Z0 boson associated b-jet production in high-energy nuclear collisions

The production of vector boson tagged heavy quark jets potentially provides new tools to probe the jet quenching effect. In this paper, we present the first theoretical study on the angular correlations (\begin{document}$ \Delta\phi_{bZ} $\end{document}), transverse momentum imbalance (\begin{document}$ x_{bZ} $\end{document}), and nuclear modification factor (\begin{document}$ I_{AA} $\end{document}) of \begin{document}$ Z^0 $\end{document} boson tagged b-jets in heavy-ion collisions, which was performed using a Monte Carlo transport model. We find that the medium modification of the \begin{document}$ \Delta\phi_{bZ} $\end{document} for \begin{document}$ Z^0$\end{document} + b-jet has a weaker dependence on \begin{document}$ \Delta\phi_{bZ} $\end{document} than that for \begin{document}$ Z^0$\end{document} + jet, and the modification patterns are sensitive to the initial jet \begin{document}$ p_T $\end{document} distribution. Additionally, with the high purity of the quark jet in \begin{document}$ Z^0$\end{document} + (b-) jet production, we calculate the momentum imbalance \begin{document}$ x_{bZ} $\end{document} and the nuclear modification factor \begin{document}$ I_{AA} $\end{document} of \begin{document}$ Z^0$\end{document} + b-jet in Pb+Pb collisions. We observe a smaller \begin{document}$ \Delta \langle x_{jZ} \rangle $\end{document} and larger \begin{document}$ I_{AA} $\end{document} of \begin{document}$ Z^0$\end{document} + b-jet in Pb+Pb collisions relative to those of \begin{document}$ Z^0$\end{document} + jet, which may be an indication of the mass effect of jet quenching and can be tested in future measurements.     

Hadronic coupling constants of the lowest hidden-charm pentaquark state,using QCD sum rules with rigorous quark-hadron duality

In this article,we illustrate how to calculate the hadronic coupling constants of the pentaquark states with QCD sum rules based on rigorous quark-hadron quality.We then study the hadronic coupling constants of the lowest diquark-diquark-antiquark type hidden-charm pentaquark state with spin-parity J~P=1/2~-in detail,and calculate the partial decay widths.The total width Г(P_c)=14.32±3.31 MeV is compatible with the experimental value T_(P_c(4312))=9.8±2.7_(-4.5)~(+3.7) MeV from the LHCb collaboration and favors assigning the P_c(4312) to be the [ud][uc]c pentaquark state with J~P=1/2~-.The hadronic coupling constants have the relation ■,and favor the hadronic dressing mechanism.The P_c(4312) may have a diquark-diquark-antiquark type pentaquark core with the typical size of the qqq-type baryon states.The strong couplings to the meson-baryon pairs DE_c lead to some pentaquark molecule components,and the P_c(4312) may spend a rather large time as the DE_c molecular state.     

Running vacuum model in a non-flat universe

We investigate observational constraints on the running vacuum model (RVM) of \begin{document}$\Lambda=3\nu (H^{2}+K/a^2)+c_0$\end{document} in a spatially curved universe, where \begin{document}$\nu$\end{document} is the model parameter, \begin{document}$K$\end{document} corresponds to the spatial curvature constant, \begin{document}$a$\end{document} represents the scalar factor, and \begin{document}$c_{0}$\end{document} is a constant defined by the boundary conditions. We study the CMB power spectra with several sets of \begin{document}$\nu$\end{document} and \begin{document}$K$\end{document} in the RVM. By fitting the cosmological data, we find that the best fitted \begin{document}$\chi^2$\end{document} value for RVM is slightly smaller than that of \begin{document}$\Lambda$\end{document}CDM in the non-flat universe, along with the constraints of \begin{document}$\nu\leqslant O(10^{-4})$\end{document} (68% C.L.) and \begin{document}$|\Omega_K=-K/(aH)^2|\leqslant O(10^{-2})$\end{document} (95% C.L.). In particular, our results favor the open universe in both \begin{document}$\Lambda$\end{document}CDM and RVM. In addition, we show that the cosmological constraints of \begin{document}$\Sigma m_{\nu}=0.256^{+0.224}_{-0.234}$\end{document} (RVM) and \begin{document}$\Sigma m_{\nu}=0.257^{+0.219}_{-0.234}$\end{document} (\begin{document}$\Lambda$\end{document}CDM) at 95% C.L. for the neutrino mass sum are relaxed in both models in the spatially curved universe.     

