arXiv subjects

J. G. Li

Publications and source records attributed to J. G. Li.

At least 19 recordsLinked to original sources

arXiv2026

Probing exotic multi-proton emitters: A Gamow shell model study of proton-rich fluorine and neon isotopes beyond the drip line

We investigate proton-rich systems beyond the proton drip line, focusing on the notably poorly known 13F and 15Ne and the yet unobserved 14Ne, whose structure properties remain weakly constrained. Using the Gamow shell model (GSM), which consistently incorporates both inter-nucleon correlations and couplings to the particle continuum, we study oxygen, fluorine, and neon isotopes with mass A=12-16. Taking 8C as an inert core, the GSM Hamiltonian based on an effective field theory nucleon-nucleon interaction is optimized for this proton-rich region. The constructed Hamiltonian reproduces the low-lying spectra and decay properties of fluorine and neon isotopes beyond the proton drip line. We quantify many-body configuration and average partial-wave occupancies to elucidate the structural evolution of the drip line nuclei 12-14O, 13-15F, and 14-16Ne. In particular, multi-proton separation energies and spectroscopic factors are analyzed in detail, leading to a prediction for the unresolved ground state of 13F. Furthermore, the candidate 4p emitter 14Ne is theoretically predicted for the first time, providing valuable guidance for future experimental investigations.

nucl-th↗

arXiv2026

Direct observation of three-neutron emission from $^7$He$^*$ and the search for the trineutron

Three-neutron emission from $^7$He has been directly measured for the first time, following neutron knockout from a $^8$He beam at 156 MeV/nucleon. A resonance-like structure at $2.08(4)$ MeV above the $^4$He+$3n$ threshold [$E_x=2.68(4)$ MeV] with a width of $3.9(2)$ MeV was observed and deduced to arise predominately from the predicted $J^π=3/2^{-}_2$ level. The three-neutron invariant-mass spectrum was reconstructed and found to peak at around 1 MeV and could, through complete simulations incorporating neutron-neutron correlations, be very well described by the sequential decay of $^7$He$^*$ via the $2_1^+$ excited state of $^6$He. No evidence was found for any significant three-neutron correlations beyond those expected from well-established two-body interactions, including a trineutron resonance.

nucl-ex↗

arXiv2026

How Threshold Effects in Spectroscopic Factors Influence Heavy-Ion Knockout Reactions

A two-decade-old puzzle in heavy-ion one-nucleon knockout reactions is the strong correlation between the reduction factor $R_s=σ_{\rm exp}/σ_{\rm th}$ and the Fermi surface asymmetry $ΔS$. Theoretical cross sections typically rely on spectroscopic factors (SFs) from shell model (SM) calculations, which neglect continuum coupling effects. Here, we employ the Gamow shell model (GSM), which explicitly incorporates continuum coupling, to compute SFs for $p$-shell nuclei and predict corresponding theoretical cross sections. Systematic calculations demonstrate that using GSM-derived SFs substantially reduces discrepancies between theoretical and experimental results. This improvement is particularly significant for deeply bound nucleon knockout in nuclei near the dripline, where traditional SM-based calculations fall short. As a result, using GSM SFs, the ratio $R_s$ exhibits no pronounced dependence on $ΔS$. Furthermore, both the ratio of GSM SFs to SM SFs and their corresponding reaction cross sections ratios exhibit a strong $ΔS$ dependence. We have also compared GSM SFs and cross sections with those from the no-core shell model calculations, giving a similar pronounced sensitivity to $ΔS$. Detailed analysis attributes these correlations to threshold effects for SFs in weakly bound systems. Overall, incorporating continuum coupling via GSM enhances the reliability of SF predictions for exotic, weakly bound nuclei and provides key insights toward resolving the enduring puzzle in heavy-ion knockout reactions from a nuclear structure perspective.

