The $\left(n,2n\right)$ cross sections and their isomeric ratios $({\sigma }_m/{\sigma }_g)$ in the 13–15 MeV neutron energy range have been measured for ${}^{196,198}\mathrm{Hg}$ by an activation and offline γ-ray spectrometric technique using the Pd-300 Neutron Generator at the Chinese Academy of Engineering Physics (CAEP). Natural Hg samples and Nb monitor foils were activated jointly to determine the reaction cross section and the incident neutron flux. The neutrons were produced via the ${}^3\mathrm{H}\left(d,n\right){}^4\mathrm{He}$ reaction. The pure cross section of the ground state was derived from the absolute cross section of the metastable state and the residual nuclear decay analysis. The ${}^{196}\mathrm{Hg}\left(n,2n\right){}^{195}\mathrm{Hg}^{m,g}$ and ${}^{198}\mathrm{Hg}\left(n,2n\right){}^{197}\mathrm{Hg}^{m,g}$ reaction excitation functions and their isomeric cross-section ratios were also calculated theoretically using the talys-1.8 code with different level density models. Results are discussed and compared with corresponding literature data.

A microscopic study of proton elastic scattering from unstable nuclei at intermediate energies using a relativistic formalism is presented. We have employed both the original relativistic impulse approximation (IA1) and the generalized impulse approximation (IA2) formalisms to calculate the relativistic optical potentials, with target densities derived from relativistic mean field (RMF) theory using the NL3 and FSUGold parameter sets. Comparisons between the optical potentials computed using both IA1 and IA2 formalisms and the different RMF Lagrangians are presented for both stable and unstable targets. The comparisons are required to study the effect of using IA1 versus IA2 optical potentials, with different RMF parameter sets, on elastic scattering observables for unstable targets at intermediate energies. We also study the effect of full-folding form versus the factorized form of the optical potentials on elastic scattering observables. As with the case for stable nuclei, we found that the use of the full-folding optical potential improves the scattering observables (especially spin observables) at low intermediate energy (e.g., $200\mathrm{MeV}$). No discernible difference is found at a projectile incident energy of $500\mathrm{MeV}$. To check the validity of using localized optical potential, we calculate the scattering observables using nonlocal potentials by solving the momentum space Dirac equation. The Dirac equation is transformed to two coupled Lippmann-Schwinger equations, which are then numerically solved to obtain elastic scattering observables. The results are discussed and compared to calculations involving local coordinate-space optical potentials.

Angular distributions of the differential cross section of ${}^{16}\mathrm{O}+{}^{12}\mathrm{C}$ elastic and inelastic scattering in the energy range $E_{\mathrm{lab}}=181-1503$ MeV were fitted with the full cluster folded approach (DFC1) using the coupled-channels (CC) method by taking into account the effect of the low-lying states, $0^{+}$ and $2^{+}$ ($E_{\mathrm{ex}}=4.44$ MeV) for the target nucleus. The cluster transition density is generated macroscopically by deforming the cluster ground state modified Gaussian density distribution of the target nucleus. The coupled-channels calculations with the fitted parameters for the elastic scattering provide a successful description of the inelastic experimental measurements. The obtained results are compared with the finding of the phenomenological Woods-Saxon potential. It was found that the characteristic features of the nuclear rainbow phenomena can be reproduced successfully by our CC calculations with both potentials but fail to reproduce the new Airy minimum of the nuclear rainbow structure. The deduced intrinsic quadrupole moment values, $Q_{20}$, derived from the analyses are compared with results of previous studies. The deformation lengths, ${\delta }_{20}$, obtained by CC calculations are in agreement with those obtained from the electromagnetic measurement values and those reported in previous studies.

Exclusive photoproduction cross sections have been measured for the process $\gamma p\to p{\pi }^0\left[e^{+}{e}^{-}\left(\gamma \right)\right]$ with the Dalitz decay final state using tagged photon energies in the range of $E_{\gamma }=1.275–5.425$ GeV. The complete angular distribution of the final state ${\pi }^0$, for the entire photon energy range up to large values of $t$ and $u$, has been measured for the first time. The data obtained show that the cross section $d\sigma /dt$, at mid to large angles, decreases with energy as $s^{-6.89\pm 0.26}$. This is in agreement with the perturbative QCD quark counting rule prediction of $s^{-7}$. Paradoxically, the size of angular distribution of measured cross sections is greatly underestimated by the QCD-based generalized parton distribution mechanism at highest available invariant energy $s=11{\mathrm{GeV}}^2$. At the same time, the Regge-exchange-based models for ${\pi }^0$ photoproduction are more consistent with experimental data.

