Recent high-energy heavy-ion collision experiments have revealed that some atomic nuclei exhibit unusual softness and significant shape fluctuations. In this work, we use the fully self-consistent mean-field theory to identify all even-even nuclei that are unstable or soft against octupole deformation. All exceptional cases of enhanced octupole transition strengths in stable even-even nuclei throughout the nuclide chart are resolved and the origin is found in basic shell structure. The presence of atomic nuclei exhibiting significant softness to quadrupole-octupole deformation is suggested. These results represent a significant advance in our understanding of the underlying mechanisms of nuclear octupole deformation and have implications for further experimental and theoretical studies.

We provide insights into the backbending phenomenon within the symmetry-adapted framework which naturally describes the intrinsic deformation of atomic nuclei. For ${}^{20}\mathrm{Ne}$, the canonical example of backbending in light nuclei, the ab initio symmetry-adapted no-core shell model shows that while the energy spectrum replicates the backbending from experimental energies under the rotor-model assumption, there is no change in the intrinsic deformation or intrinsic spin of the yrast band around the backbend. For the traditional example of ${}^{48}\mathrm{Cr}$, computed in the valence shell with empirical interactions, we confirm a high-spin nucleus that is effectively near-spherical, in agreement with previous models. However, we find that this spherical distribution results, on average, from an almost equal mixing of deformed prolate shapes with deformed oblate shapes. Microscopic calculations confirm the importance of spin alignment and configuration mixing, but surprisingly unveil no anomalous increase in moment of inertia. This finding opens the path toward further understanding the rotational behavior and moment of inertia of medium-mass nuclei.

Light (anti-) nuclei are a powerful tool both in collider physics and astrophysics. In searches for new and exotic physics, the expected small astrophysical backgrounds at low energies make these antinuclei ideal probes for, e.g., dark matter. At the same time, their composite structure and small binding energies imply that they can be used in collider experiments to probe the hadronization process and two-particle correlations. For the proper interpretation of such experimental studies, an improved theoretical understanding of (anti-) nuclei production in specific kinematic regions and detector setups is needed. In this work, we develop a coalescence framework for (anti-) deuteron production which accounts for both the emission volume and momentum correlations on an event-by-event basis: While momentum correlations can be provided by event generators, such as pythia, the emission volume has to be derived from semiclassical considerations. Moreover, this framework goes beyond the equal-time approximation, which has been often assumed in femtoscopy experiments and (anti-) nucleus production models until now in small interacting systems. Using pythia 8 as an event generator, we find that the equal-time approximation leads to an error of $\mathcal{O}(10\%)$ in low-energy processes like $\mathrm{{\rm Y}}$ decays, while the errors are negligible at CERN Large Hadron Collider energies. The framework introduced in this work paves the way for tuning event generators to (anti-) nuclei measurements.

We present predictions for the cross sections of the coherent and incoherent $J/\psi$ photoproduction in ultraperipheral collisions at the RHIC and at the LHC calculated for different classes of events depending on the presence of neutrons emitted by colliding nuclei. Since strong nucleus-nucleus interactions in UPCs are suppressed, it is usually assumed that neutrons at forward rapidities originate mainly from the electromagnetic dissociation of colliding nuclei caused by additional photon exchanges. This is a reasonable assumption for the coherent photoproduction where the state of the target nucleus remains intact. We consider additional sources of neutrons in the incoherent quasielastic and nucleon dissociative $J/\psi$ photoproduction and show that these processes significantly change probabilities of neutron emission compared to calculations when only neutrons from electromagnetic dissociation of nuclei are considered. Such studies should allow one to explore the dynamics of nuclear shadowing in the incoherent $J/\psi$ photoproduction down to $x\approx {10}^{-5}$.