nucl-th↗

arXiv2026

\textit{Ab initio} study of spectroscopic factors in $^{48}$K and neighboring $N=28$ isotones

A recent $^{47}\text{K}(d,pγ)^{48}\text{K}$ transfer reaction measurement has identified new excited states in $^{48}\text{K}$ and extracted the corresponding spectroscopic factors (SFs)[\href{https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.162504}{C. J. Paxman, \textit{et al.} PhysRevLett.134.162504 (2025)}], but they exposed sizeable discrepancies with large-scale shell-model (LSSM) calculations-especially for the low-lying states-suggesting shortcomings in the proton-neutron interaction employed by the LSSM. In this work, we revisit the low-lying states and SFs of $^{48}\text{K}$ using the \textit{ab initio} valence-space in-medium similarity renormalization group (VS-IMSRG) approach based on the chiral two- and three-nucleon forces. The calculated excitation energies reproduce the experimental data for $^{48}\text{K}$, whereas computed SFs systematically exceed experimental values. We trace this overestimation to missing reduction factors that account for non-idealities of the transfer reaction. After introducing a phenomenological reduction factor, our VS-IMSRG results and the LSSM calculations achieve agreement with experiment. We also perform the same analysis for the neutron SFs of $^{47}$Ar. Furthermore, we extend the \textit{ab initio} calculations across the $N=28$ isotones, computing excitation energies and single-neutron transfer SFs from $N=29$ isotones ranging from $^{48}$K to $^{45}$S. By systematically removing protons from $^{48}\text{K}$ to $^{45}\text{S}$, we trace the evolution of the $N=28$ shell strength via theoretical SFs values. Our results provide a microscopic pathway to quantify the weakening of the $N=28$ shell closure.

nucl-th↗

arXiv2025

Double-magicity of proton drip-line nucleus $^{22}$Si with \textit{ab initio} calculation

New magic numbers have been discovered in the neutron-rich region of the nuclear chart. However, there has been a lack of research on proton-rich nuclei. $^{22}$O, the mirror nucleus of $^{22}$Si, is a double-magic nucleus bearing a high $E(2_1^+)$. Whether $^{22}$Si exhibits double-magic characters is an intriguing topic. To investigate this matter, we utilized \textit{ab initio} valence space in-medium similarity renormalization group for $^{22}$Si/$^{22}$O, and their nearby nuclei. Our \textit{ab initio} calculations provide good descriptions for the double magicity of $^{22}$O, as well as the shell evolution of $N=14$ and $Z=14$ through $E(2_1^+)$. The computed $E(2_1^+)$ indicate that the closure of $Z=14$ sub-shell in proton-rich nuclei is weaker than the $N=14$ sub-shell closure in their mirror nuclei. Particularly, the calculated $E(2_1^+)$ of $^{22}$Si is 800 keV lower than the one of $^{22}$O. To further explore the magicity of $^{22}$Si, the mirror energy difference (MED) of $^{26}$Si/$^{26}$Mg, $^{24}$Si/$^{24}$Ne, as well as $^{22}$Si/$^{22}$O are calculated. The results demonstrate that the calculated MEDs agree well with available experimental data, and the $E(2_1^+)$ values of $^{22,24,26}$Si are all lower than their respective mirror nuclei due to the Thomas-Ehrman shift with large $s_{1/2}$ occupation. Moreover, our calculation provides that the many-body configurations of the low-lying state of $^{22}$Si/$^{22}$O are nearly identical despite the fact that the states bearing large MED. In conclusion, our \textit{ab initio} results suggest that $^{22}$Si is a double magic nucleus, similar to its mirror nucleus $^{22}$O, albeit with a lower $E(2_1^+)$.

