A method is presented to extract the neutron-skin thickness of atomic nuclei from the second and fourth moments of the electric charge distribution. We show that the value of the proton fourth moment must be independently known in order to estimate the neutron-skin thickness experimentally. To overcome this problem, we propose the use of a strong linear correlation among the second and fourth moments of the proton distribution as calculated with several energy density functionals of common use. We take special care in estimating the errors associated with the different contributions to the neutron radius and show, for the first time, the analytic expressions for the spin-orbit contribution to the charge fourth moments of neutrons and protons. To reduce the uncertainty on the extraction of the neutron radius, two neighboring even-even isotopes are used. Nevertheless, the error on the fourth moment of the proton distribution, even if determined or assumed with large accuracy, dominates and prevents the present method from being applied for a sound determination of the neutron-skin thickness.

Background: The reaction cross section ${\sigma }_R$ is useful to determine the neutron radius $R_n$ as well as the matter radius $R_m$. The chiral (Kyushu) $g$-matrix folding model for ${}^{12}\mathrm{C}$ scattering on ${}^9\mathrm{Be}, {}^{12}\mathrm{C}, {}^{27}\mathrm{Al}$ targets was tested in the incident energy range of $30\lesssim E_{\mathrm{in}}\lesssim 400$ MeV, and it is found that the model reliably reproduces the ${\sigma }_R$ in $30\lesssim E_{\mathrm{in}}\lesssim 100$ MeV and $250\lesssim E_{\mathrm{in}}\lesssim 400$ MeV.

Purpose: Our aim is to determine $r_{\mathrm{skin}}^{208}\left(\mathrm{EXP}\right)$ from ${\sigma }_{\mathrm{R}}\left(\mathrm{EXP}\right)$ for $p+{}^{208}\mathrm{Pb}$ scattering in $30\le E_{\mathrm{lab}}\le 100$ MeV.

Methods: Our model is the Kyushu $g$-matrix folding model with the densities calculated with Gongny-D1S HFB (GHFB) with the angular momentum projection (AMP).

Results: The Kyushu $g$-matrix folding model with the $\text{GHFB}+\text{AMP}$ densities underestimates ${\sigma }_{\mathrm{R}}$ in $30\le E_{\mathrm{in}}\le 100$ MeV only by a factor of 0.97. Since the proton radius $R_p$ calculated with $\text{GHFB}+\text{AMP}$ agrees with the precise experimental data of 5.444 fm, the small deviation of the theoretical result from the data on ${\sigma }_R$ allows us to scale the $\text{GHFB}+\text{AMP}$ neutron density so as to reproduce the ${\sigma }_R$ data. In $E_{\mathrm{in}}=30$–100 MeV, the experimental ${\sigma }_R$ data can be reproduced by assuming the neutron radius of ${}^{208}\mathrm{Pb}$ as $R_n=5.722\pm 0.035$ fm.

Conclusion: The present result $R_{\mathrm{skin}}=0.278\pm 0.035$ fm is in good agreement with the recent PREX-II result of $r_{\mathrm{skin}}=0.283\pm 0.071$ fm.

In the paper we present the results obtained for the effect of rotation (ROT) in the angular distribution of prompt $\gamma$ rays from the fission of ${}^{235}\mathrm{U}$ induced by monochromatic polarized “warm” neutrons ($E_n$ = 60 meV). The polarization vector direction is determined at the target position in order to correctly determine the sign of the measured effect. The asymmetry parameter was found to be equal to $R_{\gamma }=-(17.3\pm 2.8)\times {10}^{-5}$. Moreover, the rotation angle of the fission axis was determined to be equal to $0.{069}^{\circ }\pm 0.{008}^{\circ }$ taking into account the fit results of the angular distribution of the prompt fission $\gamma$ rays. The obtained value and sign of the ROT effect are consistent with the results of the ROT effect obtained for cold neutrons. We describe the experiment, methodology of sign determination, and implications of the results.

