We apply Bayesian techniques to compare a simple, empirical model for jet quenching in heavy-ion collisions to centrality-dependent jet $R_{AA}$ measured by ATLAS for $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02$ TeV. We find that the $R_{AA}$ values for central collisions are adequately described with a model for the mean $p_T$-dependent jet energy loss using only two parameters. This model is extended by incorporating two-dimensional initial geometry information from TRENTo and compared to centrality-dependent $R_{AA}$ values. We find that the results are sensitive to the value of the jet-quenching formation time, ${\tau }_f$, and that the optimal value of ${\tau }_f$ varies with the assumed path-length dependence of the energy loss. We construct a covariance error matrix for the data from the $p_T$-dependent contributions to the ATLAS systematic errors and perform Bayesian calibrations for several different assumptions for the systematic error correlations. We show that the most-probable functions and ${\chi }_d^2$ values are sensitive to assumptions made when fitting to correlated errors. This work demonstrates the utility of a simple model that can quickly demonstrate the constraining power of jet-quenching observables with corresponding uncertainties and guide future studies using more sophisticated models.

The implications of including the scalar isovector $\delta$ meson in a relativistic mean-field description of nuclear matter are discussed. A Bayesian inference approach is used to determine the parameters that define the isovector properties of the model. The properties of nuclear matter and neutron stars are discussed. The inclusion of the $\delta$ meson has only a small effect on the maximum mass of the neutron star and on the speed of sound in its interior, but it has a strong effect on the radius and the tidal deformability of low- and medium-mass stars. This is mainly due to the effect of the $\delta$ meson on the symmetry energy and its slope and curvature at saturation, increasing the range of possible values of these three properties, and in particular allowing positive values of the symmetry energy curvature. Due to the effect of the $\delta$ meson on the symmetry energy, the proton content of the star is also strongly affected. The inclusion of the $\delta$ meson in the relativistic mean-field description of nuclear matter extends the phase space spanned by the model, allowing for a more flexible density dependence of the symmetry energy compatible with experimental, observational, and ab initio constraints.

This study investigates the predictive capabilities of machine learning models in nuclear $\beta$-decay half-life predictions and their application to $r$-process nucleosynthesis. The research explores the intricacies of statistical modeling using support vector machines (SVM), focusing on understanding the learning and prediction of various nuclear configurations and features that influence $\beta$-decay half-lives. By considering a comprehensive dataset spanning from light to heavy mass nuclei, the SVM demonstrates remarkable accuracy in reproducing experimentally known half-lives across diverse nuclear structures. Evaluations reveal the effectiveness of this model across different nuclear classes, with notable improvements observed in even-even nuclei predictions. Furthermore, this study demonstrates the extrapolative capabilities of SVM predictions in solar $r$-process nucleosynthesis, emphasizing its ability to accurately predict $r$-process abundances. The SVM model, particularly when utilizing the radial basis function kernel, exhibits strong agreement with experimental data, providing valuable insights into the behavior of highly neutron-rich nuclei. These findings underscore the significance of machine learning as a powerful tool in nuclear physics research, offering promising avenues for advancing our understanding of $\beta$-decay processes and $r$-process nucleosynthesis.

The photon strength function of ${}^{58}\mathrm{Fe}$ has been extracted using both the Oslo and Shape methods from $\mathrm{particle}\text{−}\gamma$ coincidence data measured using the Detector Array for Photons, Protons, and Exotic Residues, which probes nuclei utilizing ($d,p$) reactions in inverse kinematics. Four $\mathrm{particle}\text{−}\gamma$ coincidence matrices, each constructed with different treatments of the $\gamma \text{−}\mathrm{ray}$ energies, are explored in order to observe the impact on the resulting nuclear level density and photon strength. The final photon strength function reported is found to agree well with previous Oslo measurements of other iron isotopes. Systematic uncertainties are included, using different model parameters and their reported errors to perform the Oslo method normalization. The model-independent Shape method is explored and the functional form of the photon strength function obtained is in agreement with the Oslo method results. A low-energy enhancement is not reported for ${}^{58}\mathrm{Fe}$ in this work given possible subtraction issues originating from strongly populated states.