A new one-neutron adding reaction on ${}^{11}\mathrm{Be}$ was performed at $26.9A$ MeV. The elastic-scattering data was measured simultaneously to determine the target component and optical potentials for the entrance channel. A special isomer-tagging method was used to determine the cross sections for the $0_2^{+}$ state. Based on the ratio of the $s$-wave spectroscopic factors of the $0_1^{+}$ and $0_2^{+}$ states, along with the previously reported $p$-wave intensities, the $s$- and $d$-wave components of these two states were obtained and compared with shell-model calculations using various interactions. The result shows a dominant $d$-wave strength in the ground state of ${}^{12}\mathrm{Be}$, and reveals the dominance of $sd$- and $sp$-single-particle configurations in the $2^{+}$ and $1^{-}$ state of ${}^{12}\mathrm{Be}$, respectively. Together with the configuration mixing analysis, the relative spectroscopic factors, which are shown to be less sensitive to the different choice of optical potentials, provide important insights on the wave functions for the low-lying states of ${}^{12}\mathrm{Be}$.

We present a new and simple method to prove the Flores-Tulián and Reisenegger (FR) relation between the net reaction rate and the total neutrino emissivity for Urca processes in the neutron, proton, and electron matter case in neutron star cores on the basis of the recursion relation of Fermi integral and its extension, these recursion relations are essential and applicable to both the direct and the modified Urca processes regardless of the nucleons being superfluid or not. Our analysis show that these relations instead of the FR relation are valid for all possible Urca processes (including electron capture and ${\beta }^{-}$ decay processes) in neutron star crusts. We apply these recursion relations to calculate the fraction of chemical energy converted to heat the crust during the deviated crust Urca processes and the nonequilibrium electron capture process, this method is simple and the result is well consistent with previous work. Moreover, these recursion relations are valid for the one-way neutrino process, based on this, we calculate the average energy of neutrinos for electron capture and ${\beta }^{-}$ decay in crust Urca processes during different chemical departure value cases.

The electromagnetic polarizabilities of the nucleon are fundamental nucleon-structure observables that characterize its response to external electromagnetic fields. The neutron polarizabilities can be accessed from Compton-scattering data on light nuclear targets. Recent measurements of the differential cross section for Compton scattering on the deuteron below the pion-production threshold have decreased the uncertainties in the neutron polarizabilities, yet the proton polarizabilities remain known substantially more accurately. As the sensitivity of the cross section to the polarizabilities increases with incident photon energy, measurements above the pion threshold may offer a way for an improved determination of the neutron polarizabilities. In this Rapid Communiciation, the first measurement of the cross section for coherent Compton scattering on the deuteron above the pion-production threshold is presented.

We compute the electric dipole polarizability of ${}^{48}\mathrm{Ca}$ with an increased precision by including more correlations than in previous studies. Employing the coupled-cluster method we go beyond single and double excitations and include leading-order three-particle-three-hole (3p-3h) excitations for the ground state, excited states, and the similarity-transformed operator. We study electromagnetic sum rules, such as the bremsstrahlung sum rule $m_0$ and the polarizability sum rule ${\alpha }_D$ using interactions from chiral effective field theory. To gauge the quality of our coupled-cluster approximations we perform several benchmarks with the effective interaction hyperspherical harmonics approach in ${}^4\mathrm{He}$ and with self consistent Green's function in ${}^{16}\mathrm{O}$. We compute the dipole polarizability of ${}^{48}\mathrm{Ca}$ employing the chiral interaction ${\mathrm{N}}^2{\mathrm{LO}}_{\mathrm{sat}}$ [Ekström et al., Phys. Rev. C 91, 051301 (2015)] and the 1.8/2.0 (EM) [Hebeler et al., Phys. Rev. C 83, 031301 (2011)]. We find that the effect of 3p-3h excitations in the ground state is small for 1.8/2.0 (EM) but non-negligible for ${\mathrm{N}}^2{\mathrm{LO}}_{\mathrm{sat}}$. The addition of these new correlations allows us to improve the precision of our ${}^{48}\mathrm{Ca}$ calculations and reconcile the recently reported discrepancy between coupled-cluster results based on these interactions and the experimentally determined ${\alpha }_D$ from proton inelastic scattering in ${}^{48}\mathrm{Ca}$ [Birkhan et al., Phys. Rev. Lett. 118, 252501 (2017)]. For the computation of electromagnetic and polarizability sum rules, the inclusion of leading-order 3p-3h excitations in the ground state is important, while it is less so for the excited states and the similarity-transformed dipole operator.