The effect of hadronic scatterings on the measurement of vector meson spin alignments in heavy-ion collisions

Spin alignments of vector mesons and hyperons in relativistic heavy-ion collisions have been proposed as signals of global polarization.The STAR experiment first observed the ∧ polarization.Recently,the ALICE collaboration measured the transverse momentum {PT) and the collision centrality dependence of K*,and Φ spin alignments during Pb-Pb collisions at ~(1/2)sNN=2.76 TeV.A large signal is observed in the low pT region of mid-central collisions for K~*,while the signal is much smaller for Φ,and these have not been understood yet.Since vector mesons have different lifetimes and their decay products have different scattering cross sections,they suffer from different hadronic effects.In this paper,we study the effect of hadronic interactions on the spin alignment of K~*,Φ,and p mesons in relativistic heavy-ion collisions with a multi-phase transport model.We find that hadronic scatterings lead to a deviation of the observed spin alignment matrix element p00 away from the true value for p and K*mesons(with a bigger effect on p) while the effect is negligible for the Φ meson.The effect depends on the kinematic acceptance:the observed p00 value is lower than the true value when the pseudorapidity(η) coverage is small,while there is little effect when the η coverage is large.Hence,this study provides valuable information to understand the vector meson spin alignment signals observed during the experiments.     

Relative probabilities of breakup channels in reactions of ~(6,7)Li with ~(209)Bi at energies around and above the Coulomb barrier

Coincidence measurements of breakup fragments in reactions of~ (6,7) Li with ~(209)Bi at energies around and above the Coulomb barrier were carried out using a large solid-angle covered detector array. Through the Q values along with the relative energies of the breakup fragments, different breakup components(prompt breakups and delayed breakups) and different breakup modes(α + t, α + d, α + p, and α + α) are distinguished. A new breakup mode, α + t, is observed in ~6Li-induced reactions at energies above the Coulomb barrier. Correlations between breakup modes and breakup components as well as their variations with the incident energy are investigated. The results will help us better understand the breakup effects of weakly bound nuclei on the suppression of a complete fusion, particularly for the above-barrier energies.     

Research on convergence of the nuclear matrix elements for 2νββ decays

In this work, the characteristics of \begin{document}$2\nu\beta\beta$\end{document} decays for six nuclei (\begin{document}$^{36}$\end{document}Ar, \begin{document}$^{46}$\end{document}Ca, \begin{document}$^{48}$\end{document}Ca, \begin{document}$^{50}$\end{document}Cr, \begin{document}$^{70}$\end{document}Zn, and \begin{document}$^{136}$\end{document}Xe) in a mass range from \begin{document}$A = 36$\end{document} to \begin{document}$A = 136$\end{document} are studied within the nuclear shell model (NSM) framework. Calculations are presented for the half-lives, nuclear matrix elements (NMEs), phase space factors (\begin{document}$G_{2\nu}$\end{document}), and convergence of the NMEs. The theoretical results agree well with the experimental data. In addition, we predict the half-lives of \begin{document}$2\nu\beta\beta$\end{document} decays for four nuclei. We focus on the convergence of the NMEs by analyzing the number of contributing intermediate \begin{document}$1^{+}$\end{document} states (\begin{document}$N_{\rm{C}}$\end{document}) for the nuclei of interest. We assume that \begin{document}$N_{\rm{C}}$\end{document} is safely determined when the accumulated NMEs saturate 99.7% of the final calculated magnitude. From the calculations of the involved nuclei, we discover a connection between \begin{document}$N_{\rm{C}}$\end{document} and the total number of intermediate \begin{document}$1^{+}$\end{document} states (\begin{document}$N_{\rm{T}}$\end{document}). According to the least squares fit, we conclude that the correlation is \begin{document}$N_{\rm{C}}=\left( 10.8\pm 1.2\right) \times N_{\rm{T}}^{\left( 0.29\pm 0.02\right)}$\end{document}.     

