New experimental data for the ${}^{38}\mathrm{Ar}(\alpha ,n){}^{41}\mathrm{Ca}$ and ${}^{38}\mathrm{Ar}(\alpha ,p){}^{41}\mathrm{K}$ reactions were used to find a best-fit set of parameters for statistical model calculations. The very good agreement between the experimental data and the best-fit calculation confirms the applicability of the statistical model for nuclei in the vicinity of the doubly magic ${}^{40}\mathrm{Ca}$ despite their relatively low level densities. The present study investigates the sensitivities and finds that the $\alpha$-nucleus and the nucleon-nucleus potentials are the most important ingredients for the calculation of ($\alpha ,n$) and ($\alpha ,p$) reactions in the statistical model. Furthermore, the width fluctuation correction plays an essential role in the peculiar case of ${}^{38}\mathrm{Ar}$. The best-fit parameters from ${}^{38}\mathrm{Ar}$ are applied to the mirror nucleus ${}^{38}\mathrm{Ca}$ and the neighboring ${}^{36}\mathrm{Ar}$ and ${}^{40}\mathrm{Ar}$ nuclei. For ${}^{38}\mathrm{Ca}$ this results in an astrophysical reaction rate of the ${}^{38}\mathrm{Ca}(\alpha ,p){}^{41}\mathrm{Sc}$ reaction, which has a flatter temperature dependence compared to all previous calculations. For ${}^{40}\mathrm{Ar}$ a better reproduction of ${}^{40}\mathrm{Ar}(\alpha ,p){}^{43}\mathrm{K}$ data from literature is obtained. The disagreement between calculation and an early experimental data point for the ${}^{36}\mathrm{Ar}(\alpha ,p){}^{39}\mathrm{K}$ reaction persists.

Cluster radioactivity is an exotic nuclear decay observed in actinides where a light nucleus is emitted while the remaining heavy mass residue is the doubly magic ${}^{208}\mathrm{Pb}$ or a nucleus in its neighborhood. We have investigated this type of decay in heavier nuclei up to Lv $(Z=116)$ within a microscopic theory. It has been found that the cluster radioactivity known in the light actinides may become the dominant decay channel in some superheavy nuclei. This superasymmetric fission channel is distinct from typical asymmetric fission in actinides. We predict a sharp fission fragment mass distribution with the heavy fragment close to ${}^{208}\mathrm{Pb}$.

The spin distribution populated in the ${}^{150}\mathrm{Sm}(p,t)$ reaction with 25 MeV protons has been investigated using the silicon telescope and high-purity germanium array Hyperion. Angular distributions of outgoing tritons and relative intensities of $\gamma$ rays from low-lying levels are used to deduce the initial spin distribution using statistical calculations and are compared with a semiclassical model of the $(p,t)$ reaction. Experimental and theoretical results suggest a peak strength near $4\hslash$ when gated on outgoing tritons detected in Hyperion, while the full $4\pi$ distribution may peak near $2\hslash$. Additionally, the average $\gamma$-neutron branching ratio is determined from the data with the aid of one of two new codes presented in this work. The analysis is extended to other recent studies of ${}^{152,154}\mathrm{Sm}(p,t)$ to form systematics of the spin-dependence of the surrogate method applied to heavy nuclei in the transitional to deformed region.