The production cross sections of new neutron-rich nuclei ${}^{209\text{–}212}\mathrm{Pt}$ are investigated with multinucleon transfer reactions by the dinuclear system model. It is found that the ${}^{133}\mathrm{Sn}+{}^{204}\mathrm{Hg}$ and ${}^{145}\mathrm{Xe}+{}^{208}\mathrm{Pb}$ systems are advantageous to produce the neutron-rich nuclei, in which the production cross sections are much higher than those produced in projectile fragmentation reactions. The optimal incident energies for these two systems are about 1.18 and 1.40 times the Coulomb barrier, respectively. The highest cross sections of unknown isotopes ${}^{209\text{–}212}\mathrm{Pt}$ in the ${}^{145}\mathrm{Xe}+{}^{208}\mathrm{Pb}$ reaction are 2.7 nb, 0.4 nb, 8.2 pb, and 2.7 pb, respectively, and those for the ${}^{133}\mathrm{Sn}+{}^{204}\mathrm{Hg}$ reaction are 1.7 nb, 0.4 nb, 23.3 pb, and 4.8 pb, respectively.

We introduce a new method to calculate the nuclear radius from low energy fusion and total reaction cross section measurements. We apply it for several light stable and unstable projectiles on light mass targets (${}^9\mathrm{Be},{}^{12}\mathrm{C}$, and ${}^{27}\mathrm{Al}$). Our results are in reasonable agreement with the radii obtained from high energy experimental data. We also interpreted the results as a function of the isospin of the projectile, mass of the interacting target, and neutron and proton numbers.

The empirical coupled-channel (ECC) model and the universal fusion function (UFF) prescription are used to analyze the data of capture cross sections for reactions ${}^{39}\mathrm{K}+{}^{181}\mathrm{Ta}$ and ${}^{46}\mathrm{K}+{}^{181}\mathrm{Ta}$ reported recently by Wakhle et al.[Phys. Rev. C 97, 021602(R) (2018)]. The results of the ECC model are in good agreement with the data of ${}^{39}\mathrm{K}+{}^{181}\mathrm{Ta}$, while for ${}^{46}\mathrm{K}+{}^{181}\mathrm{Ta}$ the predictions of the ECC model overestimate the above-barrier capture cross sections. Comparing the reduced data of these two reactions, it is found that the above-barrier cross sections of ${}^{39}\mathrm{K}+{}^{181}\mathrm{Ta}$ are consistent with the UFF and are larger than those of ${}^{46}\mathrm{K}+{}^{181}\mathrm{Ta}$. This implies that the capture cross sections of ${}^{46}\mathrm{K}+{}^{181}\mathrm{Ta}$ are suppressed at energies above the Coulomb barrier. Furthermore, at sub-barrier energies, the reduced calculated capture cross sections of ${}^{39}\mathrm{K}+{}^{181}\mathrm{Ta}$ are a little larger than those of ${}^{46}\mathrm{K}+{}^{181}\mathrm{Ta}$, which is owing to the coupling to the positive $Q$-value two-neutron transfer channel.