In this work, we present new data on the ${}^{182,183,184}\mathrm{W}(\gamma ,n$) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and $\gamma$-ray strength function of ${}^{186}\mathrm{W}$ from data on the ${}^{186}\mathrm{W}(\alpha ,{\alpha }^{\prime }\gamma ){}^{186}\mathrm{W}$ reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the ${}^{186}\mathrm{W}(\gamma ,n$) cross section with our new ${}^{182,183,184}\mathrm{W}(\gamma ,n$) and ($\alpha ,{\alpha }^{\prime }\gamma ){}^{186}\mathrm{W}$ data sets, we have deduced the ${}^{186}\mathrm{W}\gamma$-ray strength function in the range of $1<E_{\gamma }<6$ MeV and $7<E_{\gamma }<14$ MeV. Our data are used to extract the level density and $\gamma$-ray strength functions needed as input to the nuclear-reaction code talys, providing an indirect, experimental constraint for the ${}^{185}\mathrm{W}(n,\gamma ){}^{186}\mathrm{W}$ cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 database, our results are on average lower for the relevant energy range $k_{B}T\in [5,100]$ keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao et al. [At. Data Nucl. Data Tables 76, 70 (2000)] and the cross section experimentally constrained on photoneutron data of Sonnabend et al. [Astrophys. J. 583, 506 (2003)] are significantly higher than our result. The lower value by Mohr et al. [Phys. Rev. C 69, 032801(R) (2004)] is in very good agreement with our deduced MACS. Our new results provide an improved uncertainty estimate for the ($n,\gamma ){}^{186}\mathrm{W}$ reaction rate, which is one important ingredient in simulations for investigating the neutron density and the ${}^{186,187}\mathrm{Os}$ production in the $s$ process.

The emergence and stability of (static) octupole deformation effects in Dy isotopes from drip line to drip line ($72\le N\le 142$) are analyzed in this paper using mean-field and beyond-mean-field techniques often used for this purpose. We find static octupole deformations at the Hartree-Fock-Bogoliubov (HFB) level with the Gogny-D1M force for $N\approx 134$ isotopes, while nuclei with $N\approx 88$ exhibit reflection-symmetric ground states. It is shown that, given the softness found in the mean-field and parity-projected potential energy surfaces along the octupole direction, neither of these two levels of approximation is sufficient to extract conclusions about the (permanent and/or vibrational) nature of octupole dynamic in Dy isotopes. From the analysis of the collective wave functions as well as the excitation energies of the first negative-parity states and $B\left(E3\right)$ strengths, obtained within the framework of a two-dimensional symmetry-conserving generator coordinate method (2D-GCM), it is concluded that the increased octupole collectivity in Dy isotopes with $N\approx 88$ and $N\approx 134$ is a vibrational-like effect that is not directly related to permanent mean-field octupole deformation in the considered nuclei. A pronounced suppression of the $B\left(E1\right)$ strengths is predicted for isotopes with $N\approx 82$ and $N\approx 126$. The comparison of results obtained with other parametrizations shows the robustness of the predicted trends with respect to the underlying Gogny energy density functional.

By inverting the observational data of several neutron star observables in the three-dimensional parameter space of the constant speed of sound (CSS) model while fixing all hadronic equation-of-state parameters at their currently known most probable values, we constrain the three parameters of the CSS model and their correlations. Using two lower radius limits of $R_{2.01}=11.41$ km and $R_{2.01}=12.2$ km for PSR $\text{J0740}+\text{6620}$ obtained from two independent analyses using different approaches by the Neutron Star Interior Composition Explorer (NICER) Collaboration, the speed of sound squared $c_{\mathrm{QM}}^2$ in quark matter is found to have a lower limit of 0.35 or 0.43 in units of $c^2$, above its conformal limit of $c_{\mathrm{QM}}^2<1/3$. An approximately linear correlation between the first-order hadron-quark transition density ${\rho }_t$ and its strength $\mathrm{\Delta }\varepsilon$ is found. Moreover, the presence of twin stars is deemed improbable by the present work.