The theory of heavy-ion single-charge exchange reactions is reformulated. In momentum space, the reaction amplitude factorizes into a product of projectile and target transition form factors, folded with the nucleon-nucleon isovector interaction. The multipole structure of the transition form factors is studied in detail for Fermi-type non-spin-flip and Gamow-Teller-type spin-flip transitions, also serving to establish the connection to nuclear $\beta$ decay. The reaction kernel is evaluated for central and rank-2 tensor interactions. Initial- and final-state ion-ion elastic interactions are accounted for by a distortion coefficient. Since the ion-ion interactions are dominated by the imaginary part of the optical potentials, the distortion coefficients can be evaluated in the strong absorption limit. For a Gaussian potential form factor, the distortion coefficient is evaluated in closed form, revealing the relation to the total reaction cross section. It is shown that at small momentum transfer distortion effects reduce to a simple scaling factor, allowing us to define a reduced forward-angle cross section which is given by nuclear matrix elements of $\beta$ decay type. Thus we introduce new unit cross sections, as those traditionally used with light projectiles for spectroscopic purposes, for heavy-ion charge-exchange reactions. Results are discussed for ${\tau }_{\pm }$ excitations of ${}^{18}\mathrm{O}$ and ${}^{40}\mathrm{Ca}$, respectively. Spectral distributions of nuclear-charge-changing transitions are obtained by self-consistent Hartree-Fock-Bogolubov (HFB) and quasiparticle random phase approximation (QRPA) theory and compared to spectroscopic data. The interplay of nuclear structure and reaction dynamics is illustrated for the single-charge exchange (SCE) reaction ${}^{18}\mathrm{O}+{}^{40}\mathrm{Ca}\to {}^{18}\mathrm{F}+{}^{40}\mathrm{K}$ at $T_{\mathrm{lab}}=270$ MeV, by performing full-scale numerical calculations of the SCE cross section. We also show that the latter compare rather well with the results obtained within the strong absorption limit, thus confirming the possibility to factorize the forward-angle cross section into intrinsic nuclear transition dynamics and reaction dynamics.

We critically compare thermodynamic and kinetic approaches that have been recently used to study relations between the spin polarization and fluid vorticity in systems consisting of spin-1/2 particles. The thermodynamic approach refers to general properties of global thermal equilibrium with a rigidlike rotation and demonstrates that the spin-polarization and thermal-vorticity tensors are equal. On the other hand, the kinetic approach uses the concept of the Wigner function and its semiclassical expansion. In most of the works done so far, the Wigner functions satisfy kinetic equations with a vanishing collision term. We show that this assumption restricts significantly the applicability of such frameworks and, in contrast to many claims found in the literature, does not allow for drawing any conclusions regarding the relation between the thermal-vorticity and spin-polarization tensors, except for the fact that the two should be constant in global equilibrium. We further show how the kinetic-theory equations including spin degrees of freedom can be used to formulate a hydrodynamic framework for particles with spin. We define hydrodynamic equations starting separately from the formulation by de Groot, van Leeuwen, and van Weert and from the canonical formalism. In the former case the energy-momentum tensor is symmetric and the spin tensor is conserved, while in the latter case the energy-momentum tensor is not symmetric and the spin tensor is not conserved. Nevertheless, in the two cases the total angular momentum is always conserved. Interestingly, the two approaches are connected by the pseudo-gauge transformation, which we explicitly define.

Global spin alignment of vector mesons is a sensitive probe of system vorticity and particle production mechanism in relativistic heavy ion collisions. The measurement of global spin alignment is gaining increasing interest and deserves careful considerations. In this paper, we lay out a few practical issues that need to be taken care of when measuring global spin alignment of vector mesons. They are the correction for event plane resolution, reconciling measurements made with different event planes, the correction for the effect of finite acceptance in pseudorapidity, and the consideration for measuring the azimuthal angle dependence. Insights and methodologies offered in this paper will help experiments to measure the global spin alignment properly and accurately.

The two-channel photoproductions of $\gamma p\to K^{*+}{\mathrm{\Sigma }}^0$ and $\gamma p\to K^{*0}{\mathrm{\Sigma }}^{+}$ are investigated based on an effective Lagrangian approach at the tree-level Born approximation. In addition to the $t$-channel $K, \kappa , K^{*}$ exchanges, the $s$-channel nucleon ($N$) and $\mathrm{\Delta }$ exchanges, the $u$-channel $\mathrm{\Lambda }, \mathrm{\Sigma }, {\mathrm{\Sigma }}^{*}$ exchanges, and the generalized contact term, we try to take into account the minimum number of baryon resonances in constructing the reaction amplitudes to describe the experimental data. It is found that by including the $\mathrm{\Delta }\left(1905\right)5/2^{+}$ resonance with its mass, width, and helicity amplitudes taken from the Review of Particle Physics [Particle Data Group, C. Patrignani et al., Chin. Phys. C 40, 100001 (2016)], the calculated differential and total cross sections for these two reactions are in good agreement with the experimental data. An analysis of the reaction mechanisms shows that the cross sections of $\gamma p\to K^{*+}{\mathrm{\Sigma }}^0$ are dominated by the $s$-channel $\mathrm{\Delta }\left(1905\right)5/2^{+}$ exchange at low energies and $t$-channel $K^{*}$ exchange at high energies, with the $s$-channel $\mathrm{\Delta }$ exchange providing significant contributions in the near-threshold region. For $\gamma p\to K^{*0}{\mathrm{\Sigma }}^{+}$, the angular dependences are dominated by the $t$-channel $K$ exchange at forward angles and the $u$-channel ${\mathrm{\Sigma }}^{*}$ exchange at backward angles, with the $s$-channel $\mathrm{\Delta }$ and $\mathrm{\Delta }\left(1905\right)5/2^{+}$ exchanges making considerable contributions at low energies. Predictions are given for the beam, target, and recoil asymmetries for both reactions.

