arXiv subjects

Q. B. Chen

Publications and source records attributed to Q. B. Chen.

At least 19 recordsLinked to original sources

arXiv2026

Negative-parity high-spin structure of 105Pd

Negative-parity medium- and high-spin structure of the nucleus 105Pd was studied through the 96Zr(13C,4n)105Pd reaction at incident energies of 51 and 58 MeV, using the EUROBALL IV gamma-ray spectrometer in conjunction with the DIAMANT charged particle array. New bands have been observed and the previously reported bands have been extended to higher energies and spins. Altogether six decoupled bands with E2 transitions and one strongly coupled band with M1 + E2 transitions have been observed. The observed energy spectra and B(M1)/B(E2) ratios are compared with results of quantum particle rotor model calculations. Based on these comparisons, quasiparticle configurations can be assigned to two newly observed decoupled bands as well as to the strongly coupled band. The previously emerged possible interpretation for the third decoupled band as a two-phonon wobbling excitation lacks support. The observations indicate possible gamma-band nature for this band. The strongly coupled band, consistently with the absence of another observed strongly coupled band in this experiment, does not exhibit chirality.

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arXiv2026

Evolution of chirality from transverse wobbling in $^{135}$Pr

Chirality is a distinct signature that characterizes triaxial shapes in nuclei. We report the first observation of chirality in the nucleus $^{135}$Pr using a high-statistics Gammasphere experiment with the $^{123}$Sb($^{16}$O,4n)$^{135}$Pr reaction. Two chiral-partner bands with the configuration $π(1h_{11/2})^1\otimesν(1h_{11/2})^{-2}$ have been identified in this nucleus. Angular distribution analyses of the $ΔI = 1$ transitions connecting the two bands reveal a dominant dipole character, and quasiparticle triaxial rotor model calculations show good agreement with the data. Since the simultaneous observation of chirality and transverse wobbling in $^{135}$Pr relies critically on these angular distribution results, we also address and refute the experimental and theoretical criticisms raised in a recent work by Lv et al., presenting additional evidence that further strengthens our interpretation. This marks the first observation of both hallmarks of triaxiality-chirality and wobbling-in the same nucleus.

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arXiv2025

Triaxiality and shape dynamics in $^{70}$Ge

The electromagnetic properties of low-lying states in $^{70}$Ge were investigated via multi-step Coulomb excitation of a $^{70}$Ge beam impinging on a $^{208}$Pb target at the ATLAS facility of the Argonne National Laboratory. A total of 27 transitional elements and six diagonal matrix elements coupling 11 low-lying states, were extracted from the measured cross sections. These were used to calculate reduced transition probabilities, spectroscopic quadrupole moments, and rotational invariant shape parameters, providing enhanced precision and expanding on previous studies. The experimental data were compared within several theoretical frameworks, including the generalized triaxial rotor model, configuration interaction shell-model calculations, and computations within the combined frameworks of relativistic density functional theory and the five-dimensional collective Hamiltonian. The results demonstrate a good agreement with the experimental data and, in conjunction with calculations using a two-state mixing model, support significant triaxiality and strong mixing between the $0^+_1$ and $0^+_2$ states. This results in the magnitudes of their respective quadrupole deformations $[β_\text{rms}(0^+_1) = 0.228\,(3),\,β_\text{rms}(0^+_2) = 0.273\,(1)]$ being more similar than previously observed. The implications of these results for understanding the complex shape coexistence phenomena, the role of triaxiality, and shape evolution along the Ge isotopic chain are discussed.

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arXiv2025

Entanglement in two-quasiparticle-triaxial-rotor systems: Chirality, wobbling, and the Pauli effect

