Investigation of the ${}^{50}\mathrm{V}$ electron-capture to the $2^{+}$ 1553.8 keV level of ${}^{50}\mathrm{Ti}$ and search for ${\beta }^{-}$ decay of ${}^{50}\mathrm{V}$ to the $2^{+}$ 783.3 keV level of ${}^{50}\mathrm{Cr}$ (both those decays are fourfold forbidden with $\mathrm{\Delta }{J}^{\mathrm{\Delta }\pi }=4^{+}$) have been performed using a vanadium sample of natural isotopic abundance with mass of 955 g. The measurements were conducted with the help of an ultralow-background HPGe-detector system located 225 m underground in the laboratory HADES (Belgium). The measured value of the half-life of ${}^{50}\mathrm{V}$ for electron capture was $T_{1/2}^{\mathrm{EC}}=(2.{77}_{-0.19}^{+0.20})\times {10}^{17}$ yr. The ${\beta }^{-}$-decay branch was not detected and the corresponding lower bound of the half-life was $T_{1/2}^{\beta }\ge 8.9\times {10}^{18}$ yr at the 90% confidence level.

Background: Stellar carbon synthesis occurs exclusively via the $3\alpha$ process, in which three $\alpha$ particles fuse to form ${}^{12}\mathrm{C}$ in the excited Hoyle state, followed by electromagnetic decay to the ground state. The Hoyle state is above the $\alpha$ threshold, and the rate of stellar carbon production depends on the radiative width of this state. The radiative width cannot be measured directly, and must instead be deduced by combining three separately measured quantities. One of these quantities is the $E0$ decay branching ratio of the Hoyle state, and the current $10\%$ uncertainty on the radiative width stems mainly from the uncertainty on this ratio. The rate of the $3\alpha$ process is an important input parameter in astrophysical calculations on stellar evolution, and a high precision is imperative to constrain the possible outcomes of astrophysical models.

Purpose: To deduce a new, more precise value for the $E0$ decay branching ratio of the Hoyle state.

Method: The $E0$ branching ratio was deduced from a series of pair conversion measurements of the $E0$ and $E2$ transitions depopulating the $0_2^{+}$ Hoyle state and $2_1^{+}$ state in ${}^{12}\mathrm{C}$, respectively. The excited states were populated by the ${}^{12}\mathrm{C}(p,p^{\prime })$ reaction at 10.5 MeV beam energy, and the pairs were detected with the electron-positron pair spectrometer, Super-e, at the Australian National University. The deduced branching ratio required knowledge of the proton population of the two states, as well as the alignment of the $2_1^{+}$ state in the reaction. For this purpose, proton scattering and $\gamma$-ray angular distribution experiments were also performed.

Results: An $E0$ branching ratio of ${\mathrm{\Gamma }}_{\pi }^{E0}/\mathrm{\Gamma }=8.2\left(5\right)\times {10}^{-6}$ was deduced in the current work, and an adopted value of ${\mathrm{\Gamma }}_{\pi }^{E0}/\mathrm{\Gamma }=7.6\left(4\right)\times {10}^{-6}$ is recommended based on a weighted average of previous literature values and the new result.

Conclusions: The new recommended value for the $E0$ branching ratio is about 14% larger than the previous adopted value of ${\mathrm{\Gamma }}_{\pi }^{E0}/\mathrm{\Gamma }=6.7\left(6\right)\times {10}^{-6}$, while the uncertainty has been reduced from 9% to 5%. The new result reduces the radiative width, and hence $3\alpha$ reaction rate, by 11% relative to the adopted value, and the uncertainty to 6.1%. This reduction in width and increased precision is likely to constrain possible outcomes of astrophysical calculations.

We study theoretically medium effects on ${\mathrm{\Xi }}^{-}$ production in the ($K^{-}, K^{+}$) reaction, using the optimal Fermi-averaging procedure, which describes the Fermi motion of a nucleon on the on-energy-shell $K^{-}p\to K^{+}{\mathrm{\Xi }}^{-}$ reaction condition in nuclei. The results show the strong energy and angular dependencies of the in-medium $K^{-}p\to K^{+}{\mathrm{\Xi }}^{-}$ cross section, which affect significantly the shape and the magnitude of the production spectrum for ${\mathrm{\Xi }}^{-}$-hypernuclear states in the ($K^{-}, K^{+}$) reaction on a nuclear target. The application to the ${\mathrm{\Xi }}^{-}$ quasifree production via the ($K^{-}, K^{+}$) reaction on a ${}^{12}\mathrm{C}$ target is also discussed in a Fermi gas model.