The decays of the negative $G$-parity meson $G$-parity into even numbers of pions violate $G$-parity. Such decays, as well as other $G$-parity decays into hadrons, can be parametrized in terms of three main intermediate virtual states: one photon, one photon plus two gluons, and three gluons. Since the electromagnetic interaction does not conserve $G$-parity, $G$-parity decays into positive $G$-parity final states should be dominantly electromagnetic. Nevertheless, the one-photon contribution to $J/\psi \to {\pi }^{+}{\pi }^{-}$, that can be estimated by exploiting the cross section $\sigma (e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-})$, differs from the observed decay probability for more than 4.5 standard deviations. We present a computation of the $gg\gamma$ amplitude based on a phenomenological description of the decay mechanism in terms of dominant intermediate states $\eta \gamma , {\eta }^{\prime }\gamma$, and $f_1\left(1285\right)\gamma$. The obtained value is of the order of the electromagnetic contribution.

How the axial coupling constant $g_A$ in nuclear Gamow-Teller transitions described in shell model gets “quenched” to a universal constant close to 1 can be explained by nuclear correlations in Fermi-liquid fixed-point theory using a scale-symmetric chiral Lagrangian supplemented with hidden local symmetric vector mesons. Contrary to what one might naively suspect—and has been discussed in some circles—there is no fundamental quenching at nuclear matter density due to QCD condensates. When the density of many-body systems treated with the same Lagrangian increases beyond the density $n=n_{1/2}\gtrsim 2n_0$ (where $n_0$ is the normal nuclear matter density) at which skyrmions representing baryons fractionize to half-skyrmions, with the $\rho$ meson driven toward the vector manifestation fixed point and a scalar meson $\sigma$ driven to the dilaton-limit fixed point with the nucleons parity-doubled, the dense matter supports the “pseudoconformal” sound velocity for $n\gtrsim n_{1/2}$, while the trace of the energy momentum tensor remains nonvanishing. A plausible interpretation is that this signals the emergence of scale symmetry not explicitly present or hidden in QCD in the vacuum. The fundamental constant $g_A$, unaffected by QCD condensates for $n<n_{1/2}$, does go to 1 as the dilaton-limit fixed point is approached before arriving at chiral restoration, but it is not directly related to the “quenched $g_A$” in nuclei which can be explained as a Fermi-liquid fixed point quantity. The mechanism that produces a precocious pseudoconformal sound velocity is expected to impact on the tidal deformability $\mathrm{\Lambda }$ in gravitational waves from coalescing neutron stars.

We carefully compare the one-dimensional Wentzel, Kramers, Brillouin barrier tunneling model, and the one-channel Schrödinger equation with a complex optical potential calculation of heavy-ion fusion, for a light and a heavy system. It is found that the major difference between the two approaches occurs around the critical energy, above which the effective potential for the grazing angular momentum ceases to exhibit a pocket. The value of this critical energy is shown to be strongly dependent on the nuclear potential at short distances, on the inner region of the Coulomb barrier, and this dependence is much more important for heavy systems. Therefore the nuclear fusion process is expected to provide information on the nuclear potential in this region. We compare calculations with available data to show that the results are consistent with this expectation.

