We have studied the Gamow-Teller (GT) transitions from $N=Z+2$ neighbors to $N=Z$ odd-odd nuclei in the $p$-shell region by using isospin-projected and $\beta \gamma$-constraint antisymmetrized molecular dynamics combined with the generator coordinate method. The calculated GT transition strengths from $0^{+}1$ states to $1^{+}0$ states such as ${}^6\mathrm{He}\left(0_1{}^{+}1\right)\to {}^6\mathrm{Li}\left(1_1{}^{+}0\right)$, ${}^{10}\mathrm{Be}\left(0_1{}^{+}1\right)\to {}^{10}\mathrm{B}\left(1_1{}^{+}0\right)$, and ${}^{14}\mathrm{C}\left(0_1{}^{+}1\right)\to {}^{14}\mathrm{N}\left(1_2{}^{+}0\right)$ exhaust more than 50% of the sum rule. These $N=Z+2$ initial states and $N=Z$ odd-odd final states are found to dominantly have $S=0,T=1nn$ pairs and $S=1,T=0pn$ pairs, respectively. Based on the two-nucleon ($NN$) pair picture, we can understand the concentration of the GT strengths as the spin-isospin-flip transition $nn(S=0,T=1)\to pn(S=1,T=0)$ in $LS$ coupling. The GT transition can be a good probe to identify the spin-isospin partner states with $nn$ pairs and $pn$ pairs of $N=Z+2$ and $N=Z$ odd-odd nuclei, respectively.

Recently, various two-neutron transfer studies using the $({}^{18}\mathrm{O},{}^{16}\mathrm{O})$ reaction were performed with a large success. This was achieved because of a combined use of the microscopic quantum description of the reaction mechanism and of the nuclear structure. In the present work we use this methodology to study the two-neutron transfer reaction of the ${}^{18}\mathrm{O}+{}^{64}\mathrm{Ni}$ system at 84 MeV incident energy, to the ground and first $2^{+}$ excited state of the residual ${}^{66}\mathrm{Ni}$ nucleus. All the experimental data were measured by the large acceptance MAGNEX spectrometer at the Instituto Nazionale di Fisica Nucleare –Laboratori Nazionali del Sud (Italy). We have performed exact finite range cross section calculations using the coupled channel Born approximation (CCBA) and coupled reaction channel (CRC) method for the sequential and direct two-neutron transfers, respectively. Moreover, this is the first time that the formalism of the microscopic interaction boson model (IBM-2) was applied to a two-neutron transfer reaction. From our results we conclude that for two-neutron transfer to the ground state of ${}^{66}\mathrm{Ni}$, the direct transfer is the dominant reaction mechanism, whereas for the transfer to the first excited state of ${}^{66}\mathrm{Ni}$, the sequential process dominates. A competition between long-range and short-range correlations is discussed, in particular, how the use of two different models (Shell model and IBM's) help to disentangle long- and short-range correlations.

The $\alpha$-decay chains of the isotopes ${}^{265-279}\mathrm{Mt}$ are predicted by comparing the $\alpha$ half-lives calculated within the Coulomb and proximity potential model for deformed nuclei of Santhosh et al. [Nucl. Phys. A 850, 34 (2011)] with the spontaneous fission half-lives using the shell-effect-dependent formula of Santhosh and Nithya [Phys. Rev. C 94, 054621 (2016)]. $\alpha$ half-lives also are calculated using different theoretical formalisms for comparison. The predicted half-lives and decay modes match well with the experimental results. The use of four different mass tables for calculating the $\alpha$- decay energies indicates that the mass table of Wang et al. [Chin. Phys. C 41, 030003 (2017)], which is based on the AME2016 atomic mass evaluation, is in better agreement with experimental results. The paper predicts long $\alpha$ chains from ${}^{265,267-269,271-273}\mathrm{Mt}$ with half-lives within experimental limits. The isotopes ${}^{274-276,278}\mathrm{Mt}$ exhibit 2α chains followed by spontaneous fission. The 2α chain of ${}^{266}\mathrm{Mt}$ and the 4α chain of ${}^{270}\mathrm{Mt}$ end with electron capture. The isotopes ${}^{277,279}\mathrm{Mt}$ decay via spontaneous fission. We hope that the paper will open up new areas in this field.

