We have studied the decay pattern of the $J^{\pi }=1_{4742\mathrm{keV}}^{-}$ state of ${}^{88}\mathrm{Sr}$ to probe its quadrupole-octupole coupled two-phonon structure. In particular, a unique fingerprint to prove the two-phonon nature is the $E2$ decay strength of the $1_{4742\mathrm{keV}}^{-}\to 3_1^{-}$ transition into the one-octupole-phonon state. $\gamma$-ray spectroscopy was performed after the $\beta$ decay of ${}^{88}\mathrm{Rb}$ to obtain the necessary sensitivity for this weak-intensity decay branch. Sufficient amounts of ${}^{88}\mathrm{Rb}$ $(T_{1/2}=17.8 \min )$ were produced by neutron activation of natural Rb in the TRIGA Mark II reactor. The results show that the $B\left(E2\right)$ value of the $1_{4742\mathrm{keV}}^{-}\to 3_1^{-}$ transition is equal to the $B\left(E2\right)$ of the $2_1^{+}\to 0_1^{+}$ transition, directly demonstrating the quadrupole-octupole coupled two-phonon nature of the $1^{-}$ state. A comparison of the results with energy-density functional plus quasiparticle-phonon model calculations shows remarkable agreement, corroborating this assignment.

Nucleon-nucleon ($NN$) interactions based on chiral effective theories are commonly used in ab initio calculations of light nuclei. Here we present a study based on three different $NN$ interactions (up to next-to-next-to-leading order) for which structure and elastic proton scattering observables are consistently calculated for ${}^4\mathrm{He}, {}^{12}\mathrm{C}$, and ${}^{16}\mathrm{O}$. The interactions are compared at the two-body level in terms of Wolfenstein amplitudes, and their predictions for ground-state energies, point-proton radii, and charge form factors, as well as proton elastic scattering observables in the leading-order spectator expansion in the energy range between 65 and 160 MeV projectile energy are presented. To gain further insight into differences visible in elastic scattering observables, we investigate the behavior of the calculated effective nucleon-nucleus interactions for the ${}^{12}\mathrm{C}$ nucleus based on the different $NN$ interactions.

Spontaneous fission half-lives of actinide and superheavy nuclei are calculated using the least-action integral of the Wentzel-Kramers-Brillouin (WKB) tunneling probability through the barrier that appears in the deformation landscape obtained in the macroscopic-microscopic potential-energy surface. This deformation-energy landscape is obtained using a Fourier shape parametrization with four deformation parameters, taking into account the nuclear elongation, left-right asymmetry, neck formation, and nonaxiality degrees of freedom. The collective inertia tensor entering the WKB half-life expression is taken from the so-called irrotational flow model, whose components are scaled by an overall multiplicative factor. For a comparisons, we have also used the so-called phenomenological mass parameter depending only on the center-of-mass difference of the nascent fission fragments. Our approach is shown to be able to reproduce empirical fission half-lives of all here considered nuclei to within three orders of magnitude.

The recent observation of the object HESS J1731-347 suggests the existence of a very light and very compact neutron star, which is a challenge for commonly used equations of state for dense matter. In this work we present a relativistic mean-field model enriched with isovector and isoscalar meson crossing terms. These interactions dominate the behavior of the symmetry energy and account for the small radius. The proposed model fulfills the recent constraints concerning the symmetry energy slope and the state-of-the-art compact star constraints derived from the NICER measurements of the pulsars PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+6620$, as well as from the GW170817 event and its associated electromagnetic counterparts AT2017gfo/GRB170817A.

Background: ${}^7\mathrm{Li}$ and ${}^7\mathrm{Be}$ play an important role in big bang nucleosynthesis and nuclear astrophysics. The ${}^3\mathrm{H}({}^4\mathrm{He},\gamma ){}^7\mathrm{Li}$ radiative capture reaction is crucial for the determination of the primordial ${}^7\mathrm{Li}$ abundance. In nuclear astrophysics, lithium isotopes have attracted great interest because of the puzzling abundance of ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$.