ATLAS measurements of the production of muons from heavy-flavor decays in $\sqrt{s_{NN}}=2.76$ TeV Pb+Pb collisions and $\sqrt{s}=2.76$ TeV $pp$ collisions at the LHC are presented. Integrated luminosities of 0.14 ${\mathrm{nb}}^{-1}$ and 570 ${\mathrm{nb}}^{-1}$ are used for the Pb+Pb and $pp$ measurements, respectively, which are performed over the muon transverse momentum range $4<p_T<14$ GeV and for five Pb+Pb centrality intervals. Backgrounds arising from in-flight pion and kaon decays, hadronic showers, and misreconstructed muons are statistically removed using a template-fitting procedure. The heavy-flavor muon differential cross sections and per-event yields are measured in $pp$ and Pb+Pb collisions, respectively. The nuclear modification factor $R_{AA}$ obtained from these is observed to be independent of $p_T$, within uncertainties, and to be less than unity, which indicates suppressed production of heavy-flavor muons in Pb+Pb collisions. For the 10% most central Pb+Pb events, the measured $R_{AA}$ is approximately 0.35. The azimuthal modulation of the heavy-flavor muon yields is also measured and the associated Fourier coefficients $v_n$ for $n=2$, 3, and 4 are given as a function of $p_T$ and centrality. They vary slowly with $p_T$ and show a systematic variation with centrality which is characteristic of other anisotropy measurements, such as that observed for inclusive hadrons. The measured $R_{AA}$ and $v_n$ values are also compared with theoretical calculations.

A quark model, which reproduces the ground-state mesons and baryons, i.e., the threshold energies, is applied to the $qqqc\overline{c}$ configurations, where $q$ is a light quark and $c$ the charmed quark. In the calculation, several open channels are explicitly included such as $J/\psi +N, {\eta }_c+N, {\mathrm{\Lambda }}_c+\overline{D}$, etc. To distinguish genuine resonances and estimate their width, we employ the Gaussian expansion method supplemented by the real scaling method (stabilization). No resonance is found at the energies of the $P_c\left(4380\right)$ and $P_c\left(4450\right)$ pentaquarks. On the other hand, there is a sharp resonant state at 4690 MeV with a $J=1/2^{-}$ state and another one at 4920 MeV with a $J=3/2^{-}$ state which have a compact structure.

We report the first measurements of the $E$ beam-target helicity asymmetry for the $\vec{\gamma }\vec{n}\to K^0\mathrm{\Lambda }$ and $K^0{\mathrm{\Sigma }}^0$ channels in the energy range $1.70\le W\le 2.34$ GeV. The CLAS system at Jefferson Lab uses a circularly polarized photon beam and a target consisting of longitudinally polarized solid molecular hydrogen deuteride with low background contamination for the measurements. The multivariate analysis method boosted decision trees is used to isolate the reactions of interest. Comparisons with predictions from the KaonMAID, SAID, and Bonn-Gatchina models are presented. These results will help separate the isospin $I=0$ and $I=1$ photocoupling transition amplitudes in pseudoscalar meson photoproduction.

It was recently proved that the invariance of observables with respect to angle-dependent phase rotations of reaction amplitudes mixes multipoles, changing also their relative strength [A. Švarc et al., Phys. Rev. C 97, 054611 (2018)]. Modern partial wave analyses (PWAs) in $\eta$ photoproduction on protons in the center-of-mass energy range $1.5\le W\le 2.0$ GeV, either energy-dependent (ED) or single-energy (SE) ones, do not take this effect into consideration. It is commonly accepted that all PWAs give very similar results for the $E0+$ multipole, but notable differences in this and all other partial waves still remain. In this paper we demonstrate that once these phase rotations are properly taken into account, all ED and SE partial wave analysis in $\eta$ photoproduction become almost identical for the dominant $E0+$ multipole, and the agreement among all other multipoles becomes much better. We also show that measured observables are almost equally well reproduced in all PWAs, and the remaining differences among multipoles can be attributed solely to the difference in predictions for unmeasured observables. So, new measurements are needed.