We present a theoretical framework to study open-charm production in relativistic heavy-ion collisions. Charm quarks are regarded as an effective probes of the deconfined medium formed in these collisions, the quark-gluon plasma (QGP). The initial conditions of such collisions are simulated with a transverse profile described via a Glauber-based model, and a longitudinal behavior modeled by a data-inspired parametrization. The space-time evolution of the temperature and the flow velocity field of the medium are quantified by means of (3+1)-dimensional relativistic viscous hydrodynamics. The Brownian motion of charm quarks propagating through the QGP is described by utilizing the Langevin transport equation. The subsequent hadronization is implemented via a dual model, including fragmentation and heavy-light coalescence mechanisms. In particular, in the coalescence also the contribution from higher hadronic states components is considered. The parameters of the model are tuned based on comparison to data. The coupling strength between the charm quarks and the QGP constituents, quantified by the spatial diffusion coefficient $2\pi T{D}_s$, is obtained by performing a phenomenological fit analysis to the lattice QCD calculations, resulting in $2\pi T{D}_s=\text{const}.$ (model A) and $2\pi T{D}_s=1.3+{(T/T_c)}^2$ (model B). We find that the relative azimuthal distribution of the initially back-to-back generated $c\overline{c}$ pairs presents a broadening behavior, which is more pronounced for $c\overline{c}$ pairs with small initial $p_{\mathrm{T}}$ and when the model B approach is adopted. The competition between the initial drag and the subsequent collective effects tends to restrict the time dependence of charm quark $R_{\mathrm{AA}}$. Concerning the theoretical uncertainty on final $D$-meson nuclear modification, the nuclear shadowing and $pp$ baseline components are dominant at high and low $p_{\mathrm{T}}$ ($p_{\mathrm{T}}\lesssim 3\mathrm{GeV}/\mathit{c}$), respectively. The measured $D$-meson $R_{\mathrm{AA}}\left(p_{\mathrm{T}}\right)$ favors model A's assumption for the diffusion coefficient both at the Relativistic Heavy Ion Collider and the Large Hadron Collider, while $v_2\left(p_{\mathrm{T}}\right)$ prefers model B at moderate $p_{\mathrm{T}}$. These results confirm the necessity to consider the temperature and/or momentum dependence of $2\pi T{D}_s$ to simultaneously describe the $D$ meson $R_{\mathrm{AA}}$ and $v_2$.

Global polarization of $\mathrm{\Lambda }$ hyperons has been measured to be of the order of a few tenths of a percentage in Au+Au collisions at $\sqrt{s_{{}_{NN}}}$ = 200 GeV, with no significant difference between $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$. These new results reveal the collision energy dependence of the global polarization together with the results previously observed at $\sqrt{s_{{}_{NN}}}$ = 7.7–62.4 GeV and indicate noticeable vorticity of the medium created in noncentral heavy-ion collisions at the highest Relativistic Heavy Ion Collider collision energy. The signal is in rough quantitative agreement with the theoretical predictions from a hydrodynamic model and from a multi-phase transport model. The polarization is larger in more peripheral collisions, and depends weakly on the hyperon's transverse momentum and pseudorapidity ${\eta }^H$ within $|{\eta }^H|<1$. An indication of the polarization dependence on the event-by-event charge asymmetry is observed at the $2\sigma$ level, suggesting a possible contribution to the polarization from the axial current induced by the initial magnetic field.

The process $e^{+}{e}^{-}\to K^{+}{K}^{-}$ is described in the framework of the Nambu–Jona-Lasinio model in the energy region 1–1.7 GeV. The contact terms with intermediate photon and terms with intermediate $\rho ,\omega$, and $\varphi$ vector mesons in the ground and first radially excited states are taken into account. Our results are in satisfactory agreement with experimental data recently obtained at VEPP-2000 and SLAC.

We calculate the inverse-$\beta$-decay (IBD) antineutrino spectrum generated by nuclear reactors using the summation method to understand deviations from the smooth Huber-Mueller model due to the decay of individual fission products, showing that plotting the ratio of two adjacent spectra points can effectively reveal these deviations. We obtain that, for binning energies of 0.1 MeV or lower, abrupt changes in the spectra due to the jagged nature of the individual antineutrino spectra could be observed for highly precise experiments. Surprisingly, our calculations also reveal a peaklike feature in the adjacent points ratio plot at 4.5 MeV even with a 0.25-MeV binning interval, which we find is present in the IBD spectrum published by the Daya Bay Collaboration in 2016. We show that this 4.5-MeV feature is caused by the contributions of just four fission products, ${}^{95}\mathrm{Y}, {}^{98,101}\mathrm{Nb}$, and ${}^{102}\mathrm{Tc}$. This would be the first evidence of the decay of a few fission products in an IBD antineutrino spectrum from a nuclear reactor. This result is supported by applying the same numerical technique to the measured aggregate electron spectra.