Purpose: In this work we study spectra of ${}^7\mathrm{Be}$ and ${}^7\mathrm{Li}$ and elastic scattering cross sections ${}^4\mathrm{He}({}^3\mathrm{He},{}^3\mathrm{He})$ and ${}^4\mathrm{He}({}^3\mathrm{H},{}^3\mathrm{H})$ within the Gamow shell model (GSM) in the coupled-channel formulation (GSM-CC). The evolution of channel amplitudes and spectroscopic factors in the vicinity of the channel threshold is studied for selected states.

Methods: GSM provides the open quantum system formulation of the nuclear shell model. In the representation of GSM-CC, GSM provides the unified theory of nuclear structure and reactions which is suited for the study of resonances in ${}^7\mathrm{Be}$ and ${}^7\mathrm{Li}$ and elastic scattering cross sections involving ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$ projectiles.

Results: GSM-CC in the multimass partition formulation applied to a translationally invariant Hamiltonian with an effective finite-range two-body interaction reproduces well the spectra of ${}^7\mathrm{Be}$ and ${}^7\mathrm{Li}$ and elastic scattering reactions ${}^4\mathrm{He}({}^3\mathrm{He},{}^3\mathrm{He})$ and ${}^4\mathrm{He}({}^3\mathrm{H},{}^3\mathrm{H})$. Detailed analysis of the dependence of reaction channel amplitudes and spectroscopic factors on the distance from the particle decay threshold allowed us to demonstrate the alignment of the wave function in the vicinity of the decay threshold. This analysis also demonstrates the appearance of clustering in the GSM-CC wave function in the vicinity of the cluster decay threshold.

Conclusions: We demonstrated that GSM formulated in the basis of reaction channels including both cluster and proton/neutron channels allows us to describe both the spectra of nuclei with low-energy cluster thresholds and the low-energy elastic scattering reactions with proton, ${}^3\mathrm{H}$, and ${}^3\mathrm{He}$ projectiles. Studying dependence of the reaction channel amplitude and spectroscopic factor in a many-body state on the distance from the threshold, we showed an evolution of the ${}^3\mathrm{He},{}^3\mathrm{H}$ clustering with increasing separation energy from the cluster decay threshold and demonstrated a mechanism of the alignment of many-body wave function with the decay threshold [J. Okołowicz, M. Płoszajczak, and W. Nazarewicz, Prog. Theor. Phys. Suppl. 196, 230 (2012); J. Okołowicz, W. Nazarewicz, and M. Płoszajczak, Fortschr. Phys. 61, 66 (2013)], i.e., the microscopic reorganization of the wave function in the vicinity of the cluster decay threshold which leads to the appearance of clustering in this state.

The aim of this paper is to investigate how the choice of deuteron potential affects the nonelastic cross sections of ${}^{12}\mathrm{C}, {}^{40}\mathrm{Ca}, {}^{58}\mathrm{Ni}$, and ${}^{208}\mathrm{Pb}$ in the low-energy region below 200 MeV within the extended framework of the intranuclear cascade model, in which a three-body proton-neutron-target system is introduced to incorporate naturally the decomposition and capture reactions from weakly bound deuterons. To determine an appropriate potential for the two nucleons of the deuteron, we compare two phenomenological potentials with the Gaussian potential that we have used previously. Specifically, we examine the Reid and Coester-Yen soft-core potentials and find that they give reduced nonelastic cross sections. To investigate the role of the potential, we separate it into the tail region in the outer part and the soft-core region in the central part. By using a gluing method to connect the Gaussian potential smoothly to the Yukawa tail, we show that the tail has no appreciable effect for any of the targets. On the other hand, by adding a soft core to the ordinary Gaussian potential, we show that the soft core has appreciable effects, especially in heavier nuclei such as ${}^{208}\mathrm{Pb}$, the reason being the reduced breakup process with a soft-core potential from the deuteron rotation due to the Coulomb potential. The results of this study show that while the Yukawa tail has no appreciable effect, soft-core potentials tend to give reduced nonelastic cross sections, especially for heavy nuclei.