Emission time sequence of neutrons and protons as probes of α-clustering structure

Neutron–proton momentum correlation functions are constructed from a three-body photodisintegration channel, i.e., core\begin{document}$ + n + p$\end{document}, and used to explore the spatial-time information of the non-clustering Woods–Saxon spherical structure as well as the \begin{document}$\alpha$\end{document}-clustering structures of \begin{document}$^{12}{\rm{C}}$\end{document} or \begin{document}$^{16}{\rm{O}}$\end{document} based on an extended quantum molecular dynamics model. The emission time sequence of neutrons and protons is indicated by the ratio of velocity-gated neutron–proton correlation functions, demonstrating its sensitivity to \begin{document}$\alpha$\end{document}-clustering structures. This work sheds light on a new probe for \begin{document}$\alpha$\end{document}-clustering structures.     

Calculations of the α-decay properties of Z = 120, 122, 124, 126 isotopes

The \begin{document}$\alpha$\end{document}-decay properties of even-Z nuclei with Z = 120, 122, 124, 126 are predicted. We employ the generalized liquid drop model (GLDM), Royer's formula, and universal decay law (UDL) to calculate the \begin{document}$\alpha$\end{document}-decay half-lives. By comparing the theoretical calculations with the experimental data of known nuclei from Fl to Og, we confirm that all the employed methods can reproduce the \begin{document}$\alpha$\end{document}-decay half-lives well. The preformation factor \begin{document}$P_{\alpha}$\end{document} and \begin{document}$\alpha$\end{document}-decay energy \begin{document}$Q_{\alpha}$\end{document} show that \begin{document}$^{298,304,314,316,324,326,338,348}$\end{document}120, \begin{document}$^{304,306,318,324,328,338}$\end{document}122, and \begin{document}$^{328,332,340,344}$\end{document}124 might be stable. The \begin{document}$\alpha$\end{document}-decay half-lives show a peak at Z = 120, N = 184, and the peak vanishes when Z = 122, 124, 126. Based on detailed analysis of the competition between \begin{document}$\alpha$\end{document}-decay and spontaneous fission, we predict that nuclei nearby N = 184 undergo \begin{document}$\alpha$\end{document}-decay. The decay modes of \begin{document}$^{287-339}$\end{document}120, \begin{document}$^{294-339}$\end{document}122, \begin{document}$^{300-339}$\end{document}124, and \begin{document}$^{306-339}$\end{document}126 are also presented.     

QCD phase diagram at finite isospin and baryon chemical potentials with the self-consistent mean field approximation

The self-consistent mean field approximation of the two-flavor NJL model,with a free parameter a to reflect the competition between the "direct" channel and the "exchange" channel,is employed to study the QCD phase structure at finite iso spin chemical potential μ_I,finite bary on chemical potential μ_B and finite temperature T,and especially to study the location of the QCD critical point.Our results show that in order to match the corresponding lattice results of iso spin density and energy density,the contributions of the "exchange" channel need to be considered in the framework of the NJL model,and a weighting factor α=0.5 should be taken.It is also found that for fixed isospin chemical potentials,the lower temperature of the phase transition is obtained with increasing a in the T-μ_I plane,and the largest difference of the phase transition temperature with different a's appears at μ_I~1.5 mπ.At μ_I=0 the temperature of the QCD critical end point(CEP) decreases with increasing a,while the critical baryon chemical potential increases.At high isospin chemical potential(μ_I=500 MeV),the temperature of the QCD tricritical point(TCP) increases with increasing a,and in the low temperature regions the system will transition from the pion superfluidity phase to the normal phase as μ_B increases.At low density,the critical temperature of the QCD phase transition with different a's rapidly increases with μ_I at the beginning,and then increases smoothly around μ_I 300 MeV.In the high baryon density region,the increase of the iso spin chemical potential will raise the critical baryon chemical potential of the phase transition.     