Multinucleon transfer mechanism in the collision of ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ system is investigated at $E_{\text{c.m.}}=833$ MeV in the framework of the quantal diffusion description based on the stochastic mean-field approach. Double cross sections $\sigma (N,Z)$ as a function of the neutron and proton numbers, the cross sections $\sigma \left(Z\right)$ and $\sigma \left(A\right)$ as a function of the atomic numbers and the mass numbers are calculated for production of the primary fragments. The calculation indicates the ${}^{238}\mathrm{U}+{}^{238}\mathrm{U}$ system may be located at an unstable equilibrium state at the potential energy surface with a slightly negative curvature along the $\beta$ stability line on the $(N,Z)$ plane. This behavior may lead to rather large diffusion along the $\beta$ stability direction.

Hard photon provides a unique probe for nuclear reaction dynamics. In this work, we embedded incoherent neutron-proton bremsstrahlung photon production channel in a framework of isospin-dependent quantum molecular dynamics (IQMD) model and performed a systematic study of multiplicities of hard photons and intermediate-mass fragments (IMFs). It is found that the IQMD model with the in-medium nucleon-nucleon cross section can reproduce previous experimental data of hard-photon energy spectra better. By investigating the incident energy and centrality dependencies of multiplicities of hard photons and IMFs of ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$ collisions, it is found that the multiplicity correlation between thermal photons and IMFs can provide valuable information on nuclear liquid-gas phase transition. Additionally, temperatures from the thermal emitting sources are also investigated. The results indicate that hard photons provide some unique information of the thermodynamical state of multifragmentating nuclear system.

Several sources of angular anisotropy for fission fragments and prompt neutrons have been studied in neutron-induced fission reactions. These include kinematic recoils of the target from the incident neutron beam and the fragments from the emission of the prompt neutrons, preferential directions of the emission of the fission fragments with respect to the beam axis due to the population of particular transition states at the fission barrier, and forward-peaked angular distributions of pre-equilibrium neutrons which are emitted before the formation of a compound nucleus. In addition, there are several potential sources of angular anisotropies that are more difficult to disentangle: the angular distributions of prompt neutrons from fully accelerated fragments or from scission neutrons, and the emission of neutrons from fission fragments that are not fully accelerated. In this work, we study the effects of the first group of anisotropy sources, particularly exploring the correlations between the fission-fragment anisotropy and the resulting neutron anisotropy. While kinematic effects were already accounted for in our Hauser-Feshbach Monte Carlo code cgmf, anisotropic angular distributions for the fission fragments and pre-equilibrium neutrons resulting from neutron-induced fission on ${}^{233,234,235,238}\mathrm{U}, {}^{239,241}\mathrm{Pu}$, and ${}^{237}\mathrm{Np}$ have been introduced for the first time. The effects of these sources of anisotropy are examined over a range of incident neutron energies, from thermal to 20 MeV, and compared with experimental data from the Chi-Nu liquid scintillator array. The anisotropy of the fission fragments is reflected in the anisotropy of the prompt neutrons, especially as the outgoing energy of the prompt neutrons increases, allowing for an extraction of the fission-fragment anisotropy to be made from a measurement of the neutrons.

Background: Given the established $2\alpha$ structure of ${}^8\mathrm{Be}$, a realistic model of four interacting $\alpha$ clusters must be used to obtain a ${}^8\mathrm{Be}+{}^8\mathrm{Be}$ interaction potential. Such a four-body problem poses a challenge for the determination of the ${}^8\mathrm{Be}+{}^8\mathrm{Be}$ optical potential (OP) that is still unknown due to the lack of the elastic ${}^8\mathrm{Be}+{}^8\mathrm{Be}$ scattering data.

Purpose: To probe the complex ${}^8\mathrm{Be}+{}^8\mathrm{Be}$ optical potential in the coupled-reaction-channel (CRC) study of the $\alpha$ transfer ${}^{12}\mathrm{C}(\alpha ,{}^8\mathrm{Be})$ reaction measured at $E_{\alpha }=65$ MeV and to obtain the spectroscopic information on the $\alpha +{}^8\mathrm{Be}$ cluster configuration of ${}^{12}\mathrm{C}$.

Method: The three- and four-body continuum-discretized coupled-channel (CDCC) methods are used to calculate the elastic $\alpha +{}^8\mathrm{Be}$ and ${}^8\mathrm{Be}+{}^8\mathrm{Be}$ scattering at the energy around 16 MeV/nucleon, with the breakup effect taken into account explicitly. Based on the elastic cross section predicted by the CDCC calculation, the local equivalent OP's for these systems are deduced for the CRC study of the ${}^{12}\mathrm{C}(\alpha ,{}^8\mathrm{Be})$ reaction.