We propose a model-independent analysis of near-threshold enhancements using independent $S$-matrix poles. In this formulation, we constructed a Jost function with controllable zeros to ensure that no poles are generated on the physical Riemann sheet. We show that there is a possibility of misinterpreting the observed near-threshold signals if one utilized a limited parametrization and restricted the analysis to only one element of the $S$ matrix. Specifically, there is a possibility of the emergence of an ambiguous pair of poles which are singularities of the full $S$ matrix but may not manifest in one of its elements. For a more concrete discussion, we focused on an effective two-channel scattering where the full $S$ matrix is a $2\times 2$ matrix. We apply our method to the coupled two-channel analysis of the $P_{\psi }^N{\left(4312\right)}^{+}$ and found that the compact pentaquark interpretation cannot be ruled out yet.

Background: The quadrupole (${\beta }_2^{\pm }$) deformed targets in the actinide region are found to be of great relevance in the production of superheavy nuclei (SHN), in both the hot and cold fusion mechanisms. Recently, the application of “elongated or cold” and “compact or hot” configurations of pear-shape octupole (up to ${\beta }_3^{\pm }$) deformed nuclei was found to play significant role in the fusion-fission dynamics of heavy-ion induced reactions, in the low energy regime.

Purpose: To understand the relevance of higher-order deformed (up to ${\beta }_4^{\pm }$) actinides and their compact and elongated nuclear fusion configurations in the production cross section of SHN, we have obtained the optimum orientations $\left({\theta }_{\mathrm{opt}}\right)$ in reference to the above mentioned configurations of ${\beta }_4$-deformed targets. For this, a variety of projectile-target combinations—spherical (${}^{36}\mathrm{S}, {}^{40,48}\mathrm{Ca}$) and ${\beta }_2^{\pm }$-deformed (${}^{30}\mathrm{Si}, {}^{34}\mathrm{S}$) nuclei as incident beams and ${\beta }_4$-deformed (with different signs $\pm$ and magnitudes) actinides ($\approx 1400$ isotopes) as targets—are taken into consideration. Later, the application of ${\theta }_{\mathrm{opt}}^{\mathrm{hot}/\mathrm{cold}}\left({\beta }_2^{\pm }{\beta }_3^{\pm }{\beta }_4^{\pm }\right)$ was done to analyze the fragmentation structure of ${}^{286}\mathrm{Cn}^{*}$.

Methods: On the basis of the proximity theorem, the optimum orientations (${\theta }_{\mathrm{opt}}$) defining the compact and elongated configurations of deformed nuclei are obtained at the maximum and minimum barrier height, respectively. Further, the obtained ${\theta }_{\mathrm{opt}}$ and static deformations (up to ${\beta }_4^{\pm }$) for around 1400 isotopes of actinides are utilized in the calculations of capture cross section ${\sigma }_{\mathrm{cap}}\left(E_{\mathrm{c}.\mathrm{m}.}\right)$ using the extended $\ell$-summed Wong model at energies lying across the Coulomb barrier. Also, to study the fragmentation structure of ${}^{286}\mathrm{Cn}^{*}$ SHN, the collective clusterization approach of quantum mechanical fragmentation theory has been adopted.

Results: For a large variety of projectile-target combinations, leading to SHN, the incorporation of higher-order deformation (up to ${\beta }_4^{\pm }$) shows a significant influence on ${\theta }_{\mathrm{opt}}^{\mathrm{hot}/\mathrm{cold}}$ with the effect of $\pm$ signs and different magnitudes of ${\beta }_4^{\pm }$ deformation. Also, with the incorporation of deformations up to ${\beta }_4^{\pm }$ and corresponding ${\theta }_{\mathrm{opt}}$, the ${\sigma }_{\mathrm{cap}}\left(E_{\mathrm{c}.\mathrm{m}.}\right)$ improves and is in better agreement with the available experimental data of ${}^{238}\mathrm{U}$-based reactions, across the barrier energies. Also, in the decay channel, the ${\beta }_4$-deformed fragments, i.e., ${}^{143}\mathrm{Ba}+{}^{143}\mathrm{Ba}$, are found to minimize the fragmentation potential, as compared to the ${\beta }_2$ or ${\beta }_3$ deformed fragments.