Possibility of observation of hidden-bottom pentaquark resonances in bottomonium photoproduction on protons and nuclei near threshold

We study the \begin{document}$\Upsilon(1S)$\end{document} meson photoproduction on protons and nuclei at near-threshold center-of-mass energies below 11.4 GeV (or at the corresponding photon laboratory energies \begin{document}$E_{\gamma}$\end{document} below 68.8 GeV). We calculate the absolute excitation functions for the nonresonant and resonant photoproduction of \begin{document}$\Upsilon(1S)$\end{document} mesons off protons at incident photon laboratory energies of 63-68 GeV by considering direct (\begin{document}${\gamma}p \to {\Upsilon(1S)}p$\end{document}) and two-step (\begin{document}${\gamma}p \to P^+_b(11080) \to {\Upsilon(1S)}p$\end{document}, \begin{document}${\gamma}p \to P^+_b(11125) \to {\Upsilon(1S)}p$\end{document}, \begin{document}${\gamma}p \to P^+_b(11130) \to {\Upsilon(1S)}p$\end{document}) \begin{document}$\Upsilon(1S)$\end{document} production channels within different scenarios for the nonresonant total cross section of the elementary reaction \begin{document}${\gamma}p \to {\Upsilon(1S)}p$\end{document} and for branching ratios of the decays \begin{document}$P^+_b(11080) \to {\Upsilon(1S)}p$\end{document}, \begin{document}$P^+_b(11125) \to {\Upsilon(1S)}p$\end{document}, and \begin{document}$P^+_b(11130) \to {\Upsilon(1S)}p$\end{document}. We also calculate an analogous function for the photoproduction of \begin{document}$\Upsilon(1S)$\end{document} mesons on the ¹²C and ²⁰⁸Pb target nuclei in the near-threshold center-of-mass beam energy region of 9.0-11.4 GeV by considering the respective incoherent direct (\begin{document}${\gamma}N \to {\Upsilon(1S)}N$\end{document}) and two-step (\begin{document}${\gamma}p \to P^+_b(11080) \to {\Upsilon(1S)}p$\end{document}, \begin{document}${\gamma}p \to P^+_b(11125) \to {\Upsilon(1S)}p$\end{document}, \begin{document}${\gamma}p \to P^+_b(11130) \to {\Upsilon(1S)}p$\end{document} and \begin{document}${\gamma}n \to P^0_b$\end{document}\begin{document}$ (11080) \to{\Upsilon(1S)}n $\end{document}, \begin{document}${\gamma}n \to P^0_b(11125) \to {\Upsilon(1S)}n$\end{document}, \begin{document}${\gamma}n \to P^0_b(11130) \to {\Upsilon(1S)}n$\end{document}) \begin{document}$\Upsilon(1S)$\end{document}) production processes using a nuclear spectral function approach. We demonstrate that a detailed scan of the\begin{document}$\Upsilon(1S)$\end{document} total photoproduction cross section on proton and nuclear targets in the near-threshold energy region in future high-precision experiments at the proposed high-luminosity electron-ion colliders EIC and EicC in the US and China should provide a definite result for or against the existence of the nonstrange hidden-bottom pentaquark states\begin{document}$P_{bi}^+$\end{document} and \begin{document}$P_{bi}^0$\end{document} (\begin{document}$i$\end{document}=1, 2, 3) as well as clarify their decay rates.     

Systematic study of the α decay preformation factors of the nuclei around the Z = 82, N = 126 shell closures within the generalized liquid drop model