The UrQMD model with a density dependent equation of state, including a first-order phase transition, is used to study the time dependence of baryon number and proton number susceptibilities up to third order in heavy ion reactions of $E_{\mathrm{lab}}=2–3A\mathrm{GeV}$. A significant deviation from the Gaussian fluctuations of the baryon number fluctuation in coordinate space is observed. The proton number fluctuations are always suppressed as they constitute only a small fraction of the total baryon number during the dense phase of the collision. It is found that the only measurable, but small, signal would be an enhancement of the third order (or higher) proton cumulant in a finite rapidity window $\mathrm{\Delta }y$ that is larger than one unit of rapidity. In addition, it is found that the coordinate fluctuations will lead to an enhancement of cluster production due to the correlations in coordinate space. However, this enhancement is small and mainly occurs during the dense part of the collision before the system actually freezes out.

We report on a new spectroscopic study of the decay of high-$K$ isomers in ${}_{102}{}^{254}\mathrm{No}_{152}$, a touchstone nucleus for testing models to understand the structure of superheavy nuclei. The experiment, performed using the Argonne gas-filled analyzer (AGFA), was geared toward resolving long-standing ambiguities in spin-parity and configuration assignments for the two- and four-quasiparticle (qp) intrinsic excitations identified in this nucleus. The isomer decay schemes are firmly established with the help of the highest-statistics $\gamma \text{−}\gamma$ coincidence data collected to date, providing anchor points for competing theories. A newly measured half-life in the nanosecond range establishes a second 2-qp isomer in ${}^{254}\mathrm{No}$. The preferred decay pathways for the 2- and 4-qp isomers are discussed, providing new insights into the underlying hindrance mechanisms at play in these heavy nuclei. With firm configuration assignments, the intrinsic excitations in this deformed mass region provide stringent constraints and challenge the different theoretical approaches at play in understanding the structure of superheavy nuclei.

We investigate various interference effects in elastic scattering of the $\alpha +{}^{40}\mathrm{Ca}$ system at $E_{\mathrm{lab}}=29\mathrm{MeV}$. To this end, we use an optical-potential model and decompose the scattering amplitude into four components, that is, the near-side and the far-side components, each of which is further decomposed into the barrier-wave and the internal-wave components. Each component contributes distinctively to the angular distributions, revealing unique quantum interference patterns. We apply the Fourier-transform technique to visualize these interference effects. By analyzing the images at specific scattering angles, we identify the positions and intensities of peaks corresponding to each interference component. This analysis offers insight into structural features of the angular distribution which are not apparent from the differential cross sections alone.

Using the extended relaxation time approximation along with the theory of semiclassical spin, a framework of relativistic dissipative spin hydrodynamics is developed such that the relaxation time can depend on the momenta and spin of the constituent spin-1/2 particles. A general definition of the fluid four-velocity is considered, allowing the theory to be valid in a general frame and matching conditions. Consequently, the frame-invariant bulk, shear, particle diffusion, and spin transport coefficients are obtained, showing that the evolution of fluid remains unaffected by spin in the limit of small polarization as was the case where the relaxation time was independent of spin or momentum.