Conclusion: The present study concludes that the optimized configurations of higher-order deformed actinides up to ${\beta }_4$ participate relatively better than the optimized configurations of ${\beta }_2$ and ${\beta }_3$ deformed nuclei in the formation as well as exit channel of superheavy nuclei.

Background: The understanding of nuclear reactions between light nuclei at energies below the Coulomb barrier is important for several astrophysical processes, but their study poses experimental and theoretical challenges. At sufficiently low energies, the electrons surrounding the interacting ions affect the scattering process. Moreover, the clustered structure of some of these nuclei may play a relevant role on the reaction observables.

Purpose: In this article, we focus on a theoretical investigation of the role of clustered configurations of ${}^6\mathrm{Li}$ in reactions of astrophysical interest.

Methods: The ${}^6\mathrm{Li}$($p{,}^3\text{He}$)${}^4\mathrm{He}$ reaction cross section is described considering both the direct transfer of a deuteron as a single pointlike particle in the distorted-wave Born approximation (DWBA), and the transfer of a neutron and a proton in second-order DWBA. A number of two- and three-cluster structure models for ${}^6\mathrm{Li}$ are compared.

Results: Within the two-cluster structure model, we explore the impact of the deformed components in the ${}^6\mathrm{Li}$ wave function on the reaction of interest. Without explicit adjusting of the calculation inputs to the transfer channel, we obtain reaction cross sections in good agreement with the results of more microscopic models. Within the three-cluster structure model, we gauge the degree of $\alpha \text{−}d$ clustering and explicitly probe its role in specific features of the transfer cross section; however, cross-section absolute values are overestimated. We compare the energy trend of the astrophysical $S$ factor deduced in each case.

Conclusions: Clustered ${}^6\mathrm{Li}$ configurations lead in general to a significant enhancement of the astrophysical factor in the energy region under study. This effect only originates from clustering, whereas static deformations of the ground-state configuration play a negligible role at very low energies.

We extend a previously constructed $T$-matrix approach to the quark-gluon plasma (QGP) to include the effects of spin-dependent interactions between partons. Following earlier work within the relativistic quark model, the spin-dependent interactions figure as relativistic corrections to the Cornell potential. When applied to the vacuum spectroscopy of quarkonia, in particular their mass splittings in $S$- and $P$-wave states, the issue of the Lorentz structure of the confining potential arises. We confirm that a significant admixture of a vector interaction (to the previously assumed scalar interaction) improves the description of the experimental mass splittings. The temperature corrections to the in-medium potential are constrained by results from thermal lattice quantum chromodynamics for the equation of state and heavy-quark free energy in a self-consistent setup for heavy- and light-parton spectral functions in the QGP. We then deploy the refined in-medium heavy-light $T$ matrix to compute the charm-quark transport coefficients in the QGP. The vector component of the confining potential, through its relativistic corrections, enhances the friction coefficient for charm quarks in the QGP over previous calculations by tens of percentages at low momenta and temperatures and more at higher momenta. Our results are promising for improving the current phenomenology of open heavy-flavor observables at Relativistic Heavy Ion Collider and the Large Hadron Collider.