In this study, we systematically investigate the \begin{document}$\alpha$\end{document} decay preformation factors, \begin{document}$P_{\alpha}$\end{document} , and the \begin{document}$\alpha$\end{document} decay half-lives of 152 nuclei around Z = 82, N = 126 closed shells based on the generalized liquid drop model (GLDM) with \begin{document}$P_{\alpha}$\end{document} being extracted from the ratio of the calculated \begin{document}$\alpha$\end{document} decay half-life to the experimental one. The results show that there is a remarkable linear relationship between \begin{document}$P_{\alpha}$\end{document} and the product of valance protons (holes) \begin{document}$N_p$\end{document} and valance neutrons (holes) \begin{document}$N_n$\end{document} . At the same time, we extract the \begin{document}$\alpha$\end{document} decay preformation factor values of the even–even nuclei around the Z = 82, N = 126 closed shells from the study of Sun \begin{document}${et\ al.}$\end{document} [J. Phys. G: Nucl. Part. Phys., 45: 075106 (2018)], in which the \begin{document}$\alpha$\end{document} decay was calculated by two different microscopic formulas. We find that the \begin{document}$\alpha$\end{document} decay preformation factors are also related to \begin{document}$N_pN_n$\end{document} . Combining with our previous studies [Sun \begin{document}${et\ al.}$\end{document} , Phys. Rev. C, 94: 024338 (2016); Deng \begin{document}${et\ al.}$\end{document} , ibid. 96: 024318 (2017); Deng \begin{document}${et\ al.}$\end{document} , ibid. 97: 044322 (2018)] and that of Seif \begin{document}${et\ al.,}$\end{document} [Phys. Rev. C, 84: 064608 (2011)], we suspect that this phenomenon of linear relationship for the nuclei around the above closed shells is model-independent. This may be caused by the effect of the valence protons (holes) and valence neutrons (holes) around the shell closures. Finally, using the formula obtained by fitting the \begin{document}$\alpha$\end{document} decay preformation factor data calculated by the GLDM, we calculate the \begin{document}$\alpha$\end{document} decay half-lives of these nuclei. The calculated results agree with the experimental data well.     

Analysis of the strong decays of Pc(4312) as a pentaquark molecular state with QCD sum rules

In this article, we tentatively assign \begin{document}$P_c(4312)$\end{document} to be the \begin{document}$\bar{D}\Sigma_c$\end{document} pentaquark molecular state with the spin-parity \begin{document}$J^P={\frac{1}{2}}^-$\end{document} , and discuss the factorizable and non-factorizable contributions in the two-point QCD sum rules for the \begin{document}$\bar{D}\Sigma_c$\end{document} molecular state in detail to prove the reliability of the single pole approximation in the hadronic spectral density. We study its two-body strong decays with the QCD sum rules, and special attention is paid to match the hadron side with the QCD side of the correlation functions to obtain solid duality. We obtain the partial decay widths \begin{document}$\Gamma\left(P_c(4312)\to \eta_c p\right)=0.255\,\,{\rm{MeV}}$\end{document} and \begin{document}$\Gamma\left(P_c(4312)\to J/\psi p\right)=9.296^{+19.542}_{-9.296}\,\,{\rm{MeV}}$\end{document} , which are compatible with the experimental value of the total width, and support assigning \begin{document}$P_c(4312)$\end{document} to be the \begin{document}$\bar{D}\Sigma_c$\end{document} pentaquark molecular state.     

Simulation of neutron-tagged deep inelastic scattering at EicC

Measuring the pionic structure function is of high interest, as it provides a new area for understanding the strong interaction among quarks and testing QCD predictions. To this end, we investigate the feasibility and expected impact of a possible experiment at EicC(Electron-ion collider in China). We show the simulation results on the statistical precision of an EicC measurement, based on the model of leading neutron tagged DIS process and the parton distribution functions of the pion from JAM18 global analysis. The simulation shows that at EicC, the kinematics cover the x π range from 0.01 to 1, and the Q~2 range from 1 to 50 GeV~2, within the acceptable statistical uncertainty. Assuming an integrated luminosity of 50 fb~(-1), in the low-Q~2 region( 10 GeV~2), the Monte Carlo data show that the suggested measurement in the whole x π range reaches very high precision( 3%). To perform such an experiment, only the addition of a far-forward neutron calorimeter is needed.     