A discrepancy in the asymmetry dependence of spectroscopic factors extracted with different reaction probes calls into question whether the corresponding reaction models are properly understood. In this work, we present extracted spectroscopic factors from the ${}^{46,34}\mathrm{Ar}(p,d){}^{45,33}\mathrm{Ar}$ transfer reactions in inverse kinematics at a beam energy of 70 MeV/nucleon. The results are consistent with previous measurements of these reactions at a lower beam energy [Lee et al., Phys. Rev. Lett. 104, 112701 (2010)], indicating that the transfer reaction is a reliable probe for the nuclear structure of exotic nuclei across a wide energy range. Results from a large body of transfer reaction measurements, $(p,pN)$ measurements, and theoretical nuclear structure studies make a compelling case for much weaker asymmetry dependence than what is observed with single-nucleon knockout reactions on beryllium or carbon targets.

In this work, one-neutron transfer (pickup and stripping), complete and incomplete fusion cross sections for the ${}^9\mathrm{Be}+{}^{197}\mathrm{Au}$ system were measured over a wide range of energies around the Coulomb barrier by the offline $\gamma$-ray detection method. Coupled-channel calculations were used to determine the elastic, inelastic, and transfer cross sections. Coupled reaction channel calculations were performed to derive the one-neutron stripping and pickup cross sections. Three-body continuum discretized coupled-channel calculations were used to determine the effect of the breakup channel on the other reaction mechanisms. The reduced complete and total fusion were found to be hindered above and enhanced below the Coulomb barrier compared with the universal fusion function due to the breakup plus transfer effects.

The lifetimes of the $2_1^{+}$ and $4_1^{+}$ states of ${}^{208}\mathrm{Po}$ were measured in the $\alpha$-transfer reaction ${}^{204}\mathrm{Pb}({}^{12}\mathrm{C},{}^8\mathrm{Be}){}^{208}\mathrm{Po}$ by $\gamma$-ray spectroscopy utilizing the recoil distance Doppler shift method. The newly extracted transition strengths alongside ones of the decay of the $2_2^{+}$ state were compared to the results of large-scale shell-model calculations using an effective interaction derived from the realistic CD-Bonn nucleon-nucleon potential. The comparison indicates the importance of the quadrupole isovector excitations in the valence shell for a fine tuning of the two-body matrix elements of the shell-model interaction.

Background: The excitation energy dependence of the fission fragment mass and folding angle distributions for reactions with loosely bound projectiles are reported to be significantly different compared to the reactions with tightly bound nuclei. Extensive study to understand the reaction mechanism of weakly bound projectiles is required as it can simulate the mechanism of fission induced with radioactive ion beams.

Purpose: The effect of loosely bound nuclei on fission fragment folding angle and mass distributions in the ${}^9\mathrm{Be}+{}^{238}\mathrm{U}$ reaction near the Coulomb barrier energies is investigated and the contributions of incomplete fusion fission in the total fission cross section are studied.

Methods: Mass and folding angle distributions of the fission fragments have been measured near the Coulomb barrier energies using two large area multiwire proportional counters. Fragment masses were determined from the time-of-flight difference method. To understand the effect of breakup of loosely bound nuclei, the results are compared with tightly bound proton-, $\alpha$-particle-, and carbon-induced reactions, as well as with the predictions from semiempirical calculations.

Results: The width of folding angle distributions is found to increase with lowering excitation energy in the ${}^9\mathrm{Be}+{}^{238}\mathrm{U}$ reaction. This is in contrast to the reaction ${}^{12}\mathrm{C}+{}^{232}\mathrm{Th}$ involving tightly bound projectiles, populating similar compound nuclei. The peak-to-valley ratios of the fission fragment mass distributions for all events are found to sharply increase with lowering excitation energy in the ${}^9\mathrm{Be}+{}^{238}\mathrm{U}$ reaction. The possible contribution of incomplete fusion into the total fission cross section could be extracted. The measured mass distributions were found to be consistent with the semiempirical calculation gef and macro-microscopic two-center shell model calculations considering the admixture of incomplete fusion fission.

Conclusion: For actinide targets, mass distributions of inclusive fission are influenced by the breakup/transfer channels of the weakly bound projectiles. At the above-barrier energies, the contribution of incomplete fusion is found to be $\approx 25\pm 4\%$ which is similar to the reported value of the complete fusion suppression factor in reactions involving nuclei with low binding energies. The increase in the peak-to-valley ratio with lowering excitation energy in the fission fragment mass distribution could be explained by the combined analysis of folding angle and mass distributions.