We study whether it is possible to use high-$p_{\perp }$ data/theory to constrain the temperature dependence of the shear viscosity over entropy density ratio $\eta /s$ of the matter formed in ultrarelativistic heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). We use two approaches: (i) We calculate high-$p_{\perp }{R}_{AA}$ and flow coefficients $v_2, v_3$, and $v_4$ assuming different $(\eta /s)\left(T\right)$ of the fluid-dynamically evolving medium. (ii) We calculate the quenching strength ($\widehat{q}/T^3$) from our dynamical energy loss model and convert it to $\eta /s$ as a function of temperature. It turned out that the first approach cannot distinguish between different $(\eta /s)\left(T\right)$ assumptions when the evolution is constrained to reproduce the low-$p_{\perp }$ data. In distinction, $(\eta /s)\left(T\right)$ calculated using the second approach agrees surprisingly well with the $(\eta /s)\left(T\right)$ inferred through state-of-the-art Bayesian analyses of the low-$p_{\perp }$ data even in the vicinity of $T_c$, while providing much smaller uncertainties at high temperatures.

We calculate the cold neutron-deuteron ($nd$) capture cross section,${\sigma }_{nd}$ to next-to-next-to leading order (NNLO) using the model-independent approach of pionless effective-field theory [EFT($\cancel{\pi }$)]. At leading order we find ${\sigma }_{nd}=0.314\pm 0.217$ mb, while the experimental result is 0.508(15) mb [Phys. Rev. C 25, 2810 (1982)] for a laboratory neutron velocity of 2200 m/s. At next-to-leading-order (NLO), we show that ${\sigma }_{nd}$ is sensitive to the low-energy constant (LEC) $L_1^{\left(0\right)}$ of the two-nucleon isovector current appearing at NLO. A fit of $L_1^{\left(0\right)}$ at NLO to the triton magnetic moment yields a NLO prediction of ${\sigma }_{nd}=0.393\pm 0.164$ mb, where the error comes from propagating the error from the $L_1^{\left(0\right)}$ fit. At NNLO, we find that a new three-nucleon magnetic moment counterterm is required for renormalization-group invariance of both ${\sigma }_{nd}$ and the triton magnetic moment. Fitting the NNLO correction to $L_1^{\left(0\right)}$ (denoted $L_1^{\left(1\right)}$) to cold neutron-proton capture (${\sigma }_{np}$) yields a NNLO prediction of ${\sigma }_{nd}=0.447\pm 0.130$ mb, where the error comes from propagating the error from the $L_1^{\left(1\right)}$ fit. We also study different fittings of $L_1^{\left(0\right)}$ and $L_1^{\left(1\right)}$ to ${\sigma }_{np}, {\sigma }_{nd}$, and/or the triton magnetic moment. For example, fitting $L_1^{\left(0\right)}$ simultaneously to ${\sigma }_{np}, {\sigma }_{nd}$, and the triton magnetic moment at NLO, and fitting $L_1^{\left(1\right)}$ simultaneously to ${\sigma }_{np}$ and ${\sigma }_{nd}$ at NNLO, yields ${\sigma }_{nd}=0.480\pm 0.114$ mb and $0.511\pm 0.042$ mb, respectively, where errors are naively estimated from EFT($\cancel{\pi }$) power counting. In addition, we discuss how Wigner SU(4) symmetry may alter the naive EFT($\cancel{\pi }$) expansion of ${\sigma }_{nd}$.

The production cross section of inclusive $J/\psi$ pairs in $pp$ collisions at a center-of-mass energy $\sqrt{s}=13$ TeV is measured with ALICE. The measurement is performed for $J/\psi$ in the rapidity interval $2.5<y<4.0$ and for transverse momentum $p_T>0$. The production cross section of inclusive $J/\psi$ pairs is reported to be $10.3\pm 2.3(\mathrm{stat}.)\pm 1.3(\mathrm{syst}.)$ nb in this kinematic interval. The contribution from nonprompt $J/\psi$ (i.e., originated from beauty-hadron decays) to the inclusive sample is evaluated. The effective double-parton scattering cross section is computed, neglecting the single-parton scattering contribution.

