• Spin determination by in-plane angular correlation analysis in various coordinate systems
    In the excitation of the resonant state followed by the sequential cluster-decay, the in-plane angular correlation method is usually employed to determine the spin of the mother nucleus. However, the correlation pattern exhibited in a two-dimensional angular-correlation spectrum depends on the selected coordinate system. In particular, the parity-symmetric and axial-symmetric processes should be presented in a way to enhance the correlation pattern, whereas the non-symmetric process should be plotted separately to reduce the background. In this study, three coordinate systems previously adopted for correlation patterns in the literature are described and compared to each other. The consistency among these systems is evaluated based on the experimental data analysis for the 10.29-MeV state in 18O. A spin-parity of 4+ is obtained for all three coordinate systems.
  • Perturbative QCD for J/ψ inclusive production via initial state radiation in ${{e^+e^-}}$ collisions
    The process $ e^+e^-\to J/\psi +X $ with the center-of-mass (CM) energy in the range from 3.7 to 10.6 GeV is calculated up to the next-to-leading order (NLO) in quantum chromodynamics (QCD). At 10.6 GeV, the result is consistent with the experimental result from Belle. However, the predictions are much smaller than the background in the measurements at BESIII in the low CM energy range from 3.7 to 4.6 GeV. This indicates that the convergence of the QCD perturbative expansion becomes worse as the CM energy is closer to the inclusive $ J/\psi $ production threshold. For a further study of the QCD mechanism of $ J/\psi $ production in $ e^+e^- $ collisions with different CM energies, the initial state radiation effect of $ e^+e^-\to J/\psi+gg $ and $ e^+e^-\to J/\psi+c \bar{c} $ are calculated in QCD NLO. The results are plotted and the number of events for different CM energy bins are provided for SuperKEKB. This provides a method to precisely test the validity of perturbative predictions for $ J/\psi $ production in future measurements.
  • Extinction coefficients of surface atmospheric aerosol above LHAASO
    We investigate the extinction coefficients of the surface atmospheric aerosol over the Large High Altitude Air Shower Observatory (LHAASO), located at the Haizi Mountain, Daocheng County, China. To this end, we utilize the Longtin model, Mie scattering theory, and experimental data obtained by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Our theoretical calculations show that the total extinction coefficients of the atmospheric aerosol at the wavelength of 200–500 nm are inversely proportional to the laser wavelength, and influenced by the wind speed. From July 2015 to October 2016, the extinction coefficient of the surface atmospheric aerosols at 532 nm wavelength reached 0.04 km−1 with no wind, while it increased to 0.1 km−1 with gusts. In this period, the extinction coefficients of the surface atmospheric aerosol at 532 nm wavelength, obtained by the CALIPSO, change from 0.01 to 0.07 km−1, which is less than the values obtained the theoretical calculation and larger than the average of Tibetan Plateau in 2006−2016. These calculations and experimental evidence provide important arguments to the model of atmospheric aerosol to be applied in the calibration of LHAASO. Our results suggest that the extinction coefficients over LHAASO require further study, including research on the size distribution, shape, concentration of aerosols particles, wind dependence, relative humidity dependence, etc.
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  • Prediction of the cross-sections of isotopes produced in deuteron-induced spallation of long-lived fission products
    Published: 2019-08-17, doi: 10.1088/1674-1137/43/10/104101
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    The spallation cross-section data for the long-lived fission products (LLFPs) are scarce but required for the design of accelerator driven systems. In this paper, the isospin dependent quantum molecular dynamics model and the statistical code GEMINI are applied to simulate deuteron-induced spallation in the energy region of GeV/nucleon. By comparing the calculations with the experimental data, the applicability of the model is verified. The model is then applied to simulate the spallation of 90Sr, 93Zr, 107Pd, and 137Cs induced by deuterons at 200, 500 and 1000 MeV/nucleon. The cross-sections of isotopes, the cross-sections of long-lived nuclei, and the reaction energy are presented. Using the above observables, the feasibility of LLFP transmutation by spallation is discussed.
  • Symmetry properties of nonlocal quark bilinear operators on a Lattice (LP3 Collaboration)
    Published: 2019-08-17, doi: 10.1088/1674-1137/43/10/103101
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    Using symmetry properties, we determine the mixing pattern of a class of nonlocal quark bilinear operators containing a straight Wilson line along a spatial direction. We confirm the previous study that mixing among the lowest dimensional operators, which have a mass dimension equal to three, can occur if chiral symmetry is broken in the lattice action. For higher dimensional operators, we find that the dimension-three operators will always mix with dimension-four operators, even if chiral symmetry is preserved. Also, the number of dimension-four operators involved in the mixing is large, and hence it is impractical to remove the mixing by the improvement procedure. Our result is important for determining the Bjorken-x dependence of the parton distribution functions using the quasi-distribution method on a Euclidean lattice. The requirement of using large hadron momentum in this approach makes the control of errors from dimension-four operators even more important.
  • Exact recession velocity and cosmic redshift based on cosmological principle and Yang-Mills gravity
    Published: 2019-08-17, doi: 10.1088/1674-1137/43/10/105103
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    Based on the cosmological principle and quantum Yang-Mills gravity in the super-macroscopic limit, we obtain an exact recession velocity and cosmic redshift z, as measured in an inertial frame $ F\equiv F(t,x,y,z). $ For a matter-dominated universe, we have the effective cosmic metric tensor $ G_{\mu\nu}(t) = (B^2(t),-A^2(t), -A^2(t),-A^2(t)),$ $ \ A\propto B\propto t^{1/2} $, where $ t $ has the operational meaning of time in $ F $ frame. We assume a cosmic action $ S\equiv S_{\rm cos} $ involving $ G_{\mu\nu}(t) $ and derive the ‘Okubo equation’ of motion, $ G^{\mu\nu}(t)\partial_\mu S \partial_\nu S - m^2 = 0 $, for a distant galaxy with mass $ m $. This cosmic equation predicts an exact recession velocity, $ \dot{r} = rH/[1/2 +\sqrt{1/4+r^2H^2/C_o^2} ]<C_o $, where $ H = \dot{A}(t)/A(t) $ and $ C_o = B/A $, as observed in the inertial frame $ F $. For small velocities, we have the usual Hubble's law $ \dot{r} \approx rH $ for recession velocities. Following the formulation of the accelerated Wu-Doppler effect, we investigate cosmic redshifts z as measured in $ F $. It is natural to assume the massless Okubo equation, $ G^{\mu\nu}(t)\partial_\mu \psi_e \partial_\nu \psi_e = 0 $, for light emitted from accelerated distant galaxies. Based on the principle of limiting continuation of physical laws, we obtain a transformation for covariant wave 4-vectors between and inertial and an accelerated frame, and predict a relationship for the exact recession velocity and cosmic redshift, $ z = [(1+V_r)/(1-V_r^2)^{1/2}] - 1 $, where $ V_r = \dot{r}/C_o<1 $, as observed in the inertial frame $ F $. These predictions of the cosmic model are consistent with experiments for small velocities and should be further tested.