An attempt has been made to investigate the role of various entrance channel parameters in low-energy ($\approx 4\text{–}7$ MeV/nucleon) incomplete fusion reactions through excitation function measurements. The analysis of measured excitation functions, in the framework of statistical model code pace4, reveals that the $xn$/$pxn$ channels are populated, predominantly, via complete fusion processes. However, in the production of $\alpha$-emitting channels, even after correcting for the precursor decay contribution, a significant enhancement as compared to statistical model predictions has been observed, which may be attributed due to the contribution of breakup processes. The observed enhancement is found to increase with projectile energy. Further, the comparison of present work with literature data reveals the dependence of incomplete fusion on mass-asymmetry of interacting partners, $\alpha \text{−}Q$ value of the projectile, and also on $Z_P{Z}_T$ (the Coulomb factor). From the present analysis, it may be concluded that a single entrance channel parameter (i.e., mass asymmetry or $Z_P{Z}_T$ or $\alpha \text{−}Q$ value) is not able to explain, completely, the yields of the low-energy incomplete fusion component. Therefore, a combination of these parameters and/or a parameter which can incorporate all gross features of interacting partners should be chosen to get a systematics for such reactions.

In a recent transfer reaction measurement of ${}^{208}\mathrm{Pb}$(${}^7\mathrm{Li},{}^6\mathrm{He}$)${}^{209}\mathrm{Bi}$ at energies around and below the Coulomb barrier, the optical model potentials of the halo nuclear system ${}^6\mathrm{He}+{}^{209}\mathrm{Bi}$ were extracted by fitting the experimental data with the theoretical frameworks of the distorted-wave Born approximation and coupled reaction channels, respectively. With the high-precision result, a complete picture of the behavior of the optical potential for this halo system is clearly derived for the first time. The real potential presents a bell-like shape around the barrier as a normal threshold anomaly. However, for the imaginary part, it first increases with the energy decreasing below the barrier and then falls quickly to 0, hence the threshold energy can be determined by fitting the variation trend. Moreover, the result also provides some evidence that the dispersion relation does not hold for this halo nuclear system, which calls for further investigation of the underlying physics.

With the parameters fitted by the particle multiplicity, the energy density at chemical freeze-out, and the charged particle elliptic flow, we have studied the effects of the hadronic mean-field potentials on the Hanbury-Brown and Twiss (HBT) correlation in relativistic heavy-ion collisions based on a multiphase transport model. The hadronic mean-field potentials are found to delay the emission time of the system and lead to large HBT radii extracted from the correlation function. Effects on the energy dependence of $R_o^2-R_s^2$ and $R_o/R_s$ as well as the eccentricity of the emission source are discussed. The HBT correlations can also be useful in understanding the mean-field potentials of protons, kaons, and antiprotons as well as baryon-antibaryon annihilations.

We show that in the three-polytrope model of Hebeler et al. [Astrophys. J. 773, 11 (2013)] for the neutron star equation of state (EoS) at supersaturation densities a third family of compact stars can be obtained which confirms the possibility of high-mass twin stars that have coincident masses $M_1=M_2\approx 2M_{\odot }$ and significantly different radii $|R_1-R_2|>2–3$ km. We show that the causality constraint puts severe limitations on the maximum mass of the third family sequence which can be relaxed when this scheme is extended to four polytropes thus mimicking a realistic high-density matter EoS.

We describe the propagation of charm quarks in the quark-gluon plasma (QGP) by means of a Boltzmann transport approach. Nonperturbative interaction between heavy quarks and light quarks have been taken into account through a quasiparticle approach in which light partons are dressed with thermal masses tuned to lattice quantum chromodynamics (lQCD) thermodynamics. Such a model is able to describe the main feature of the nonperturbative dynamics: the enhancement of the interaction strength near $T_c$. We show that the resulting charm in-medium evolution is able to correctly predict simultaneously the nuclear suppression factor, $R_{\text{AA}}$, and the elliptic flow, $v_2$, at both Relativistic Heavy Ion Collider and Large Hadron Collider (LHC) energies and at different centralities. The hadronization of charm quarks is described by mean of an hybrid model of fragmentation plus coalescence and plays a key role toward the agreement with experimental data. We also performed calculations within the Langevin approach, which can lead to very similar $R_{\text{AA}}\left(p_T\right)$ as Boltzmann, but the charm drag coefficient as to be reduced by about a $30\%$ and also generates an elliptic flow $v_2\left(p_T\right)$ is about a $15\%$ smaller. We finally compare the space diffusion coefficient $2\pi T{D}_s$ extracted by our phenomenological approach to lattice QCD results, finding a satisfying agreement within the present systematic uncertainties. Our analysis implies a charm thermalization time, in the $p\to 0$ limit, of about $4–6\text{fm}/\text{c}$, which is smaller than the QGP lifetime at LHC energy.