We study the recently measured β decay of ${}^{70}\mathrm{Kr}$ into ${}^{70}\mathrm{Br}$ within the framework of the large-scale shell model. The enhancement in the Gamow-Teller (GT) transition strength in ${}^{70}\mathrm{Br}$ compared to the β decay of the lighter ${}^{62}\mathrm{Ge}$ was suggested as an indication for increased neutron-proton ($\mathit{np}$) pairing correlation. To explore the $\mathit{np}$ correlations in nuclei, we systematically examined the $\beta \text{−}\mathrm{decay}$ properties of the even-even nuclei $A=58,62,66,$ and 70 into $N=Z$ odd-odd nuclei. By employing an interaction involving solely $J=1,T=0$ and $J=0,T=1$ pairing matrix elements, we observe that the pairing does not necessarily lead to an enhancement in the GT strength for the same coupling strength. But with the inclusion of the $g_{9/2}$ orbital, the GT strength can be increased with increasing $\mathit{np}$ pairing in connection with the enhanced contribution from the $g_{9/2}$ orbital. We further compare those results with realistic calculations in the $fp$ and $f_{5/2}p{g}_{9/2}$ model space to gauge the contribution from $f_{7/2}$ and $g_{9/2}$ orbitals in the GT strengths. With the JUN45 interaction, there is an increment for the yrast $1^{+}$ state for the decay of ${}^{70}\mathrm{Kr}$ as compared to the decay of ${}^{62}\mathrm{Ge}$ due to increased $g_{9/2}$ contribution. Additionally, we probe the effect of $\mathit{np}$ pairing on $B_{\mathrm{GT}}$ by modifying the single-particle energies and the $T=0$ matrix elements of the interaction responsible for the decay transition strength. In calculations with realistic interaction, we find that the accumulated transition strength can increase with enhanced $\mathit{np}$ pairing.

We study the α-decay half-lives of $84\le Z\le 92$ even-even nuclei in the semiclassical Wentzel, Kramers, Brillouin (WKB) approximation framework using the density-dependent cluster model and the density distribution described by various Korea-IBS-Daegu-SKKU (KIDS) models. Main goal of this work is to find a correlation between the α-decay half-lives and the stiffness of the symmtery energy. Parameters of KIDS model are determined to reproduce the nuclear data (energy and charge radii of ${}^{40}\mathrm{Ca}, {}^{48}\mathrm{Ca}$, and ${}^{208}\mathrm{Pb}$) and the neutron star observations including constraints by NICER, tidal deformability from GW170817, and the maximum mass limit of neutron star observations. We use the KIDS models (A–D) which have distinctive values for the parameters controlling the stiffness of the nuclear matter equation of state. We find that the α-decay half-lives increase systematically from KIDS-A model to KIDS-D model. This implies a correlation between the α-decay half-lives and the symmetry energy. We find that the correlation can be understood from the dependence of the particle distribution in the core and the surface region on the symmetry energy.

We report on experimental evidence for a new, second tetrahedral band in ${}_{62}{}^{152}\mathrm{Sm}_{90}$. It was populated via fusion evaporation reaction ${}^{150}\mathrm{Nd}(\alpha ,2n){}^{152}\mathrm{Sm}$, employing a 26 MeV beam of $\alpha$ particles from the K-130 cyclotron at the Variable Energy Cyclotron Centre, Kolkata, India. The newly observed possible mixed parity sequence with absence of $E2$ and strong indication of $E3$ transitions is consistent with the spectroscopic criteria for a tetrahedral-symmetry rotational band that could be constructed from the allowed spin-parity assignments. This structure differs from the structure of the band previously found in the same nucleus, the new one manifesting tetrahedral symmetry not accompanied by the octahedral one. Our new experimental results are interpreted in terms of group representation theory and the collective nuclear-motion theory of Bohr. We propose to generalize the notion of the tetrahedral vibrational bands and believe that our new experimental results support a number of theory predictions related to nuclear tetrahedral symmetry published earlier and bring a new light into the issue of spontaneous symmetry breaking in heavy nuclei.