Prompt-fission $\gamma$-ray spectra (PFGS) have been measured for the ${}^{238}\mathrm{U}(n,f$) reaction using fast neutrons produced by the LICORNE directional neutron source. Fission events were detected with an ionization chamber containing actinide samples placed in the neutron beam, and the coincident prompt-fission $\gamma$ rays were measured using a number of ${\mathrm{LaBr}}_3$ scintillation detectors and a cluster of nine phoswich detectors from the PARIS array. Prompt-fission $\gamma$ rays (PFGs) were discriminated from prompt-fission neutrons using the time-of-flight technique over distances of around 35 cm. PFG emission spectra were measured at two incident neutron energies of 1.9 and 4.8 MeV for ${}^{238}\mathrm{U}(n,f$) and also for ${}^{252}\mathrm{Cf}(sf$) as a reference. Spectral characteristics of PFG emission, such as mean $\gamma$ multiplicity and average total $\gamma$-ray energy per fission, as well as the average $\gamma$-ray energy, were extracted. The sensitivity of these results to the width of the time window and the type of spectral unfolding procedure used to correct for the detector responses was studied. Iteration methods were found to be more stable in low-statistics data sets. The measured values at $E_n=1.9\text{MeV}$ were found to be the mean $\gamma$ multiplicity ${\overline{M}}_{\gamma }=6.54\pm 0.19$, total released energy per fission $E_{\gamma ,\mathrm{tot}}=5.25\pm 0.20$ MeV, and the average $\gamma$-ray energy ${\epsilon }_{\gamma }=0.80\pm 0.04$ MeV. Under similar conditions, the values at $E_n=4.8\text{MeV}$ were measured to be ${\overline{M}}_{\gamma }=7.31\pm 0.46, E_{\gamma ,\mathrm{tot}}=6.18\pm 0.65$ MeV, and ${\epsilon }_{\gamma }=0.84\pm 0.11$ MeV.

The baryon and energy densities attained in fragmentation regions in central Au+Au collisions in the energy range of the Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) are estimated within the model of the three-fluid dynamics. It is shown that a considerable part of the baryon charge is stopped in the central fireball. Even at 39 GeV, approximately 70% of the total baryon charge turns out to be stopped. The fraction of this stopped baryon charge decreases with collision energy rise, from 100% at 7.7 GeV to $\approx 40\%$ at 62 GeV. The highest initial baryon densities of the equilibrated matter, $n_B/n_0\approx 10$, are reached in the central region of colliding nuclei at $\sqrt{s_{NN}}=20–40$ GeV. These highest densities develop up to quite moderate freeze-out baryon densities at the midrapidity because the matter of the central fireball is pushed out to fragmentation regions by one-dimensional expansion. Therefore, consequences of these high initial baryon densities can be observed only in the fragmentation regions of colliding nuclei in AFTER@LHC experiments in the fixed-target mode.

Taking into account the recently developed van der Waals (VDW)-like equation of state (EoS) for grand canonical ensemble of fermions, the temperature-dependent profiles of normalized entropy density ($s/T^3$) and the ratio of shear viscosity and entropy density ($\eta /s$) for hadron resonance gas have been evaluated. The VDW parameters, corresponding to interactions between (anti)baryons, have been obtained by contrasting lattice EoS for QCD matter at finite chemical potentials (${\mu }_B$) and for $T\le$ 160 MeV. The temperature- and chemical-potential-dependent study of $s/T^3$ and $\eta /s$ for hadron gas, by signaling onsets of first-order phase transition and crossover in the hadronic phase of QCD matter, helps in understanding the QCD phase diagram in the ($T,{\mu }_B$) plane. An estimation of probable location of critical point matches predictions from other recent studies.

The hadron-resonance gas (HRG) approach, used to model hadronic matter at small baryon potentials ${\mu }_B$ and finite temperature $T$, is extended to finite and large chemical potentials by introducing interactions between baryons in line with relativistic mean-field theory defining an interacting HRG (IHRG). Using lattice data for ${\mu }_B=0$ as well as information on the nuclear equation of state at $T=0$ we constrain the attractive and repulsive interactions of the IHRG such that it reproduces the lattice equation of state at ${\mu }_B=0$ and the nuclear equation of state at $T=0$ and finite ${\mu }_B$. The formulated covariant approach is thermodynamically consistent and allows us to provide further information on the phase boundary between hadronic and partonic phases of strongly interacting matter by assuming constant thermodynamic potentials.