Fluctuations of conserved quantities are believed to be sensitive observables to probe the signature of the QCD phase transition and critical point. It was argued recently that measuring the genuine correlation functions (CFs) could provide cleaner information on possible nontrivial dynamics in heavy-ion collisions. With the AMPT (a multiphase transport) model, the centrality and energy dependence of various orders of CFs of net protons in Au + Au collisions at $\sqrt{s_{NN}}=7.7$, 11.5, 19.6, 27, 39, 62.4, and 200 GeV are investigated. The model results show that the number of antiprotons is important and should be taken into account in the calculation of CFs at high energy and/or in peripheral collisions. It is also found that the contribution of antiprotons is more important for higher order correlations than for lower ones. The CFs of antiprotons and mixed correlations play roles comparable to those of protons at high energies. Finally, we make comparisons between the model calculation and experimental data measured in the STAR experiment at the BNL Relativistic Heavy Ion Collider.

Background: Challenging questions of the $\alpha$-particle optical-model potential (OMP) are still pointed out by recent high-precision measurements of $\alpha$-induced reaction data below the Coulomb barrier. Moreover, the reliability of a previous OMP for $\alpha$ particles on nuclei within the mass number range $45\le A\le 209$ has been recently proved for emitted $\alpha$ particles as well, but only in the case of proton-induced reactions on Zn isotopes [Phys. Rev. C 91, 064611 (2015) (Paper I)].

Purpose: Analysis of most recent $(\alpha ,\gamma )$ reaction data for Ge and Zr isotopes, which provides an additional validation of the above-mentioned potential, is related to a further account of $\alpha$-particle emission in neutron-induced reactions on Zr isotopes, at the same time with a suitable description of all competitive processes.

Methods: A consistent parameter set, established or validated by independent analysis of recent various data, particularly $\gamma$-ray strength functions, has been involved within model calculation of the $(\alpha ,\gamma )$ as well as $(n,\alpha )$ reaction cross sections. The latter are part of the whole analysis of the neutron activation of Zr isotopes, in order to avoid any error compensation or latent ambiguity.

Results: The aforesaid potential provides a consistent description of recent $\alpha$-induced reaction data with no empirical rescaling factors of the $\gamma$ and/or nucleon widths. On the other hand, its use leads to underestimated predictions of the pre-equilibrium emission and statistical models for the $(n,\alpha )$ reaction cross sections.

Conclusions: An optical potential with a volume imaginary component seems to be needed to describe the low-energy $\alpha$-particle evaporation, while only surface absorption occurs in $\alpha$-induced reactions at similar energies.

The average angular momenta and widths of the spin distributions of reaction products are calculated within the dinuclear system model. The thermal excitation of rotational bearing modes is considered in the dinuclear system. The calculated fragment spins ($\gamma$ multiplicities) and their variances in the reactions ${}^{20}\mathrm{Ne}$ (166 MeV) + ${}^{63}\mathrm{Cu}, {}^{40}\mathrm{Ar}$ (280 MeV) + ${}^{58}\mathrm{Ni}, {}^{20}\mathrm{Ne}$ (175 MeV) + ${}^{\mathrm{nat}}\mathrm{Ag}, {}^{40}\mathrm{Ar}$ (237 MeV) + ${}^{89}\mathrm{Y}, {}^{40}\mathrm{Ar}$ (288 and 340 MeV) + ${}^{107,109}\mathrm{Ag}$, and ${}^{16}\mathrm{O}$ (100 MeV) + ${}^{58}\mathrm{Ni}$ are compared with the available experimental data. The influence of the entrance channel charge (mass) asymmetry and bombarding energy on the characteristics of spin distribution is studied.