Results: Using the CDCC-based OP's and $\alpha$ spectroscopic factors given by the cluster model calculation, a good CRC description of the $\alpha$ transfer data for both the ${}^8\mathrm{Be}+{}^8\mathrm{Be}$ and ${}^8\mathrm{Be}+{}^8\mathrm{Be}_{2^{+}}^{*}$ exit channels is obtained without any adjustment of the (complex) potential strength.

Conclusion: The $\alpha +{}^8\mathrm{Be}$ and ${}^8\mathrm{Be}+{}^8\mathrm{Be}$ interaction potential can be described by the three- and four-body CDCC methods, respectively, starting from a realistic $\alpha +\alpha$ interaction. The $\alpha$ transfer ${}^{12}\mathrm{C}(\alpha ,{}^8\mathrm{Be})$ reaction should be further investigated not only to probe of the $4\alpha$ interaction but also the cluster structure of ${}^{12}\mathrm{C}$.

The principal component analysis (PCA), a mathematical tool commonly used in statistics, has recently been employed to interpret the $p_T$-dependent fluctuations of harmonic flow $v_n$ in terms of leading and subleading flow modes in heavy ion collisions. Using simulated data from ampt and hijing models, we show that the PCA modes are not fixed, but depend on the choice of the particle weight and the $p_T$ range. Furthermore, the shape of the leading mode is affected by the presence of nonflow correlations, and a fake subleading mode may arise from the mixing of nonflow correlations with leading flow mode with a magnitude that could be larger than the genuine subleading flow mode. Therefore, the meaning of PCA modes and their relations to physical leading and subleading flow modes associated with initial state eccentricities need to be further clarified/validated in realistic model simulations.

The production of $K^{*}{\left(892\right)}^0$ and $\varphi \left(1020\right)$ in $pp$ collisions at $\sqrt{s}=8$ TeV was measured by using Run 1 data collected by the ALICE collaboration at the CERN Large Hadron Collider (LHC). The $p_{\mathrm{T}}$-differential yields $d^{2}N/dyd{p}_{\mathrm{T}}$ in the range $0<p_{\mathrm{T}}<20$ GeV/$c$ for $K^{*0}$ and $0.4<p_{\mathrm{T}}<16$ GeV/$c$ for $\varphi$ have been measured at midrapidity, $\left|y\right|<0.5$. Moreover, improved measurements of the $K^{*0}\left(892\right)$ and $\varphi \left(1020\right)$ at $\sqrt{s}=7$ TeV are presented. The collision energy dependence of $p_{\mathrm{T}}$ distributions, $p_{\mathrm{T}}$-integrated yields, and particle ratios in inelastic $pp$ collisions are examined. The results are also compared with different collision systems. The values of the particle ratios are found to be similar to those measured at other LHC energies. In $pp$ collisions a hardening of the particle spectra is observed with increasing energy, but at the same time it is also observed that the relative particle abundances are independent of the collision energy. The $p_{\mathrm{T}}$-differential yields of $K^{*0}$ and $\varphi$ in $pp$ collisions at $\sqrt{s}=8$ TeV are compared with the expectations of different Monte Carlo event generators.

The Coulomb correction factor is derived for $M1$ scattering on a pointlike nucleus in the second Born approximation. The Coulomb correction for $M1$ scattering off the proton is larger than that for $C0$ scattering by 2%. The difference affects the determination of the proton radius where an identical Coulomb correction has been applied for both components so far. A new Rosenbluth formula, that includes the Coulomb corrections, is applied to electron scattering on the proton with low-energy electron beams. The Coulomb corrections are essential to discuss the electric and magnetic radii of the proton.

On the basis of an extended antisymmetrized molecular-dynamics calculation, we study the cluster structure of the $0^{+}$ and $1^{-}$ states in ${}^{18}\mathrm{O}$. We discuss that several different kinds of the cluster states appear in the excitation spectrum, and their monopole and dipole transitions are interesting fingerprints of unique cluster structure. We show that the monopole and dipole transitions are enhanced for the ${}^{14}\mathrm{C}+\alpha$ cluster states, while they are hindered for the molecular-orbit state. We also point out that a ratio of the electric and isoscalar monopole transition strengths gives a good hint for the structure of the excited states.