nucl-th↗

arXiv2025

Gamow shell model predictions for six-proton unbound nucleus $^{20}$Si

Proton-rich nuclei beyond the proton drip line are of great interest in nuclear structure physics, due to exotic phenomena such as proton emissions and the Thomas-Ehrman shift (TES). In this work, we employ the Gamow shell model (GSM) to investigate the structure and decay of $^{20}$Si, a candidate for six-proton (6$p$) emission, which can be produced via two-neutron knockout from the drip line nucleus $^{22}$Si. We predict that its ground state decays via $6p$ emission to the ground state of $^{14}$O, with a decay energy $E_{6p} = 10.125$ MeV and a width of 371~keV. A $2^+$ state is predicted at 1.7 MeV, comparable with that in $^{18}$Mg, indicating the disappearance of the $Z=14$ magic number in $^{20}$Si. Instead, analyses of the many-body configurations and the average occupancies of the mirror states suggest the presence of $dynamic$ TES in low-lying states of $^{19}$Al/$^{19}$C and $^{20}$Si/$^{20}$C. Further evidence is provided by analyzing the contributions of different components of the GSM Hamiltonian. Moreover, this study offers the first theoretical description of $^{20}$Si and guidance for future experiments.

nucl-th↗

arXiv2025

Improved thermonuclear rate of $^{42}$Ti($p$,$γ$)$^{43}$V and its astrophysical implication in rp-process

Accurate $^{42}$Ti($p$,$γ$)$^{43}$V reaction rates are crucial for understanding the nucleosynthesis path of the rapid capture process (rp-process) that occurs in X-ray bursts. We aim to improve the thermonuclear rates of $^{42}$Ti($p$,$γ$)$^{43}$V based on more complete resonance information and accurate direct component, together with the recently released nuclear masses data. We reevaluated the $^{42}$Ti($p$,$γ$)$^{43}$V rate by the sum of the isolated resonance contribution instead of the Hauser-Feshbach statistical model. A Monte Carlo method is used to derive the uncertainties of new rates. The nucleosynthesis simulations are performed via the NuGrid post-processing code ppn. The new rates differ from previous estimations because of using a series of updated resonance parameters and direct S-factor. Compared with the previous results from Hauser-Feshbach statistical model, which assumes compound nucleus $^{43}$V with a sufficiently high-level density in the energy region of astrophysical interest, differences exist over the entire temperature region of rp-process interest, even up to 4 orders of magnitude. Using a trajectory with a peak temperature of 1.95$\times$10$^9$ K, we perform the rp-process nucleosynthesis simulations to investigate the impact of the new rates. Our calculations show that the adoption of the new forward and reverse rates result in abundance variations for Sc and Ca by 128\% and 49\% respectively compared to the case using statistical model rates. On the other hand, the overall abundance pattern is not significantly affected. The results of using new rates also confirm that the rp-process path does not bypass the isotope $^{43}$V. It is found that the Hauser-Feshbach statistical model is inappropriate to the reaction rate evaluation for $^{42}$Ti($p$,$γ$)$^{43}$V.

astro-ph.SR↗

arXiv2025

The role of the overlap function in describing angular distributions of single-nucleon transfer reactions

Single-nucleon transfer reactions offer a valuable way to probe nuclear structure. We explore the effect of directly introducing overlap functions computed using the Gamow shell model (GSM) into reaction calculations, taking the $\left< ^7\mathrm{Li} \mid \protect{^6\mathrm{He}} + p \right>$ single proton overlap as a case study. By incorporating both inter-nucleon correlations and continuum coupling, the GSM provides accurate overlap functions in both interior and asymptotic regions, together with the corresponding spectroscopic factors (SFs). These theoretical SFs and overlap functions were included in a coupled channels Born approximation analysis of the $^{6}{\rm He}(d,n)^7{\rm Li}$ transfer reaction. Overlap functions derived from \textit{ab initio} no-core shell model (NCSM) calculations as well as standard single-particle (s.p.) wave functions were also considered for comparison. Our results reveal significant differences between the calculated angular distributions when employing theoretical SFs with standard s.p.\ wave functions compared to the full theoretical overlap functions. Discrepancies were also observed between angular distributions calculated with GSM and NCSM overlap functions, highlighting the importance of internal structure and correct asymptotic behavior in reliable reaction calculations. The GSM overlap functions also provided a good description of the $^{208}$Pb($^7$Li,$^6$He)$^{209}$Bi reaction when included in a coupled reaction channels calculation.