Proton-halo breakup dynamics for the breakup threshold in the ε0 → 0 limit

Proton-halo breakup behavior in the \begin{document}$ \varepsilon_0\to 0 $\end{document} limit (where \begin{document}$ \varepsilon_0 $\end{document} is the ground-state binding energy) is studied around the Coulomb barrier in the \begin{document}$ ^8{\rm{B}}+{}^{58}{\rm{Ni}} $\end{document} reaction for the first time. For practical purposes, apart from the experimental \begin{document}$ ^8{\rm{B}} $\end{document} binding energy of 137 keV, three more arbitrarily chosen values (1, 0.1, 0.01 keV) are considered. It is first shown that the Coulomb barrier between the core and the proton prevents the \begin{document}$ ^7{\rm{Be}}+p $\end{document} system from reaching the state of an open proton-halo system, which, among other factors, would require the ground-state wave function to extend to infinity in the asymptotic region, as \begin{document}$ \varepsilon_0\to 0 $\end{document}. The elastic scattering cross section, which depends on the density of the ground-state wave function, is found to have a negligible dependence on the binding energy in this limit. The total, Coulomb and nuclear breakup cross sections are all reported to increase significantly from \begin{document}$ \varepsilon_0 = 137 $\end{document} to 1.0 keV, and converge to their maximum values as \begin{document}$ \varepsilon_0\to 0 $\end{document}. This increase is mainly understood as coming from a longer tail of the ground-state wave function for \begin{document}$ \varepsilon_0\leqslant 1.0 $\end{document} keV, compared to that for \begin{document}$ \varepsilon_0 = 137 $\end{document} keV. It is also found that the effect of the continuum-continuum couplings is to slightly delay the convergence of the breakup cross section. The analysis of the reaction cross section indicates a convergence of all the breakup observables as \begin{document}$ \varepsilon_0\to 0 $\end{document}. These results provide a better sense of the dependence of the breakup process on the breakup threshold.     

Fine tuning problem of the cosmological constant in a generalized Randall-Sundrum model

To solve the cosmological constant fine tuning problem, we investigate an \begin{document}$(n+1)$\end{document}-dimensional generalized Randall-Sundrum brane world scenario with two \begin{document}$(n-1)$\end{document}-branes instead of two 3-branes. Adopting an anisotropic metric ansatz, we obtain the positive effective cosmological constant \begin{document}$\Omega_{\rm eff}$\end{document} of order \begin{document}$10^{-124}$\end{document} and only require a solution \begin{document}$\simeq50-80$\end{document}. Meanwhile, both the visible and hidden branes are stable because their tensions are positive. Therefore, the fine tuning problem can be solved quite well. Furthermore, the Hubble parameter \begin{document}$H_{1}(z)$\end{document} as a function of redshift \begin{document}$z$\end{document} is in good agreement with the cosmic chronometers dataset. The evolution of the universe naturally shifts from deceleration to acceleration. This suggests that the evolution of the universe is intrinsically an extra-dimensional phenomenon. It can be regarded as a dynamic model of dark energy that is driven by the evolution of the extra dimensions on the brane.     

Constraints on the generalized natural inflation after Planck 2018

Based on the dynamics of single scalar field slow-roll inflation and the theory of reheating, we investigate the generalized natural inflationary (GNI) model. We introduce constraints on the scalar spectral index \begin{document}$n_{s}$\end{document} and the tensor-to scalar ratio r for the \begin{document}$\Lambda$\end{document}CDM \begin{document}$+r$\end{document} model, according to the latest data from Planck 2018 TT, TE, EE+low E+lensing (P18) and BICEP2/Keck 2015 season (BK15), i.e., with \begin{document}$n_{s}=0.9659\pm0.0044$\end{document} at 68% confidence level (CL), and \begin{document}$r<0.0623$\end{document} at 95% CL. We find that the GNI model is favored by P18 and BK15 in the ranges \begin{document}$\log_{10}(f/M_{p})= 0.62^{+0.17}_{-0.18}$\end{document} and \begin{document}$m=0.35^{+0.13}_{-0.23}$\end{document} at 68% CL. In addition, the corresponding predictions of generalized and two-phase reheating are discussed. It follows that the parameter m has significant effect on the model behavior.     

Evolution of intrinsic nuclear structure in medium mass even-even Xenon isotopes from a microscopic perspective

In this study, the multi-quasiparticle triaxial projected shell model (TPSM) is applied to investigate \begin{document}$\gamma$\end{document}-vibrational bands in transitional nuclei of \begin{document}$^{118-128}{\rm{Xe}}$\end{document}. We report that each triaxial intrinsic state has a \begin{document}$\gamma$\end{document}-band built on it. The TPSM approach is evaluated by the comparison of TPSM results with available experimental data, which shows a satisfactory agreement. The energy ratios, B(E2) transition rates, and signature splitting of the \begin{document}$\gamma$\end{document}-vibrational band are calculated.     