We investigate the entanglement in two-quasiparticle plus triaxial-rotor (PTR) model for the particle-hole configuration $π(1h_{11/2})^1 \otimes ν(1h_{11/2})^{-1}$, the particle-particle configuration $π(1h_{11/2})^1 \otimes ν(1h_{11/2})^1$, and two-proton particles configuration $π(1h_{11/2})^2$ for different values of the triaxiality parameter. The entanglement between the angular momenta of the two quasiparticles and the total angular momentum is quantified by the three bipartite concurrences $\mathcal{C}$ of one type of angular momentum with the other two angular momenta and the area $\mathcal{F}$ of the triangle formed by the bipartite concurrences. Collective chiral and wobbling modes are identified for $γ>15^\circ$ via spin coherent state (SCS) maps and spin squeezed state (SSS) plots. Their entanglement increases from moderate values at the band head to near-maximal values at $I=20$. The area $\mathcal{F}$ of the chiral partners changes order as function of $I$ which reflects the crossing of the partner bands as a signature of chirality. For the $π(1h_{11/2})^2$ configuration, the antisymmetrization required by the Pauli exclusion principle causes strong entanglement between the two protons, which significantly amplifies the area $\mathcal{F}$. For $γ<15^\circ$, the lowest bands become various uniformly rotating quasiparticle configurations, which have large values of $\mathcal{F}$ for all values $I$.

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arXiv2024

Entanglement and coherence of the wobbling mode

The entanglement and coherence of the wobbling mode are studied in the framework of the particle plus triaxial rotor model for the one-quasiparticle nucleus $^{135}$Pr and the two-quasiparticles nucleus $^{130}$Ba. The focus lies on the coupling between the total and the particle angular momenta. Using the Schmidt decomposing, it is quantified in terms of the von Neumann entropy of the respective sub-systems, which measures their mutual entanglement. The entropy and the entanglement increase with spin $I$ and number of wobbling quanta $n$. The coherence of the wobbling mode is studied by means of the eigenstate decomposition of its reduced density matrix. To a good approximation, the probability distributions of the total angular momentum can be interpreted as the incoherent combination of the coherent contributions from the first two pairs of eigenvectors with the largest weight of the reduced density matrix. Decoherence measures are defined, which, in accordance, scatter between 0.1 to 0.2 at low spin and between 0.1 and 0.3 at high spin. Entanglement in the framework of the adiabatic approximation is further analyzed. In general, the coherent eigenstates of the effective collective Hamiltonian approximate the reduced density matrix with the limited accuracy of its pair of eigenstates with the largest weight. As the adiabatic approximation becomes more accurate with decreasing excitation energy, the probability distribution of the angle of the total angular momentum around a principal axis approaches the one of the full reduced density matrix. The $E2$ transition probabilities and spectroscopic quadrupole moments reflect this trend.

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arXiv2024

Shape coexistence in Ne isotopes and hyperon impurity effect on low-lying states

Based on the beyond-mean-field Skyrme-Hartree-Fock model, we investigate the shape coexistence in Ne isotopes and the effect of $\la$ hyperon on the energy level structure in the nuclei. The up-to-date Skyrme-type $N\la$ interaction SLL4 and the $NN$ interaction SGII are employed. Low-lying energy spectra of $^{20,22,24,26,28,30,32,34}$Ne, including the low-lying states with $J\leq 6$, are predicted, discussed in detail, and found in good agreement with experimental results. The electric quadrupole transition rate is also examined. The coexistences of a ground state rotational band and a $\be$ vibrational band are revealed in $^{20,22,24}$Ne. Unlike the previously discovered shrinkage effect of $\la_{s}$ on the ground state nuclei, it is found that the $\la_{s}$ may alter the excitation mode of the second band by affecting the distribution of the collective wave function, thereby causing the $\be$ vibrational band transitions to a vibrational band with equidistant energy levels.

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arXiv2024

Proton drip line of deformed hypernuclei

The proton drip line of (hyper)nuclei is examined within the framework of the deformed Skyrme-Hartree Fock approach by adjusting the nuclear force parameters to exactly reproduce the core binding energies. The impact of adding a Λ hyperon in a s or p state is studied, and it is found that in some cases the deformation effect facilitates the extension of the drip line by an added p-state hyperon. However, no extension of the drip line is found for s-state hypernuclei.

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arXiv2024

Spin squeezed states and wobbling motion in collective Hamiltonian

A semiclassical approach is proposed to calculate the collective potential and mass parameters to formulate a collective Hamiltonian capable of describing the wobbling motion in both even-even and odd-mass systems. By diagonalizing the resulting collective Hamiltonian (CH), one can obtain the energies and wave functions associated with the wobbling states. Furthermore, a novel technique called spin squeezed state (SSS) maps is introduced based on the derived wave functions. To validate the results obtained from the collective Hamiltonian, a comparative analysis is conducted against predictions from the triaxial rotor model (TRM) and particle triaxial rotor (PTR) model. Notably, the SSS plots determined using the TRM and PTR models exhibit a strong correlation with the probability density distributions of the wave functions obtained from the CH. This correlation highlights the consistency and coherence between the different theoretical approaches when describing the wobbling phenomenon and associated rotational dynamics.