The enhancement of the parity-violating asymmetry in the vicinity of $p$-wave compound nuclear resonances was observed for a variety of medium-heavy nuclei. The enhanced parity-violating asymmetry can be understood using the $s\text{−}p$ mixing model. The $s\text{−}p$ mixing model predicts several neutron energy-dependent angular correlations between the neutron momentum ${\widehat{\mathit{k}}}_n$, neutron spin ${\mathit{\sigma }}_n, \gamma$-ray momentum ${\widehat{\mathit{k}}}_{\gamma }$, and $\gamma$-ray polarization ${\widehat{\mathit{\sigma }}}_{\gamma }$ in the $(n,\gamma )$ reaction. In this paper, the improved value of the transverse asymmetry of $\gamma$-ray emissions, corresponding to a correlation term ${\mathit{\sigma }}_n·({\widehat{\mathit{k}}}_n\times {\widehat{\mathit{k}}}_{\gamma })$ in the ${}^{139}\mathrm{La}(\vec{n},\gamma ){}^{140}\mathrm{La}$ reaction, and the transverse asymmetries in the transitions to several low excited states of ${}^{140}\mathrm{La}$ are reported.

Background: The nuclear charge radius and distribution are the most fundamental quantities of the atomic nucleus. From the muonic transition energies, the absolute charge radius has been experimentally obtained, while there have been no established methods to discuss the distribution.

Purpose: The muonic transition energies for five palladium isotopes with a mass number $A=104$, 105, 106, 108, and 110 were measured. The procedure to deduce the charge radii and the method to discuss the charge distribution from the muonic transition energies are proposed.

Method: The experiment was performed at the MuSIC-M1 beamline at Research Center for Nuclear Physics, Osaka University. A continuous muon beam impinged on the enriched palladium targets. Muonic x rays were measured by high-purity germanium detectors.

Results: The muonic transition energies up to $4f\text{−}3d$ transitions were determined for five palladium isotopes.

Conclusions: The root-mean-square charge radii are deduced assuming the two-parameter Fermi distribution. The charge distribution of the nucleus is discussed by employing the Barrett model. The muonic transition energies of the $3d\text{−}2p$ transitions are crucial for discussing both the charge radius and the charge distribution.

The studies of transuranium nuclei are of vital significance in exploring the existence of the “island of superheavy nuclei.” This work presents the systematic investigations for the ground-state properties and structure evolutions of $\mathrm{odd}\text{−}A$ transuranium Bk isotopes taking the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with PC-PK1 density functional, in comparison with those by spherical relativistic continuum Hartree-Bogoliubov (RCHB) theory. The DRHBc calculations offer improved descriptions of the binding energies, closely aligning with the experimental data. The incorporation of deformation effects in DRHBc results in enhanced nuclear binding energies and a notable reduction in $\alpha \text{−}\mathrm{decay}$ energies. With the rotational corrections further incorporated, the theoretical deviation by DRHBc from the experimental data is further reduced. Based on the two-neutron gap ${\delta }_{2\mathrm{n}}$ and the neutron pairing energy $E_{\mathrm{pair}}^n$, prominent shell closures at $N=184$ and 258, as well as potential subshell structures at $N=142,150,162,178,218$, and 230 are exhibited. A quasiperiodic variation among prolate, oblate, and spherical shapes as well as prolate deformation predominance have been shown in the evolutions of the quadrupole deformation. Possible shape coexistence is predicted in ${}^{331}\mathrm{Bk}$ with the oblate and prolate minima in close energies, which is further supported by the triaxial relativistic Hartree-Bogoliubov theory in continuum (TRHBc) calculations. The neutron, proton, and charge radii predicted by DRHBc reveal pronounced kink structures at $N=184$ and 258 in their evolutions with neutron number and compared to those by RCHB, deformation effect significantly enhances the radii of open-shell nuclei.

We compute the magnetic dipole ($M1$) $\gamma$-ray strength functions ($\gamma \mathrm{SF}\text{s}$) for the odd-mass lanthanides ${}^{143–151}\mathrm{Nd}$ and ${}^{147–153}\mathrm{Sm}$ using the shell-model Monte Carlo method in combination with the static-path approximation and the maximum-entropy method. In particular, we quantify the statistical uncertainties in the calculated $M1\gamma \mathrm{SFs}$ and show that they are under control for the excitation energies relevant to the experiments despite a Monte Carlo sign problem that originates in the projection onto an odd number of neutrons. We identify a low-energy enhancement (LEE) in the $M1\gamma \mathrm{SFs}$ of these odd-mass lanthanides, which was recently observed experimentally in some of them. We also find a scissors mode resonance (SR) in the strongly deformed isotopes. We observe that the decrease in the LEE strength with neutron number along an isotopic chain is compensated for by an increase in the SR strength in the deformed nuclei. We compare our results with recent experiments.