New ground-state level with spin-parity $1/2^{+}$ is established in ${}^{109}\mathrm{Mo}$, 69.8 keV below the previously reported $5/2^{+}$ ground state in this nucleus, based on precise spectroscopy measurements of $\gamma$ radiation following spontaneous fission of ${}^{248}\mathrm{Cm}$ performed using the Eurogam2 array of anti-Compton spectrometers. Analogous measurement of $\gamma$ radiation following spontaneous fission of ${}^{252}\mathrm{Cf}$, performed using the Gammasphere array, confirms the new $1/2^{+}$ ground state of ${}^{107}\mathrm{Mo}$, proposed recently and establishes the isomeric character of the $5/2^{+}$ first excited state in ${}^{107}\mathrm{Mo}$. Two $\beta$-decaying isomers are suggested in ${}^{111}\mathrm{Mo}$ nucleus based on regular energy systematics, supporting previous predictions. Low-energy excitations in Mo isotopes are interpreted and compared to calculations reported in the literature. The results suggest shape transition from prolate to oblate deformation at $N\ge 67$.

Background: Modern ab initio theory combined with high-quality nucleon-nucleon (NN) and three-nucleon (3N) interactions from chiral effective field theory (EFT) can provide a predictive description of low-energy light-nuclei reactions relevant for astrophysics and fusion-energy applications. However, the high cost of computations has so far impeded a complete analysis of the uncertainty budget of such calculations.

Purpose: Starting from NN potentials up to fifth order (${\mathrm{N}}^4\mathrm{LO}$) combined with leading-order 3N forces, we study how the order-by-order convergence of the chiral expansion and confidence intervals for the 3N contact and contact-plus-one-pion-exchange low-energy constants ($c_E$ and $c_D$) contribute to the overall uncertainty budget of many-body calculations of neutron ${}^4\mathrm{He}$ ($n-\alpha$) elastic scattering.

Methods: We compute structure and reaction observables for three-, four-, and five-nucleon systems within the ab initio frameworks of the no-core shell model and no-core shell model with continuum. Using a small set of design runs, we construct a Gaussian process model (GPM) that acts as a statistical emulator for the theory. With this, we gain insight into how uncertainties in the 3N low-energy constants propagate throughout the calculation and determine the Bayesian posterior distribution of these parameters with Markov-Chain Monte Carlo.

Results: We find rapidly converging $n-\alpha$ phase shifts with respect to the chiral order. With the adopted leading-order 3N force, calculations based on the NN interaction at ${\mathrm{N}}^4\mathrm{LO}$ of Entem, Machleidt, and Nosyk [Phys. Rev. C 96, 024004 (2017)] are unable to reproduce the experimental phase shifts in the $3/2^{-}$ channel within the estimated chiral truncation errors. Closer agreement with empirical data is found when using an older parametrization of the NN interaction at order ${\mathrm{N}}^3\mathrm{LO}$ [Entem and Machledit, Phys. Rev. C 68, 041001(R) (2017)], and the position and width of the $P$-wave resonances can be used to reduce the uncertainty of the 3N low-energy constants.

Conclusions: The present results point to a lack of spin-orbit strength when the newer parametrization of the chiral NN force up to fifth order is combined with the leading-order 3N force. The inclusion of higher-order 3N-force terms may be required to recover the missing strength. GPMs can act as fast and accurate emulators of ab initio many-body calculations of low-energy scattering and reactions of light nuclei, opening the way to a robust quantification of theoretical uncertainties grounded in the description of the underlying chiral Hamiltonian.

The mass distribution in ${}^{136}\mathrm{Xe}+{}^{208}\mathrm{Pb}$ is investigated within the dinuclear system model. With the contribution of quasifission yields, the probability of all the fragments is conserved, and the mass distribution becomes wider with increasing the evolution time. The difference between including and excluding the contribution of quasifission yields is more obvious at a lower angular momentum. The cross sections, including quasifission yields in the region with mass less than the projectile and more than the target, are closer to the experimental data. The impact from the quasifission yields on the neutron-deficient isotopes is greater than the neutron-rich ones. The quasifission yields concentrate on the initial stage of evolution time, corresponding to a lower excitation energy. Considering the time-dependent excitation energy of the quasifission fragments produced within the interaction time, fewer neutrons are evaporated comparing to the case with the excitation energy at the interaction time.

Correlations of symmetry planes are important observables used to quantify anisotropic flow phenomena and constrain independently the properties of strongly interacting nuclear matter produced in the collisions of heavy ions at the highest energies. In this paper, we point out current problems in measuring correlations between symmetry planes and elaborate on why the available analysis techniques have a large systematic bias. To overcome this problem, we develop the first estimator for true symmetry plane correlations, and we introduce a new approach to approximate multiharmonic flow fluctuations via a two-dimensional Gaussian distribution. Employing this approximation, we introduce a new estimator, dubbed the Gaussian estimator (GE), to extract pure correlations between symmetry planes. We validate the GE by using the realistic event generator iebe-vishnu and demonstrate that it outperforms all existing estimators. Based on event-shape engineering, we propose an experimental strategy to improve the GE accuracy even further.