nucl-th↗

arXiv2025

Gamow shell model study of the 17Ne(p, p) reaction and of isospin symmetry breaking in 18Na

The unbound nucleus 18Na, acting as an intermediate nucleus in the sequential decay of 19Mg, is situated beyond the proton drip line. We employ the coupled-channel Gamow shell model (GSM-CC) to investigate the properties of 18Na, as well as the 17Ne(p, p) cross section. GSM-CC treats the nucleus as an open quantum system and provides a unified framework for studying both nuclear structure and reaction cross sections. Our calculations reproduce the energies and partial decay widths of low-lying states in 18Na, as well as the 17Ne(p, p) cross section. Additionally, the mirror nucleus 18N is also described. The isospin symmetry breaking induced by the Coulomb interaction and continuum coupling is clearly obtained in our description of 18Na and 18N properties, arising from the extended s1/2 partial wave. The isospin symmetry breaking in the 18Na/18N pair is compared to that occurring in the mirror pair 16F/16N, whereby similarities and differences are analyzed.

nucl-th↗

arXiv2025

Large scale shell model calculation for collectivity in nuclei beyond 78Ni

A shell model effective interaction for nuclei beyond the double magic nucleus 78Ni is constructed. First, the single-particle evolutions for valence neutrons above the double magic 78Ni are systematically explored in the N = 51 isotones using the large scale shell model (LSSM) calculations based on the constructed effective interaction. Subsequently, we calculate the excitation energies of 2+1 states and reduced electric quadrupole transition probabilities B(E2; 2+ to 0+) for N = 52 isotones. Notably, our calculation gives the result most consistent with the trend of the B(E2) values observed in the N = 52 isotones, especially for 84Ge, a result that poses a serious challenge to the theoretical model. Furthermore, the collectivity in N = 52 isotones, as well as the roles of pseudo-SU(3) symmetry, are investigated via the calculated primary configurations of their ground states and the first excited states. Additionally, the low-lying structures and band characteristics of neutron-rich Ge and Se isotopes are investigated. The ground state and the γ-soft band are constructed in our LSSM calculations, aligning well with available experimental evidence. Finally, we present the calculated evolutions of low-lying states in neutron-rich Ge and Se isotopes. The predictions for the as-yet unobserved low-lying states in these nuclei provide a comprehensive dataset to guide and inform future experimental efforts to decipher the evolution of shell structures and collectivity.

nucl-th↗

arXiv2025

Gamow shell model calculations for the Thomas-Ehrman shift in new isotopes 21Al

Proton-rich nuclei beyond the proton drip line exhibit unique phenomena, such as the Thomas-Ehrman shift (TES), providing valuable insights into nuclear stability and isospin symmetry breaking. The discovery of the lightest new isotope, 21Al, situated beyond the proton drip line, was recently reported in the experiment. In this study, we employ the Gamow shell model (GSM) to explore the TES in mirror pairs 21Al/21O, focusing on how this phenomenon affects the energy levels of these nuclei. Our calculations describe the ground state energies and reveal significant TES with large mirror energy differences in the excited mirror 1/2+ states in 21Al/21O. The large mirror energy difference is primarily due to the significant occupation of weakly bound or unbound s1/2 orbitals, resulting in the extended radial density distributions, and variations in Coulomb energy and nuclear interaction contributions between the mirror states. Additionally, the low-lying states of 21Al are also calculated with the GSM in coupled-channel (GSM-CC) representation, Furthermore, we also predict the cross-section of 20Mg(p, p) scattering, which serves as another candidate approach to study the unbound structure of 21Al in the experiment, offering a theoretical framework for studying the structure and reaction dynamics of 21Al in future experiments.