Motivated by the Gottesman-Knill theorem, we present a detailed study of the quantum complexity of $p$-shell and $sd$-shell nuclei. Valence-space nuclear shell-model wave functions generated by the bigstick code are mapped to qubit registers using the Jordan-Wigner mapping (12 qubits for the $p$ shell and 24 qubits for the $sd$ shell), from which measures of the many-body entanglement ($n$-tangles) and magic (nonstabilizerness) are determined. While exact evaluations of these measures are possible for nuclei with a modest number of active nucleons, Monte Carlo simulations are required for the more complex nuclei. The broadly applicable Pauli-string $\widehat{I}\widehat{Z}$ exact (PSIZe) Markov chain Monte Carlo (MCMC) technique is introduced to accelerate the evaluation of measures of magic in deformed nuclei (with hierarchical wave functions), by factors of $\approx 8$ for some nuclei. Significant multinucleon entanglement is found in the $sd$ shell, dominated by proton-neutron configurations, along with significant measures of magic. This is evident not only for the deformed states, but also for nuclei on the path to instability via regions of shape coexistence and level inversion. These results indicate that quantum-computing resources will accelerate precision simulations of such nuclei and beyond.

Background: Enhanced production of prompt $\gamma$ rays peaked at 4 and 6 MeV in the mass region of fission fragments around ${}^{132}\mathrm{Sn}$ is a known phenomenon for 30 years. Various contradictory interpretations of their origin can be found in the literature: either discrete or statistical $\gamma$ rays originating from the light or heavy fragment.

Purpose: The present work aims at lifting this uncertainty by looking at the prompt $\gamma$ spectrum in coincidence with isomeric decays and its evolution with the excitation energy of the isomeric nucleus.

Method: The experimental setup made of a nearly $4\pi$ NaI array coupled to a twin Frisch-gridded ionization chamber allowed the detection of both fragments and the measurement of their kinetic energy with a resolution of 570 keV, leading to a mass resolution of 0.68 u. in the case of neutronless fission events, and about 4 u. for standard fission events. Fifteen isomers were measured near the double shell closure $Z=50,N=82$.

Results: The study of the prompt $\gamma$ spectrum in coincidence with these isomers revealed that the aforementioned structures are incompatible with a discrete nature. The comparison of the prompt $\gamma$ spectra in coincidence with two isomers of ${}^{134}\mathrm{Te}$ differing by 4.1 MeV in excitation energy unambiguously attributes these structures to the decay of the heavy fragments.

Conclusions: From the study of the photon emission probability we interpret these structures as arising from the competition between the “strength-driven” decay of the heavy fragments and the “density-driven” decay of the light fragments.

Background: Halo structure is an interesting exotic configuration developed in some light weakly bound nuclei, where a valence particle orbits a nuclear core. Signatures of halo structure can be observed in the angular distributions of the elastic scattering induced by these nuclei at energies around the Coulomb barrier. There are some well-studied reactions with neutron-rich halo nuclei, such as ${}^6\mathrm{He}$ and ${}^{11}\mathrm{Li}$. However, the information is scarce on the proton-rich side. Recent works confirm the halo structure in the ${}^8\mathrm{B}$ nuclei but still lack more experimental studies for other proton-halo candidates, such as ${}^{12}\mathrm{N}$ and ${}^{17}\mathrm{F}$.

Purpose: In this work, we report experimental data for the elastic scattering of ${}^{12}\mathrm{N}$ on ${}^{197}\mathrm{Au}$ target at $E_{\text{lab}}=70$ MeV. The ${}^{12}\mathrm{N}$ is a proton-rich nucleus with proton separation energy $S_p=600$ keV, which is higher than the ${}^8\mathrm{B}$ ($S_p=137$ keV) and almost the same as the ${}^{17}\mathrm{F}$ ($S_p=601$ keV).

