}$ quasiparticle alignments in the other observed correlated band structures are also presented. The results are interpreted in terms of total Routhian surface (TRS) calculations and the level structure systematic of the neighboring nuclei.

Background: At the forefront of nuclear science, unstable nuclei are of special significance, in which the deformation and pairing correlations play an essential role in determining the nuclear structure. Under the mean field approach, the pairing and deformation effects have been uniformly considered within the deformed nonrelativistic Hartree-Fock-Bogoliubov model and the deformed relativistic Hartree-Bogoliubov (D-RHB) model. However, due to the limitation of the Hartree approach, an important ingredient of the nuclear force—the tensor force that contributes via the Fock diagram—is missing in the D-RHB model. Recently, the axially deformed relativistic Hartree-Fock (D-RHF) model was established for deformed nuclei, in which the $\pi$-pseudovector ($\pi$-PV) coupling can take into account the tensor force effects naturally. While limited by the BCS pairing, it cannot be safely applied to describe unstable nuclei.

Purpose: The aim of this work is to develop the axially deformed relativistic Hartree-Fock-Bogoliubov (D-RHFB) model for the reliable description of a wide range of unstable nuclei, by utilizing the spherical Dirac Woods-Saxon (DWS) base.

Method: Staring from the Lagrangian density that is based on the meson-propagated picture of nuclear force, the full Hamiltonian, that contains both mean field and pairing contributions, is derived by quantizing the Dirac spinor field in the Bogoliubov quasiparticle space, and the expectation with respect to the Bogoliubov ground state gives the full energy functional. As an extension of the D-RHF model, the degree of freedom associated with the $\rho$-tensor ($\rho \text{−}\mathrm{T}$) coupling is implemented, and incorporating with the Bogoliubov scheme the finite-range Gogny force D1S is utilized as the pairing force. Moreover, qualitative analyses on the nature of the $\pi$-PV and $\rho \text{−}\mathrm{T}$ couplings are presented to better understand their enhancements on the deformation effects.

Results: Space convergence related to the spherical DWS base is confirmed for the D-RHFB model by taking light nucleus ${}^{24}\mathrm{Mg}$ and mid-heavy one ${}^{156}\mathrm{Sm}$ as candidates. Compared to light nuclei, extraordinarily more negative energy states are necessitated to keep the expansion completeness on the spherical DWS base for mid-heavy and heavy nuclei, due to the enhanced correlations between the expansion components with large $\kappa$ quantity, as indicated by the nature of the $\pi$-PV and $\rho \text{−}\mathrm{T}$ couplings. Furthermore, because of the enhanced deformation effects by the $\pi$-PV and $\rho \text{−}\mathrm{T}$ couplings, the RHF Lagrangian PKA1 presents a deeper bound ground state for ${}^{24}\mathrm{Mg}$ than the other selected Lagrangians, in addition to predicting a fairly deep bound local minimum with large oblate deformation.

Conclusions: The axially deformed relativistic Hartree-Fock-Bogoliubov model has been established with confirmed convergence checks. The effects of the $\pi$-PV and $\rho \text{−}\mathrm{T}$ couplings, coupled with nuclear deformation, are analyzed in both light and mid-heavy nuclear systems, and are expected to be manifested in a wide range of unstable nuclei.

Based on the covariant density functional theory, the magnetic dipole ($M1$) resonance is described in the framework of relativistic random-phase approximation with density-dependent meson-nucleon coupling. The isovector-pseudovector interaction channel, represented by the exchange of $\pi$ meson, is included in the residual interaction to describe unnatural parity transitions. The strength distributions of $M1$ resonances are studied in doubly magic nuclei ${}^{48}\mathrm{Ca}$, ${}^{90}\mathrm{Zr}$, and ${}^{208}\mathrm{Pb}$, in comparison with their analog Gamow-Teller (GT) excitations. It is found that the $\pi$ meson and its zero-range counterterm are responsible for almost all of the energy shift caused by residual interaction, which is similar to the case of GT excitation. However, the strength of the counterterm suggested by the GT study is not suitable to simultaneously reproduce the experimental $M1$ peak energies from ${}^{48}\mathrm{Ca}$ to ${}^{208}\mathrm{Pb}$. To improve the descriptions of $M1$, effects caused by adjusting the strength of pionic counterterm and introducing the density dependence of the $\pi$ meson channel are explored. Finally, from the analyses of dominant transition configurations of GT and $M1$ resonance, we find that the proper spin-orbit splitting is the key to simultaneously reproduce the $M1$ strength distributions from light to heavy nuclei.