nucl-th↗

arXiv2025

Quenching of single-particle strength inferred from nucleon-removal transfer reactions on $^{15}$C

The difference in the proton and neutron separation energies ($ΔS$) of the weakly bound $^{15}$C ground state is -19.86 MeV, an extreme value. Data from intermediate-energy heavy-ion induced (HI-induced) knockout reactions on nuclei spanning $-20\lesssimΔS\lesssim+20$ MeV, suggest that the degree to which single-particle strength is quenched, $R\mathrm{_{s}}$, has a negative correlation with $ΔS$, decreasing from unity around $-20$~MeV to around 0.2 at $+20$~MeV. For the $^{15}$C ground state ($R_s=0.96(4)$ in HI-induced knockout), contrasting results have recently been obtained via the neutron-adding transfer reaction, which reveal a value of $R_s=0.64(15)$, similar to the value observed at modest $ΔS$ and more extreme values of $ΔS$ with reaction probes other than HI knockout. In order to explore the any potential differences between $adding$ and $removing$ processes in transfer reactions at extreme $ΔS$, single-neutron removal transfer reactions on $^{15}$C were performed at 7.1MeV/u in inverse kinematics. The removal of a valence neutron in 2$s_{1/2}$ orbit using both ($p$,$d$) and ($d$,$t$) reactions shows consistent quenching factors and agrees with those from the neutron-adding reaction. The present results, which can be compared with neutron knockout reaction, suggest that correlations, represented by the quenching factor, show limited dependence on neutron-proton asymmetry under the most extreme asymmetry conditions so far achieved in transfer reactions.

nucl-ex↗

arXiv2025

Gamow shell model description of neutron-rich He hyper-isotopes

The Gamow shell model (GSM) framework has been extended to the study of weakly bound hypernuclei. As a first application, the neutron-rich He hyper-isotope chains, from 6ΛHe to 9ΛHe have been investigated to accurately account for the loosely bound or neutron-unbound character of hypernuclear many-body states. The energy spectra calculated with a phenomenological Hamiltonian show good agreement with experimental data. In particular, neutron-emitting resonant states are predicted for the neutron-rich nuclei 5-7He and the hypernucleus 6ΛHe. Furthermore, one-neutron densities exhibit the long-range character of weakly bound and resonant states. This study demonstrates that GSM is a practical tool for describing the complex structure of hypernuclei, especially for those close to drip lines.

nucl-th↗

arXiv2025

$Z=14$ Magicity Revealed by the Mass of the Proton Dripline Nucleus $^{22}$Si

Using the $Bρ$-defined isochronous mass spectrometry technique, we conducted the first mass measurement of the proton dripline nucleus $^{22}$Si. We confirm that $^{22}$Si is bound against particle emission with $S_p/S_{2p}=+1412(114)/+229(54)$ keV, fixing the proton dripline location for the Si element. By analyzing the mass differences of the neighboring $sd$-shell nuclei, we find that $^{22}$Si exhibits a doubly-magic character similar to its mirror partner $^{22}$O, and that the mirror energy difference of $^{22}$Si-$^{22}$O deviates from the predictions assuming mirror symmetry. Gamow shell-model calculations reveal that the average occupations of valence protons in $^{22}$Si are nearly identical to those of valence neutrons in $^{22}$O, supporting the $Z=14$ magicity in $^{22}$Si. The observed mirror-symmetry breaking is attributed to the extended proton distribution in $^{22}$Si arising from a small contribution of the unbound $\pi2s_{1/2}$ orbital.