In this work, we first investigate how to reproduce and how well one can reproduce the Woods-Saxon density distribution of initial nuclei in the framework of the improved quantum molecular dynamics model. Then, we propose a new treatment for the initialization of nuclei which is correlated with the nucleonic mean-field potential by using the same potential energy density functional. In the mean field potential, the three-body force term is accurately calculated. Based on the new version of the model, the influences of precise calculations of the three-body force term, the slope of symmetry energy, the neutron-proton effective mass splitting, and the width of the wave packet on heavy ion collision observables, such as the neutron to proton yield ratios for emitted free nucleons $\left[R\right(n/p\left)\right]$ and for coalescence invariant nucleons $\left[R_{ci}(n/p)\right]$ for ${}^{124}\mathrm{Sn}+{}^{112}\mathrm{Sn}$ at the beam energy of 200 MeV per nucleon, are discussed. Our calculations show that the spectra of neutron to proton yield ratios $\left[R\right(n/p\left)\right]$ can be used to probe the slope of symmetry energy ($L$) and the neutron-proton effective mass splitting. In detail, the $R(n/p)$ in the low kinetic energy region can be used to probe the slope of symmetry energy ($L$). With a given $L$, the inclination of $R(n/p)$ to kinetic energy ($E_k$) can be used to probe the effective mass splitting. In the case where the neutron-proton effective mass splitting is fixed, $R(n/p)$ at high kinetic energy can also be used to learn the symmetry energy at suprasaturation density.

At large virtuality $Q^2$, the coupling to the $\rho$ meson production channels provides us with a natural explanation of the surprisingly large cross section of the $\omega$, as well as the ${\pi }^{+}$, meson electroproduction recently measured at backward angles, without destroying the good agreement between the Regge pole model and the data at the real photon point. Together with elastic re-scattering of the outgoing meson it also provides us with a way to explain why the node, that appears at $u\sim -0.15{\mathrm{GeV}}^2$ at the real photon point, disappears at moderate virtuality $Q^2$. Predictions are given for the electroproduction of the ${\pi }^0$ meson.

Mirror energy differences (MED) between excited states in the $A=31, T=1/2$ mirror pair ${}^{31}\mathrm{S}$ and ${}^{31}\mathrm{P}$ have been measured up to high spin yrast states of positive and negative parity. The mirror nuclei were populated in the ${}^{24}\mathrm{Mg}({}^{12}\mathrm{C}, \alpha n$) and ${}^{24}\mathrm{Mg}({}^{12}\mathrm{C}, \alpha p$) reactions, respectively. For the first time the MED are described in the framework of the shell model in a valence space that includes three main shells. The theoretical MED values as a function of angular momentum indicate that the main contribution arises from the Coulomb interaction, however, the isospin symmetry breaking term is not at all negligible and needs to be considered to reproduce the experimental findings.

The competitive double-$\gamma$ decay of the $2_1{}^{+}$ state of an even-even spherical nucleus is studied for the first time. The coupling of one-, two-, and three-phonon terms in the wave functions of excited states is taken into account within the microscopic model based on the Skyrme energy density functional. The approach enables one to perform the calculations in very large configurational spaces. We estimate the generalized electric dipole polarizabilities involved in the $\gamma \gamma /\gamma$ decay process and make a prediction for the branching ratio of the competitive $\gamma \gamma$-decay relative to its single $\gamma$-decay calculated to be $3\times {10}^{-8}$ for the case of ${}^{48}\mathrm{Ca}$.

Within the transport model evaluation project (TMEP) of simulations for heavy-ion collisions, the mean-field response is examined here. Specifically, zero-sound propagation is considered for neutron-proton symmetric matter enclosed in a periodic box, at zero temperature and around normal density. The results of several transport codes belonging to two families (BUU-like and QMD-like) are compared among each other and to exact calculations. For BUU-like codes, employing the test particle method, the results depend on the combination of the number of test particles and the spread of the profile functions that weight integration over space. These parameters can be properly adapted to give a good reproduction of the analytical zero-sound features. QMD-like codes, using molecular dynamics methods, are characterized by large damping effects, attributable to the fluctuations inherent in their phase-space representation. Moreover, for a given nuclear effective interaction, they generally lead to slower density oscillations, as compared to BUU-like codes. The latter problem is mitigated in the more recent lattice formulation of some of the QMD codes. The significance of these results for the description of real heavy-ion collisions is discussed.