The requirements for hadron polarimetry at the future Electron-Ion Collider (EIC) include measurements of the absolute helion $({}^3\mathrm{He},h)$ beam polarization with systematic uncertainties better than ${\sigma }_P^{\text{syst}}/P\le 1\%$. Recently, it was proposed that the Polarized Atomic Hydrogen Gas Jet Target (HJET) be utilized for the precision measurement of the polarization of the $\approx 100\mathrm{GeV}/n$ helion beam. At the Relativistic Heavy Ion Collider, HJET serves to determine the absolute proton beam polarization with low systematic uncertainties of about ${\delta }^{\text{syst}}P/P\lesssim 0.5\%$. To adapt the HJET method for the EIC helion beam, the experimentally determined ratio of the beam and target (jet) spin-correlated asymmetries should be adjusted by the ratio of $p^{\uparrow }h$ and $h^{\uparrow }p$ analyzing powers. A potential problem with the suggested method is that the breakup of ${}^3\mathrm{He}$ in polarization measurements could drastically affect the analyzing power ratio. However, an analysis of the breakup corrections, presented in this paper, reveals that while these corrections can be as substantial as $\approx 4\%$, the effect cancels out to a negligible level in the measured beam polarization.

The observations of PSR J0952-0607 $(M=2.{35}_{-0.17}^{+0.17}{M}_{\odot })$ and the second object in the GW190814 event $(M=2.{59}_{-0.09}^{+0.08}{M}_{\odot })$ indicate the possible existence of supermassive neutron stars. In this work, by using the constant-sound-speed (CSS) parametrization to describe the equation of state (EOS) of quark matter, the constraints on the EOS parameters from supermassive hybrid stars are investigated through the Maxwell and Gibbs constructions. It is shown that to support a supermassive hybrid star (e.g., $M=2.5M_{\odot }$), a lower transition energy density $\left({\varepsilon }_{\mathrm{tran}}\right)$, a smaller energy density discontinuity $\left(\mathrm{\Delta }\varepsilon \right)$, and a higher sound speed of quark matter $\left(c_{\mathrm{sq}}\right)$ are favored. For the constructed hybrid star EOS model, the maximum mass of the corresponding hybrid stars will not meet the lower mass limit of the second object in the GW190814 event if $\mathrm{\Delta }\varepsilon$ takes a value higher than 180 MeV ${\mathrm{fm}}^{-3}$. Moreover, it is confirmed that the supermassive neutron star observation can also rule out the existence of twin stars as a supermassive hybrid star requires a relatively small $\mathrm{\Delta }\varepsilon$. Finally, we give a rough estimate of the lower limit of the dimensionless tidal deformability of neutron stars that ranges from 2 to 3.

Background: The ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ reaction plays a major role both in the big bang nucleosynthesis producing the majority of the primordial ${}^7\mathrm{Li}$, and in the $pp$ chain of solar hydrogen burning, where it is the branching point between the $pp$-I and $pp$-II,-III chains. As a few-nucleon system, this reaction is often used to validate ab initio theoretical calculations and/or test $R$-matrix theory and code implementations. For the latter, experimental data in an extended energy range is of crucial importance to test the fit and extrapolation capabilities of the different codes.

Purpose: The ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ reaction cross section has been measured by several groups up to the first resonance ($E_{\mathrm{c}.\mathrm{m}.}\approx 3$ MeV) in the reaction. However, only one data set exists above the ${}^7\mathrm{Be}$ proton separation threshold measured in a narrow energy range ($E_{\mathrm{c}.\mathrm{m}.}=4.0–4.4$ MeV). In this work we extend the available experimental capture cross section database to the energy range of known ${}^7\mathrm{Be}$ levels, where only particle scattering experiments are available for testing the models.

Method: The activation method was used for the ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ reaction cross section determination. The experiment was performed using a thin-window gas cell with two high-purity Al foils as entrance and exit windows. The activity of the ${}^7\mathrm{Be}$ nuclei implanted in the exit/catcher foil was measured by detecting the yield of the emitted $\gamma$ rays using shielded high-purity germanium detectors.