Re-visiting supersymmetric Janus solutions: a perturbative construction

We construct holographic Janus solutions, which describe a conformal interface in the theory of M2-branes, in four-dimensional gauged supergravities using a perturbative method. In particular, we study three Einsteinscalar systems and their BPS equations, which are derived by Bobev, Pilch, and Warner(2014). The actions of our interest are all consistent truncations of D=11 supergravity, chosen to be invariant under SO(4)×SO(4),SU(3)×U(1)×U(1), and G_2 symmetry subgroups of SO(8). The utility of our semi-analytic result is illustrated by the calculation of minimal area surface and the associated holographic entanglement entropy.     

New behaviors of α-particle preformation factors near doubly magic 100Sn

The \begin{document}$ \alpha $\end{document}-particle preformation factors of nuclei above doubly magic nuclei \begin{document}$ ^{100} $\end{document}Sn and \begin{document}$ ^{208} $\end{document}Pb are investigated within the generalized liquid drop model. The results show that the \begin{document}$ \alpha $\end{document}-particle preformation factors of nuclei near self-conjugate doubly magic \begin{document}$ ^{100} $\end{document}Sn are significantly larger than those of analogous nuclei just above \begin{document}$ ^{208} $\end{document}Pb, and they will be enhanced as the nuclei move towards the \begin{document}$ N = Z $\end{document} line. The proton–neutron correlation energy \begin{document}$ E_{p-n} $\end{document} and two protons–two neutrons correlation energy \begin{document}$ E_{2p-2n} $\end{document} of nuclei near \begin{document}$ ^{100} $\end{document}Sn also exhibit a similar situation, indicating that the interactions between protons and neutrons occupying similar single-particle orbitals could enhance the \begin{document}$ \alpha $\end{document}-particle preformation factors and result in superallowed \begin{document}$ \alpha $\end{document} decay. This also provides evidence of the significant role of the proton–neutron interaction on \begin{document}$ \alpha $\end{document}-particle preformation. Also, the linear relationship between \begin{document}$ \alpha $\end{document}-particle preformation factors and the product of valence protons and valence neutrons for nuclei around \begin{document}$ ^{208} $\end{document}Pb is broken in the \begin{document}$ ^{100} $\end{document}Sn region because the \begin{document}$ \alpha $\end{document}-particle preformation factor is enhanced when a nucleus near \begin{document}$ ^{100} $\end{document}Sn moves towards the \begin{document}$ N = Z $\end{document} line. Furthermore, the calculated \begin{document}$ \alpha $\end{document} decay half-lives fit well with the experimental data, including the recent observed self-conjugate nuclei \begin{document}$ ^{104} $\end{document}Te and \begin{document}$ ^{108} $\end{document}Xe [Phys. Rev. Lett. 121, 182501 (2018)].     

Nucleon effective mass splitting and density-dependent symmetry energy effects on elliptic flow in heavy ion collisions at E_(lab)= 0.09 ～ 1.5 GeV/nucleon

By incorporating an iso spin-dependent form of the momentum-dependent potential in the ultra-relativistic quantum molecular dynamics(UrQMD) model,we systematically investigate effects of the neutron-proton effective mass splitting m*_(n-p)=m*_n-m*_p/m and the density-dependent nuclear symmetry energy E_(sym)(ρ) on the elliptic flow v_2 in~(197)Au+~(197) Au collisions at beam energies from 0.09 to 1.5 GeV/nucleon.It is found that at higher beam energies(≥0.25 GeV/nucleon) with the approximately 75 MeV difference in slopes of the two different E_(sym)(ρ),and the variation of m*_(n-p) ranging from-0.03 to 0.03 at saturation density with isospin asymmetry δ=(ρ_n-ρ_p)/ρ-0.2,the E_(sym)(ρ) has a stronger influence on the difference in v_2 between neutrons and protons,i.e.,v_2~n-v_2~p,than m*_(n-p) has.Meanwhile,at lower beam energies(≤0.25 GeV/nucleon),v_2~n-v_2~p is sensitive to both the E_(sym)(ρ) and the m*_(n-p).Moreover,the influence of m*_(n-p) on v_2~n-v_2~p is more evident with the parameters of this study when using the soft,rather than stiff,symmetry energy.