• Revisiting the heavy vector quarkonium leptonic widths
    We revisit the heavy quarkonium leptonic decays $ \psi(nS) \to \ell^+\ell^- $ and $ \Upsilon(nS) \to \ell^+\ell^- $ using the Bethe-Salpeter method. The emphasis is on the relativistic corrections. For the $ \psi(1S-5S) $ decays, the relativistic effects are $ 22^{+3}_{-2} $%, $ 34^{+5}_{-5} $%, $ 41^{+6}_{-6} $%, $ 52^{+11}_{-13} $% and $ 62^{+14}_{-12} $%, respectively. For the $ \Upsilon(1S-5S) $ decays, the relativistic effects are $ 14^{+1}_{-2} $%, $ 23^{+0}_{-3} $%, $ 20^{+8}_{-2} $%, $ 21^{+6}_{-7} $% and $ 28^{+2}_{-7} $%, respectively. Thus, the relativistic corrections are large and important in heavy quarkonium leptonic decays, especially for the highly excited charmonium. Our results for $ \Upsilon(nS) \to \ell^+\ell^- $ are consistent with the experimental data.
  • Axialvector tetraquark candidates for Zc(3900), Zc(4020), Zc(4430), and Zc(4600)
    We construct the axialvector and tensor current operators to systematically investigate the ground and first radially excited tetraquark states with quantum numbers $J^{PC}=1^{+-}$ using the QCD sum rules. We observe one axialvector tetraquark candidate for $Z_c(3900)$ and $Z_c(4430)$, two axialvector tetraquark candidates for the $Z_c(4020)$, and three axialvector tetraquark candidates for $Z_c(4600)$.
  • Extraction of the CKM phase γ from the charmless two-body B meson decays
    Using all experimentally measured charmless $B \to PP$, $PV$ decay modes, where $P(V)$ denotes a light pseudoscalar (vector) meson, we extract the CKM angle $\gamma$ by a global fit. All hadronic parameters are determined from the experimental data, such that the approach is least model dependent. The contributions of the various decay modes are classified by the topological weak Feynman diagram amplitudes, which are determined by the global fit. To improve the precision of the approach, we consider the flavor SU(3) breaking effects of the topological diagram amplitudes of the decay modes by including the form factors and decay constants. The fit result for the CKM angle $\gamma$ is $(69.8 \pm 2.1 \pm 0.9) ^{\circ }$. It is consistent with the current world average values but has a smaller uncertainty.
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  • Novel relativistic mean field Lagrangian guided by pseudo-spin symmetry restoration
    Published: 2020-06-03, doi: 10.1088/1674-1137/44/7/074107
    Show Abstract
    The relativistic mean field (RMF) model has achieved great success in describing various nuclear phenomena. However, several serious defects are common. For instance, the pseudo-spin symmetry of high-l orbits is distinctly violated in general, leading to spurious shell closures $ N/Z = 58 $ and $ 92 $. This leads to problems in describing structure properties, including shell structures, nuclear masses, etc. Guided by the pseudo-spin symmetry restoration [Geng et al., Phys. Rev. C, 100: 051301 (2019)], a new RMF Lagrangian DD-LZ1 is developed by considering the density-dependent meson-nucleon coupling strengths. With the newly obtained RMF Lagrangian DD-LZ1, satisfactory descriptions can be obtained for the bulk properties of nuclear matter and finite nuclei. In particular, significant improvements on describing the single-particle spectra are achieved by DD-LZ1. In particular, the spurious shell closures $ Z = 58 $ and $ 92 $, commonly found in previous RMF calculations, are eliminated by the new effective interaction DD-LZ1, and consistently the pseudo-spin symmetry (PSS) around the Fermi levels is reasonably restored for both low-l and high-l orbits. Moreover, the description of nuclear masses is also notably improved by DD-LZ1, as compared to the other RMF Lagrangians.
  • Analytical investigation of γNN** transition helicity amplitudes
    Published: 2020-06-03, doi: 10.1088/1674-1137/44/7/074109
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    We study the structure of nonstrange baryons by analytically calculating the electromagnetic transition helicity amplitudes of the nucleon and Δ resonances. We employ an improved hypercentral constituent quark model and obtain the corresponding eigenenergies and eigenfunctions in closed forms. Then, we calculate the transverse and longitudinal helicity amplitudes for nucleon and Δ resonances. The comparison of evaluated observables and experimental data indicates good agreement between the proposed model and available data.
  • Formation region of emitted α and heavier particles inside radioactive nuclei
    Published: 2020-06-01, doi: 10.1088/1674-1137/44/7/074105
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    We investigate the formation distance (R0) from the center of the radioactive parent nucleus at which the emitted cluster is most probably formed. The calculations are performed microscopically starting with the solution to the time-independent Schrödinger wave equation for the cluster-core system, using nuclear potentials based on the Skyrme-SLy4 nucleon-nucleon interactions and folding Coulomb potential, to determine the incident and transmitted wave functions of the system. Our results show that the emitted cluster is mostly formed in the pre-surface region of the nucleus, under the effect of Pauli blocking from the saturated core density. The deeper α-formation distance inside the nucleus allows less preformation probability and indicates a more stable nucleus for a longer half-life. Furthermore, the α-particle tends to be formed at a slightly deeper region inside the nuclei, with larger isospin asymmetry, and in the closed shell nuclei. Regarding the heavy clusters, we observed that the formation distance of the emitted clusters heavier than α-particle increased via increasing the isospin asymmetry of the formed cluster rather than by increasing its mass number. The partial half-life of a certain cluster-decay mode increased with increase of either the mass number or the isospin asymmetry of the emitted cluster.