Results: New experimental ${}^3\mathrm{He}(\alpha ,\gamma ){}^7\mathrm{Be}$ reaction cross section data were obtained for the first time in the $E_{\mathrm{c}.\mathrm{m}.}=4.3–8.3$ MeV energy region, corresponding to $E_x=5.8–10$ MeV excitation energies of ${}^7\mathrm{Be}$. The new data set with about 0.2 MeV step covers the energy range of known levels and particle separation thresholds. No prominent structures are observer around the ${}^7\mathrm{Be}$ levels.

Conclusions: The measured reaction cross section is slowly increasing with increasing energy in the range of $E_x=6–8$ MeV from $10\mu \mathrm{b}$ to $13\mu \mathrm{b}$. Above the ${}^6\mathrm{Li}+p_1$ threshold, a decrease starts in the cross section trend and reaches a value of about $8\mu \mathrm{b}$ around $E_x=10$ MeV. The overall structure of the cross section suggest a broad resonance peaking around $E_x=7.5$ MeV ${}^7\mathrm{Be}$ excitation energy, with a width of 8 MeV.

A new effective field theory is developed to describe shallow $P$-wave resonances using nonlocal, momentum-dependent two-body potentials. This approach is expected to facilitate many-body calculations and is demonstrated to converge and to be renormalizable in perturbative calculations at subleading orders. The theory is applied to the neutron-$\alpha$ system, with good agreement found between its predictions and a phase-shift analysis of neutron-$\alpha$ elastic scattering. In the three-body system consisting of two neutrons and an $\alpha$ particle, the nonlocal potential in this framework is found to recover the same qualitative features as previously shown with energy-dependent formulations.

Two formulations of relativistic hydrodynamics of particles with spin 1/2 are compared. The first approach, dubbed the canonical one, uses expressions for the energy-momentum and spin tensors that have properties that follow a direct application of Noether's theorem, which yields a totally antisymmetric spin tensor. The other one is based on a simplified form of the spin tensor and is commonly used in the current literature under the name of a phenomenological approach. We show that these two frameworks are equivalent, i.e., they can be directly connected by a suitably defined pseudogauge transformation, only if the first framework is initially improved by a suitable modification of the energy-momentum tensor (addition of a divergence-free term that cannot be interpreted as a pseudogauge). Our analysis uses arguments related to the positivity of entropy production. The latter turns out to be equivalent for the improved canonical and phenomenological frameworks.

Chiral effective field theory ($\chi \mathrm{EFT}$) provides a framework for obtaining internucleon interactions in a systematically improvable fashion from first principles, while also providing for the derivation of consistent electroweak current operators. In this work, we apply consistently derived interactions and currents towards calculating the magnetic dipole moments of the $A=3$ systems ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$. We focus here on LENPIC interactions obtained using semilocal coordinate-space (SCS) regularization. Starting from the momentum-space representation of the LENPIC $\chi \mathrm{EFT}$ vector current, we derive the SCS-regularized magnetic dipole operator up through next-to-next-to-leading order (${\mathrm{N}}^2\mathrm{LO}$). We then carry out no-core shell-model calculations for ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$ systems using the SCS LENPIC interaction at ${\mathrm{N}}^2\mathrm{LO}$ in $\chi \mathrm{EFT}$ and evaluate the magnetic dipole moments obtained using the consistently derived one-nucleon and two-nucleon electromagnetic currents. As anticipated by prior results with $\chi \mathrm{EFT}$ currents, the current corrections through ${\mathrm{N}}^2\mathrm{LO}$ provide improved, but not yet complete, agreement with experiment for the ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$ magnetic dipole moments.

Background: Deuteron-induced transfer reactions are a popular probe in nuclear structure and nuclear astrophysics studies. The interpretation of these transfer measurements relies on reaction theory that takes as input effective interactions between the nucleons and the target nucleus.