Charge exchange process ${\pi }^{-}p\to {\pi }^{0}n$ and elastic scatterings ${\pi }^{\pm }p\to {\pi }^{\pm }p$ are investigated within the Regge framework where the relativistic Born amplitude is Reggeized for the $t$-channel meson exchange. The charge exchange cross section is featured by single $\rho$ exchange. Additional corrections by Regge cuts, $\rho \text{−}{f}_2$ and $\rho$-Pomeron, agree with differential cross sections, and a new trajectory for the ${\rho }^{\prime }\left(1450\right)$ exchange is attempted to reproduce polarization data. For the description of elastic scattering data up to pion momentum $P_{\mathrm{Lab}}\approx 250$ GeV/c, Pomeron exchange of the Donnachie-Landshoff type is newly constructed and applied in this work. Elastic cross section data are well reproduced with the dominance of $f_2$ and Pomeron exchanges in intermediate and high energies. Analysis of nucleon resonances is presented to test the validity of the present Regge framework below $W\le 2$ GeV.

The Gamow-Teller (GT) matrix element contributing to tritium $\beta$ decay is calculated with trinucleon wave functions obtained from hyperspherical-harmonics solutions of the Schrödinger equation with the chiral two- and three-nucleon interactions including $\mathrm{\Delta }$ intermediate states that have recently been constructed in configuration space. Predictions up to next-to-next-to-next-to-leading order (N3LO) in the chiral expansion of the axial current (with $\mathrm{\Delta }$'s) overestimate the empirical value by 1–4%. By exploiting the relation between the low-energy constant (LEC) in the contact three-nucleon interaction and two-body axial current, we provide new determinations of the LECs $c_D$ and $c_E$ that characterize this interaction by fitting the trinucleon binding energy and tritium GT matrix element. Some of the implications that the resulting models of three-nucleon interactions have on the spectra of light nuclei and the equation of state of neutron matter are briefly discussed. We also provide a partial analysis, which ignores $\mathrm{\Delta }$'s, of the contributions due to loop corrections in the axial current at next-to-next-to-next-to-next-to-leading order (N4LO). Finally, explicit expressions for the axial current up to N4LO have been derived in configuration space, which other researchers in the field may find useful.

Improved knowledge of prompt emission in fission has significant implications for our understanding of the fission process. It is also important for improving nuclear data evaluation, with impact on applications. The correlation between prompt neutrons and fragments emitted in binary neutron induced fission of ${}^{235}\mathrm{U}$ has been studied at the GELINA facility. The experiment employs an array of proton recoil scintillators and a position-sensitive twin ionization chamber. This experimental arrangement permits measurement of the correlations between neutron emission, fragment angle, and mass and energy of the fission fragments. In this article, we present results on prompt fission neutron energy and multiplicity correlations with mass and total kinetic energy of the fission fragments. Results from the present measurement shows distinct differences compared to earlier studies of the correlated fission fragment and prompt neutron emission quantities. The differences with respect to earlier investigations are interpreted as improved fission fragment energy resolution in the present measurement. The present result supports several recent model calculations of prompt neutron and fission fragment correlations.

The properties of deexcitation of the same ${}^{220}\mathrm{Th}$ compound nucleus (CN) formed by different mass (charge) asymmetric reactions are investigated. It is demonstrated that the effective fission barrier $\langle B_{\mathrm{fis}}\rangle$ value being a function of the excitation energy $E_{\mathrm{CN}}^{*}$ is strongly sensitive to the various orbital angular momentum $L=\ell \hslash$ distributions of CN formed with the same excitation energy $E_{\mathrm{CN}}^{*}$ by the very different entrance channels ${}^{16}\mathrm{O}+{}^{204}\mathrm{Pb}$, ${}^{40}\mathrm{Ar}+{}^{180}\mathrm{Hf}$, ${}^{82}\mathrm{Se}+{}^{138}\mathrm{Ba}$, and ${}^{96}\mathrm{Zr}+{}^{124}\mathrm{Sn}$. Consequently, the competition between the fission and evaporation of light particles (neutron, proton, and $\alpha$ particle) processes along the deexcitation cascade of CN depends on the orbital angular momentum distribution of CN. Therefore, the ratio between the evaporation residue cross sections obtained after emission of neutral and charged particles and neutrons only for the same CN with a given excitation energy $E_{\mathrm{CN}}^{*}$ is sensitive to the mass (charge) asymmetry of reactants in the entrance channel.