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arXiv2021

Effects of $\bm\la$ hyperons on the deformations of even-even nuclei

The deformations of multi-$\la$ hypernuclei corresponding to even-even core nuclei ranging from $^8$Be to $^{40}$Ca with 2, 4, 6, and 8 hyperons are studied in the framework of the deformed Skyrme-Hartree-Fock approach. It is found that the deformations are reduced when adding 2 or 8 $\la$ hyperons, but enhanced when adding 4 or 6 $\la$ hyperons. These differences are attributed to the fact that $\la$ hyperons are filled gradually into the three deformed $p$ orbits, of which the [110]1/2$^-$ orbit is prolately deformed and the degenerate [101]1/2$^-$ and [101]3/2$^-$ orbits are oblately deformed.

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arXiv2021

The drip lines of kaonic nuclei

The effects of an additional $K^-$ meson on the neutron and proton drip lines are investigated within Skyrme-Hartree-Fock approach combined with a Skyrme-type kaon-nucleon interaction. While an extension of the proton drip line is observed due to the strongly attractive $K^-p$ interaction, contrasting effects (extension and reduction) on the neutron drip line of Be, O, and Ne isotopes are found. The origin of these differences is attributed to the behavior of the highest-occupied neutron single-particle levels near the neutron drip line.

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arXiv2021

$g$-factor and static quadrupole moment of $^{135}$Pr, $^{105}$Pd, and $^{187}$Au in wobbling motion

The $g$-factor and static quadrupole moment of the nuclides $^{135}$Pr, $^{105}$Pd, and $^{187}$Au in the wobbling motion are investigated in the particle-rotor model as functions of the total spin $I$. The $g$-factor of $^{105}\mathrm{Pd}$ increases with increasing $I$, due to the negative gyromagnetic ratio of a neutron valence-neutron. This behavior is in contrast to the decreasing $g$-factor of the other two nuclides, $^{135}$Pr and $^{187}$Au, which feature a valence-proton. The static quadrupole moment $Q$ depends on all three expectation values of the total angular momentum. It is smaller in the yrast band than in the wobbling band for the transverse wobblers $^{135}$Pr and $^{105}$Pd, while larger for the longitudinal wobbler $^{187}$Au.

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arXiv2021

Pseudo spin doublet bands and Gallagher Moszkowski doublet bands in $^{100}$Y

New transitions in neutron rich $^{100}$Y have been identified in a $^9$Be+$^{238}$U experiment with mass- and Z- gates to provide full fragment identification. These transitions and high spin levels of $^{100}$Y have been investigated by analyzing the high statistics $γ$-$γ$-$γ$ and $γ$-$γ$-$γ$-$γ$ coincidence data from the spontaneous fission of $^{252}$Cf at the Gammasphere detector array. Two new bands, 14 new levels and 23 new transitions have been identified. The $K^π=4^+$ new band decaying to an 1s isomeric state is assigned to be the high-$K$ Gallagher-Moszkowski (GM) partner of the known $K^π=1^+$ band, with the $π5/2[522] \otimes ν3/2[411]$ configuration. This 4$^+$ band is also proposed to be the pseudo spin partner of the new $K^π=5^+$ band with a 5$^{+}$ $π5/2[422] \otimes ν5/2[413]$ configuration, to form a $π5/2[422] \otimes ν[312$ $5/2,3/2]$ neutron pseudospin doublet. Constrained triaxial covariant density functional theory and quantal particle rotor model calculations have been applied to interpret the band structure and available electromagnetic transition probabilities and are found in good agreement with experimental values.

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arXiv2020

Interpretation of the quasiparticle plus triaxial rotor model

We discuss in depth the application of the classical concepts for interpreting the quantal results from the triaxial rotor core without and with odd-particle. The corresponding limitations caused by the discreteness and finiteness of the angular momentum Hilbert space and the extraction of the relevant features from the complex wave function and distributions of various angular momentum components are discussed in detail. New methods based on spin coherent states and spin squeezed states are introduced. It is demonstrated that the spin coherent state map is a powerful tool to visualize the angular momentum geometry of rotating nuclei. The topological nature of the concepts of transverse and longitudinal wobbling is clarified and the transitional axis-flipregime is analysed for the first time.