Purpose: Previous work quantified the uncertainty associated with the optical potentials between the nucleons and the target. In this study, we extend that work by also including the parameters of the mean field associated with the overlap function of the final bound state, thus obtaining the full parametric uncertainty on transfer observables.

Method: We use Bayesian Markov chain Monte Carlo simulations to obtain parameter posterior distributions. We use elastic-scattering cross sections to constrain the optical potential parameters and use the asymptotic normalization coefficient of the final state to constrain the bound-state interaction. We then propagate these posteriors to the transfer angular distributions and obtain confidence intervals for this observable.

Results: We study $(d,p)$ reactions on ${}^{14}\mathrm{C}$, ${}^{16}\mathrm{O}$, and ${}^{48}\mathrm{Ca}$ at energies in the range $E_d=7-24$ MeV. Our results show a strong reduction in uncertainty by using the asymptotic normalization coefficient as a constraint, particularly, for those reactions most sensitive to ambiguities in the mean field. For those reactions, the importance of constraining the bound-state interaction is equal to that of constraining the optical potentials. The case of ${}^{14}\mathrm{C}$ is an outlier because the cross section is less sensitive to the nuclear interior.

Conclusions: When minimal constraints are used on the parameters of the nucleon-target interaction, the $1\sigma$ uncertainties on the differential cross sections are large ($\approx 50\text{–}100\%$). However, if elastic-scattering data and the asymptotic normalization coefficient are used in the analysis, with an error of 10% (5%), this uncertainty reduces to $\approx 30\%$ ($\approx 15\%$).

The synthesis of neutron-rich heavy and superheavy nuclei is one of the key concerns of nuclear physics. There are only two ways to synthesize nuclei $Z>92$: fusion evaporation reactions and multinucleon transfer reactions. To theoretically unify the description of fusion evaporation reactions and cross sections of multinucleon transfer reactions, the current model of the dinuclear system is further improved in the present work. The traditional statistical approach of calculating the chance of survival of compound nucleus in fusion evaporation reactions is replaced by using $\mathrm{gemini}++$. The results reproduce well the experimental values and trends of the evaporation residue cross sections. Further, the best synthesis of $Z=100–106$ even-$Z$ nuclei is predicted using the improved model. The results show that radioactive projectile nuclei can be applied to fusion evaporation reactions for the synthesis of new neutron-rich nuclei.

We study the effects of three-nucleon short-range correlations on nuclear coordinate-space densities. For this purpose, novel three-body densities are calculated for ground-state nuclei using the auxiliary-field diffusion Monte Carlo method. The results are analyzed in terms of the generalized contact formalism, extended to include three-body correlations, revealing the universal behavior of nucleon triplets at short distances. We identify the quantum numbers of such correlated triplets and extract scaling factors of triplet abundances that can be compared to upcoming inclusive electron-scattering data. We also show that the dynamics of these triplets is sensitive to three-body forces, and, therefore, the short-range part of three-body force models could be tested against appropriate exclusive electron-scattering data.

We explore the possibility of evaluating flow harmonics by employing the maximum likelihood estimator (MLE). For a given finite multiplicity, the MLE simultaneously furnishes estimations for all the parameters of the underlying distribution function while efficiently suppressing the variance of measures. Also, the method provides a means to assess a specific class of mixed harmonics, which is not straightforwardly feasible by the approaches primarily based on particle correlations. The results are analyzed using the Wald, likelihood ratio, and score tests of hypotheses. Besides, the resultant flow harmonics obtained using MLE are compared with those derived using particle correlations and event plane methods. The dependencies of extracted flow harmonics on the multiplicity of individual events and the total number of events are analyzed. It is shown that the proposed approach works efficiently to deal with the deficiency in detector acceptability. Moreover, we elaborate on a fictitious scenario where the event plane is not a well-defined quantity in the distribution function. For the latter case, the MLE is shown to largely perform better than the two-particle correlation estimator. In this regard, one concludes that the MLE furnishes a meaningful alternative to the existing approaches for flow analysis.