Methods: Data were obtained at the Cyclotron Institute of Texas A&M University where the ${}^{12}\mathrm{N}$ radioactive beam was produced by the momentum achromatic recoil spectrometer. The calculation of the optical model was used to fit the measured angular distribution for the elastic scattering and to obtain the reaction cross section ${\sigma }_R$. We also performed continuum discretized coupled-channel calculations to compare with the experimental data.

Results: The angular distribution of the elastic cross sections exhibits a suppression of the Fresnel peak. From the fitting of the optical model, we obtain the total reaction cross section, ${\sigma }_R=1269\pm 41$ mb. The agreement between the CDCC calculation and the experimental elastic scattering data is limited and the breakdown does not exhaust the measured ${\sigma }_R$.

Conclusions: The resulting reduced reaction cross section ${\sigma }_{\text{Red}}$ for ${}^{12}\mathrm{N}+{}^{197}\mathrm{Au}$ is large and comparable to the one obtained for the ${}^8\mathrm{B}+{}^{208}\mathrm{Pb}$ system. This suggests a strong decoupling of the valence proton from the core because of the low binding energy and a dynamic polarization effect. More research is required to estimate the contribution of core excitation.

Nonelastic breakup (NEB) reactions induced by the halo nucleus ${}^{11}\mathrm{Be}$ on ${}^{64}\mathrm{Zn}$ at 28.7 MeV are investigated using the Ichimura-Austern-Vincent (IAV) model combined with the continuum discretized coupled channels (CDCC) method. NEB cross sections calculated with full CDCC wave functions (including continuum states), ground-state-only CDCC wave functions, and single-channel calculations are compared. The results indicate that continuum effects are negligible and that NEB cross sections are dominated by the ground-state contribution. This validates the use of simpler models like the distorted wave Born approximation for such reactions. Additionally, by varying the binding energy in a toy model, the feasibility of using halo nuclei in the Trojan horse method (THM) for synthesizing heavy isotopes is explored. It is demonstrated that THM significantly enhances sub-barrier fusion cross sections due to the weak binding of halo nuclei, offering a promising approach for the synthesis of new elements.

Constraining the equation of state (EOS) of strongly interacting, dense matter is the focus of intense experimental, observational, and theoretical effort. Chiral effective field theory ($\chi \mathrm{EFT}$) can describe the EOS between the typical densities of nuclei and those in the outer cores of neutron stars, while perturbative QCD (pQCD) can be applied to properties of deconfined quark matter, both with quantified theoretical uncertainties. However, describing the full range of densities in between with a single EOS that has well-quantified uncertainties is a challenging problem. Bayesian multimodel inference from $\chi \mathrm{EFT}$ and pQCD can help bridge the gap between the two theories. In this work, we introduce a correlated Bayesian model mixing framework that uses a Gaussian process (GP) to assimilate different information into a single QCD EOS for symmetric nuclear matter. The present implementation uses a stationary GP to infer this mixed EOS solely from the EOSs of $\chi \mathrm{EFT}$ and pQCD while accounting for the truncation errors of each theory. The GP is trained on the pressure as a function of number density in the low- and high-density regions where $\chi \mathrm{EFT}$ and pQCD are, respectively, valid. We impose priors on the GP kernel hyperparameters to suppress unphysical correlations between these regimes. This, together with the assumption of stationarity, results in smooth $\chi \mathrm{EFT}$-to-pQCD curves for both the pressure and the speed of sound. We show that using uncorrelated mixing requires uncontrolled extrapolation of at least one of $\chi \mathrm{EFT}$ or pQCD into regions where the perturbative series breaks down and leads to an acausal EOS. We also discuss extensions of this framework to nonstationary and less differentiable GP kernels, its future application to neutron-star matter, and the incorporation of additional constraints from nuclear theory, experiment, and multimessenger astronomy.