Symmetry-conserving density-functional theory (DFT) based no-core-configuration-interaction framework (DFT-NCCI) is an excellent tool for precision calculation of diverse (pseudo-)observables related to isospin symmetry breaking from elusive isospin impurities through isospin corrections to superallowed beta decays to mirror- and triplet-displacement energies and mirror energy differences (MED) along rotational bands. In our recent work [Phys. Rev. C 106, 024327 (2022)] we performed axial DFT-NCCI calculations and failed to reproduce a sign of MED in positive-parity ($\pi =+$) bands of ${}^{45}\mathrm{Sc}/{}^{45}\mathrm{Cr}, T=3/2$ mirror pair what casts a shadow on credibility of the model. In this work we aim to perform a thorough analysis of this case with the focus on sensitivity of our predictions with respect to ($i$) low-energy constants (LECs) of our effective contact charge symmetry breaking force and ($\mathit{ii}$) nuclear shape. We demonstrate, among other things, that inclusion of triaxial $\pi =+$ ground state—which is actually the global $\pi =+$ minimum in our unconstrained mean-field calculation—in the DFT-NCCI calculations instead of the axial one used before leads to MED which are consistent with experimental data concerning both their sign as well as magnitude without any need for fine-tuning of the model's LECs.

Background: The nuclear energy-density functional (EDF) approach is widely employed to describe nuclear-matter equations of state (EoS) and the properties of finite nuclei. Recent advancements in neutron-star (NS) observations have imposed constraints on the nuclear EoS. The Korea-IBS-Daegu-SKKU (KIDS) functional has been then developed to satisfy the NS observations and applied to homogeneous nuclear matter and spherical nuclei.

Purpose: We examine the performance of the KIDS functional in this study by calculating the masses and charge radii of even-even nuclei towards the drip lines.

Method: The Kohn-Sham-Bogoliubov equation is solved by taking into account the axial deformation.

Results: The root-mean-square deviations of the binding energy and the charge radius for the KIDS models are 4.5–5.1 MeV and 0.03–0.04 fm, which are comparable to those for existing EDFs. The emergence and development of nuclear deformation in open-shell nuclei are well described. The location of the neutron drip line is according to the nuclear-matter parameter characterizing the low-mass NS.

Conclusions: The NS-observation-inspired EDF offers a reasonable reproduction of the structures of finite nuclei. A future global optimization that incorporates more nuclear data will enhance the accuracy and predictive power of neutron-rich nuclei.

The nuclear level density is a fundamental quantity in nuclear physics, governing various nuclear reactions and astrophysical processes. In this study, we report on the collective enhancement of nuclear level density and its fade-out with excitation energy in the deformed ${}^{161}\mathrm{Dy}$, obtained through an exclusive measurement of neutron evaporation spectra. The ${}^{162}\mathrm{Dy}$ nucleus was populated via the transfer of a triton in a ${}^7\mathrm{Li}$-induced reaction on ${}^{159}\mathrm{Tb}$. Statistical model analysis of the neutron spectra revealed a large collective enhancement factor of $42\pm 2$, consistent with microscopic calculations. This enhancement factor is similar to the one obtained for mass $A\sim 170$ in our previous measurement. The energy-dependent collective enhancement over a wide range of excitation energies was inferred by combining the present results with the available Oslo level density below the neutron binding energy.

Liquid argon detectors are employed in a wide variety of nuclear and particle physics experiments. The addition of small quantities of xenon to argon modifies its scintillation, ionization, and electroluminescence properties and can improve its performance as a detection medium. However, a liquid argon-xenon mixture can develop instabilities, especially in systems that require phase transitions or that utilize high xenon concentrations. In this work, we analyze the causes of these instabilities and describe a small (liter-scale) apparatus with a unique cryogenic circuit specifically designed to handle argon-xenon mixtures. The system is capable of condensing argon gas mixed with $\mathcal{O}(1\%)$ xenon by volume and maintains a stable liquid mixture near the xenon saturation limit while actively circulating it in the gas phase. We also demonstrate control over instabilities that develop when the detector condition is allowed to deviate from optimized settings. This progress enables future liquid argon detectors to benefit from the effects of high concentrations of xenon doping, such as more efficient detection of low-energy ionization signals. This work also develops tools to study and mitigate instabilities in large argon detectors that use low concentration xenon doping.