nucl-ex↗

arXiv2025

Effective proton-neutron interaction in mirror nuclei

Effective proton-neutron interactions, $V_{pn}$, in mirror nuclei are systematically analyzed using the ground-state atomic masses. A mirror symmetry of $V_{pn}$ is found for bound nuclei with a standard deviation of $σ=32$ keV. However, this mirror symmetry is apparently broken for some mirror-nuclei pairs when a proton-unbound nucleus is involved in extracting the $V_{pn}$ values. Such a mirror-symmetry breaking is attributed to the Thomas-Ehrman shift of the proton-unbound nucleus and investigated by using the Gamow shell model. It is concluded that the Thomas-Ehrman shift originates mainly from reduced Coulomb energies in the proton-unbound nuclei due to the extended radial density distribution of valence protons.

nucl-th↗

arXiv2024

Mirror Symmetry Breaking Disclosed in the Decay of Three-Proton Emitter 20Al

The previously-unknown nucleus 20Al has been observed for the first time by detecting its in-flight decays. Tracking trajectories of all decay products with silicon micro-strip detectors allowed for a conclusion that 20Al is unbound with respect to three-proton (3p) emission. The 3p-decay energy of 20Al ground state has been determined to be 1.93(+0.11,-0.09) MeV through a detailed study of angular correlations of its decay products, 17Ne+p+p+p. This value is much smaller in comparison with the predictions inferred from the isospin symmetry by using the known energy of its mirror nucleus 20N, which indicates a possible mirror symmetry violation in the structure of 3p emitters. Such an isospin symmetry breaking is supported by the calculations of the continuum embedded theoretical frameworks, describing the observed 20Al ground state as an 1p s-wave state with a spin-parity of 1-, which contradicts to the spin-parity (2-) of the 20N ground state. The 20Al ground state decays by sequential 1p-2p emission via intermediate ground state of 19Mg, which is the first observed case of daughter two-proton radioactivity following 1p decay of the parent state.

nucl-ex↗

arXiv2024

Spectroscopic factor calculations in the \textit{ab initio} no-core shell model

The convergence properties of spectroscopic factors in the \textit{ab initio} no-core shell model are hereby investigated. For this, we consider nuclear energies and spectroscopic factors in $A = 6$ and 7 isotopes, using the chiral forces NNLO$_{\rm opt}$ and N$^3$LO. While low-lying spectrum energy demonstrates remarkable convergence with the increase of model space within the no-core shell model, the spectroscopic factor exhibits no definitive convergence trend and seems independent of the employed nuclear interaction. The use of spectroscopic factors issued from the no-core shell model to calculate cross-sections of knockout reaction might then be questionable. The results are compared with that of the standard shell model and \textit{ab initio} Monte Carlo calculations.

nucl-th↗

arXiv2024

Nuclear structure of dripline nuclei elucidated through precision mass measurements of $^{23}$Si, $^{26}$P, $^{27,28}$S, and $^{31}$Ar

Using the B$ρ$-defined isochronous mass spectrometry technique, we report the first determination of the $^{23}$Si, $^{26}$P, $^{27}$S, and $^{31}$Ar masses and improve the precision of the $^{28}$S mass by a factor of 11. Our measurements confirm that these isotopes are bound and fix the location of the proton dripline in P, S, and Ar. We find that the mirror energy differences of the mirror-nuclei pairs $^{26}$P-$^{26}$Na, $^{27}$P-$^{27}$Mg, $^{27}$S-$^{27}$Na, $^{28}$S-$^{28}$Mg, and $^{31}$Ar-$^{31}$Al deviate significantly from the values predicted assuming mirror symmetry. In addition, we observe similar anomalies in the excited states, but not in the ground states, of the mirror-nuclei pairs $^{22}$Al-$^{22}$F and $^{23}$Al-$^{23}$Ne. Using $ab~ initio$ VS-IMSRG and mean field calculations, we show that such a mirror-symmetry breaking phenomeon can be explained by the extended charge distributions of weakly-bound, proton-rich nuclei. When observed, this phenomenon serves as a unique signature that can be valuable for identifying proton-halo candidates.

nucl-ex↗