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arXiv2020

Covariant density functional theory for nuclear chirality in $^{135}$Nd

The three-dimensional tilted axis cranking covariant density functional theory (3D-TAC CDFT) is used to study the chiral modes in $^{135}$Nd. By modeling the motion of the nucleus in rotating mean field as the interplay between the single-particle motions of several valence particle(s) and hole(s) and the collective motion of a core-like part, a classical Routhian is extracted. This classical Routhian gives qualitative agreement with the 3D-TAC CDFT result for the critical frequency corresponding to the transition from planar to aplanar rotation. Based on this investigation a possible understanding of tilted rotation appearing in a microscopic theory is provided.

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arXiv2020

First Observation of Multiple Transverse Wobbling Bands of Different Kinds in $^{183}$Au

We report the first observation of two wobbling bands in $^{183}$Au, both of which were interpreted as the transverse wobbling (TW) band but with different behavior of their wobbling energies as a function of spin. It increases (decreases) with spin for the positive (negative) parity configuration. The crucial evidence for the wobbling nature of the bands, dominance of the $E2$ component in the $ΔI = 1$ transitions between the partner bands, is provided by the simultaneous measurements of directional correlation from the oriented states (DCO) ratio and the linear polarization of the $γ$ rays. Particle rotor model calculations with triaxial deformation reproduce the experimental data well. A value of spin, $I_m$, has been determined for the observed TW bands below which the wobbling energy increases and above which it decreases with spin. The nucleus $^{183}$Au is, so far, the only nucleus in which both the increasing and the decreasing parts are observed and thus gives the experimental evidence of the complete transverse wobbling phenomenon.

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arXiv2020

Multiple chiral bands in $^{137}$Nd

Two new bands have been identified in $^{137}$Nd from a high-statistics JUROGAM II gamma-ray spectroscopy experiment. Constrained density functional theory and particle rotor model calculations are used to assign configurations and investigate the band properties, which are well described and understood. It is demonstrated that these two new bands can be interpreted as chiral partners of previously known three-quasiparticle positive- and negative-parity bands. The newly observed chiral doublet bands in $^{137}$Nd represent an important support to the existence of multiple chiral bands in nuclei. The present results constitute the missing stone in the series of Nd nuclei showing multiple chiral bands, which becomes the most extended sequence of nuclei presenting multiple chiral bands in the Segré chart.

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arXiv2020

Prolate-to-oblate transition and backbending along the yrast line induced by quasiparticle alignment

The yrast lines in Kr isotopes with $N=42$, 44, and 46 are investigated in a beyond mean field framework with both prolate-oblate coexistence and quasiparticle alignment taken into account. Quasiparticle orbitals with high-$j$ and low-$Ω$ on the oblate side are shown to be responsible for the sharp backbending observed in $^{82}$Kr, by driving the yrast shape from prolate to oblate. This suggests that quasiparticle alignment may not be neglected in the investigation of the shape evolution along the yrast line.

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arXiv2020

$g$-factor and static quadrupole moment for the wobbling mode in $^{133}$La

The $g$-factor and static quadrupole moment for the wobbling mode in the nuclide $^{133}$La are investigated as functions of the spin $I$by employing the particle rotor model. The model can reproduce the available experimental data of $g$-factor and static quadrupole moment. The properties of the $g$-factor and static quadrupole moment as functions of $I$ are interpreted by analyzing the angular momentum geometry of the collective rotor, proton-particle, and total nuclear system. It is demonstrated that the experimental value of the $g$-factor at the bandhead of the yrast band leads to the conclusion that the rotor angular momentum is $R\simeq 2$. Furthermore, the variation of the $g$-factor with the spin $I$ yields the information that the angular momenta of the proton-particle and total nuclear system are oriented parallel to each other. The negative values of the static quadrupole moment over the entire spin region are caused by an alignment of the total angular momentum mainly along the short axis. Static quadrupole moment differences between the wobbling and yrast band originate from a wobbling excitation with respect to the short axis.

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