Motivated by the precise measurement of the $1S$ level shift of kaonic hydrogen, we perform accurate three-body calculations for the spectrum of kaonic deuterium using a realistic antikaon-nucleon $\left(\overline{K}N\right)$ interaction. In order to describe both short- and long-range behaviors of the kaonic atomic states, we solve the three-body Schrödinger equation with a superposition of a large number of correlated Gaussian basis functions covering distances up to several hundreds of fm. Transition energies between $1S,2P$, and $2S$ states are determined with high precision. The complex energy shift of the $1S$ level of kaonic deuterium is found to be $\mathrm{\Delta }E-i\mathrm{\Gamma }/2=(670-i508)$ eV. The sensitivity of this level shift with respect to the isospin $I=1$ component of the $\overline{K}N$ interaction is examined. It is pointed out that an experimental determination of the kaonic deuterium level shift within an uncertainty of 25% will provide a constraint for the $I=1$ component of the $\overline{K}N$ interaction significantly stronger than that from kaonic hydrogen.

The exotic decay process of $\beta$-delayed fission ($\beta \mathrm{DF}$) has been studied in the neutron-deficient isotope ${}^{230}\mathrm{Am}$. The ${}^{230}\mathrm{Am}$ nuclei were produced in the complete fusion reaction ${}^{207}\mathrm{Pb}({}^{27}\mathrm{Al},4n){}^{230}\mathrm{Am}$ and separated by using the GARIS gas-filled recoil ion separator. A lower limit for the $\beta \mathrm{DF}$ probability $P_{\beta \text{DF}}\left({}^{230}\mathrm{Am}\right)>0.30$ was deduced, which so far is the highest value among all known $\beta \mathrm{DF}$ nuclei. The systematics of $\beta \mathrm{DF}$ in the region of ${}^{230}\mathrm{Am}$ will be discussed.

The low-lying dipole strength in ${}^{52}\mathrm{Cr}$ was measured in nuclear resonance fluorescence experiments using a quasimonochromatic, linearly polarized photon beam. The parities of the excited dipole states were determined by the intensity asymmetry of resonantly scattered $\gamma$ rays with respect to the polarization plane of the incident photon beam. We observed 62 resonances at excitation energies between 7.5 and 12.1 MeV. The observed $M1$ and $E1$ strengths were compared via random-phase-approximation calculations using the Skyrme interaction. The effects of two-particle–two-hole configuration mixing and tensor force on dipole strength distributions were investigated.

Background: The $(\alpha ,n)$, and $(\alpha ,\gamma )$ reactions on ${}^{17,18}\mathrm{O}$ have significant impact on the neutron balance in the astrophysical $s$ process. In this scenario stellar reaction rates are required for relatively low temperatures below $T_9\lesssim 1$.

Purpose: The uncertainties of the ${}^{17,18}\mathrm{O}(\alpha ,n){}^{20,21}\mathrm{Ne}$ reactions are investigated. Statistical model calculations are performed to study the applicability of this model for relatively light nuclei in extension to a recent review for the $20\le A\le 50$ mass range.

Method: The available experimental data for the ${}^{17,18}\mathrm{O}(\alpha ,n){}^{20,21}\mathrm{Ne}$ reactions are compared with statistical model calculations. Additionally, the reverse ${}^{20}\mathrm{Ne}(n,\alpha ){}^{17}\mathrm{O}$ reaction is investigated, and similar studies for the ${}^{17}\mathrm{F}$ mirror nucleus are provided.

Results: It is found that, on average, the available experimental data for ${}^{17}\mathrm{O}$ and ${}^{18}\mathrm{O}$ are well described within the statistical model, resulting in reliable reaction rates above $T_9\gtrsim 1.5$ from these calculations. However, significant experimental uncertainties are identified for the ${}^{17}\mathrm{O}(\alpha ,n_0){}^{20}\mathrm{Ne}$ (ground state) channel.

Conclusions: The statistical model is able to predict astrophysical reaction rates for temperatures above 1 GK with uncertainties of less than a factor of two for the nuclei under study. An experimental discrepancy for the ${}^{17}\mathrm{O}(\alpha ,n){}^{20}\mathrm{Ne}$ reaction needs to be resolved.

Background: The isoscalar monopole response of neutron-rich nuclei is sensitive to both the incompressibility coefficient of symmetric nuclear matter and the density dependence of the symmetry energy. For exotic nuclei with a large neutron excess, a low-energy component emerges that is driven by transitions into the continuum.