We report a systematic measurement of cumulants, $C_n$, for net-proton, proton, and antiproton multiplicity distributions, and correlation functions, ${\kappa }_n$, for proton and antiproton multiplicity distributions up to the fourth order in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4, and 200 GeV. The $C_n$ and ${\kappa }_n$ are presented as a function of collision energy, centrality and kinematic acceptance in rapidity, $y$, and transverse momentum, $p_T$. The data were taken during the first phase of the Beam Energy Scan (BES) program (2010–2017) at the BNL Relativistic Heavy Ion Collider (RHIC) facility. The measurements are carried out at midrapidity ($\left|y\right|<$ 0.5) and transverse momentum $0.4<p_T<2.0\mathrm{GeV}/c$, using the STAR detector at RHIC. We observe a nonmonotonic energy dependence ($\sqrt{s_{NN}}$ = 7.7–62.4 GeV) of the net-proton $C_4/C_2$ with the significance of $3.1\sigma$ for the 0–5% central $\mathrm{Au}+\mathrm{Au}$ collisions. This is consistent with the expectations of critical fluctuations in a QCD-inspired model. Thermal and transport model calculations show a monotonic variation with $\sqrt{s_{NN}}$. For the multiparticle correlation functions, we observe significant negative values for a two-particle correlation function, ${\kappa }_2$, of protons and antiprotons, which are mainly due to the effects of baryon number conservation. Furthermore, it is found that the four-particle correlation function, ${\kappa }_4$, of protons plays a role in determining the energy dependence of proton $C_4/C_1$ below 19.6 GeV, which cannot be understood by the effect of baryon number conservation.

A series of new flow observables mixed harmonic multiparticle cumulants, which allow for the first time to quantify the strength of the correlation between different orders of flow coefficients with various moments, was investigated using the hydrodynamic model. These new observables are constructed based on multiparticle cumulants and, thus, by design, will be less sensitive to the nonflow contaminations. In addition to the previous study of correlation involving two flow coefficients with their second moments both correlations of three flow coefficients and the correlations of higher-order moments of $v_2$ and $v_3$ are systematically investigated using the iebe-vishnu hybrid model with two different initial conditions, ampt and trento, respectively. These systematic studies using hydrodynamic models will significantly improve the understanding of the correlations between different orders (and moments) of flow coefficients. Furthermore, the hydrodynamic predictions shown in this paper and the future comparisons to experimental measurements will provide more constraints on theoretical models and extract more information about the transport properties of the quark-gluon plasma created in heavy-ion collisions.

The predictive power of the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) for nuclear mass is examined in the superheavy region, $102\le Z\le 120$. The accuracy of predicting the 10 (56) measured (measured and empirical) masses is 0.635 (0.642) MeV, in comparison with 0.515 (1.360) MeV by WS4 and 0.910 (2.831) MeV by FRDM. Possible stability against multineutron emission beyond the two-neutron drip line is explored by the DRHBc theory, which takes into account simultaneously the deformation effects, the pairing correlations, and the continuum effects. Nuclei stable against two- and multineutron emissions beyond the two-neutron drip line are predicted in ${}_{106}\mathrm{Sg}, {}_{108}\mathrm{Hs}, {}_{110}\mathrm{Ds}$, and ${}_{112}\mathrm{Cn}$ isotopic chains, forming a peninsula of stability adjacent to the nuclear mainland. This stability is mainly due to the deformation which significantly affects the shell structure around the Fermi surface. The pairing correlations and continuum influence the stability peninsula in a self-consistent way.

The signatures of inversion between normal and intruder configurations of particle-hole excitations across the $N=20$ shell gap in the neutron-rich isotope ${}^{32}\mathrm{Mg}$ have long been of keen interest. Electromagnetic transition rates in the ground-state band are key quantities that provide insights into collective properties associated with the contributions of the 2p2h and 4p4h intruder configurations. The combination of TRIPLEX, GRETINA, and the S800 spectrograph enables model-independent lifetime measurements to determine electromagnetic transition rates in rare isotopes. The reduced $E2$ transition rates in ${}^{32}\mathrm{Mg}$ between the $2_1^{+}$ and $0_1^{+}$ states and between the $4_1^{+}$ and $2_1^{+}$ states have been measured, the latter representing the first experimental $B\left(E2\right)$ value for this transition. The $B\left(E2\right)$ strengths indicate large collectivity and strong contributions from the 2p2h and 4p4h intruder configurations that may change with spin in the ground-state band of ${}^{32}\mathrm{Mg}$.