Beta-decay spectroscopy of the ${}^{187}\mathrm{Ta}$ ground state was performed at the KEK Isotope Separation System. $\beta$-delayed $\gamma$ rays corresponding to the previously reported in-beam transitions were observed. The $\beta$-decay half-life of the ${}^{187}\mathrm{Ta}$ ground state was determined to be 283(10) s by analyzing a time spectrum of $\beta \text{−}\gamma$ coincidence events. The $\beta$-decay branching ratio and log($ft$) values were evaluated for the first time. Based on the newly evaluated log($ft$) values of $>6.0$ and a decay scheme, spin-parity values of $I^{\pi }=7/2^{+}$ originating from the odd-proton orbit $\pi 7/2\left[404\right]$ were assigned with high confidence, which is consistent with the systematics of neighboring odd-$A$ nuclides.

Direct hard photon emissions from incoherent proton-neutron bremsstrahlung in collisions of the neutron-rich projectile ${}^{50}\mathrm{Ca}$ with ${}^{12}\mathrm{C}$ and ${}^{40}\mathrm{Ca}$ targets are simulated in the framework of the isospin-dependent quantum molecular dynamics (IQMD) model. By adjusting the diffuseness parameter of neutron density in the droplet model to obtain different neutron skin thicknesses for ${}^{50}\mathrm{Ca}$, the effects of neutron skin thickness on direct hard photon emission are investigated via several probes. The results show that more direct hard photons are produced with increasing neutron skin thickness in peripheral collisions. Meanwhile, we find that the multiplicity yield ratio $R_{cp}\left({\sigma }_{\gamma }\right)$ between central collisions and peripheral collisions as well as the rapidity dependence of multiplicity for direct hard photons are sensitive to neutron skin thickness. The results indicate that direct hard photon emission can be taken as an experimental observable to extract information on neutron skin thickness.

The nuclear transparency of charged hadrons produced in the $(e,e^{\prime })$ reaction on nuclei has been calculated using the Glauber model for the nuclear reaction. The color transparency (CT) of produced hadrons and the short-range correlation (SRC) of nucleons in the nucleus have been incorporated in the Glauber model to investigate their effects on nuclear transparency. The calculated results for the proton and pion are compared with the data.

Direct lifetime measurements via $\gamma \text{−}\gamma$ coincidences using a fast timing detector array consisting of ${\mathrm{LaBr}}_3\left(\mathrm{Ce}\right)$ scintillators has been applied to determine the lifetime of low-lying states in the semimagic $(N=50)$ nucleus ${}^{94}\mathrm{Ru}$. The experiment was carried out as the first in a series of “FAIR-0” experiments with the DESPEC experimental setup at the Facility for Antiproton and Ion Research (FAIR). Excited states in ${}^{94}\mathrm{Ru}$ were populated primarily via the $\beta$-delayed proton emission of ${}^{95}\mathrm{Pd}$ nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon ${}^{124}\mathrm{Xe}$ beam impinging on a 4 g/${\mathrm{cm}}^2{}^9\mathrm{Be}$ target. While the deduced $E2$ strength for the $2^{+}\to 0^{+}$ transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate $4^{+}\to 2^{+}$ transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell model predictions in the $fpg$ proton hole space with respect to doubly magic ${}^{100}\mathrm{Sn}$. The anomalous behavior is ascribed to a subtle interference between the wave function of the lowest seniority $\nu =2$, $I^{\pi }=4^{+}$ state and that of a close-lying $\nu =4$ state that exhibits partial dynamic symmetry. In addition, the observed strongly prohibitive $6^{+}\to 4^{+}$ transition can be attributed to the same mechanism but with a destructive interference. It is noted that such effects may provide stringent tests of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations.

Background: While many phenomenological models for nuclear fission have been developed, a microscopic understanding of fission has remained one of the most challenging problems in nuclear physics.

Purpose: We investigate an applicability of the generator coordinate method (GCM) as a microscopic theory for cluster radioactivities of heavy nuclei, which can be regarded as a fission with large mass asymmetry, that is, a phenomenon in between fission and $\alpha$ decays.

Methods: Based on the Gamow theory, we evaluate the preformation probability of a cluster with GCM while the penetrability of the Coulomb barrier is estimated with a potential model. To this end, we employ Skyrme interactions and solve the one-dimensional Hill-Wheeler equation with the mass octupole field. We also take into account the dynamical effects of the pairing correlation using Bardeen-Cooper-Schrieffer (BCS) wave functions constructed with an increased strength of the pairing interaction.

Results: We apply this scheme to the cluster decay of ${}^{222}\mathrm{Ra}$, i.e., ${}^{222}\mathrm{Ra}\to {}^{14}\mathrm{C}+{}^{208}\mathrm{Pb}$, to show that the experimental decay rate can be reproduced within about two order of magnitude. We also briefly discuss the cluster radioactivities of the ${}^{228}\mathrm{Th}$ and ${}^{232}\mathrm{U}$ nuclei. For these actinide nuclei, we find that the present calculations reproduce the decay rates with the same order of magnitude and within two or three order of magnitude, respectively.

Conclusions: The method presented in this paper provides a promising way to describe microscopically cluster decays of heavy nuclei.