Purpose: While understanding the scaling of the giant monopole resonance with mass number is central to this work, the main goal of this paper is to explore the emergence, evolution, and origin of low-energy monopole strength along the even-even calcium isotopes: from ${}^{40}\mathrm{Ca}$ to ${}^{60}\mathrm{Ca}$.

Methods: The distribution of isoscalar monopole strength is computed in a relativistic random phase approximation (RPA) using three effective interactions that have been calibrated to the properties of finite nuclei and neutron stars. A nonspectral approach is adopted that allows for an exact treatment of the continuum without any reliance on discretization. This is particularly critical in the case of weakly bound nuclei with single-particle orbits near the continuum. The discretization of the continuum is neither required nor admitted.

Results: For the stable calcium isotopes, no evidence of low-energy monopole strength is observed, even as the $1f^{7/2}$ neutron orbital is being filled and the neutron-skin thickness progressively grows. Further, in contrast to experimental findings, a mild softening of the monopole response with increasing mass number is predicted. Beyond ${}^{48}\mathrm{Ca}$, a significant amount of low-energy monopole strength emerges as soon as the weak-binding neutron orbitals ($2p$ and $1f^{5/2}$) become populated. The emergence and evolution of low-energy strength is identified with transitions from these weakly bound states into the continuum—which is treated exactly in the RPA approach. Moreover, given that models with a soft symmetry energy tend to reach the neutron-drip line earlier than their stiffer counterparts, an inverse correlation is identified between the neutron-skin thickness and the inverse energy weighted sum.

Conclusions: Despite experimental claims to the contrary, a mild softening of the giant monopole resonance is observed in going from ${}^{40}\mathrm{Ca}$ to ${}^{48}\mathrm{Ca}$. Measurements for other stable calcium isotopes may be critical in elucidating the nature of the discrepancy. Moreover, given the early success in measuring the distribution of isoscalar monopole strength in the unstable ${}^{68}\mathrm{Ni}$ nucleus, new measurements along the unstable neutron-rich calcium isotopes are advocated in order to explore the critical role of the continuum in the development of a soft monopole mode.

Annual modulation of $\gamma$ rays from ($\alpha ,\gamma$) reactions in the Soudan Underground Laboratory was observed using a 12-liter scintillation detector. This significant annual modulation, measured over 4 years, can mimic the signature for dark matter and can also generate potential background events for neutrinoless double-$\beta$ decay experiments. The measured annual modulation of the event rate from ($\alpha ,\gamma$) reactions is strongly correlated with the time-varying radon concentration observed independently in the laboratory. The $\alpha$ flux from radon decay is simulated starting from the measured radon concentration, and the $\gamma$-ray flux is determined using the convolution of the $\alpha$ flux and the cross sections for ($\alpha ,\gamma$) reactions. The calculated $\gamma$-ray flux is sufficient to generate the measured event rate that exhibits an annual modulation.

By means of the Salgado-Wiedemann (SW) quenching weights and the analytic parametrizations of quenching weights based on the Baier-Dokshitzer-Mueller-Peigné-Schiff (BDMPS) formalism, the leading-order computations for nuclear Drell-Yan differential cross section ratios as a function of the quark momentum fraction are performed with the nuclear geometry effect in Drell-Yan dimuon production and the HKM nuclear parton distribution functions, avoiding overestimation of the nuclear modification in the sea quark distribution. By a global analysis of the Drell-Yan experimental data from NA3 and E866 Collaborations, the extracted transport coefficient with the SW quenching weights is $\widehat{q}=0.32\pm 0.04{\mathrm{GeV}}^2/\mathrm{fm}$, which is approximately equal to the value $\widehat{q}=0.37\pm 0.05{\mathrm{GeV}}^2/\mathrm{fm}$ determined with the analytic parametrizations of BDMPS quenching weights. It is found that the theoretical results are in good agrement with the experimental measurements, and especially the agreement of calculations with NA3 experimental data has a significant improvement. We have also given the predictions for the forthcoming Sea Quest experiment. It is hoped that the obtained value of the transport coefficient in cold nuclear matter can provide a useful reference for determining the precise values of the transport properties of the quark-gluon plasma.