The $\beta$ decay of ${}^{125m,125}\mathrm{Ag}$ into levels in ${}^{125}\mathrm{Cd}$ was investigated at the Holifield Radioactive Ion Beam Facility (HRIBF). Uranium-238 targets were bombarded with 50-MeV protons with an intensity of $15\mu$A, and the induced fission products were mass separated and deposited on a moving tape in the center of the VANDLE array consisting of $\gamma$ detectors and plastic scintillators. A partial decay scheme has been assigned for both $\beta$ decay of the (9/$2^{+}$) ground state of ${}^{125}\mathrm{Ag}$ and its low-lying (1/$2^{-}$) isomer, with the energy of the low-lying (11/$2^{-}$) isomeric state in ${}^{125}\mathrm{Cd}$ assigned as 188.5 keV. In addition, $\beta$-delayed neutron emission probabilities were also determined to be 1.2(2)% for the (9/$2^{+}$) ${}^{125}\mathrm{Ag}$ ground state and 4.6(10)% for the (1/$2^{-}$) isomer, which are substantially lower than the previously reported value.

The asymmetric initial geometry in $p+\text{Pb}$ collisions provide an opportunity to probe the initial matter distribution in these collisions. Using a multiphase transport (AMPT) model, we have studied the production of light and heavy quark particles in $p+\text{Pb}$ collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. The pseudorapidity density $(dN/d\eta )$ and elliptic flow $\left(v_2\right)$ of light quark particles from AMPT reasonably agrees with the measurements by ALICE. We predicted the directed flow of light and heavy quarks in $p+\text{Pb}$ collisions. The $v_1$ of both light and heavy quark mesons show a nontrivial $p_T$ dependence in $p$- and Pb-going directions. When integrated over the transverse momentum range 0 $<p_T<5$ GeV/c, the magnitude of heavy quark directed flow $\left(v_1\right)$ is found to be 15 times larger than the light quark species in the Pb-going direction while the same in the $p$-going direction are comparable. The light and heavy quarks $v_1$ may offer the possibility to probe the initial matter density as well as the collective dynamics in $p+\text{Pb}$ collisions.

We study the expansion of neutron star (NS) matter containing hyperons $\mathrm{\Lambda }$ from high densities up to the end of nucleosynthesis. This process should occur in NS-NS or NS–black hole collisions. Hyperons $\mathrm{\Lambda }$ decay by mesonic and nonmesonic reactions on a very short timescale to form proton and neutron matter. When material becomes diluted enough, the formation of helium and heavier nuclei releases energy and increases its temperature to reach nuclear statistical equilibrium (NSE) conditions with high entropy per baryon. From then on, nucleosynthesis proceeds and the final composition is largely determined by the proton per baryon fraction $Y_p$. We consider a recent equation of state that considers the presence of $\mathrm{\Lambda }$ hyperons [D. Logoteta, I. Vidaña, and I. Bombaci, Eur. Phys. J. A 55, 207 (2019)] and simultaneously allows for the existence of NSs with masses $M\gtrsim 2M_{\odot }$. We assumed the composition of NS matter at densities above the threshold for the occurrence of $\mathrm{\Lambda }$ hyperons and computed its decay, finding that it appreciably increases $Y_p$. Then, we computed the subsequent nucleosynthesis starting from NSE assuming that the density falls exponentially. We find that, depending on the initial composition of the ejected material, the increase in $Y_p$ due to hyperon decay is sufficient to sizeably affect the final isotopic composition of ejected matter (for example, lanthanide production may be strongly inhibited). These results indicate that $\mathrm{\Lambda }$ hyperons may affect the final composition of matter ejected in kilonova events. We also discuss the case of pure $\mathrm{\Lambda }$ matter as a possible scenario for the collision by strange stars, where we have obtained values $Y_p\approx 0.4\text{–}0.5$, which leads to final isotopes far lighter than in the former case.