A dynamical calculation of the strange hidden charm pentaquark systems ${\mathrm{\Lambda }}_{c\overline{c}}$ is performed in the framework of the quark delocalization color screening model. The effective potentials between two clusters are calculated to investigate the interaction between the baryons and mesons. The dynamic calculations indicate that the strange hidden charm pentaquark system with $I{J}^P=0{\frac{1}{2}}^{-}$ and $I{J}^P=0{\frac{3}{2}}^{-}$ can form bound states with the help of the channel coupling. The energies of these two system are 4068.7 and 4186.3 MeV, respectively. These two ${\mathrm{\Lambda }}_{c\overline{c}}$ states are possible intriguing pentaquark candidates, which are worth searching for in experiments. In contrast, for the systems with isospin $I=1$, the effective potentials of all channels are repulsive, and there are no bound states for these systems.

High-spin states of ${}^{38}\mathrm{K}$ above the $31.67\mu \mathrm{s}$ (${\tau }_m$) isomer, populated through the ${}^{12}\mathrm{C}({}^{28}\mathrm{Si},np){}^{38}\mathrm{K}$ reaction with a 110 MeV ${}^{28}\mathrm{Si}$ beam, have been studied by using the Indian National Gamma Array (INGA) facility. Two new levels and four new transitions have been added to the existing level scheme. The spins and parities of most of the levels above the isomer have been assigned, modified, and confirmed from $R_{\mathrm{DCO}}$, $R_{\mathrm{ADO}}$, and linear polarization measurements. The multipole mixing ratios ($\delta$) for a few transitions have been measured. Large-basis shell-model calculations have been performed to understand the microscopic origin of these levels. In our calculations, different particle restrictions in $sd$- and $pf$-shell orbitals were used to reproduce the experimental level energies. Two-nucleon transfer spectroscopic factors have also been calculated for the levels above the isomer to support the new spin and parity assignments. Prediction of collective excitation at high excitation energy in ${}^{38}\mathrm{K}$ is also discussed.

We investigate the dynamics of spontaneous fission in a configuration-interaction (CI) approach. In that formalism the decay rate is governed by an effective interaction coupling the ground-state configuration and a fission doorway configuration, with the interaction strength determined by inverting a high-dimensioned CI Hamiltonian matrix that may have a block-tridiagonal structure. It is shown that the decay rate decreases exponentially with the number of blocks at a rate determined by the largest eigenvalue of a matrix in the block space for Hamiltonians with identical off-diagonal blocks. The theory is greatly simplified by approximations similar in spirit to the adiabatic and the least-action approximations in continuum representations. Here each block is replaced by a single matrix element. While the adiabatic reduction underestimates the coupling, a reduction based on a maximum-coupling approximation works well in a schematic CI model.

Using a more reasonable separate density-dependent scenario instead of the total density-dependent scenario for in-medium $nn, pp$, and $np$ interactions, we examine effects of differences of in-medium nucleon-nucleon interactions in two density-dependent scenarios on isospin-sensitive observables in central ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ collisions at 400 MeV/nucleon. It is shown that the symmetry potentials and resulting symmetry energies in two density-dependent scenarios indeed begin to deviate at nonsaturation densities, especially at suprasaturation densities. Naturally, several typical isospin-sensitive observables such as the free neutron-proton ratios and the ${\pi }^{-}/{\pi }^{+}$ ratios in heavy-ion collisions are affected significantly. Moreover, to more physically detect the differences between the nucleon-nucleon interactions in two density-dependent scenarios, we also map the nucleon-nucleon interaction in the separate density-dependent scenario into that in the total density-dependent scenario through fitting the identical constraints for symmetric nuclear matter as well as the identical slope parameter of nuclear symmetry energy at the saturation density. It is shown that two density-dependent scenarios also lead to essentially different symmetry potentials especially at high densities although they can lead to the identical equation of state for the symmetry nuclear matter as well as the identical symmetry energy for the isospin asymmetric nuclear matter. Consequently, these isospin-sensitive observables are also appreciably affected by the different density-dependent scenarios of in-medium nucleon-nucleon interactions. Therefore, according to these findings, it is suggested that effects of the separate density-dependent scenario of in-medium nucleon-nucleon interactions should be taken into account when probing the high-density symmetry energy using these isospin-sensitive observables in heavy-ion collisions.